I started a couple of threads on the 'DIY CNC Wood Routers' forum some time ago but now I've started building I realised I should be posting on this forum and Paul (CNCAdmin) suggested I start a new thread.

Those wishing to read the history of the project can look at:

http://www.cnczone.com/forums/showthread.php?t=2849
http://www.cnczone.com/forums/showthread.php?t=2971

To recap: I teach Design Technology in the UK and was responsible for introducing CNC into the school's curriculum some six years ago. We have a small (300mm x 250mm x 90mm) Isel Automation machine which is OK for small items and as an introduction tool for key stage 3 (11-14), but when it comes to GCSE and A level work it is somewhat lacking in the work area department - some of our students think big! :)

It was apparent we needed something bigger. However, the phrase " I want to spend big sums of money" and the word 'Bursar' do not sit comfortably together and the cash could not be made available to finance a machine outright and by the time the department had saved enough, I would be looking for early retirement. (Don't want to be teaching much past 55, as there are plenty of things I want to do with my time)

The solution is that I will build the machine and finance the major items and the school will have use of it till I retire at which time the machine retires with me to my workshop at home. Bursar's happy - I'm happy.

At this point, it must be said that I would not have contemplated this had it not been for CNCZone where I had lurked for some time before realising that it was possible to think the unthinkable. I will be leaning heavily on you guys over the coming months, particularly when it comes to the electrics.

Below is an unfinished CAD rendering of the proposed design and I will follow this with progress photos. This could be a long journey.


Mike

Items bought to date:

2200mm THK Linear guides and blocks
700mm THK Linear guides and blocks
300mm THK Linear guides and blocks
2000mm THK C7 Precision rolled 25mm ballscrew & preloaded nut
600mm THK C7 Precision rolled 20mm ballscrew & preloaded nut
300mm THK C7 Precision rolled 16mm ballscrew & preloaded nut
Fixed and supported end bearings for above ballscrews.

That little lot from THK at a supposed educational discount was £2,500.00 :eek:

Welded, 60mm x 40mm x 4mm box section, steel frame made by local firm £160
Facing, drilling and tapping of frame for linear guides £250 (essential for getting faces in the same plane and guides parallel)

Photos of the THK goodies and frame are on the other threads and will be updated here as and when progress is made. Next job is to mount the frame on the wall and get it trued.

Hi Mike,

My first question would be the possible cantilever problem when the axis that carries the z reaches it's greatest distance from the long axis. I am by no means a design person as far as machines go but I currently have a machine that quite a bit of overhang and has much more vibration than I care about.

Mike

Sorry if i missed it in your writing, but is this to be mounted to a wall ?
If so, why?

I also agree with Turmite, you may get a sort of gate effect happening. I would recomend some serious bracing.

Good luck with your unique project Mike

Termite & Ynneb,

Thanks for the posts.

Yes, the whole thing is attached to a wall. The idea is that, with limited space, the table can be removed, gantry parked at one end and the floor area used for other purposes. I know it's not an ideal arrangement but the need for a larger machine outweighed the other details. A bonus is that any size of material can be placed under the machine - I even had thoughts of students driving their cars under it and doing some serious artwork on the bonnets (trunks?) :D

I appreciate that the worst case is with the Y axis at its furthest point and that there might be cause for concern with movement but there are a couple of design details that minimise the problem. One, the Y axis motor, and hence its mass, is placed as close to the X axis as possible giving very little moment about the X axis. Two, the intention is to make the whole gantry out of carbon fibre. Composites is one of my interests and it struck me as an ideal material for this type of work as it has very low thermal expansion and is far more rigid than aluminium. Another plus is that the expansion ratios of steel (ballscrews and linear guides) and carbon are closer than steel and aluminium, the two materials most people are using.

I have built a computer controlled oven for baking pre-preg carbon and am confident I can make this work. My initial thoughts are going to be tested out using MDF but will then be replaced as the design gets verified. I know I will have problems with the MDF but at least I can test the structure.

If you have read the other threads you will be aware I have already got the frame made and X axis rails mounted. Just waiting to screw it to the wall now.

Mike

Mike, we have a commercial router at work. A Routech 220, made in Italy that is designed almost exactly like your machine. Its not mounted to a wall, but the concept is similar.
They have a wider spread on the X axis bearings for stability (horizontally, not vertically) and use a large tubular frame for the for cantilevered part.
I'm sure that your idea will work, just allow double, maybe triple your anticipated build and debug time.
I hope that you are going to add some support for your X axis ball screw. That thing will whip like crazy. If you can do it, maybe mount it stationary and spin the nut.

Keep us posted, as this is going to be really spectacular.
Trent

Buscht,

Distance between rails on the X axis is 640mm and the distance between the blocks is 350mm. THK assure me that at this spacing, there should be no skew at all and so far, with the MDF board in place, there is no discernable movement.

I'm a bit concerned about the build time too, especially the electrics as this is definitely not my forte. Will have to lean heavily on you guys for info. I want to use servos but have no idea of size needed for this machine. Any thoughts?

Working volume should be about 1800mm x 600mm x 100mm.

As for the whip on the X axis ballscrew, if only I could find a way to mount everything in fresh air it would save an inordinate amount of time :-) Seriously, THK claim that with both ends supported the 25mm screw should be stiff enough.

Mike

Things are progressing slowly. Problem with teaching is that pupils tend to get in the way of personal projects :) and progress can only be made while I am in school.

Managed to machine the stand-offs to go between the wall and the frame. This will allow me to finely tune the parallelism and trueness of the rails once mounted to the wall. Below are pictures of the stand-offs and CAD rendering of how they will be positioned and used. The nuts either side of the frame will allow very fine adjustment and although the whole leveling and truing process is likely to be lengthy, at least I know I can get it right.

Well, by the skin of my teeth I have made my first deadline and that was to have the frame mounted on the wall by the end of this week - don't forget, I can only work on this project during school time, when not teaching.

The photos show the wall mountings and the frame in place. Not yet got it perfectly true but have thought of a good way of doing it. I am going to mount a laser line to the X axis plate and place an 8' x 4' board of MDF some 20' infront of the machine on which is drawn a perfectly straight line. As the X slide is moved along the rails the laser line should follow the line. With the board being so far infront of the machine, it will exagerate any misalignment of the rails. If the laser deviates from the line, the rails can be adjusted to bring it back on track. This method should true the rails up for parallelism and twist.

I'll report back as to how successful I am with this method.

Mike

Hope to start on the MDF test version of the gantry next week.

Mike, this is a fantastic project. Great job and thanks for sharing.
Trent

I love alternative thinking like this. Thats how new inventions are formed.
Keep up the great work and the pictures.

Buscht & Ynneb,

thanks for the encouragement, I am going to need plenty before this little beast is up and running. Still unsure about motor sizes for this machine. Any help will be most welcome. The intention is to use servos and with having linear guides and ballscrews all round, I am assuming I can get away with smaller motors i.e. less friction to overcome. I would like it to be capable of machining aluminium in light cuts - time not really an issue.

I keep hearing of 100, 200, 300 - 800 oz in motors but have no way of getting an idea of what this means in actual cutting and operating terms. For example, would the cheap servos, often mentioned on this site, be suitable? I believe Jeff Davies of HomeCNC still sells them.

Hope someone can help.

Thanks,

Mike

Mike,

check the article I wrote (PDF) here: http://www.cnczone.com/forums/showthread.php?t=5866

It tells you how to calculate what linear force you can expect to get from your motors. Then there's another matter to know if that will be enough or not, but at least it should be easier to get a "feel" for than motor torque.

Arvid

Arvid,

Thanks for that. I've read through your article and printed it for further digestion- bed time reading, I'm at that age now :)

It's interesting that you use the same screw pitch and speeds I am considering for my project so it was pretty easy to translate. However, I don't know what a cutting force of 200N equates to in terms of cutting speed, depth of cut and material. I appreciate there are many other variables too like spindle speed/power, tool diameter etc.

I am really quite worried about the electrics as it is something I have always fought shy of and I don't want to go to all the trouble of making a good, accurate machine only to make an expensive mistake with the motors/drivers and all. Having said that, I do have some local expertise and I am sure a call to the zoners will bring the right results.

Many thanks again,

Mike

For ballpark comparison only ....
My table uses Jeff's -Homecnc servos, the 430 oz in jobbers, with Gecko 320s on a 2700 mm x 1270 mm table, they work fine; the rack and pinion X axis with a 80 lb (36 kg) gantry does 2500 mm/min rapids; the Y with cheesy Allthread (temporary :rolleyes: ) will do about half that speed. Still testing the limits for cutting speeds, but relatively aggressive cutting in wood can move at 700 mm/min.
Ninewgt sells plans for a 4' x 8' table he made that uses 470 oz in steppers, I think :confused: ...Says it is all he needs...
Today I was rewiring the control box into something less rat's nesty and was struck by how long it took to do it the first time and how straight forward it seems the second time. So anyway no need to worry about the electrics...lots of helpful souls here.

Nice project you have going there! :)

Sol,

Thanks very much for the info - quite reassuring. It is apparent that the quality of the drive system plays a large part in motor selection. Your reply has definitely given me a clearer picture of what I should be looking for - I am more of a hands-on type, empirical designer/worker and sometimes have difficulty working purely theoretically. Once I can visualise something, the numbers become much more meaningful.

Managed to get round to trying the laser line technique for truing the rails. The photos show how it was done. The close up of the pencil marks on the board show how far out the top rail was to begin with - there was some 10mm difference from top to bottom. By placing the board well away from the rail, it exaggerated any discrepancy. In fact the amount the rail was out was immeasurable by any other means.

The rail was then adjusted till there was no discernible deviation of the laser line. The full board was then placed on the rails and was further tested and everything was spot on. By using just the one block to begin with, I was able to find larger errors, as the distance between two blocks tends to even out some of the minor errors.

The next job is to check the two rails for perpendicularity and I will do this with the laser pointing away, perpendicular to the frame, aimed at a board some 6 metres away.

More anon,

Mike

Good use of the laser line. Smart thinkin'

Frame work looks good, nice "factory" looking paint job too. No one will know you built this yourself :)

What a bummer! :( Once I had trued the top rail, I began checking the bottom one and to my horror the two top surfaces of the rails were not in the same plane - this despite them being supposedly trued on a large CNC machine, for which I paid a not inconsiderable sum! Placing a straight edge on the top rail I measured a 3mm gap between the straight edge and the bottom rail surface, with the rails being 640mm between centres.

Problem, how do I fix this? I decided the error was too small to shim behind the rails so eventually opted to shim the blocks. A few calculations later and it was realised that I needed shims that tapered 0.115mm over the 50mm block width. I pressed our little Isel machine into service and produced the four shims as seen in the photos. Now when the board is mounted, it is true - job sorted!

Shame it had to be done though.

What are the dimensions of the THK rails you bought? I am looking at a set of rails 1300 mm long, x 20 mm x 15 mm.

Mícheál.

BTW, really nice job, and fascinating to read about your alignment problem. All credit to you to be able to make up these precise shims, that's the kind of stumbling block that can make or break a project! Best of luck through to completion!

Mícheál,

I bought 2 off 2200 x 25 GSR linear guides for the X axis, 2 off 700 x 20 GSR guides for the Y axis and 2 off 300 x 15 for the Z axis. The THK rep was very helpful and said that customers usually order linear guides that are far too big for the anticipated loads (a comment I have also read somewhere on this site) and he assured me that at the sizes I ordered, they were more than enough to meet my specification of a machine capable of cutting aluminium.

I have always kept an eye on eBay for such components but here, in the UK, eBay carries nowhere near the quantity of useful stuff than the American site and many of them will not ship to UK - besides which shipping costs and possible duties make it difficult to assess the 'real' cost.

At this moment in time, I cannot put my hands on the costs of the rails separately but can let you know if you need that kind of information.

Progress is a little slow at the moment - too much teaching to do :)

Mike

Got some work done over the last couple of days and managed to get the rails to within 0.0007" using an old, imperial DTI. The purists among you will no doubt cringe at the mounting technique - but when means must. :nono: I think this is probably OK but with no terms of reference, it is difficult to know for certain. It took some considerable time to tweak the linear guide mounting bolts to this level of accuracy and the simple application of a little more torque on the allen key, sent the dial spinning.

The GSR blocks have been mounted against a reference edge on small plates that will then be linked with a large plate that will carry the gantry. The last pic shows this whole assembly held together with cramps to check for sliding smoothness. Movement is very smooth with no discernable play though I am quite surprised at how noisy the balls are in the blocks - they rattle away like mad when traversing, not excessively though.

I must stress again that I am testing the layout of the system by using MDF that I know will not be stiff enough for any serious machining but I will then use the MDF version to machine the patterns for making the composite version that will have all the rigidity I will need.

Oh well, the bell has just gone for afternoon school so it's back to the grind.

Mike

As you can see in the pictures, I have managed to make up most of the gantry in 18mm MDF. Although it is only clamped to the slides, it moves very smoothly - can't wait to get it powered but I realise I am a long way off that just yet.

I am beginning to see the wisdom of all those posts on this site that say, 'build in as much adjustment as possible.' Already I am at the stage where being able to adjust something to a fine degree, makes all the difference. Thanks to all those who offered that advice and woe betide those that don't heed it.

I will shortly have to consider how I am going to mount the X axis ballscrew and bearings but I can put this off a while by mounting the Y rails and slide and sorting out the Z axis.

More anon,

Mike

Nice work!

What kind of screws did you use in the MDF? Did you pre-drill for the screws in the horisontal "support bars"? If so, any tip on how to get those holes straight? I guess the drill likes to wander when drilling into the edge of an MDF sheet?

Arvid

Arvid,

The screws are called 'Confirmat screws' and are specifically designed for use in MDF. You need also to purchase the special bit that drills the pilot hole and the clearance hole in both pieces at the same time. The drill is stepped to accommodate this operation. The pieces of MDF are clamped together accurately before drilling through both, once drilled, the screws are inserted before the clamps are removed thus maintaining accuracy.

The screws have a very coarse, thin and sharp thread that anchors well in the MDF 'end grain' and to my knowledge are the only screws that do not allow the MDF to delaminate. Because you drill through both pieces at the same time, the drill bit does not wander in the 'end grain' as it is supported by the hole through the face of the outside piece.

Hope that makes sense,

Mike

Mike, thanks, that makes perfect sense and will be great to know when my build starts! I've been wondering a bit on how to do this...

Arvid

I don't know whether anyone else has had similar problems but when I tried to bolt everything together, the gantry did not want to slide at all freely and it seemed as though it was riding on square balls. Individually, the blocks move extremely freely and smoothly - so nothing wrong with the blocks. However, when bolted to the MDF carriers - square balls.

On checking the alignment of the blocks they were found to be slightly out of plane yet the MDF had not been touched. I figured that MDF is nowhere near accurate enough for my linear guides. Has anyone here used THK linear guides on an MDF machine? Have you too found a problem with alignment?

I have now machined some 50mm x 25mm x 4mm box section steel to mount the blocks on which will hopefully be accurate enough for the tolerances of the THK blocks.

MDF is a wonderful material but perhaps I was expecting too much of it.

Mike

Is it worth doing the final tightening as you would on a cylinder head, just add a little on each screw and go around checking that it is not binding until all is tight and hopefully not sticking.

Graham

Good point Graham.

I did in fact try adjusting the tightness of each screw and yes, there was a point at which it all rode smoothly but unfortunately, it was not holding the gantry at all well. One of the things I noticed was that after tightening the bolts reasonably well, I could go back a few minutes later and have to re-tighten them. It appears the MDF is compressing under the load and obviously needs some oversized washers on both sides to spread the load better.

I have concluded that if you need the highest accuracy, because of the nature of the running gear, you cannot make do with MDF. Hence the move to steel for gantry attachment.

Thanks for the reply.

MDF is actually pretty soft. Even with big washers it will compress easily. One thing you can do is to drill a counterbored hole, and epoxy in steel washers. But, the opposite side will also compress too. This will happen with any type of wood panels, and even with hardwoods to some extent.

Mike, I'm pretty interesed in the composite stuff you talked about. I've been reading a lot of composite fab info for the last few months, and would like to make a composite gantry machine. Can't wait to see how that goes for you.

MDF shrinks and swells a lot over time with temp and humidity.
Recently I noticed how a once smooth MDF work surface had dimpled at every screw head; the wood had become thicker even though it was very well sealed with multiple layers of quality paint.
Yes, and I had the same problem with bearing tensioning...MDF has its place but an application of high precision isn't it.

Gerry & Sol,

Thanks for your observations, it is surprising just how much MDF does move and expand with moisture. If allowed to, and exposed to high humidity, it can double in thickness quite easily and then becomes quite useless. I don't know whether the waterproof versions fare much better? Attached are photos of the replacement steel holders. I still have to face the edges and bolt on a shoulder piece for the blocks to sit against.

Gerry, composites is one of my main interests and I build competition model gliders with prepreg material. In fact I recently became World Champion in S8E which is rocket propelled, R/C gliders. The whole model only weighs 200g and launches to well over 1000' on a 40Ns motor!

I have to build the MDF version of the router first so I can use it to manufacture the patterns for the composite version. This is going to be a fairly lengthy project so I hope you have the staying power - me also :p

Mike

I have to build the MDF version of the router first so I can use it to manufacture the patterns for the composite version. This is going to be a fairly lengthy project so I hope you have the staying power - me also :p

Mike

I started my first router about 18 months ago. A lot of things have kept me from finishing it. My second router will be the composite one. I already have some THK and IKO rails for it, but it's probably 2 years away.

Gerry,

You must be an early riser to respond to my post so quickly. It's only 12:40pm over here!!!

Mike

Not by choice. :D

This is probably the wrong forum but you are talking about using MDF and moisture issues... so here goes... I was just curious if 5/4 Composite Decking material could be used in place of MDF. I'm thinking of using it on my first router so that moisture isn't an issue. You can find it all over the web and at most lumberyards. I think that in most applications you would still need to use some MDF or "plastic plywood". Unfortunately the plastic plywood is outragous in price. I found some that was 3/4 inch thick [4 x 8 foot sheets] for around $100 US. That didn't include shipping. :p

"3/4 inch thick [4 x 8 foot sheets] for around $100 US"

If this is HDPE thats a cheap price, here in Louisville KY a 4' x 8' sheet of 3/4 HDPE costs 280.00 plus tax

"3/4 inch thick [4 x 8 foot sheets] for around $100 US"

If this is HDPE thats a cheap price, here in Louisville KY a 4' x 8' sheet of 3/4 HDPE costs 280.00 plus tax

I was incorrect on the price... it is $131.00 plus shipping. As far as being HDPE... well... I am not for sure. Here is the link:

[I am not affiliated with this website in any way.]

http://www.epsplasticlumber.com/plasticplywoodsheets.shtml

Check it out. :)

****UPDATE*** incorrect on the material.. it isn't HDPE it is a product called Durapoly. I don't know the difference.

The material at $131 is re-cycled plastic and, in my experience, would not be suitable as it is difficult to machine and join - too plastic (plastic used in its true sense). If it is the same as similar material over here, it is also fairly flexible. I did note that the HDPE was considerably more expensive. To choose between the re-cycled plastic and MDF, it would be MDF every time despite its drawbacks.

Mike

I built a composite deck this summer. That stuff is like a wet noodle. It won't hold screws, and I don't think it's as stable as MDF. They recommend 1/4" gaps for expansion, although I haven't noticed it really expand or contract since July.

Instead of that plastic "plywood", why not use Baltic Birch. Very strong, lighter than MDF, holds screws better. Less dust when cutting. Won't swell like MDF. Twice the price.

Hi
as long as you guys are dicussing alternative materials, does anyone have any experience with HDU High Density Urethane, I think it is used in sign making for outdoor use?
Boxwood

Sorry Boxwood, HDU is something I know nothing about. I have used plenty of the expanding urethane in sandwich structures and urethane block for machining patterns/plugs from, but not the high density stuff. The filled urethane block material could be useful in its higher densities, maybe as a table surface but not for structural purposes.

Mike

I hate to chime in ...since I'm not sure what you're trying to accomplish....seems that all the alternatives to MDF are very much in the same price range as some surplus aluminum plate....I would use the aluminum for the table surface...the rest can be 80/20, aluminum plate or MDF if you so desire.

I cannot believe the trouble it has been trying to get the THK blocks to run freely when the bolts are tightened. Despite my latest efforts of milling flats on 50mm x 25mm x 4mm steel box section, the blocks still ran with lumpy balls. On closer inspection the flats were not in the same plane which can only mean that the 'crappy', cheap milling machine's spindle is not perpendicular to the bed.

What now? - I superglued some aluminium shims to the flats and stuck two bits of wet and dry paper to an expensive surface plate. After some considerable time the two shims had been flattened and the whole lot tested on the surface plate - bingo! - perfectly flat.

With added enthusiasm I tightened up the blocks and placed them on the guides only to find they still were not right - better, but not perfect. At least the movement was smooth but it still did not sound right. I have now given up for the day and will look again tomorrow.

Has anyone else experienced this problem?

Mike

Mike, Your problem might be the alignment of the rails. You mentioned earlier that the rail mounting surfaces were not in the same plane and you shimmed the carriages to match.

From my experience, the rails need to be parallel in several planes for everything to work right. Not just the obvious, being in line along the length, but they can't be tilted vertically out of alignment across the cross section. It could be that when you tighten up the carriages you are introducing a bind in the rails.

Try loosening up the lower rail, but keep the upper rail tight and the carriages tight to the plate. See if you can get a smooth action that way. Then slowly start tightening up the lower rail. You might have to shim behind it, or fill in with some kind of bedding compound.

If that works, great. If not, just reverse the procedure with respect to the top and bottom rails.

Good luck
Trent

Trent,

I am only attaching the blocks to one rail - the top one! I can appreciate that if I were bolting the carriage across the two rails I would have a problem if they were out of plane. If you look at the second photo of post #34 you will see the arrangement - the two blocks are bolted to the box section then the box section hung on the top rail and it is this simple arrangement that is not sliding as it should. Woe betide me when I try to tie the two rails together if I cannot get this right!!!

Mike

So, a technique that Thomson (darn I always forget...Thomsen) anyway.....what they recommend when mounting their round rails to the t-bar rail support...was a bed of metal epoxy to help the alignment...so you would only tighten the end bolts until the epoxy had set then you'd tighten the others. In your case you are setting the carriages on the surface plate and then placing your machined plate on top of the carriages...Is that correct?

Mike, it's always tough the first time. THK has good information about mounting rails and carriages in their catalogs and website. If you haven't done so, I highly recommend reading it.

I might have missed something in an earlier post. Do the individual carriages move smoothly on the rail? I do know that you can impart a twist or bow in the rail if it isn't mounted to a perfectly flat surface. The problem has to be in rail mounting, or the flatness of the rectangular tubing.

Are your bolt holes sufficiently oversize so you let the carriage align themselves? Tighten one carriage and leave the other just slightly loose. Move the assembly back and forth and check for smoothness. Then slowly tighten up the other carriage trying to see when it starts binding.

Another wild idea, get your THK distributor to come in and help you out. He might be willing to help out of the goodness of his heart, and the good publicity.

Another wild idea, get your THK distributor to come in and help you out. He might be willing to help out of the goodness of his heart, and the good publicity.

That idea has certainly crossed my mind! All the other suggestions I have tried. I also have the THK General Catalogue with all the mounting information in and have followed it as closely as I can with the limited machining available to me.

My hair is getting thinner by the day but I will crack this one and that's a promise.

Thanks for your interest. This site is brilliant.

Mike

Trent,

Sorry, missed one of your points - the individual blocks glide as beautifully as Torville & Dean (sorry showing my age and colours there :) )

Mike

Finally got it sorted today. :banana: These things are so fussy. One of THK's boasts is that their systems of linear guides are quite forgiving of alignment discrepancies. Obviously not the kind of discrepancies I was able to build in :)

Well on the way to finishing the second carriage for the bottom rail after which I have to tie the two together with the gantry and probably find a new set of misalignments to sort out.

It is such a great feeling when something actually works after you begin to doubt your ability to do it.

Mike

Mike, after its all together and running, you wonder what the big deal was. Until then every little thing is a major hurdle.

Be prepared for more alignment issues once you go and try to attach the ball screw. I fought that for an entire weekend.
Trent

Mike, what did you do to get it working?

Arvid

Arvid,

Back in post #19 I attached a photo of the aluminium shims made to correct the out of plane rails. These were to be placed between the blocks and the mounting system. These shims were superglued to the box section steel shown in post #34 - that was the easy bit. Because the machined flats, on either end of the box section, were not in the same plane (dodgy, out of perpendicular milling machine), these had to somehow be corrected.

I used some peelable spray on adhesive to stick some 150 grit wet and dry paper to a surface plate then painstakingly rubbed the two shims down till they were perfectly level. This worked very well indeed though was time consuming.

Next, to make sure the top of the box section was flat this too was milled and a piece of aluminium screwed to it, against which the blocks are aligned. (see photo) You can just make out the aluminium strip at the top of the assembly. The blocks were clamped to this while they were bolted through the box section. Everything was now square and true - phew!

What I have learned from this is that when THK say their system of linear guides are tolerant of misalignment, they are not talking the same kind of figures that I am :)

Mike

Well, progress at last, the clamps are off and the whole gantry is self supporting and moving freely - I've had a good day today after solving the problem of the square balls yesterday. The second block carrier went together first time and ran beautifully. I just had to get the gantry mounted that ties the two block carriers together. I was a little nervous as I was expecting the whole assembly to bind up and jam again but, to my surprise, it didn't. It ran almost perfectly, slightly stiffer than before but perfectly acceptable. The rails now need some slight adjustment to take out some very slight binding in one or two places.

Now I can press the laser line into action again to test for rail perpendicularity. I'll post some more pictures as I do it.

Trent, I've not yet worked out how I am going to mount the ballscrews but I am sure you are right about more alignment problems.

Mike

A bit more progress.

The gantry was disassembled, cleaned up and lacquered prior to attaching the Y axis rails. This was done to stop the oil from the rails staining the MDF and the whole thing becoming grubby from handling. The lacquer used was a two part, acid curing cellulose that was sprayed on. Two coats were given, rubbing down after the first. This stuff is good as it goes hard very quickly and can be rubbed down with wet and dry paper (or very fine glass paper) after just half an hour, without the paper clogging.

Our small, Isel machine was again pressed into service to machine a drilling jig for the Y axis rail mounting. This was simply a piece of 6mm MDF that was accurately drilled with the appropriate spacing. The jig was clamped to the gantry side and the holes drilled through - perfect alignment :)

I had to work out how to attach the rails, as this time they would be fixed to MDF, not steel as for the X-axis. I figured it would not be wise to screw into the MDF so I drilled and tapped a piece of 700mm x 9mm x 5mm brass strip to take the 5mm bolts. You can see one of them in the photo below that shows one rail attached and the other not. This works well and spreads the mounting load much more evenly and there is no chance of it pulling through the MDF under operational loads.

The other photos show the gantry re-assembled and a close-up. I hope to get the Y-axis, Z carrying plate in place before we break for Christmas at the end of this week. Only two days to go!

Mike

For some reason the photos did not appear with the previous post :confused:

Mike, great job! I can't thank you enough for sharing all this information.

I have had good luck screwing into MDF with something that we call a EURO screw. They are used in 32mm systems. You drill a 5mm hole in the MDF and these screws are designed for cabinet hinges and drawer slide mountings.

Also, threaded tee nuts work pretty well but aren't as pretty as your solution.

Thanks again
Trent

Trent,

I was actually thinking of rebating the brass strip into the back of the MDF which would have been even neater but decided it would probably weaken the structure too much. MDF has two quite hard surfaces which take all the bending loads whereas the centre is really mushy and if you break one of the surfaces, you end up with a very weak member.

My advice to anyone using MDF would be not to break the load bearing surfaces if at all possible.

Mike

Trent,

I was actually thinking of rebating the brass strip into the back of the MDF which would have been even neater but decided it would probably weaken the structure too much. MDF has two quite hard surfaces which take all the bending loads whereas the centre is really mushy and if you break one of the surfaces, you end up with a very weak member.

Mike

Go ahead and cut the rabbet (american sp.), just epoxy in the brass strip. The epoxy will solidify the soft core and still give you a neat and clean installation.

Are you sure your x-axis blocks are spread out far enough? It looks to me like you may get some flex if you do any heavy cutting. I guess that's where the composite comes in. :)

Gerry,

According to the THK rep I have more than enough spacing - he quoted a spacing of just one block width, between the blocks, as being adequate, I have four block width spacing so I should be well within limits.

I know the MDF version will flex somewhat more than the composite version but will beef it up where necessary. I have already spotted an area that needs some attention - the left hand side of the back plate flexes slightly when I swing on the end of the gantry or push it up with some force - a bit of vertical, buttress style bracing should fix it. Also the open side of the box structure at the bottom of the gantry will be filled in with a removable panel. This too will brace the whole structure, making a decent torsion box.

I don't plan on doing too much heavy cutting with this machine, just enough for it to cut its replacement :)

Mike

I guess I really didn't mean the spacing itself, but if the spacing was a bit farther, you could brace the gantry better.

Not a huge amount of progress this week but the Y axis rails are in place and the Y axis carriage almost complete. The MDF looks real rough compared with the nicely finished gantry but it will look similar eventually.

The Y carriage plate was small enough to be machined in full on our small Isel machine so I am hoping there will be no alignment problems. The shoulder that the blocks are indexed against are made from top quality oak, cut slightly oversize and the edges machined on the Isel to be perfectly parallel. The mounting holes for both the blocks and the Z axis rails were drilled at the same time.

I'm going to have to start thinking seriously about mounting the ballscrews soon and finding some suitable servos. So difficult to find bargains here in the UK. Does anyone know the approximate cost of shipping motors to the UK from USA? I'm thinking, if I buy say three motors and encoders for $500, what will that be in actual GBP by the time they are in my hands?

There won't be much activity on the construction for the next three weeks - school workshops are locked up!!

Mike

Mike,
I've been enjoying reading this as you progress along. I too can't wait until you get to the carbon fibre gantry stage. Keep the pics coming and enjoy your Christmas break.

Phil

Phil,

I hope you've got plenty of staying power - this could end up being a veeeeeery long thread. I am not the fastest worker in town even when I have enough time. I am hoping the first, MDF, version will take no more than twelve months to complete and starting from zero knowledge (apart from professional interest in operating our small, Isel machine), it is also a steep learning curve. This will be particularly true of the electrics which I keep putting off.

New year's resolution maybe to get stuck in :)

Thanks for the Christmas wishes and I extend mine to all those reading this thread. May you all get what you deserve :)

Mike

Mike,
Keep it coming. Your endeavor is certainly helping as I design and build my machine. I am also thinking about a composite gantry solution, although I think my gantry is going to be more conventional (not cantelevered). Because of this I was thinking about just purchasing some pultruded carbon fiber wide-flange I-beam and using it. It seems to me that while you generally want weight throughout the machine to combat vibration, having a lighter gantry would ease some of the inertia loads put on the machine as the gantry stops and changes direction along the x axis. Anyways, keep it coming Mike...I'm really enjoying your progress.
-Eli

Eli,

Thanks for the comments. The carbon fibre approach is very logical in one sense but it does throw up this quandary about mass. My reasoning has always been that the lighter the machine, the less force required to move it and the stiffer the machine, the greater the proportion of that force getting to the tool. I do however take the point about vibration and I have been thinking along the lines of somehow damping the movement with some kind of viscous fluid - haven't quite worked out how yet but it will come.

Have you worked out how you will tie the beams together? I think there may be a problem if you use a lot of aluminium in conjunction with carbon fibre because of the huge differential in coefficients of expansion.

By using prepreg materials I can use the facilities I have already built for my modelling i.e. computer controlled oven and vacuum bagging equipment. As an interesting aside I have attached some photos of my World Championship winning model. There's probably another thread there somewhere. The whole model is constructed using prepreg glass and carbon and weighs in at just 200g complete with five channel radio, ready to fly.

Have a great Christmas

Mike

Mike,
As far as tying it all together, I would most likely be tying steel to the carbon fiber. I would bolt and use epoxy to join all of the pieces. Being a boatbuilder, I have quite a bit of confidence in the solidity of epoxy as a structural adhesive. Also, wherever there is an interface between steel and carbon fiber, I will make sure to put a layer of fiberglass so as to isolate the carbon from the steel. Carbon is more noble than steel, and consequently will corrode it quite quickly. I know this is more of a problem whilst on salt water, but it can still be an issue if the machine is located near som salt air (mine will be a stones throw from Boston harbor here in the states). Cool looking plane!

Eli,

I agree about the merits of epoxy - if it will hold military aircraft together, I am sure it will do the business for us. However, I was not aware of any electrlytical (?) problems between carbon and steel. Am I to assume these are similar to the dissimilar metals problem? If so, does it not need some kind of electrolyte before problems occur? I appreciate that even the humidity in the air is enough for some metals to behave badly but with the carbon, supposedly, integrated in a resin matrix, is it really going to be a problem? I know that glassfibre in a polyester matrix is hygroscopic but not sure about carbon in an epoxy matrix. Any thoughts?

Mike

Mike,
Even if the carbon is integrated in the epoxy matrix it is still a problem, particularly if you are tapping screws. Obviously in this situation you will have steel contacting carbon directly. Yes, you will need an electrolyte to start corrosion problems, but this is a "better safe than sorry" situation for a precision piece of equipment like a router. Whenever I am building a boat or component out of carbon fiber I am very careful to isolate steel/aluminum from the carbon with either fiberglass or aramid. The effect is exactly the same as dissimilar metals if you do not isolate the materials. As far as epoxy being hydroscopic, to a very small degree it is....epoxy being 99% waterproof. If you coat and saturate a piece of wood with epoxy, and then leave it in a tub of water for a year, a small amount of water will have penetrated the epoxy and migrated into the wood fibers. In an epoxy glass matrix water will not penetrate so as to cause osmotic blistering like you sometimes see in boats that are built with polyester resins. Vinylester resin is the most waterproof. At the end of the day though this really doesn't have much to do with water penetration, but more to do with electrolytic action caused by dissimilar metals (carbon not really being a metal, but being more noble than steel).
-Eli

Eli,

Thanks for that insight - I will certainly now bear that in mind when planning the construction of the gantry. I was thinking of laminating steel into the structure, to take the assembly bolts, which will then be drilled and tapped. Maybe now I'm thinking - mould the holes in place for the various mounting bolts for linear guides, ballscrew bearings etc. then bond the gantry sections together with reinforced epoxy.

The disadvantage of this approach, and a big one at that, is that it becomes difficult if not impossible to make substantial changes or modifications once assembled.

Going back to the bolted together sections - does anyone know if nylon bolts would be strong enough to hold a machine together? Or, am I now worrying about something that is not going to be too much of a problem? Maybe someone out there has experience of dissimilar metals/materials being a problem or not?

One of the great things about this forum is the ability to bounce ideas off others - so much easier than re-inventing :)

Mike

Mike,
One thing to think about is bushings. You could epoxy in nylon bushings where steel bolts will be in way of the carbon. I don't think there will be any problem here since the compressive strength of the nylon is quite good. I wouldn't want to use nylon bolts if I had the choice. Also, thickened epoxy set in larger holes and then drilled to suit whatever bolt you pass through works well too.

*snip* Does anyone know the approximate cost of shipping motors to the UK from USA? I'm thinking, if I buy say three motors and encoders for $500, what will that be in actual GBP by the time they are in my hands? *snip*

I have ordered stuff from Ebay (US) before to Sweden. I've used the United States Postal Service (USPS) Global Express Mail (EMS). You can calculate the shipping cost on their homepage if you know the weight - 20 pounds to UK would be $83.75. This is for "3-5 day" delivery - which usually drags out up to two weeks including customs clearance and local delivery. Also expect someone to charge $10-$20 for doing the customs clearance, and a few percent of actual customs duty.

Arvid

Arvid,

It's the 'small' customs duty that is annoying me. I think it will be at least 17.5% here in the UK which is crazy when you consider that most of what you buy has already had tax paid on it some two or three times since manufacture! Somebody once told me that I would probably have to pay about the same in GBP as US$ i.e. if I buy something for $500 I should be prepared to pay £500 and with the dollar close to 2/GBP, I find that hard to bear.

What is more, even if the goods are second hand, the customs officials will work out their cut on their perceived value of the goods.

Thinks - I wonder if I know anyone flying out to the States?

I'm going to have to bite the bullet shortly and, with there being virtually nothing on offer this side of the pond, will probably have to purchase from the States.

Mike

Mike

Arvid,

It's the 'small' customs duty that is annoying me. I think it will be at least 17.5% here in the UK which is crazy when you consider that most of what you buy has already had tax paid on it some two or three times since manufacture! Somebody once told me that I would probably have to pay about the same in GBP as US$ i.e. if I buy something for $500 I should be prepared to pay £500 and with the dollar close to 2/GBP, I find that hard to bear.

What is more, even if the goods are second hand, the customs officials will work out their cut on their perceived value of the goods.

Thinks - I wonder if I know anyone flying out to the States?

I'm going to have to bite the bullet shortly and, with there being virtually nothing on offer this side of the pond, will probably have to purchase from the States.

Mike

Mike


Mike,

Can't you have someone here buy the item in question, ship it to you... and give them a small service charge? I don't see how you'd have to pay the "customs" charges then.... how could they make you do that?

Jimmy,

I've just contacted Jeff Davies of HomeCNC www.cnczone.com to see what he can do for me. He is still offering the 430oz/in servos on his site. Noticed he also has some very nice looking 360oz/in servos on ebay - cheaper too, but I think I will need the more powerful ones. I was really looking for something around the 600-800oz/in but can't find anything within a reasonable price range.

Mike

Jimmy,

I've just contacted Jeff Davies of HomeCNC www.cnczone.com to see what he can do for me. He is still offering the 430oz/in servos on his site. Noticed he also has some very nice looking 360oz/in servos on ebay - cheaper too, but I think I will need the more powerful ones. I was really looking for something around the 600-800oz/in but can't find anything within a reasonable price range.

Mike

If he has to ship them to you with some type of customs slip from our postal system then have him put the value at $20 US dollars and the description of the motors as "used something or other..." That should keep them off of your back. I have no experience with sending stuff to the British Isles, but when I send stuff to Canada they do have me fill out a slip that I mentioned above. Make the seller aware of your situation and I am sure he can try to help you out. If not... contact an individual *like myself or others on the board* and see if you can't work something out by having them purchase the item themselves and then sending it to you via the mail as mentioned above. :cheers:

Thanks for the offer, Jimmy. I'll wait and see what Jeff can do for me first but may well be in touch.

Cheers,

Mike

Well, I've been and gone and done it! I've ordered three 430 oz/in servo motors from Jeff Davis at HomeCNC. He was very helpful and answered all my questions by return email - thanks Jeff.

I now have to decide between Gecko and Rutex drivers. The advantage with Gecko is that Jeff uses these and knows the set up for his servos however, Rutex offer mother boards and IO boards for easily setting up home switches, spindle on/off etc. but I'm not sure how this is done using Geckos. I have emailed Gecko and await their response.

Any help from others would be much appreciated.

Mike

A lot of people using Geckos use the breakout boards from http://www.campbelldesigns.com

Gerry,

I've just looked on the Campbell Designs site and added up the costs of both systems and there really is nothing in it. However, there is something you may be able to help me with. On the Rutex it has a step multiplier (with Gecko it is an extra) and I was wondering exactly how does this work? Does it multiply the steps from the software or does it multiply from the encoder? For example; if my software indicates 100 steps and I use the 10x multiplier, does my motor move 1000 steps or 1? In other words, does this improve the resolution of the system or detract from it?

Am I right in assuming this is not the same as stepper motor microstepping where one step is divided into many, smaller steps and that a servo motor can only be moved by whatever the resolution of the encoder is (x4 with quadrature)?

Many more questions to come.

Mike

Mike, I was getting ready to answer, and got confused just thinking about it. The multipliers multiply the steps sent from the computer. The step size is determined by the encoder resolution. I THINK this is right: Like you said above, if you use the 10x multiplier, when the software says 100 steps, the motor will turn 1000 steps. The difference is that you have to tell the software that the step size is 10x bigger than without the multiplier. Say your not using the multiplier, and your encoders give you 1000 steps per inch. The step size is .001. If you want to move 1 inch, the computer sends 1000 steps. With the 10x multiplier, you only need to send 100 steps. The step size would be .01. (The step size you tell the controller is .01. Your actual step size would still be .001, based on your encoders)

The only reason you should be using the multiplier is if your computer can't output steps fast enough. Your motors should have 250 cpr encoders, which should give you 1000 steps per revolution. If you use a 10 tpi leadscrew, that's 10,000 steps per inch. With a good computer, Mach2 can output 45,000 steps per second. That's 4.5 inches per second, or 270ipm (MAX, you'd probably want to stay a little under that). If you need to go faster, I'd use either a higher lead screw, or maybe try DeskCNC to control the machine, which I think can output 125,000 steps per second. Within the next year or so, Gecko should have a product that can produce even faster step rates (G2005?).

Gerry

So, if I am understanding this correctly, there is absolutely no difference in accuracy, just speed. The purpose of the multiplier is simply to overcome the problems of slower processors? Therefore, with a good PC, multipliers are not worth having?

I'm still not quite with it. Suppose I am machining a circle and I use the x10 multiplier. Does the machine interpolate these extra 10 steps or does it simply go in a straight line between the PC's given steps?

I'm still confused - I think :)

Mike

Gerry

So, if I am understanding this correctly, there is absolutely no difference in accuracy, just speed. The purpose of the multiplier is simply to overcome the problems of slower processors? Therefore, with a good PC, multipliers are not worth having?

I'm still not quite with it. Suppose I am machining a circle and I use the x10 multiplier. Does the machine interpolate these extra 10 steps or does it simply go in a straight line between the PC's given steps?

I'm still confused - I think :)

Mike

I'm not really sure, but it seems like it would go in a straight line. The PC just says to the controller - turn the motor 1 step. So the Gecko or Rutex would just turn it 10 steps. Like I said, from what I understand, the sole reason for their existence was that not long ago, you couldn't get affordabe software to produce steps fast enough. That's changing now, although servos tend to need higher step rates than steppers. Even with servos, I couldn't see the reason to use more than 2x or maybe 5x multipliers, unless you use very high resolution encoders. The multiplier basically makes your higher res encoder a lower res encoder. Nothing more.

What leadscrews are you going to be using? Any gearing? Do the math, figure out the steps/ second you'll need, based on the speed you want to go, and determine if you'll need to use it. If not, I think the Gecko's are quite a bit cheaper than the Rutex.

I forgot to mention the accuracy issue. If you really needed the 10x multiplier, the resolution of your machine would be 1/10, ie, if your step size was .0001, with the multiplier it would in reality be .001. BUT, if your step size was .0001, can your machine really move .0001 at a time? Not very likely. Your likely to have more backlash than that, and it most certainly will flex more than that. (At least the MDF version :) )
But like I said above, you really shouldn't need the 10x multiplier.

The best thing you can do is keep reading, try to learn and understand everything you can, and make your choices based on what you think YOU need.

Cheers Gerry, Happy New Year - just leaving for the festivities. I'll post again next year !

Mike

WOW - doesn't time fly - 2005 already and may it be a good one for all zoners.

Gerry,

I am using 5mm pitch ballscrews with preloaded nuts, all riding on THK linear guides so I am hoping there will minimal, if any, backlash. As one of my main interests is in model aircraft, I wanted to make a machine capable of machining wing profiles as accurately as possible. The preferred material for machining the patterns is an epoxy block, so this should be perfectly OK without too much strain on the machine. I hope also that the composite version will be capable of machining aluminium.

The motors I have bought from Jeff Davis have 250cps encoders on board which will give me 2000 steps at the ballscrew after quadrature and 2:1 reduction via timing belts. If my calculations are correct this should give me a theoretical resolution of 5/2000mm = 0.0025mm or 0.0001" - just as in your example!

Mike

.... which should give you up to 240+ ipm, if you can get a 45 Khz step rate from Mach2..... with no need for the step multiplier. :)

OK, so now I'm confused again because the motors are rated at 1700rpm which will only give me, after reduction, 850 x 5 mm/min = 4250mm/min approx 170 in/min or 70mm/sec 2.8 in/sec, OK but not excessively fast. Are you saying that these motors can/will be driven faster than their rated rpm if the software/PC can output the steps at 45 khz?

What are the limiting factors on speed? I understand, from the literature, that I should not drive my X axis ballscrew faster than 900rpm despite being fixed one end and supported the other. I would love to be able to have 240 inch rapids but is it realistic? Will the motors/drivers get excessively hot at these speeds?

Too many question - aaaaargh :)

Mike

Sorry, Mike. I didn't realise the motors are rated at 1700rpm. I haven't used servos, but I wouldn't try to run them faster than their rated speed, regardless.

Some trial and error will probably be needed on your part. First, I'm assuming you'll use Mach2 to get the 45Khz step rate. Be aware that you'll possibly need a 2Ghz PC for this. (Not entirely sure). The rapid speed (Max RPM) of the motors will be set in the Mach2. This will take into account your encoders resolution (1000), screw lead (.2), and the gearing you use (2:1?). As you mentioned, you may well be limited by the screw whipping at higher speeds. Here's what I'd probably do. If you think you'll be limited bya screw speed of 900 rpm, I'd gear it to spin maybe 1200 rpm (+30%)with the motor spinning at around 1600 rpm (3:4). Once up and running do some tests to see how fast you really can go, and set your top speed accordingly. If 900 rpm is really your maximum speed you feel it can run at, then just set this in Mach2. You will sacrifice a bit of torque from the lower gearing. But you could always replace the pulleys to maximize torque once you determine your max speed. This way you allow for a higher rapid speed. Also, the shorter the screw, the faster you can spin it, so your Y axis may have faster rapids than the x axis, which you may want to use different gearing on.

Make sense? Or even more confused? :)

What are the lengths of screws you'll be using? And where did you get the rpm info? Looking at the critical speed charts from Nook http://www.nookind.com , it looks like a 26" long screw can spin about 2000 rpm or more, but an 80" screw only 500 rpm.

Gerry,

X axis is 25mm diameter x 2000mm long, Y axis 22mm diameter x 700mm and Z axis 16mm x 300mm

I'm sure one of the sites I visited had a critical speed calculator on it, as does nookind.com, and it gave critical speed as 888rpm which I rounded up to 900. However, checking out the THK manual, with all its complex formulae tends to agree with you at around 550rpm for the X axis.

Your previous post makes a lot of sense and I like the idea of trying different reduction ratios to find the optimum speed for my setup. It would also be possible to make the X axis ballscrew fixed and have a rotating nut - this would allow much faster speeds would it not?

The murk is slowly clearing, many thanks.

Mike

Mike,

Interesting machine and posting.

With the critical speed calculations Nook and THK use different bearing configurations which affects the final number. The nook calculator gives four options of end 'fixity' (don't you just love the american language).

Simply put, what ever speed you end up with I'd suggest that you look at putting two support bearings on each end of your 2m screw, with a space of at least 25mm between. Effectively a cantilever support at both ends this could be incorporated into the thrust bearing arrangement. That would stiffen the screw immensely and so push up the safe rotational speed.

A rotating nut would solve the whip problem and some machines use it. The problem comes in the engineering. If you could machine a replacement for the ball nut flange to incorporate a bearing and timing drive pulley and mount the servo that would be possible.

Another idea to reduce whip in a rotating leadscrew which has worked for me is to put bearings either side of the lead nut. This reduces whip and takes the loads off the nut. Down side is you need to have a bearing that will not mar the screw but ride on it both rotationally and axially. I've used some plastic bearings from Igus for this. It's a bit of a bodge to fix a too small a diameter screw at too fast a speed and only if you're getting too much movement.

hth

Andrew

Andrew,

Thanks for the reply.

Wow, by using the double fixed with spacing between the bearings (Fixity (ugh) D) in the Nook calculations, it more than doubles the critical speed! It goes from 671rpm to 1496rpm. I used the correct measurements from the THK catalogue i.e. 22.2mm minimum thread diameter at 2000mm spacing.

I have heard of adding a preload to double fixed bearings by, effectively stretching the ballscrew between the two, fixed bearings. The problem I face if wanting to increase the speed this way is that the ballscrew is already machined to accept one fixed and one supported end and I am not sure I have the necessary equipment to alter this.

For this first machine I will probably make it as it is, see what the problems are, then alter and modify if necessary.

Thanks for the input.

Mike

Mike, disregard my critical speed calculations. I mistakenly thought you said you were using 5/8 (16mm) screws. :(

Looks like you have a handle on it now.

Yes, thanks Gerry and Andrew for your input. Having you guys to call on when posed with a problem is so reassuring.

Please keep watching - there will be plenty more questions before I'm through.

Should be able to get back to the machine soon. It seems so long, I'm getting withdrawal symptoms :)

Mike

You're assuming I know what I'm talking about :D

My motors arrived today, all the way from Oregon to Liverpool in just over two weeks - not bad. I have to credit Jeff Davis of HomeCNC for some excellent packaging, each motor was separately packed and all three well insulated against the vagaries of all the postal systems they went through.

They look the business and I am pleased they are relatively light in weight which is just what I need for my rather unconventional, cantilevered gantry.

Just need to make the decision between Gecko or Rutex now and I'll soon have these beauties singing.

Mike

Now I have the motors, I need to think about the drive train and I intend driving the screws through 2:1 timing belt reduction. Looking on the internet for possible options leaves me somewhat puzzled. There are hundreds of different belts and pulleys. Can anyone suggest the type I should be looking for and where I could purchase some from. I don't mind buying online (in fact I prefer it) - would prefer to buy from UK but not fussy if cheaper elsewhere.

I am using the 430oz/in servos shown in the previous thread.

Work has started mounting the ballscrews on the X and Y axes. Hope to be able to post some pictures next week.

Mike

I used HTD belts and pulleys on my machine. They have a rounded tooth form and seem to engage better than the square type. RS and Farnell have them. Seem quite expensive tho'. I got mine from work (free). I thought ondrives in the UK stocked them, but looking at their website, it seems not.

Regards Terry.....

Mike, a good source of belts (not UK, though :( ) is http://www.sdp-si.com They have a lot of good info, too.

WHile HTD belts are better than the square tooth styles, GT2 (Gates brand) are supposed to be the best for backlash. The info is available at the site I mentioned.

Gerry & Terry (got to be a joke there somewhere :) ) thanks for the replies. Still a little confused though - On the SDP-SI site I can select metric measurements and pick 16mm T5 belts, there are no matching pulleys. If I then select metal timing pulleys and select HTD 5mm pitch, 15mm width, there are only neoprene, fibreglass reinforced belts available. Will these do the job or should I really be looking for polyurethane, steel reinforced belts?

Should I be looking for something other than 5mm pitch?

Will plastic pulleys be OK? I have only been looking for aluminium ones so far.

Ooooh so many questions - but I need to get these things right.

Mike

I've done some Google-ing and Gerry is correct, in that GT2 does have less backlash that HTD.

Neo+fibreglass belts should be OK. I read that steel reinforced is only very slightly better and is mainly used for harsh shock and impulse loads.

Regards Terry.....

SDP-SI website has pulley and belts for GT 5mm pitch, 15 & 9mm widths.

Not sure you ever got a clear answer on motor speed.
Your servos ( I have them too) run comfortably at 1360 rpm (80% of 1700).

When ordering pulleys I was glad that I bought extras that allowed for different reduction ratios...2:1, 3:1 and 3:2. That is 12 teeth, 24 teeth, and 36 teeth; this permitted trial and error tuning for speed vs. brute force. Sure, there will be extra pulleys laying around, but at this point what is another $50- £30.

I am using the fiberglass reinforced belts. So far so good.

Oh yes, the belts can be purchased in increments of 5 teeth elsewhere; it may be worth sizing things to the nearest 5 rather than the exact number so that things are easier at replacement time...but then I'm on the other side of the pond.... :)

Gerry & Terry (got to be a joke there somewhere :) ) thanks for the replies. Still a little confused though - On the SDP-SI site I can select metric measurements and pick 16mm T5 belts, there are no matching pulleys. If I then select metal timing pulleys and select HTD 5mm pitch, 15mm width, there are only neoprene, fibreglass reinforced belts available. Will these do the job or should I really be looking for polyurethane, steel reinforced belts?

Should I be looking for something other than 5mm pitch?

Will plastic pulleys be OK? I have only been looking for aluminium ones so far.

Ooooh so many questions - but I need to get these things right.

Mike
They seem to only stock the T5 in 10mm width.

Mike,

Do not use the T style belts/pullies. These are made to have some backlash built in. I believe the same is true for HTD. Use the AT or GT2 instead.

(I am having the same problems/confusion with timing belt reductions as you are. There's also a lot of different choices for hubs - setscrew, taperlock etc.)

Arvid

Wow - lots of response, thanks.

OK, it seems that AT or GT2 are the best choices for no backlash, from Arvid, probably go for 2:1 and 3:1 to have a choice of reductions. Max speed of my X axis ballscrew is in the region of 600 - 800 rpm with motors giving 1700 rpm max, from Sol and from Terry it looks like most of the common reinforcements will do.

Gerry, I am thinking that 10mm is probably too narrow and am looking for 15-16mm.

Arvid, I like the idea of the taperlock pulleys - no annoying grubscrews or filing of flats :) Problem is finding sources that will sell small quantities. Good luck with your searching. Maybe we can keep each other posted about progress?

Right, a bit more surfing in order.

Mike

Gerry, I am thinking that 10mm is probably too narrow and am looking for 15-16mm.

Mike

I've got a feeling the 9mm would be more than strong enough, but if it were me, I'd buy the 15mm. :) The prices aren't much different, are they?

I agree. Like I said. I got my belts & pulleys for free, but having now used the machine a little, if I were buying some, I'd go for 15mm GT type, 5mm pitch.

Regards Terry.....

Right then, that seems to be sorted - 15mm GT it is. Now all I've got to do is find a supplier :)

Thanks for all the information, I'm sure you all realise how much time and effort you have saved me and that is the beauty of this forum - everyone is so keen to share their hard earned experiences. I only hope I can be as useful once I've gained the knowledge.

Mike

Hey Mike F. Glad to see the motors got to you in one piece :) I'm a little behind in seeing this post.

Mike, Are you going to be able to find the parts to build the controller box OK?

Jeff,

Not really thought that far into the electrics yet but I will be press ganging a friend into service who is an electronics genius - works on top secret MOD stuff!! Not sure I should be saying this :) He will want to know why I am not building the controllers myself instead of buying Geckos or Rutex :) I am not anticipating too much of a problem here.

I have spent the last three days scouring the web for compatible pulleys and belts but keep drawing blanks. The problem is that the motors are 1/4" shafts and the ballscrews are 10mm, 12mm and 15mm shafts and trying to find a firm that can supply all these sizes, preferably with taperlock hubs, is proving difficult, especially when I am also specifying GT type belts.

Still, if this game were that easy, everyone would be doing it.

Mike

Mike, try emailing Gates europe and see if they can hook you up with a distributor. While I was just looking at their site, I noticed they now offer an even better belt, the GT3.

Cheers Gerry, I'll do that right now.

Mike

I have spent the last three days scouring the web for compatible pulleys and belts but keep drawing blanks. The problem is that the motors are 1/4" shafts and the ballscrews are 10mm, 12mm and 15mm shafts and trying to find a firm that can supply all these sizes, preferably with taperlock hubs, is proving difficult, especially when I am also specifying GT type belts.

Still, if this game were that easy, everyone would be doing it.

Mike

Mike, for the 1/4" motor shaft. Don't worry about getting taperlock hubs for it. Just get a pulley with the correct number of teeth that has a small hole that you can drill out to 1/4" and then drill a small cross hole through the entire pulley and motor shaft and pin them together. This will keep the pulley on the shaft and it will never slip. This is what I do because of the shaft being so small.

Mike,

I've used misumi in the UK for some mechanical components including timing belts in the sizes you're looking at. They carried both metric and imp including gates and the pully to match, but it was a while ago so don't hold me to it!

UK presence used to be in Staines, and the number was 01784 465530, sales@misumi-europe.com Their catalogs where worth the read alone since there was loads of engineering data.

Andrew

Jeff,

How can you be sure there is no backlash after the pin is inserted? Surely after time, with the motor changing direction quickly, the pin must wear loose and have play in it. For this same reason, I have read that keyways and grubscrews are not recommended. Am I being over cautious? By the way, how many teeth and what pitch are your small pulleys?

Andrew,

I have the Misumi catalogue and most impressive it is too. Maybe I am not looking hard enough but I could not find exactly what I wanted. I have emailed Gates UK and had a promising response. Their project engineer reckons he can sort me out with just what I want - hope so.

Thanks for the input.

Mike

You are only talking 430 oz/in maximum. You get a metal pulley and put a 1/16" roll pin in and you will not see any slop develop. If you were talking some real horse power then a pin can wear out.

For my 2:1 setup I have 12 teeth on the server motor and 24 teeth on the ball screw.

Thanks Jeff, that's brilliant. I can now get down to some serious work without the nagging doubt.

Cheers,

Mike

I received a quote today for three small timing belt pulleys (15 teeth) and three large pulleys (30 teeth) and nearly collapsed - couldn't decide whether to laugh or cry. I had asked for the belts too but they were missing from the quote but I don't think I will be pursuing this one anyway. The quote was for 413.44 GBP :eek: that is about $780 :eek: :eek: These were just grub screw hubs too and I had asked for taperlocks!!

Where do these companies get their pricing from? That is not too far off double what I paid for three servo motors with encoders - which is more difficult to make? I am dumbfounded and more than a little upset. :(

Oh well, carry on searching I suppose.

Mike

Boy, that price seems a bit excessive... unless they are solid gold... I'm sure you can find much better. If nothing else hunt the web. I just did a quick check and found prices to be much lower at Mcmaster-Carr. Don't know what size your motors are but checked 3/8in shaft 14 teeth and was $15.00 us. Shipping etc can't be too bad considering your last quote. Good luck.

http://www.mcmaster.com/

-marc

Marc

They say they are specials because I wanted the small pulleys to have 0.25" bore and the large ones to have 10mm, 12mm and 15mm bores. I need to contact them and ask if they produce them with no bores, and then bore them myself. Be interesting to know what their price will be for unbored pulleys.

It is looking more and more likely that I will be purchasing from the USA again but what an endictment on British industry!

Mike

Marc

It is looking more and more likely that I will be purchasing from the USA again but what an endictment on British industry!

Mike

The Swedish industry :boxing: is not any better. I have discovered that thretening to buy from the US often gets their attention and a better price. :)

A little more information from the firm who quoted me ridiculous. I asked them to quote me for standard pulleys from their catalogue, without specific bores. That I did and noted they have a zero backlash option which was obviously the one to go for. The quote came back and the rep said that zero backlash was also a special and quoted me £43 GBP for the 16 teeth pulleys and £70.80 GBP for the 32 teeth pulleys. When totalled and VAT included it comes to an impressive £401 GBP. That's a massive saving of £12.44!!!!!!!!

Can someone please tell me whether the GT2 or AT are zero backlash?

Thanks,

Mike

I don't think any pulleys are truly zero backlash. All I can tell you is from what I've read, GT2 is the one to get.

I have managed to get the Y axis ballscrew mounted in a rather temporary manner just to test the arrangement. I was pleasantly surprised to find the Y axis plate moved quite smoothly throughout its entire length. It is rather tedious though having to turn the ballscrew by hand.

The great thing about this design is that the whole gantry assembly detaches from the X axis rails with just four screws and can then be worked on easily from a bench.

Next stage is to dismantle the Y axis, tidy up the mounting arrangements, clean up the pieces, spray where necessary then re-assemble. Just hope everything goes back together as well as the first time :)

Mike

Mike, beautiful job!
Could you hook the end of the ball screw to an electric drill and use that to move the carriage?
Trent

Trent,

Yes, that was the intention but when it is mounted on the wall I cannot get at the drive end :( For the next stage of fine adjustment I will drill an access hole through which I can use an electric drill but this will have to be done off the wall and for now, I wanted to see what it looked like in situ. I bet more time is wasted on projects by just standing back and looking at progress than by actual progress itself :) :)

Mike

Finally got my pulleys :banana: :banana:

I ordered them through www.sdp-si.com at a cost of $136, approx 72 GBP, just a little better than the 413 GBP quoted over here!!! However, there was a little sting in the tail as the postage, advertised as "Freight amounts to be determined using standard published list rate." , turned out to be $69. I am still a happy bunny though as the total cost was still just about a quarter of the original quote. It certainly pays to shop around.

I ended up getting 3 x 16 teeth, 3 x 32 teeth, 1 x 48 teeth pulleys and 3 x 60 teeth belts - all are GT2 specification as recommended here. The 48 teeth pulley is to allow a 3:1 reduction on the X axis if the 2:1 gives whipping problems on my 2000mm ballscrew.

I could not get the bores I required so will have to bore these out to suit. One of the ballscrew, 32 teeth pulleys will need a sleeve but should not be a problem.

At last I can start working again. :)

Mike

Finally got my pulleys...
This is all a bit over my head at the moment, but from what I can make out, you are going with the GT2 belts based on a trade off of backlash versus cost.

...First, they recommend the AT tooth profile with polyurethane belts to get minimum backlash. If I understand correctly, HTD is worst in this respect, followed by T, GT, and AT, in that order.
For my design I was considering going with the T2.5mm profile 6mm wide stuff that rswww sells. For a similar shopping list to yours, this would come out around £56 ex VAT. These would be more than ample spec for my bodgy design. Is the GT - T difference that great or are there other considerations?

BTW - great looking machine!

10bulls

I too was very confused by the huge number of different spec belts and pulleys, hence my questions to the zone. As far as I can make out, the reason GT are so good is the profile of the teeth, they are rounded giving much quieter operation. I don't know whether I have gone over the top by specifying 15mm belts but that decision seems to have been supported here by others.

Reliance, a company in the UK, offer backlash free versions of GT pulleys but these are the ones they quoted me silly for (£413) Obviously there is a very real cost consideration here.

I have yet to get the motors mounted so cannot comment yet on how well the system performs but they look pretty good and I cannot distinguish any backlash when fitted over the pulleys by hand. Incidentally, Jeff Davis who supplied my servo motors, says he uses standard pulleys and belts and has no problems with backlash.

I have seen your thread but cannot recall the size of your machine. Mine is fairly large which is why I went for the 15mm x 5mm pitch belts but 6mm x 2.5mm pitch seems awfully small, but there again, I'm a beginner too so what do I know?? :)

Mike

I am now at the point where I really do have to make the decision between Rutex and Gecko. Although price is not a fundamental issue I still do not want to pay more than I need to. As I see it, the advantage of Rutex is that I, as a complete electronic moron, can simply buy a mother board and IO board and plug it into the system. On the other hand, Geckos are cheaper but require a third party IO board and home/limit switch board.

Now the question. Bearing in mind my total incapacity for all thing electronic, how easy is it to interface Geckos with the necessary gizzmos for home/limit switches and IO functions such as spindle, coollant etc.? Is there something I can simply plug in?

Mike

Mike, If you've made it this far I don't beleive the Geckos will be a problem. Go take a look at the PMDX breakout boards at http://www.pmdx.com/ .
Something like the PMDX120 should do everything you need and has all of the pinout/in connectors and relays built on the board. You can set things to your softwares preferences (like pulled low or high, charge pump settings, etc) There are other brands so look around and read the manuals (PMDX has them online for download). They will make connections a snap.
I only mention PMDX because I have one and am happy with it.
-marc

Also llok at this breakout board. http://www.campbelldesigns.com/

Marc & Gerry,

like pulled low or high, charge pump settings, etc

This is what is worrying me - I don't understand the terminology so don't know exactly what I will need but thanks for the replies, I will be investigating the sites suggested. I just hope they cater for electronic dunces :)

Mike

The high or low are software settings, not a big deal. The charge pump is a safety circuit that basically keeps your motors from spinning when the software doesn't have control yet.

The breakout boards really make setting up Geckos (or Rutex) drives almost plug and play.

Mike, Take a look at this guys products for Break-out-boards and charge pump board. He sent me a full set of his products to test. He is also working with Art and the Mach 2 software for full compatability with it.

http://www.cnc4pc.com/

Mike, Take a look at this guys products for Break-out-boards and charge pump board. He sent me a full set of his products to test. He is also working with Art and the Mach 2 software for full compatability with it.

http://www.cnc4pc.com/

Nice price on that board. Think it'll be comparable to the PMDX board?
Gotta let us know how the testing goes!

Most software like Mach 2 will let you select either pulled active low or high, so it's not a big issue except that if it's not built into the board and you manually wire it, you need resistors and a specific voltage to pull the pin(s) high or low. Basically, the software is either reading a low or high voltage at a specific pin as either active (on) or inactive (off) and just does whatever the software is programed to do (like turn a spindle on with an M3 g-code) when the active signal changes from low to high or high to low.

Charge Pump is simply a software safety feature that will work with any software that will send a signal via the parallel port (normally pin 17). If for any reason the software driving your machine burps, bumps, locks or quits (windows error, power bump, driver error whatever) it makes an emergecy stop and the breakout board stops all motors, turns off all the relays etc. It's a very nice safety feature.

The reason I choose the PMD over Campbells was it had the relays built in and avoided the cost of additional "daughter boards" or wiring relays.
I think PMD 120 board has 4 a/c relays to power things like spindle for on/off, coolant pump for on/off or whatever you want. You only have so many pins available for stuff like limit/home switches and relay output signals. Doesn't matter what breakout board, as you are limited by the 25 pins per parlallel port and only so many allow signals in and so many allow signals out. Any board will basically do the same thing, but others may have 1 or more relays built on. Mainly breakout boards keep things isolated from your computer motherboard LTP port and ensures that you don't damage your computer when a problem occurs with a driver board (and visa versa). You can also get a cheap PCI multi I/O card that will give you another LPT port effectively doubling available pin in & outs. Of course if you do that you may need another breakout board to use that ports effectively also. That way you could use a number of limit, home or reference switch setup alternatives. For example I'm currently setting up a plasma table with a torch height controller and a torch height sensor and since I already have a number of limit and home switchs connected, I required more pin in/outs than one parallel affords. You'll have no problem setting up/wiring the stuff you're talking about... and the cost is minimal compared to motors, drivers, linear bearings and the like... the hardest part will be running the wires and mounting the switches! (sorry for the long post and blabbing on about stuff you may already be aware of, but hope it helps a little)
-marc

To all those who have recently replied - many, many thanks. I am so glad I found this site after contemplating a self build. Unfortunately my mechanical skills far outweigh my electrical skills and, as I have said previously, I will be leaning heavily on the good, patient, expertise here.

Marc - long winded or not, it was just what I needed and I am sure it is probably not the first time you have explained this detail. Thanks. If I want both home and limit switches on a three axis machine plus spindle and coolant, does this mean I need to occupy eight additional pins of the parallel port? If so are there that many available to me without the added complexity of another parallel port?

Presuming I will be using Mach II or III, does the software give me enough control to negate the need for limit switches and thereby save the need for using pins I probably haven't got? The small Isel machine we have at the moment has no limit switches, you just tell the software what the cutting limits are.

Jeff - When are you likely to be able to report on the CNC4PC boards?

So, bottom line is that there is definitely something out there that is comparatively idiot proof that can just be plugged into Geckos to do the necessary additional functions other than driving the motors. That being the case it looks like Gecko may well be getting a sale.

Mike

Jeff - When are you likely to be able to report on the CNC4PC boards?Mike

The items are still in the mail. I will let everyone know how they test out.

I kind of like the modular method that cnc4pc has used. If you don't want releays you don't have to buy them. If you don't want the charge pump option you don't have to get that as well. Get the options you want and only pay for the options you want.

To all those who have recently replied - many, many thanks. I am so glad I found this site after contemplating a self build. Unfortunately my mechanical skills far outweigh my electrical skills and, as I have said previously, I will be leaning heavily on the good, patient, expertise here.

Marc - long winded or not, it was just what I needed and I am sure it is probably not the first time you have explained this detail. Thanks. If I want both home and limit switches on a three axis machine plus spindle and coolant, does this mean I need to occupy eight additional pins of the parallel port? If so are there that many available to me without the added complexity of another parallel port?

Presuming I will be using Mach II or III, does the software give me enough control to negate the need for limit switches and thereby save the need for using pins I probably haven't got? The small Isel machine we have at the moment has no limit switches, you just tell the software what the cutting limits are.

Mike

Usually 8 pins are used for 4 axis of step and direction. From a website I just looked at, there are 5 more input pins (limits, home, probe) and 4 more outputs (relays, coolant). If you're only using 3 axis, you have 2 of the first 8 available as well. Usually limit switches are all wired to one pin, either in series or parallel. Each home switch gets it's own pin. If you need more, you can always add a parallel port via PCI card.

From what I've read, limit switches can be pretty important on a servo machine, because if an encoder fails (or wire breaks), the machine will take off with nothing to stop it until it crashes. You could always stand there with your hand on the E-stop button (another pin for that) :)

Gerry,

To help adjust my ignorance, do you know of a web site that explains this detail in non-technical terms? It is obviously something I have to get my head round if I am to consider any kind of success. I understand the concept of how the printer port works in terms of each pin capable of being either on or off but your post suggests that some are dedicated as input only and some as output only - is this correct?

I would like to consider a fourth axis at some stage so would preferably like to keep those pins spare. I will need spindle on/off, extraction on/off (is it possible to put these two together?) and possible coolant along with both home and limit switches. I take your point about servo runaways. Could be disastrous. :eek: I take it that if all limits are wired to one pin that any one will trip the system which seems to make eminent sense.

Thanks,

Mike

Mike.. go to the PMDX site and download the PDF manual (It's not too big) for the PMDX120 breakout board. Take a look at table 12. It shows what the pins are used for. Basically, it uses 2 thru 9 for step/dir control. (so 4 axis's posssible) It uses 10, 11, 12, 13, & 15 for switches (so you could use one for all the limits wires parallel or series and 4 for home switches). It uses 1, 14, 16, 17 for relay control, so you could connect up to 4 devices like spindle, coolant pump etc. This card also has gecko 300 series servo driver fault signal input. This card or (or simular) would do everything you need with one parallel and no external relays etc. If you ever need more reference switches or specific table setups or part fixtures, then plugging in another lpt port card is cheap and very simple and would double things. Simple!
-marc

Eli (Spank), when you say you build boats, do you mean model or full size?
Marc (Coherent), Mike wasn’t the only one helped by your explanation. Me too.
Gerry (Ger21), thanks for the links to the fibreglass articles some weeks ago. They sure kept me busy for some time. I read the Corsair article twice over.
Hi Mike, your machine’s looking great. I just re-read this thread from the start. I realise you are past the screw in MDF stage however for others reading this thread I just wanted to explain that when Buscht was talking about Euro screws, these are the special screws used in for example, Ikea furniture. (Countersunk allen head requiring a special drill, produces a very strong joint) Well I spent about 2 hours tonight searching the internet for the article below on aluminium honeycomb sandwiched by carbon fibre. I couldn’t figure out why I couldn’t find it until I realised that I had it in the physical form (i.e. a magazine article) as opposed to virtual. The only reason I linked your project to the one in the article is because they are both using flat 2D sections bonded together to make a 3D shape. Although this method might not have the same strength/weight ratio of a true monocoque, it is however achievable by people like us and doesn’t cost trillions. Just out of curiosity, I wonder whether you would be better off to use a foam core (PE or PU) and just plain old fibreglass instead of carbon fibre? If with fibreglass, you had to use one or two more layers than you otherwise would have had to with carbon, so what! If it weighed a few more kilos but cost one tenth of that of carbon, then good! I must admit however that carbon looks the piece. Anyway, this is for you to decide as you are more experienced in composites than I am.
Skippy

Thanks Marc for a very informative answer. I like the idea of a single solution that caters for all my perceived needs - I will be taking a longer, better look at the PMDX site.

Skippy - I think that Euro screws and the Confirmat screws I used are probably one and the same thing. (see picture)

The idea of using flat sections was to simplify the construction and yes, a monocoque would be much stronger but I figured that a well thought out alternative would be much easier to make. I am definitely thinking of a sandwich structure but not yet determined what the core material will be. I use Rohacell, an acrylic foam, for the models. It is extremely light weight 31k/M^3, 51k/M^3 and 71k/M^3 available yet it has very good compressive strength. If the core is reinforced locally where the pieces will be bolted together, I think it will work OK. However, I am a long way off that yet. :)

When considering composites, it is worth noting that you really ought to use just one type of fibre and not mix them. Glass and carbon have a quite marked difference in coefficients of expansion and considering I am using prepreg material, baked in an oven, when mixed the results can be quite alarming. I know because I have done it - if you want panels like bananas, laminate one side with carbon and the other with glass - you will be quite amazed at the outcome.

Carbon prepreg is about twice the price of glass weight for weight but you have twice as much fibre in the carbon so there works out to be not too much significant difference if you compare strength to strength.

Mike

All of the pin configurations described by Coherent are now a standard, set by the research and development of EMC that was paid for by a government grant many years ago. Thus all the step and direction controller software that use the LPT port has followed this standard for pin usage. As a result of that, all the break-out-board manufactures use these pins too. For a very full description of the pin usage for two (2) LPT port options, you can look at the latest Mach 2 manual from Arts site.

Here's a Euroscrew. This might be just US terminology. In Europe, it might be called something else.

Typically Euroscrews like Trent shows are used for attaching cabinet hardware, usually in 5mm holes.

Right then, Euro screws are for fixing things to MDF whereas the confirmat screws are designed for fixing MDF to itself. Looking at the diagram from Trent, it looks like the Euro screw would not be as good as the confirmat screw for screwing MDF boards together, as someone had previously suggested they had done. I have to say that I am very pleased with the way the confirmat screws work and they can be assembled and disassembled many times without fear of compromiseing the thread.

Jef - Thanks for the confirmation and insight into the standardisation of the pin outs for the parallel port usage. It looks like I've got a lot of reading to do.

Mike

I don't want to contradict anyone but to me, Mike's picture and Buscht's picture are one and the same. i.e. Euroscrews (Europe/US) and confirmat screws (UK) are the same thing. Just that in UK the brand name is used instead of the generic name. (same way as acrylic sheet becomes perspex and backhoe becomes JCB in the UK. Absolutely no critisism intended) The idea being that they act as both screw and dowel (the shank area) at the same time, for holding mdf or particle board to itself. Buscht's image is a little deceptive because it looks short in the screw area but that's only because they are showing "Lange" (length) to say that it can be bought in multiple lengths. To work effectively they need a special drill bit that has the shank diameter at the top and the diameter suitable for the screw at the bottom.
Skippy

The carbon does't seem to be too bad if it's only double the price. I was looking at Fibre Glast Dev. Corp.'s prices of normal looking weaves and they are between $32 and $45 per yard. I wonder how many yards you'll need for yours? Sorry Mike, it's not my intention to distract you as I realise that the composite gantry subject is about the furtherest thing from your mind at the moment.
Skippy

I don't want to contradict anyone but to me, Mike's picture and Buscht's picture are one and the same. i.e. Euroscrews (Europe/US) and confirmat screws (UK) are the same thing. Skippy

No, they're not the same. Like Mike says, Confirmat screws are for screwing Partical board and mdf together. To work properly, a special drill bit is required. And like I said, Euroscrews are used to screw hardware into 5 mm holes. They do look similar, though, now that you mention it.

Skippy,

No offence taken, we will just have to differ on the screw thing. Now onto some real issues - when I write about the glass and carbon, I am comparing prepreg, mould making materials that I use for my model making activities and the heavy weight glass cloth works out at around £36/M^2 and the equivalent carbon at approximately £70/M^2. These cloths are 600 - 800g/M^2 and I use seven layers on the moulds to give a thickness of 5-6mm. These are, of course, woven cloth materials but I am seriously considering the bulk of the structure being uni-directional carbon, with the fibres being oriented at the most beneficial angle for the expected loads. The final layer will probably be a reasonably lightweight cloth to give that, all important, sex appeal :) :)

However, I must not get carried away with what will be and must concentrate on the here and now and get the prototype working. It is a huge struggle at the moment, trying to get some time to work on the machine. For my sins, I am the examinations officer at my school and this takes up an awful lot of time and is not as seasonal as some might think. Add to that a full teaching commitment and my working hours are pretty dammed full :(

Mike

When you're wrong, you're wrong and in this instance I'm wrong twice over! Firstly, if you have a look at Buscht's image and see the two vertical lines above the head of the screw that denote the head diameter. Well it was 1am in the morning and I quickly looked at those two lines thinking they were the shank area of the screw and that the head was above but not shown in the diagram. After seeing Gerry's response I looked again today and immediately saw my mistake. (sorry Gerry) Secondly, regarding the screws that Mike showed a picture of, I've been wrongly calling them Euroscrews for the last couple of years. Nothing like eating a bit of humble pie! It does us good at times.
Skippy

Why would you want a gantry made of a composite material?

ViperTX,

I suppose there is not one, simple answer to your question other than, Why not? Which of couse is not an answer. However, if you have read the thread so far, you will appreciate that my design is a little 'Off the Wall' literally and as such I figured the lighter the construction the better the performance. There is no better material than carbon fibre for the combination of strength, stiffness and lightness. If you factor in my interest in composites as well, you may begin to understand where I am coming from.

I am also something of a free radical in that I do not always believe that convention necessarily gives us the ultimate designs. It is something I am keen my students learn. Conventional design is good for the majority of cases and works well but we are not exploring anything in just copying what already works. For me, this project is as much about exploring possibilities, materials, construction techniques and my abilities as ending up with a functional machine.

I happen to believe that, provided I can manufacture the parts, that a composite gantry will give me better performance than an aluminium one due to the properties of the material. Whatever the outcome, I know it will be better than the MDF prototype :)

Sorry if this all sounds a little philosophical but you did ask the question :)

Mike

Why would you want a gantry made of a composite material?

Stronger, stiffer, lighter, faster.

I just went to order some (what I think) has been referrd to as confirmat screws...that is a large thread wood screw for 5mm hole, with a 15mm x 6mm shank and small countersunk alan key head...used for screwing wood to itself. The company referred to them as "carcass" (carcase sp?) screws. Thought this might help if someone was trying to find these in the UK.

Also, while I'm on the subject of thrashing a dead horse...
www.hpcgears.co.uk do a comprehensive line of toothed pulleys and belts.
My (oldish) catalogue only lists 3mm HTD pulleys up to 9mm.
They do 'reduced backlash' timing pulleys from 5mm pitch (ABT profile) at 10,15 and 25mm. For example, 48 tooth 5mm ABT pitch, 16mm wide - list is £22.58.
Similar in 3mm HTD 9mm wide are £9.08. They also do a nice range of rack an pinion and general gears.

BTW. Well done for trying such an different design. It would be a dull old world if everyone copied the same design over and over.

OK, I'll go back in my box now.

Also, while I'm on the subject of thrashing a dead horse...
www.hpchears.co.uk do a comprehensive line of toothed pulleys and belts.
My (oldish) catalogue only lists 3mm HTD pulleys up to 9mm.
They do 'reduced backlash' timing pulleys from 5mm pitch (ABT profile) at 10,15 and 25mm. For example, 48 tooth 5mm ABT pitch, 16mm wide - list is £22.58.
Similar in 3mm HTD 9mm wide are £9.08. They also do a nice range of rack an pinion and general gears.


10bulls, I cant get that url to work, any idea's

Steve

10bulls - At school, we order all our screws and fittings from Hafele. They have an on-line catalogue too at: www.hafele.co.uk Hafele certainly call them confirmat screws but as with many things, other users/manufacturers have other names - probably a copyright/patent thing.

Question - does a masochistic, dead horse enjoy being flogged?

Unfortunately, I could not open the link to HPCHEARS in your post but thanks for the contact. They are still much more expensive than the ones I got from the States but good for future reference. I wonder how much difference there is between the standard and reduced backlash pulleys?

Mike

10bulls - At school, we order all our screws and fittings from Hafele....
...They are still much more expensive than the ones I got from the States but good for future reference. I wonder how much difference there is between the standard and reduced backlash pulleys?
Sorry guys, try www.hpcgears.co.uk.
They say "Never knowingly outpriced", so probably some scope for haggling...especially if you lay on the 'Educational' aspect ;).
They had a stand at Model Engineering Expo last year so I'm presuming they're 'friendly' to the little guy.

I too have a Hafele catalogue...but it hurts my back too much picking it up!

[Question - does a masochistic, dead horse enjoy being flogged?]

Nay! :D Come on...why such a long face? etc. etc.

Maso...confir....carc.....scre.....See what you've done Mike! I'm too scared to even write the words now. Where are you? No one's heard from you (in full swing that is) since Feb 1st. Hope all is well and hope to hear from you soon.
Skippy

Skippy,

I'm still here but the machine is gathering a little dust at the moment. As I have said before, I am a teacher and can only work on the project when not teaching (the machine is not at home but in school so I cannot work on it in the evenings or weekends) and added to that, I am the examinations officer and this is my busiest time of the year so any non-teaching time is spent organising the exams.

Roll on retirement :) not wanting to wish my life away of course.

Thanks for the concern - I do keep looking in from time to time and I promise it won't be too long before building is recommenced.

Cheers,

Mike

PS In the evenings I have been building my own electric motors which has been fun.

Well, it's time to get this project back on the road. I'm still in the middle of the examination period at school but there may be just a few gaps in the busy schedule when I can dust off the work so far. You won't believe the ammount of dust this thing has collected over the past three months

I've just ordered three Gecko 320s and will have to start thinking about power supplies also and breakout boards. I notice the Campbell boards also require a relay board before it can all be hooked up. Are there any boards with relays incorporated?

I am really looking for Home and limit switches on all three axes, spindle on/off, extraction on/off and coolant on/off - maybe even spindle speed control. Any help much appreciated.

It's good to be back.

Mike

Campbell makes a nice board. Also cnc4pc has a modular approach that I like.

Jeff,

I have looked at both the Campbell and CNC4PC web sites but am still confused. As I have said many times before, I have no electronics knowledge and trying to decipher exactly what I need from the electronic jargon is nigh on impossible.

The Geckos are ordered - do these plug into a parallel port interface board, a breakout board or what? If I then want to add limits and home switches, are they on the breakout board, interface board or is this another board? I then want to control spindle, coolant and extraction. I believe this requires a relay board - where does this plug in?

Aaaaaaargh - Maybe I've bitten off too much and should just sit back and admire the unmoving machine :drowning:

Mike

Jeff,

Have you had a chance yet to review the CNC4PC boards yet?

Mike

FANTASTIC :banana: :banana: My Geckos have arrived already - only ordered them last Thursday!! Thanks Mariss, most impressed.

Now I really must tackle the power supply and breakout board issues.

Marc (Coherent), I've been trying to weigh up the pros and cons of the three suggested breakout boards, PMDX-120, CNC4PC and Campbell Designs. You are happy with your PMDX - do you know whether it will support a 220VAC supply? I have emailed all three suppliers with the same question and only had a reply from Campbell Designs (a bonus point for them :) ). Campbell Designs say they have a jumper that can be set for either 120V or 220V.

Jeff (HomeCNC), same question was sent to CNC4PC without reply. Can you help there also?

Going to go and press my electronics friend into a bit of action now on the power supply - won't it be good to get those motors spinning?

Mike

Got a reply from Arturo Duncan at CNC4PC and he also confirms that his products support 220VAC. His range of boards certainly seem well priced. I just have a slight doubt about the capabilities of the relays to switch 220V for spindle, extractor etc.

Does anyone else have experience of using CNC4PC products, apart from Jeff (HomeCNC), and can offer any help?

If the relays can't hack it on 220V I am considering using the Campbell Designs relay board with CNC4PC's other boards. Should be OK shouldn't it?

Mike

Mike you might want to look at the breakout board made by
Olivier ADLER in France. I got a quote from him last month and it
was "380 euro assembled and tested, with manual and I/O
schematics". He's at digitalaudiopro@wanadoo.fr
It's not yet available in the US so I will have to wait but it
looks good. Olivier is real active in the Mach2 Yahoo forum:
http://groupyahoo.com/group/mach1mach2cnc/

Campbell designs.com/ gets real high marks for support too.
Seems always eager to help.

As usual I have no interest in the products or companies but appreciate
good engineering and mfg's willing to support their products.

I like your design..how's it coming? A little like the Italian routers common
in the wood working industry. Do you have any recent pictures?
Jim K

Now had a reply from PMDX and they can also supply their 120 board configured for 220VAC. So, it's just down to choice now.

I have also emailed CNC4PC to see if they can supply uprated relays for switching 220VAC as the solid state ones on their relay board may be a touch on the light side - we wait and see.

Jim, thanks for the interest and the link. I shall investigate and report back.

Not much done on the mechanical side since February :eek: , far too much work to do in school :tired: However, now I've begun gathering the electrical bits and pieces, there will be some progress to report on - expect a lot more questions, I'm no good with electrics. :confused: I may even get a bit of time over the next three weeks to do a bit on the machine too - I'll post as soon as there is something to report.

Got a reply from Arturo at CNC4PC about the relay board, he says "Sorry for the delay in getting to you. I had crazy days around here. You are right about the amperage at 220, had not thought about it (I know I should have). I will clarify this on the website. I am going to offer individual relay boards as of next week. They will come with a larger amperage thanks to your suggestion."

Sounds like pretty good service to me and at his prices, I think he may well be getting an order.

Jeff (HomeCNC) are you still looking in? Any news on your review of CNC4PC boards?

Mike

CPU coolers arrived today and with a little bit of judicious bending of the retaining clips, they fit the Geckos perfectly. At just £1, a time I bought eight. The idea being that at that price it wasn't worth buying just three as the postage worked out more than the coolers, plus I may just want to add a fourth drive at some time, plus 100% redundancy - total outcome eight coolers. I also bought a tube of silicone heatsink gloop for a grand total price of £17 delivered.

I have to thank Cyclone for the great thread on his control box http://www.cnczone.com/forums/showthread.php?t=10680& I am attempting to emulate his build.

Mike

Hey Mike!

I've been following your thread. Love the idea.

Just wondering how the pogress is coming. Give us an update, because if you don't I am going to fall off the edge of my seat. This thread has been a serious cliffhanger. :stickpoke

Keep the posts coming!
Thanks a Bunch
Jimmy Southern :withstupi

Jimmy,

There has been some progress and you are right, it is time I did an update.

The CNC4PC boards have arrived - I ordered a parallel port interface board, safety charge pump, mini power supply and a solid state relay board. The four boards look fine but I have not yet managed to check them out. However, the parallel port interface card supplied was the wrong one, I had ordered the opto-isolated one but the bi-directional one was shipped and this one is not opto-isolated. After some discussion with a very good electronics friend of mine, I decided to keep the one sent as apparently there is very little chance of any damage to the computer the way things are set up. It remains to be seen whether this was a wise decision or not.

I also have an enclosure to put the whole power supply and control cards/boards/geckos in. Although this was a little pricey at £90, I felt this was justified as the machine will be used by pupils and I do have to make sure things are just right. I probably could have found a cheaper one somewhere.

As you are aware, having read through the thread, I can only work on the mechanics while at school and it is now the long summer break here in the UK so there will be no more progress on the actual machine. However, I did bring all the electronics and the enclosure home so I can work on it during the break. This means I should be able to post some more progress reports and photos as the control box comes together.

Mike

Mike, if you're worried about the parallel port, just add a $20 PCI parallel port card and use that port.

Gerry,

Not sure I understand. I thought the idea of opto-isolation was that any extraneous signals could not find their way into the computer via the parallel port. Surely by adding another, it still provides a pathway into the computer? or am I missing something? Is a PCI parallel port already opto-isolated?

Mike

Hello Mike; What Gerry is saying is you can purchase an additional parallel port and install it in an open PCI slot on your PC. This way if for some reason something goes wrong you blow up a $20 add on card, not your motherboard. There are no promises that it will only kill your add on card, it may continue further and kill other things on your motherboard, this is however cheap insurance to protect against it. It is better than using the "onboard" motherboard parallel port as you will surly kill a motherboard with a "direct hit" if something went wrong in your CNC control box.

Not all break out boards are opto isolated. You should really save the money and buy one that is, it will save you problems later. From memory, the Cambell BOB looks really good, and he will help you with questions if you email him. I'm certain there are other good BOB's that are opto-isolated also.

Thanks rboeser, I understand now.

The CNC4PC parallel interface card I ordered was in fact the opto-isolated one but the wrong one was delivered and rather than the hassle of return packaging and the wait to and from the USA and UK, I have decided, after some invaluable help from my local electronics expert, to continue with the one supplied. I was just trying to gauge the chances of doing some serious damage to my PC.

Cheers,

Mike

You are welcome, please stay safe.

Attached are pictures of the control box and all the bits that have to be stuffed inside. I am sure I will find a more elegant way to insert them rather than stuffing but you get the idea.

I am not sure whether to put the Geckos, with their attached coolers on the front panel, back or sides. Does anyone have any advice on this? I quite like the idea of having them on the front for 'Technical' aesthetic appeal but am worried that there is more chance of dust ingress than if they were mounted on the back or sides when the whole box is housed in a cabinet. I am well aware that whatever the method used, I will have to ensure adequate ventilation all round.

Just got to find a bigger capacitor now as the one shown is only 10,000uF @ 40V.

Another question if I may, what indicator lights/LEDs, switches, fuses etc. should I have on the front panel? I would like to get this as right as possible first time.

Thanks,

Mike

I really could do with some answers to the previous post.

There must be someone out there who has built a control box only to find they should have included another indicator, switch or whatever on the front panel. It would be a shame if I had to make all the same mistakes. After all, is'nt this what this forum is all about, sharing ideas, mistakes, highs and lows?

So far, the forum has been extremely helpful and I could not have got this far without it. Just a bit more help pleeeeeease so I can get on with the control box happy that I have not missed something obvious.

Mike

Hi Mike

I'm not sure if you are still in need of a reply but seeing as no one else has responded, I might as well share what I am planing to do with my contol box. First, I would suggest a main power switch. This will control the AC power to the big transformer and power to the control power supply you have. Then, I another power switch controlling power from the smaller control power supply. If you want you could put leds with the correct resistors for power indication. As for fuses, I would use resetable breakers. The make them panel mountable and in many different ratings. This way, if you blow one, you don't have to replace a fuse. I know Mouser Electronics sells them but most other electronics places have them too. A main power breaker and a breaker for each gecko should be good. (However you might need them in other places). It looks like you have the safety charge pump from CNC4PC so you will need an override switch for this so that the breakout board can be powered to send the signal to the charge pump. Also, if you are going to be controling your gecko's err/res state, you will need a SPDT momentary toggle swith to engage and disengaged the drives. A fault led can also be installed to monitor the state of the drives. Look in the gecko manual for information about controlling the err/res pin. Finally you may want to have an e-stop button.

I would suggest mounting the geckos on the side of the enclosure. This way you minimize the dust intake and you can have room for rear connections. Also, for good air flow and to prevent overheating, make sure you have enough intake fans to keep the pressure equal inside and outside of the box.

On the back, you are going to need an AC power input. And, since you have a solid state relay board, you probally are going to want to have AC outlets to plug your spindle motor, coolant pumps, etc. into. Finally for connection to the servos and encoders, I would suggest circular connectors. These look cool and provide a good conncetion between the cable and your box. Make sure that all of you cables are sheilded and that the drain wires are all connected together within the box to avoid ground loops.

Hopefully, this will help you.

Mike,

I have found where you can get yourself a larger capacitor to use. It is from the altronics website. Rated at 10,000 and 100vdc, i think from memory about $28AUD. I am going to use one of these myself.

Cheers

Peter

Jason,

Many thanks for that - I thought for some time that my thread had become invisible :) As a complete electronics novice, I really do appreciate the input and had put off doing anything on the control box until I had some feedback.

You mention circular connectors for the outputs to each of the servos and encoders, can both be put together on one connector? Wouldthere not be problems running the two alongside each other? I thought I had read somewhere that encoder cables should be kept as far away as possible from the servo cables. Presumably this is what the shielding is for?

Not quite sure I understand the need for the override switch for the charge pump.

Peter,

Thanks for the contact but postage from Australia would probably double the cost. I am sure there must be somewhere over here I can purchase a capacitor that size.

Thanks again for the much valued input,

Mike

Hi Mike,

I Dont think that it would be a good idea to out both the encoder and servo connection in one connector. The encoder signal may be interfered with due to the servo signals. Shielding prevents crosstalk in the cable, but if you are using plastic connectors, they will not shield from crosstalk within the connector. I mentioned circular connectors simply because they provide a secure connection and they look good. I got the idea from cyclone's box which you mentioned before. You could use any connector as long as there are enough pins (including one for a shielding drain wire) and that they can handle the current of the servo motors.

The saftey charge pump bypass switch is something in the CNC4PC instruction manual. It simply bypasses the saftey charge pump momentarily (Push button or similiar switch) to allow power to the breakout board so that the signal from Mach 2 can get to the saftey charge pump switch to enable the system. I have attached an image from the instruction book for the saftey charge pump.

Hi,

This is a very interesting project I will follow the progress.
Keep up the good work.

Tom

Hi,

I was just wandering, why do you want a bigger capacitor then 10000 uF.
That is already a big one, or are looking for a higher voltage ?
You can always connect several capacitors in parallel to get a bigger capacity. (There are some real nice ones in frequency inverters, if you can get hold of a broken one).

From what I see by dismanteling machines is that for smaller servo motors they generaly do not use shielded wires for the power supply, however for the encoder you must as these are very prone to magnetical fields.

And indeed you best use some metal connectors.
Get some robust items as they are subjected to swarf of wood and metal particals, resonance and quite some abuse by moving parts of the machine.

Good luck with your project.

Domdec,

As a complete dunderhead, when it comes to electronics, I can only go by the experiences and expertie of others and the general concensus seems to be that for my 36V x 20amp system, I need a 56,000uF capacitor. I don't pretend to understand the maths behind solution or, indeed, the science :)

Again, the beauty of this forum.

Mike

OK, now for a couple of technical questions posed by my electronics friend who is helping me out with my control box.

1/ In the Gecko manual it shows a centre biased, three way switch used to enable/disable the drives. On HomeCNC's (Jeff) instructions each of the drives are wired to the same switch. Question 1 - If I have indicator LEDs on the front panel for each of the drives, surely all will come on when any one of the three faults, if so how do I know which drive has faulted? Question 2 - If pressing the switch one way arms the drives and the other turns the drives off is the off position not the same as an emergency stop? If this is the case surely it would be fairly simple to catch this swtch accidentally and turn all the drives off - Does it have to be connected?

2/ Which side of the power supply should the emergency stop be? Should it turn power off to everything, in which case it can be put in the supply line or, should it only stop power to the servos, in which case it can be placed on the Gecko ERR/RES pin?

Thanks in anticipation,

Mike

Mike

The err/res terminal has been somewhat vague for most who approach its use. It is needed to reset the drives only. What you do with it from there is up to you. The stop function I use for a hardware stop and the EStop switch is a software stop. I can turn the drives off without alarming the software. You can go with a 3PDT switch to reset and stop the drives if you intend to use LEDS for individual drive condition indicators. The Gecko manual shows you a small circuit for this purpose. If you use Jeff’s circuit then you only need one LED for error indication. When you tune your motors and set up your drives you will be looking at the drives and will notice any error. Once you have them set up properly they should not error so having the indicator may just be extra effort on your part. The easy way is just wire the switch as Jeff shows. There are fancy boards out there to handle the err/res terminal and if one drive errors it will shut down all three as well as auto reset. I have seen circuits shown here on the zone as well if you feel up to making the circuit boards. But from what I have read you may want to take the keep it simple approach. If you want to get rid of the switch completely just tie the err terminal to encoder b+ and leave it that way.
The EStop will just be a switch that wires into your parallel port interface board and can be configured by your software. The easy way is to have it ground the pin on the board to make your software stop sending step pulses to the drives.

Ken

Ken,

I am puzzled. I would have thought that an E-stop was an emergency stop and as such that it would be an immediate hardware stop. Am I missing something?

thanks,
Alan

Ken,

I am puzzled. I would have thought that an E-stop was an emergency stop and as such that it would be an immediate hardware stop. Am I missing something?

thanks,
Alan

No. The correct way to use an estop is for it to cut power to everything. Not just have it stop the software. Usually they have 2 sets of contacts so you can do both.

I am afraid it is a little bit more complicated.

The E stop with servo driven motors schould send the message to the drives to that there is an emergency.
The drives should then boost the motors to a stop (as quick as possible) and after that releasing the axis (let it be posible to free run). But what about a Z axis that can drop down ?
At the university I am working at we have people teaching couses about technical security and there is something as a safety guidance to machine desing (European normalisation). Heavy stuff.

Do not cut the power supply but the lines between the power supply and the spindle motor (if applicable) (or make them quick stop by electrical braking) and in worst case cut the power line (by contactor of couse) to the servo drives (if they don not have a inboard breaking system) , otherwise follow the manufactors guidline.

Hoping to solve this together :)

Thanks for all the responses.

It still seems a little complicated and somewhat confusing but if I can assimilate all the information, it looks like I need the emergency stop to cut power to the spindle (preferably with electrical braking) and to turn the drives off via the err/res pin. Presumably by doing this the servos will hold position and therefore the Z axis will not drop?

If this is correct, for the Gecko/servo application using Mach2, how do you then safely move the axes? Is this something that is set up in Mach2 so that when it sees a reset, all axes are homed by zeroing Z first then either X or Y?

Some progress has been made on the control box, just waiting for all the plugs and sockets to arrive.

Mike

Art did a bang-up job putting together a pair of tutuorial videos for Mach3:

http://www.machsupport.com/Inputs-Outputs/Inputs-Outputs.swf

Even though the tutorial is for Mach3, I think he did an outstanding job of explaining how to jog back off of the limit switch when you trigger an error and the system goes into reset mode. At least that part of it should pertain to Mach2 users too.

Damae,

I've just sat through both tutorials and they are indeed excellent. I have not yet got Mach loaded onto a computer as I am still running Windows 98. As soon as I can persuade 'she who must be obeyed' that we need a new, domestic PC, I will clean this one up and install XP. It is a 2Ghz machine which should be perfectly adequate for Mach2/3.

I notice that Mach3 has now been officially released so it would seem to make sense getting the newest version from the beginning.

Mike

...tutuorial videos for Mach3...

Damae,

So can you pause this during play? How?

Rance,

Yes you can - it took me a little while to find it because it was off the bottom of my screen but if you scroll down, the normal, video style buttons for 'Play', 'Pause', 'Fast Forward' etc. are all there.

Mike

Mike waay-ay back in this thread... you were having probs with the MDF mounting on to your bearings - yes I realise about your Composite plans and tempory nature of the MDF...that sounds great (Not that I know alot about Comps mind).

anyhow the thought occured to me that It might save you some future headaches if you changed that 'first' MDF board for something like an Aluminium plate - you can get lovely flat Ally plate sometimes called 'tooling' plate over here - ok it does cost a significant amount more, but heres the big plus - if you've got a half-decent plate - I'd guess at least 12mm from your size - I'm guessing somewhat there... then whatever you hang from that plate won't warp or twist the plate and the bearing assemblys behind them.

kind of rigid 'interface' plate if you like.

I'm reckoning you're going to want it anyway even with your composite structure. ?

sorry - if I'm way off track Mike.

Oh... hope that walls a good-un and don't forget to take it with you when you go :stickpoke LOL you lucky....

EDIT I realise you're past needing the pullys n belts but

http://www.hpcgears.com/ are worth trying - their catalogue's good, includes prices which is nice! unfortunately their website is very lacking in detail.

Pat

Pat,

I work quite a bit with composites and am always astonished at how much aluminium expands when heated. I make a lot of parallel carbon and glass tubes, anywhere from 200 - 500mm long, 3 - 40mm diameter. If I use aluminium for the mandrel, the carbon tube just slides off so easily after lowering the temperature of the mandrel. If I use a steel mandrel the tube is a ?*&$%?&% to get off, if I manage it at all.

Unfortunately I cannot afford a temperature controlled workshop and, when I retire, I would be spending a lot of time in a workshop where the temperature may range from below freezing to the high twenties (centigrade of course) :)

Now, I may be worrying too much here but aluminium has one of the highest coefficients of expansion of all the metals and I would be surprised if no-one has experienced troubles mixing steel and aluminium in a situation where temperature is likely to fluctuate a lot. I decided early on in the design process that I would not use aluminium for any of the parts where expansion may be a problem. The plate between the two rails is one such part. These THK blocks and rails seem to be quite fussy over the fit.

I appreciate that many, many here have made aluminium machines and I am perhaps way out of line but I also wanted to try something a little bit different. It may well come back to bite me one day - we'll see.

Thanks for the link to HPC Gears, I am bound to need more sometime.

Mike

ahh.. between the rails... yes, although it would be interesting to do the expansion calcs, I like thinking 'outside the box' as they say! so do keep up the posting, hope you wangle the time to crack on.

It won't bite... if you've nice wall anchors !! :cheers:

hi all., whats happened to the posts here, no one seemis to be working lol

Madmickiii,

I have put in an order for a thirty hour day but have been refused :) Even then, I doubt I would have the time this project demands. I am supposed to be writing school reports right now but you have side-tracked me - so that's another few minutes gone :( Only another one hundred and fift two to go :(

Seriously, I do not get enough time at the moment. As a school teacher and examinations officer, my time is prioritised elswhere whilst at school and it is only at school I can work on the machine so I'm afraid it's catch 22 at the moment.

After Christmas there should be a few weeks where progress can be made - all being well. Rest assured, I have not lost enthusiasm for it but am getting mighty frustrated - maybe that's another story :)

Mike

Hi Mike,

Guess it's that time of year, for you school folk's, what with mock exam's etc. I hope to keep a check on your progress ;) ...

Mike

Nice thread, I am learning alot as well.
Keep up the good work. And let us know of the progress too.

Thanks for the words of encouragement.

I did say, right at the start, that this would be a verrrrry long thread but I was expecting rather better progress than I am making. One of my current problems (no pun intended) is the electronics. I have all the necessary components and the enclosure but I am so short of confidence with anything electrical that I keep putting it off. I know that once I get it all installed and get the motors spinning, it will give me such a boost that the rest will seem like child's play.

I asked some time ago what was needed for a front panel and did not get any replies that were complete enough for me to have the confidence to start cutting out the front plate so it's still here waiting. I have more or less decided I want my Geckos mounted on the front with their associated heat sinks and fans (http://www.cnczone.com/forums/showpost.php?p=93936&postcount=186) but what else should there be? I have an ON/Off, illuminated power switch, an emergency stop button, three fuse holders (one for each drive) and an error LED. Should there be anything else?

Another thing is that the toroidal transformer I have has a multitude of wires coming from it and I haven't a clue as to which ones are which or how it should be wired. My electronics wizard friend is a very busy chap and I cannot bother him too much with my problems. It is a shame, as the control box is something I can do at home while waiting for school work to subside and give an opportunity to get back to work on the mechanics.

I do appreciate the prompts and do promise to get this thing going sometime.

Cheers,

Mike

MikeF,

Just curious if you've made any further progress on your very interesting machine. I hope all is well in the UK. Take care and good luck.

jimmyd7

Jimmy,

This is really weird. After quite a few months of inactivity, I receive two enquiries in two days!!

The truth is I have not had much time recently as I am preparing to leave for Khazakstan in ten days time for the Space Modelling World Championships where I am trying to defend my title in rocket gliding. I still do not have any models ready so time very tight. I have models from two years ago but they are one piece models and I need models that break down for transport.

It is for modelling purposes that I need the CNC too so it's almost catch twenty two.

After the World Champs it is my intention to get stuck into the machine. I now have the power chain and all the cabling - just need some electronic expertise to help put the control box together and I think I have that sorted too.

I did say, right at the start of this epic that it would be a long drawn out affair and that I would need the support of this forum to keep spirits up and it's good to see there are those out there taking an interest - it makes sooooooo much difference.

Thanks,

Mike

Well folks, I'm back from Kazakhstan - what a memorable trip it was too. Unfortunately, I could not retain my crown but did manage to get on the podium again, in third place. So, from first in the World to third - still not too bad :)

As for the machine - now the World Champs are out of the way, I cleared my bench, got all the control box components out, bullied my electronics mate into coming round and we promised ourselves that progress will be made.

More anon,

Mike

MikeF,

Good luck with further progress on this project. I can't wait to see the results. Your design is very unique, and should gain a lot of attention as more progress is made.

Jimmyd7

Well folks, I'm back from Kazakhstan - what a memorable trip it was too. Unfortunately, I could not retain my crown but did manage to get on the podium again, in third place. So, from first in the World to third - still not too bad :)

As for the machine - now the World Champs are out of the way, I cleared my bench, got all the control box components out, bullied my electronics mate into coming round and we promised ourselves that progress will be made.

More anon,

Mike


Congrats on your third place, now back to the obsession of CNC.:)

Jason

Thanks Jason & Jimmy, maybe finishing the CNC will enable me to get back on top :) :)

Done some online buying today of bits and pieces for the control box, just some circular, power plugs and sockets and some finger guards for the fans. Oh, and my electronics friend came up with a 40000uf capacitor so if I parallel that with the existing 10000uf capacitor, I believe it should be in the right area. Yes?

On holiday for a week, next week, (half term don't you know) so hope to get some work done. It would be great to think I could get some motors spinning - we'll see. I'll post some pics as I go. I'm sure you guys will be on my case if I start slacking again!!

Mike

That's right, we will be on your case if you start slacking again.
As of next week (mid-term holiday) we will expect daily progress reports inclusive of pictures. :)

Jason

I've had an awesome day today!!

I have actually started laquering the internal doors, hung some weeks back. She who must be obeyed was getting rather anxious that things around the house were not getting done. Oh, while the laquer was drying, I got stuck into the front panel of the control box.

The 4mm thick aluminium was rather soft and when I tried to mill the cutouts, the tool kept clogging so I had to resort to chain drilling first and finishing off with the milling cutter. Worked out rather well I think. After a slight amount of deburring og the cutouts, the heatsinks and fans were fitted. The heatsinks were drilled and tapped 4mm to take longer machine screws as they had to go through the finger guard, 4mm front plate and the fan before entering the heatsink. Everything fitted perfectly, first time.

Underneath the fans are the fuses for each drive and to the right are the E stop, on/off, illuminated switch, the momentary toggle switch for arming and disarming the Geckos and the empty hole is for the fault indicator.

I am well chuffed with today's progress and I get some brownie points too for the laquered door :) :) Well Jason, that's the first day of my half term and so far, so good.

Mike

Today, I have been tidying up all the unwanted wires from the toroidal transformer and working out where everything is going to fit. Mike, my electronics friend has a question concerning the grounding of things on the low voltage side of the transformer, including the Geckos.

Are the Geckos and other, low voltage boards such as the 12v and 5v supply, interface board, relay board etc., assumed to be tied to ground via the chassis or should there be a physical connection? Supposing the Geckos are mounted on insulating material - how are they then grounded? Without a physical tie to ground, my electronics friend says they are floating and this is not a good idea.

Mains voltage is tied to ground by the chassis, should everything else do the same?

Don't ask me, I haven't a clue but I hope someone out there can help.

Mike

I too had the same questions when I did mine. I ended up using a wooden box so that nothing would be conductive and cause any sparks. But now I want to put it all in a nice fancy box.

They are a direct connection, as in I have run the -ve to the ground terminal of the gecko. Not as in bolt the wire to the chassis.

Because my box is wood (MDF) I don't have any grounds, even my earth wire from the mains isn't attatched to anything.

Peter
Australia

Thanks for the reply Peter, I was really expecting quite a few others to chip in but maybe it was too stupid a question. I emailed Mariss, Gecko supremo, and got this reply: It won't make any difference if you: (1) Use a seperate ground and +supply wire from your supply to each drive and (2) connect a single wire from your power supply ground to your chassis. Mariss However, being the electronics dunderhead that I am, it still does not make much sense and I cannot figure out what Mariss is actually saying here. Failing any replies to this, I will just have to plough on regardless.

A bit more progress today. Cutting the eight 'D' holes for the servo and encoder outlets was not a job I was looking forward to as the chassis back is 1.5mm steel. I started by carefully marking the centre of each hole and centre punching it, then drilled a 6mm hole through each. It then struck me that I could make an accurate template from 1.6mm ply using my small Isel CNC machine (it's not man enough to machine steel). The template was stuck over the pilot holes with double sided tape and the holes filed to shape.

All connectors fitted perfectly and a job I was not looking forward to only took just under one hour to complete. Moral is to stop prevaricating and get on with it :) Photos attached.

Mike

Hi Mike, just read through the ENTIRE thread...Phew!!! Amazing that you started two years ago and haven't given up the project at all, congrats on that alone!

As for your wiring question, personally I would take a positive and negative cable from the power supply to the drives, I don't like relying on the framework for a current carrying function, just the thought of eddy currents, electrolysis (got any different metals touching?) etc.

For a grounding function only then no problem, but for the sake of another wire to the drives, you are covered.

Nice work so far, hope to see motion soon...

Russell.

It won't make any difference if you

Probably because the PSU smoothing sits inside the Gecho's and the maybe 1V drop over wires won't make any difference.

One usually ground the negative supply in an attempt to help minimising static that may (and still will) build up especially when working with plastics.
Static has a tendency to jump where it shouldn't and could abruptly end or disrupt a current process...

Funny how you need the CNC to make CNC stuff... it's like you need the soldering iron to fix the soldering iron eh !

Don't give up.

Fanie,

I have found the small machine invaluable during the build so far and don't know how some of the zone guys can make such superb machines with just hand tools - there is an incredible amount of talent out there.

I appreciate the comment about static and will do everything possible to minimise the risk. On my small machine, with the extractor working, drawing air through a plastic pipe, there is a huge amount of static build up yet the machine has never missed a beat - must be well insulated.

Mike

Yeah a cnc machine would have been handy while building, either that or a time machine, go ahead in time, cut some parts on the finished machine, then travel back and fit them.

Guess its plan C...

Russell.

A little progress.

Six out of the seven doors are now finished and I am just waiting for the weals on my back to improve before getting stuck into the machine :violin: (I hope she doesn't read this)

Got the mains side ot the power supply all rigged up and ready for testing - switched on and ----- nothing, not a dickie bird, zilch. Mains indicator light came on and the E stop turned it off so that part was OK but nothing from the transformer. A quick call to my electronics friend had him scurrying down the road.

It turned out that when I joined the windings, from the secondary side of the transformer, I had not removed the shellac lacquer insulation (chair) I told you that electrics was not my forte. You cannot see anything moving - so how can anything be working??? However, it was not that obvious a mistake as my friend did not spot it for some time and the lacquer used was crystal clear so it looked like good, clean copper, unlike some of the other windings that had a red lacquer on them.

Oh well, nothing broken, just a little dented pride and a red face. All sorted now so on with the rest of the wiring. Didn't make my objective of getting the control finished by the end of the week though.

Mike

Lol, fault finding is always best when you actually FIND the fault. Just think, you will be prepared for that on the next machine....

Russell.

Well, at last some progress on the mechanics. The pictures probably tell the story better than words so just a short explanation.

The X axis ballscrew is mounted directly onto the wall, not the frame, and the first photo shows the fixed, motor end of the ballscrew. Second photo shows the supported end, mounted in a similar fashion. All mountings are temporary, at the moment, and once the nut has been positioned and mounted to the gantry, final adjustments can be made.

The third photo shows that the X axis and Y axis are mounted in the same, horizontal plane. This should help negate any extreme twisting moments when taking heavy cuts. The final photo is an overview of the gantry showing the relative positions of the X and Y axes ballscrews in relation to the whole machine.

Mike

Mike,
Brilliant! I just read the whole thread. Very impressive. I am currently in the process of gathering parts to build a 6' X 3' X 8" machine. Your experience will help me with my build. I believe I'll start a thread of my own.
Regards,
Travis

Travis,

Yes, please do start your own thread, you won't regret it as the advice you get here is fantastic. Sometimes you have to decide between opinions but generally, someone, somewhere will have the answer to any of you questions or concerns. There is no doubt that had I not found this site, I would not have attempted to build my own machine. It remains to be seen whether my radical design idea works as well as I hope.

A small amount of progress today. I got the motor mounts made for X and Y and a little more done on the control box. The electrics are still causing me some restless nights.

Mike

Yeah a cnc machine would have been handy while building, either that or a time machine, go ahead in time, cut some parts on the finished machine, then travel back and fit them.

This would be very handy... time travel...you'd also know where you'd end up eh ! It's the getting back that worries me !

To add a comment on static, it's not so hard to get rid of, you get static removers, works on the principle of blowing the static air over a high voltage and the high voltage removes the static from the air. Ideally you'd have the 'same' air circulate over the cutter / workpiece but it's easier said than done.

The shellac lacquer insulation is nothing new, but it does help to break down self confidence a bit ! Keeps one humble...

Progress is in dribs and drabs - managed to get the X axis motor mounted in temporary fashion. The brass straps work well but a slight mis-judgement on the positioning of the aluminium saddles has meant the two pulleys do not quite line up as they should. I will probably re-machine the slots and move them about 20mm to the right. Unfortunately I cannot just move the motor through the straps as the motor terminals get in the way.

Question - How tight should the belt be? If I were to squeeze the belt together, between the pulleys, how much movement should I expect? I appreciate that too much slack introduces quite a bit of backlash so I would expect the answer to be as tight as possible.

It's almost getting to the stage where I can apply some power to the motor and watch the ballscrew revolving - doesn't achieve much but it's fun to do and all helps with the feel good factor.

Oh well, back to the workshop and the bowl of spaghetti that is the control box!

Mike

Nice, dunno 'bout your belt question, but good to see more progress.

Russell.

Fanie,

I have found the small machine invaluable during the build so far and don't know how some of the zone guys can make such superb machines with just hand tools - there is an incredible amount of talent out there.

I appreciate the comment about static and will do everything possible to minimise the risk. On my small machine, with the extractor working, drawing air through a plastic pipe, there is a huge amount of static build up yet the machine has never missed a beat - must be well insulated.

Mike


Static? What are you doing, using pvc/plastic for dust collection? If so I had the same problem hooking up my entire shop with dust ports and floor sweeps with PVC. It's cheap, lightweight but unlike metal it draws tons of static. I ended up getting a kit from woodcraft, wiring the copper wire and then grounding it to the dust collector. Works great, 0 static now :)

bp092 ( a bit impersonal! Brian, Barry, Boris???)

Static? What are you doing, using pvc/plastic for dust collection?

Just like you, it was cheap. Lol.!!! Thanks for the tip. Do I assume you are still using the PVC pipe but have grounded the dust collector or have you replaced everything? Do you have a url for 'Woodcraft'?

Mike

www.woodcraft.com :rolleyes: but a piece of regular copper wire run through the tube with an earth and suitable attachments works fine..

great to see you back on the case again.. I've been looking to see how you've been progressing.

Congrats on the 3rd place too.. any photos of the glider? Presumably the cnc machine is to build those rocket things?

Andrew

bp092 ( a bit impersonal! Brian, Barry, Boris???)



Just like you, it was cheap. Lol.!!! Thanks for the tip. Do I assume you are still using the PVC pipe but have grounded the dust collector or have you replaced everything? Do you have a url for 'Woodcraft'?

Mike


Brian, yes, impersonal. http://www.woodcraft.com/family.aspx?familyid=3536


Surely you can just buy the stuff sep. but for $10 you can't go wrong, especially if you're always on the run like me, just grab it, no hunting around home depot! I'm still using PVC, I'm going to switch to metal when I move into my own commercial space and also plumb an all copper air system.

Brian,

Just found the same kit in the UK, with slightly less copper wire but was virtually the same image, at http://www.axminster.co.uk/user_search/1/sfile/1/jump/0/product-Jet-Dust-Collection-Grounding-Kit-365542.htm Look at the price!!!! £18.35 is about $35 yet 'Woodcraft' sell it for $9.99 - no wonder it's called rip-off Britain :eek:

Andrew,

Yes, it's good to get back into the build - it will still be a long haul but at least things are moving in the right direction. Your bit of copper wire down the tube is looking good :)

Kazakhstan was brilliant - photos of gliders are attached. First is me with my model and the next three are a sequence of one of my models being launched by a team mate. In the last one, you can just begin to see the rocket motor's thrust.

The idea of the machine is to enable me to manufacture the wing moulds for myself without having to rely on expensive, third parties.

Mike

LOL it's probably distributed here in the US and you're getting the end of things with all the taxes, shipping internationally and customs for merchandise.. we all have our disadvantages and advantages. I think woodcraft ships intl?

At long last, I have a motor spinning under control :banana: :banana: :banana:

But for the patience of my electronics wizard, I would still be puzzling over some non movement. I thought I had meticulously wired everything correctly but there are so many, I suppose it was inevitable I would miss something. It was just as well I took the wizard's advice and only wired one drive. As you can see from the photo, the wiring is not exactly tidy but my excuse is that I was told to wire it first, in any way I could, test it, then worry about tidying everything up once working correctly.

To be honest, there was only one wire misplaced and even the wizard did not spot it before many heads were scratched - well two actually but many times :) It turned out that that the wire that was supposed to be in pin three of the breakout board was in fact wired to ground (on the CNC4PC breakout board the connectors are labelled 2, Gnd, 3, 4, Gnd, 5, 6, Gnd, 7, Gnd, 8, Gnd, 9, Gnd - not exactly logical, to me anyway)

Once that was solved, it was plain sailing. Everything worked as it should and the motor responded accordingly.

Well, after all that, I just had to put the X axis motor through its paces and loaded the ubiquitous 'Road Runner' program in Mach and pressed 'Cycle Start'. It was magic just watching the motor spin up and down and changing direction - boy, I'm easily pleased :) :) Now I suppose I had better stop watching this thing and get on with the other axes.

You just don't know the weight that is now off my shoulders - my hat is off to all those who understand the black art of electronics.

Mike

Mike, what's the tiny monitor up on your tower for? Seen them used for car stereos to be mounted on the dash, never seen them for cnc :)

Brian,

That tiny monitor is a very clever device that enables my wife to keep in touch with her beloved soaps --- it's a TV set :) :) :) LOL

I set the thing up in the kitchen as there is no room in the workshop at the moment and the PC just happened to be in front of the small shelf that holds the very small TV set.

I will be taking the controller into school tomorrow just to see if the motor is man enough for the machine. Going to have it move the gantry in X only for the road runner. Should get the enthusiasm levels up somewhat.

Mike

heh, you mean you have that all in the kitchen? God speed Mike, that's a line you don't cross in this household, I'm limited to the basement :D

If you do cross the line like I did, you had better be ready to run. Trust me. I know.....

oh man, MrBean, you gotta good lawyer or just a really cool wife? lol

oh man, MrBean, you gotta good lawyer or just a really cool wife? lol

Yeh I guess I do have a cool wife. She puts up with a lot.
Okay enough messing. I don't want to become a thread hijacker.

Hey mike I notice you're running the Mach screenset that SantiniUK and I designed. How do you like it?

Brian & Mr Bean,

I'm sure we could start a new thread on 'where not to set up your machine' - could get some interesting replies. I have promised, she who must be obeyed, that the PC and collective bits will shortly be removed, problem is I can't yet determine how long, short is :)

Mr Bean - only just started using Mach3 but your screen set seems just fine. I like its logical, clean and well organised layout with all buttons and features lined up. Having done a little programming myself for school administration, I am well aware of how important the user interface is. However, I did come across one anomally and I don't know whether it's down to you or Art but when I changed the scaling factor, the toolpath was accurate on the 'Program Run' screen but not the others. It looks like the scaling was not applied to the other graphics objects.

I managed to hook up the X axis to the controller this morning and took great delight in watching the gantry trundle up and down to the tune of 'Road Runner' :) The drive faulted a few times before I got the acceleration sorted out but now it's just fine. It looks like I can get about 3600mm/min or 60mm/sec at the moment with Mach3 set to 25000Hz. Not as fast as I would like but the motors are limited to 1700 rpm and if my calculations are correct, 25000Hz will give me 1500 with a 250 line, quadrature encoder.

Can't wait to hook up the Y axis now.

I have been playing with the X axis and its settings in Mach3 and it does not seem to make any difference to the speed whatsoever if I have the pulses set to 25000Hz, 35000Hz or even 45000Hz. Can anybody explain this or is it that the servos are internally limitted to 1700rpm?

I have a licenced version of Mach so it's not that it's stuck on 25000Hz.

Mike

Are you just altering the pulse engine frequency, or are you entering the motor tuning section, and increasing the velocity setting for X too?

Just altering just the pulse engine will not do anything in itself. It will only give you more headroom in the motor tuning > velocity settings.

Regards Terry.

Terry,

Thanks for the reply.

Yes, I am altering the velocity too but not seeing any difference in speed. Maybe these servos cannot go any faster. Am I right in assuming there is nothing to be gained by a faster pulse train if the motors cannot go any quicker?

Mike

Yes. That's correct. If your motors will only go so fast, there's no benefit in going with the higher pulse rates. I'm not familiar with servo's, I've only ever used steppers. I had to use the 45K pulse engine setting, as I geared my motors down and used 16* microstepping, therefore I needed the extra to get enough pulses for reasonable speed.


Terry...

In 25Khz mode, you'll be limited to 750rpm. 25000 steps per second divided by 2000 steps per rev X 60 seconds per minute.
1050rpm in 35Khz mode, and 1350rpm in 45Khz mode.

You must restart Mach3 after switching modes for them to take effect. If you didn't restart, you wouldn't see any difference.

Thanks Gerry, I didn't realise I had to re-start for the change to take effect. I won't get the chance to try it today but will report back tomorrow.

Mike

I re-set Mach3 to 35000Hz then re-started Mach and there was indeed an increase in speed from the motors - thanks Gerry :-)

However, although the motors worked well on the bench, the one attached to the X axis struggled to achieve any greater speed, faulting as the speed increased no matter how slow the acceleration was set. What I concluded from this was that there was an upper speed limit above which the servos could not keep up with, once loaded.

The upshot is that at 25000Hz Mach would let me achieve 3750 mm/min and at 35000Hz the motor limited itself to 3900 mm/min. This all equates quite well with the motor manufacturer's figures of 1700rpm max, my 250 line encoders and 2:1 reduction driving my 5mm pitch ballscrew.

I just needed to know if I could drive them faster - now I know. I assume the only way of getting more speed would be to swap the servos for higher rpm versions? I don't suppose I really need to go faster than 3900mm/min - but it would be good :devious:

Mike

If my math is right, you have 400 steps per mm. Is that what you have in the Mach3 motor tuning? Again, if my math is right, 1700 rpm would require 28,333 steps per second. 1700*1000 steps per rev/60 seconds. If indeed your motor was turning at 1700 rpm, that would be 4250mm/min. 35Khz mode should be good for 5250mm/min, but that would exceed the motors top rpm, so you're limited by the motor. A little higher voltage might squeeze that extra few rpm. 3900mm/min is 1560 rpm.

So, I see three options. Differrent motors, different scres, or different gearing. Different motors would most likely require a bigger power supply (higher voltage). I'm guessing you don't want to go there. :) Different screws = $$$$. Probably don't want to go there, either. That leaves different gearing. 1:1 would double your speed, IF you have enough power to do it. 1.5:1 or 1.75:1 might be something you want to look at.

As for your percieved lack of power, it might be a matter of tuning the Geckos. Never used them, though, so can't really help you there.

Hi

Very nice work Mike and well documented thread

keep up the good work

cheers

Gerry,

I've been away for the weekend so apologies for not replying earlier.

Numbers add up to the same both sides of the pond so I must be doing something right. :)

Different gearing is probably the easiest solution to the speed issue, though I think I will wait and try the machine out before making any changes. The other point you made, about the current adjustment, is also valid but I am not sure of how to go about optimising this setting. Do I need to measure the current under load, while the machine is running? I appreciate you do not use Geckos so if anyone else knows the answer to this, please chip in.

Mike

Well, it really is beginning to look like a CNC machine!!

The controller is all but finished - only have to put in the charge pump and auxillary relays for spindle etc. However, there was a problem that I am sure others have come across and were it not for my electronics friend, I would still be staring at an imobile lump of hardware. We were getting all sorts of oscillations on the oscillascope instead of a solid high or low signal when operating the toggle switch to arm the system. It was tracked down to the fact that the mini power supply, giving 5v for the boards, and the main supply giving 40v to the Geckos did not share a common ground. The fix was simply a piece of wire from the main supply ground to the mini power supply ground - job fixed. This goes back a few posts when I queried the apparent 'floating' Geckos.

Got everything wired up in a temporary fashion just to see the X and Y operating in unison. Of course, as with many projects here, I just had to put in a pen and test something. You can see from the photo that it seems to behave just fine. I used the roadrunner program and ran it twice. I was very impressed to find the second run went exactly over the top of the first. WOW!!! this thing looks like it might perform OK. I realise there is a world of difference between pushing a pen round and actually cutting something, but hey, it's progress. Because I have no Z yet, there are some stray lines where the rapids would be.

I also drew some squares and circles and as far as I could check, by eye, everthing was just fine.

Oh well, I suppose I had better get on with the Z axis rather than playing with the pen. :)

I am thinking about limit and home switches and wondered why most, if not not everyone, puts two on each axis. If one switch is mounted on the moving part of each axis and is operated when the switch hits a fixed block on either end of the travel, this would mean only three switches are needed for limits and home, on a three axis machine instead of six.

Can anyone think of reasons why this approach cannot or should not be adopted? It would also make the wiring simpler and allow the existing power chain to be used rather than additional, fixed wiring along the frame.

Any advice would be appreciated.

Mike

I think the Limit switches will trigger an e-stop condition, meaning that the drives will cut out if used to home the axis, so if you just wanted to "home" all axis then cut a part, you can't, as the drives will cut out, untill you get them off the switch, you have now lost your home position. That's why you have seperate home switches that trigger, usually just before the limit switches.
So you home your axis and if for any reason the motors carry on past "home", the limit switch triggers an e-stop condition, halting all motors.

I have neither limits or home on my machine :nono:
So I may be wrong on this. Best to get another opinion just in case.

Regards Terry.

I think it will work. In Mach3, somewhere you can tell it to use the home switch as a limit, and I think you can assign the switch from the opposite end to the same pins as the home switch. So You actually set up the same switch twice, using the same pins. Try it and see to make sure it works before you wire everything up.

It's the Terry and Gerry show again :) Thanks guys for the input. Gerry, on the face of it, I could not see why it would not work, just needed a second opinion and wondered why it wasn't common practice. I will wire one up and try then report back. Terry, I do know that Mach3 can be set up as Gerry suggests, allowing limit switches to double up as homes too on one end of the travel.

I have uploaded a very short (10sec) video of X and Y moving. The camera is a very old one that take floppy discs, do you remember those, it is pretty low res but works.

Mike

I am thinking about limit and home switches and wondered why most, if not not everyone, puts two on each axis. If one switch is mounted on the moving part of each axis and is operated when the switch hits a fixed block on either end of the travel, this would mean only three switches are needed for limits and home, on a three axis machine instead of six.

Can anyone think of reasons why this approach cannot or should not be adopted? It would also make the wiring simpler and allow the existing power chain to be used rather than additional, fixed wiring along the frame.

Any advice would be appreciated.

Mike

Have a look at page 36 (or 4-10) of that excellent mach 3 documentation

downloadable from http://www.machsupport.com/documentation/

you want the 'using mach 3 mill' one :idea: but I reckons you should all ready have that one LOL.

light bedtime reading!! - hey pleased for you Mike, keep going now...

pat

Thanks Pat, I guess it's a case of 'if in doubt, read the manual'. (chair)

I've been doing a little bit of tidying up in the controller box this evening - all those wires!! but it's beginning to look a bit better - just hope everything has gone back the right way.

Mike

Picture attached of the tidied controller box. Compared to post 242, I think there is a considerable difference and not being an electronics guru, I was rather reluctant to disconnect everything, trim wires and then have to re-assemble everything. I have to report that everything went without any problems and all three axes are still working :) :) .

The eagle eyed among you will notice there is a charge pump and relay board in there now although they are not yet connected - got to work out how to do the charge pump :confused:

Still not got round to figuring out the Z axis and am undecided as to having a fixed ballscrew/motor or fixed ballnut and moving ballscrew and motor. There seem to be good and bad reasons for both.

Mike

Looks well organized and thought through. Where'd you pick up the e-stop and other components?

Nice work Mike, good to see more progress, keep it going!!! Thats a pretty sweet looking electronics box.

Russell.

BP092,

As this machine is built in school, I relied on our sparky, in the works department, for supplying the e-stop button so I can't say where it came from. Suffice to say it is a good one, designed for workshop type machinery. As for the other components; drivers are Geckos, toroid transformer, large capacitor and rectifier came from surplus power supplies sourced by my electronics friend, he also provided the plugs, sockets, leds and switches. (A very useful buddy :) ), CPU coolers came from ? and the parallel interface, mini power supply, relay board and charge pump came from CNC4PC.

Russell,

Yes, I feel a great relief after getting the electronics out of the way. If you have read through the whole thread (as I am sure you have) you will realise that I was not looking forward to the electronics at all but now they are out of the way, there is a huge feeling of satisfaction, especially as I didn't fry any components along the way.

Just the Z to complete now before cutting something - shouldn't be too long now - maybe another twelve months or so judging by progress so far :D :D

Mike

E-Stop switches are very expensive for what they are.
For a cheap and cheerful alternative, I used a push-pull switch from Farnell part #7712600 @ £4.79.
They probably won't pass ISO BS XYZZY standard relating to operating them in a thunderstorm using a bloody stump but hey.

Andy,

It's a valid point you raise, about standards etc., and it is something I hadn't really thought about but seeing as this machine is in a school workshop and liable to be used by students, albeit always with my supervision, I suppose I should get it checked out by the authorities and get it duly stamped - what a PITBS. :( :(

Mike

...I suppose I should get it checked out by the authorities and get it duly stamped - what a PITBS. :( :(
You may have read this one..."Mince pie danger to be assessed" http://news.bbc.co.uk/1/hi/england/north_yorkshire/6207970.stm
The world's gone crackers!

...then there was the one about the over zealous building site H&S that insisted they put 'STOP' signs at the end of all their ladders. ;)

BTW: Congratulations on getting things moving! Are you still planning to replace some of the parts with composite ones? (sorry if you've already covered that).

I am thinking about limit and home switches and wondered why most, if not not everyone, puts two on each axis. If one switch is mounted on the moving part of each axis and is operated when the switch hits a fixed block on either end of the travel, this would mean only three switches are needed for limits and home, on a three axis machine instead of six.
Hi Mike
Great job on the machine!
Wish I had a teacher like you when I was at school! :)
About the limit switches.....
When I built my machine I initially built 6 limit switches into the electronics, but when I was finishing the machine, like you I realised that I had 3 extra switches that were surplus, and could cause problems.
So I used one switch on each axis, and then I made up some 'ramps' that I fitted each end of each axis. Using a ramp allows for the machine to slow down and ride up the ramp tripping the limit switch, machines don't stop instantly! I made the ramps so the microswitch will trip when it hits the 'ramp' and then it can continue to ride up the ramp without damaging the switch.
I stole the idea off of my parents stair lift! :D
I don't have any home switches fitted, because I use the limit switches to act as the home switches. In Mach2 there is a setting to tell it to use the limit switches as homing switches.All you do is tell the machine in which direction you want it to go to search for the limit switch.
When I reference my machine, first the Z Axis goes up, when it hits the limit switch it then reverses off of the limit switch and stops and resets the DRO
It then does the same on the Y Axis, and finally the X Axis.
This works fine for me, and the only problem with this is if you want to machine mulitple parts from the 'home' position everytime you need to put in a high quality optical switch (so I have been told....)
I don't need this because I position the machine everytime to a datum on the workpiece and cut from there.
Hope some of this helps, I look forward to the final photos!

Andy

Andy (although your username is Normansthename) :confused: ,

Many thanks for the input - just what I wanted to hear :)

Incidentally, I have now read and re-read the Mach3 manual and concluded I could use just three switches, just as you have. However, I am not too sure how these are arranged in terms of connecting them to the interface board. Do you wire then all together and have just one output or do you use three outputs, one for each axis? Reading the manual suggests I can wire all three to one output, treat one end of each axis as the home and limit switch and the other end as the other limit.

This all seems just a little too good to be true - I can get nine operations from three switches wired to one output - is this correct?

I am aware of the sequence of homing as the method you describe is exactly what happens on my small, Isel machine - first the Z homes then the Y and finally the X, each one hitting the switch then backing off slightly.

Andy, do you have a thread here so I can see your machine?

Mike.

Andy (10Bulls),

Just realised there is an unanswered question in your last post. The answer is yes, I have every intention of replacing the MDF parts with carbon composite parts but that is way in the future and I'm just itching to get this one completed. The idea was to get this one to machine the patterns for making the moulded, carbon parts to replace itself. It's a weird thought of a machine making its own, better replacement - smacks of more than just a little sci-fi - now if I can just get it to think for itself :idea:

Mike

Mike, as long as each axis is homing seperately, you can use one pin. However, I'm not sure if the stadard homing procedure will work, or if you need to individually home each axis seperately. You'll have to try it and see.

Andy (although your username is Normsthename)
Mike, its a long story........ :rolleyes:
Do you wire then all together and have just one output or do you use three outputs, one for each axis?
Not sure if you can just have one switch. My machine has 3 separate outputs, so if one switch is tripped, looking on the diagnostic screen I can that is the Y Axis that is tripped etc.
Andy, do you have a thread here so I can see your machine?
That is something that I must get around to doing! :)
I have been so busy building the machine and now cutting things out I have not got around to taking a picture!
Here is a 3D CAD Drawing showing the machine.
The main frame is built from 60mm Square Steel Box Section, and the gantry is made from 30mm Square Box Section.
Capacity of the machine is approx. X900mm, Y600, Z140mm
It is fitted with a heavily modified (read butchered!) 2050 watt Router and has a dust extraction system with a homemade Cyclone fitted which really does the business and I would recommend that you look into fitting one to your machine.
I also have a homemade 3D Scanning device that fits to the Router for scanning parts in (my business makes motorcycle parts)
Attached is a couple of test scans of a mini-moto tank and seat unit that I did with it, I will post more information when it is a little bit more refined.....

Andy

Andy,

Not sure if you can just have one switch.

No, not just one switch, but one on each axis, all in series, on one output pin. So the sequence would be that if any one of the three were tripped as limit switches, the machine and Mach3 would stop. Also, when doing a homing move, the Z axis would move first, in the defined direction, until its limit switch was broken. then it would drive itself off the switch. That sequence would then be repeated for the Y then X axis in their defined direction.

If this is all possible, and I think Mach3 can cope with it, then all I need is three switches, six ramps and one output pin.

Mike

Edit: PS I would be interested to know more about your digitising head.

No, not just one switch, but one on each axis, all in series, on one output pin.
Sorry, I meant to say three switches in series on one output!
PS I would be interested to know more about your digitising head.
The above scan took me about 45 minutes to do from start to finish.
I have a couple of tweaks to do to the software and it will be up and running :)
I will then post some more details......

Mike I forgot to suggest something about your machine.
Would it be possible to have the 'A' Frame gantry removable (or even hinged!) so freeing up even more space when not in use, just a thought.......

Andy

Andy,

It does!!!!

The Linear guides I am using enable me to very easily unbolt the bottom and remove the whole gantry. It was one of those unforseen and unplanned 'Eureka' moments when I realised how easy it would be to make the whole thing removeable. Having said that, with all the wiring, cabling etc. to consider, I doubt it will be removed that often :)

I look forward to your posts on the digitising.

Mike

Having said that, with all the wiring, cabling etc. to consider, I doubt it will be removed that often
Hi Mike
Have a look around at some of the Electrical sites Maplins, Farnells, Radio Spares etc
I am sure you will find multi-pin plugs that you could wire into the machine to make it very easy to unplug the electrics etc.

Andy

Just thought I'd mention a small problem I had with CNC4PC boards and how I have solved the problem.

Way back in the posts I mentioned I had been sent a bi-directional interface board instead of the opto-isolated, parallel port interface card I had ordered. Because of shipping costs and the associated returns hassle, I was persuaded that the bi-directional card would do the job so I went ahead and constructed the control box.

My previous testing and movement of the X and Y axes was done without the charge pump or relay board wired in. Happy that everything was working OK, I wired in the charge pump but no matter what I tried, it would not operate as planned. It was wired as per instructions to switch the interface card on and off as appropriate. The relay would switch but I could still drive the motors despite the interface board not receiving power from the power supply. I had noticed that when I plugged the interface board into the parallel port, without the mains power turned on to the box, the LED on the board lit. This was an indication of the problem. The bi-directional board is not opto-isolated and is receiving power from the PC, enough for it to carry on working without a supply through the charge pump.

Problem - how can I now use the charge pump to ensure the motors cannot spin when Mach or Windows crashes out?

The solution was fairly simple but I am not sure it is a recognised method. What I did was simply take the 5v common (pin 12 on the Gecko) from the mini power supply through the charge pump and then to the Geckos. The charge pump now works just fine. Every time I fault any of the drives, Mach drops out and the relay switches off. I have also tried turning Mach off whilst running and this also trips the relay as does clicking the on screen e-stop.

I have emailed Arturo Duncan of CNC4PC but not had a reply yet.

Mike

Hey, I've just noticed, somebody has given me five stars!!! Must be for sheer perseverance more than anything else :)

Thanks,

Mike

After my post about light weight versus mass in Deltaman's thread http://www.cnczone.com/forums/showthread.php?t=28868 , where he is using carbon/MDF in his construction, I did a few more experiments with acceleration and feed rates. Although the experiments are not exactly scientific, they do illustrate a point and could provide some help to others beginning their design process.

What I was considering was the time element involved with accelerating and decelerating the machine during a cut cycle. The method is quite crude but something anyone can try for themselves given software like Mach and a decent sized gcode program. All I did was to set the feed rate and motor acceleration to certain values then ran the program to see how long it took to cut. The program used was the 'Roadrunner' file found in Mach3 scaled by 25.4 to cut the metric size equivalent.

Test 1:
Acceleration set to 15 mm/sec/sec
Feed rate set to 3500 mm/min (this happens to be the top speed for my motors)
Time Taken: 10:02 minutes

Test 2:
Acceleration set to 2500 mm/sec/sec
Feed rate set to 3500 mm/min
Time Taken: 2:59 minutes

Test 3:
Acceleration set to 15 mm/sec/sec
Feed rate set to 350 mm/min
Time Taken: 16:58 minutes

Test 4:
Acceleration set to 2500 mm/sec/sec
Feed rate set to 350 mm/min
Time Taken: 14:25 minutes

Conclusions:
Feed rates and accelerations are not necessarily typical values but have been chosen at extremes for illustrative purposes only. However, I would suggest that 350 mm/min is not a bad cutting speed for many smaller machines.

The 'Roadrunner' program has over 4000 lines of code and consequently the motors are spending a lot of time accelerating and decelerating the machine so one would expect to see a difference in time taken. What was interesting was that the difference was far more significant when feed rates were high. High feed rates with a heavy machine requires huge motors to give the accelerations necessary to realise the time saving. Lightweight machines, provided they can be made extremely stiff, will outperform heavy machines for a given size of motor.

What remains to be seen is whether these lightweight machines can deliver in terms of quality of cut. That they can be made stiff enough is without doubt, just look at the figures of carbon versus aluminium, but I still have some nagging doubts about longevity. One of carbon's failings is that it does not like shock loads and, unless the structure is well thought out and engineered, stress fractures are far more likely than in equivalent aluminium or steel structures.

Food for thought?

Mike

Still no reply from Arturo Duncan at CNC4PC - I've sent another email. Does anyone know if everything is OK his end?

Mike

Arturo has been in touch. :)

Shortly after I posted the previous message, he emailed me. It appears the original email did not get through - obviously floating aimlessly in the ether somewhere.

Suffice to say - he has responded as quickly as he could and you can't say fairer than that.

Mike

Hats off to Arturo at CNC4PC, by return email, he has offered to replace my parallel interface board and a mini power supply that was overheating quite badly. Apparently the new parallel interface has an 'Enable' pin that can be wired to the charge pump. My, earlier version does not have this and is picking up power from the PC, negating the effect of the charge pump.

Doesn't it do your belief in human nature a good turn when things like this happen?

Thanks again Arturo,

Mike

I am looking at the design of your rail. I really like the positioning of the ball screw on the back side of the rail, keeping the carriage close in for rigidity. I do not see the placement of the ball screw for the vertical slide, though. I just built a drilling machine, and the requirement for enough space for the ball screw and ball nut made the carriage stand out a good bit. Just wondering if you dad a solution for that, as your rendering showe it sinched up pretty close.

Ahyway, it looks like a great project, and I wish you the best of luck

Mrtool,

Ah, another one slinking off from the festivities to grab a fix on the zone!!! :) We are not alone.

If you notice on the rendering, I do not show the ballscrew and that is because I haven't yet decided how I am going to do it. You are quite right in that should I place it between the Y axis plate and the Z plate, the overhang is going to be substantial and I want to negate this as far as possible. I have one or two ideas and need to model them first to see if they will work. Thank goodness for CAD!

It may mean pressing my composite skills into practice rather sooner than anticipated as I know I could mould in a recess, in both the Y and Z plate, to accommodate the screw and nut, getting the two plates much closer together. I think it is also possible with aluminium but probably not with MDF.

I will post ideas as I get them modelled. Thanks for the best wishes - now where's that mince pie.................

Mike

May I start by wishing all 'Zoners' the very best for 2007, may your ballscrews never go rusty!! :rainfro:

Well, Arturo Duncan, of CNC4PC, came up trumps and I collected my replacement interface board and mini power supply today from the Post Office, who had kindly looked after them for me over the new year festivities after trying to deliver them on 30th.

Wired the new interface board up today and everything appears to work just fine with the exception of the charge pump that is not signalling a fault to the PC when it trips out. I think the problem comes from the fact that the original board had active low outputs and the new one has active high outputs. That in itself is not a problem as Mach3 can be set up for either condition but my electronics friend had made me a board, attached to the re-set/enable toggle switch, that indicated externally, which of the drives had faulted. This board sends an active low signal to the interface board that is now expecting an active high signal.

I really wish I knew more about electronics :( because I now have to wait for my electronics friend before I can make any more progress with the controller. This is frustrating as it is 95% done but just needs the finishing touches.

Once again, my heart felt thanks to Arturo for his response to my predicament. An excellent advert for CNC4PC products.

Mike

Finally managed to get some time to sit at the computer and re-model the Z axis. I'm sure it is a problem many face that, with the necessary layers of plates, guides, blocks and ballscrews, the physical width/thickness of the Z axis becomes quite substantial, and with a large overhang, the mechanics become less efficient.

I was facing this problem, with the main culprit being the height of the Z axis ballscrew bearing blocks. If I mounted the bearings conventionally, the gap between the Y axis plate and the Z would have to be a minimum of 45mm, yet without the ballscrew I would only need 20mm, the distance from the bottom of the Z rail to the top of the Z blocks (or back of the Z plate).

By fabricating the assembly I have got the overhang down to just 73mm from a massive 104mm. Nearly all this was achieved by recessing the ballscrew between the two vertical members and relieving the horizontal members to allow the bearing blocks adequate depth.

The attached CAD renderings should explain better. Keen eyes will notice I have not included the bolts. If only the real thing could be made this rigid just by aligning and mating surfaces :) :)

Mike

Here's a CAD drawing of the whole lot together. I haven't bothered to update the X axis ballscrew mounting - doesn't seem much point in spending time drawing up what has already been made. However, being able to model the Z axis in 3D CAD has been extremely useful and if anyone is in two minds as to whether getting to grips with CAD is useful, I would urge you to give it a go - it really isn't that difficult and it can save a huge amount of time and/or material.

Still got to figure out where to put the Z axis servo and that will be the next thing to model but I could really do with knowing what spindle motor will be used :confused:

Mike

I've been playing again - this time the CAD rendering shows the Z axis complete with servo motor mount and spindle mount (still don't know which one to use though).

As mentioned before, the Z axis will be made from aluminium as I did not like the idea of fabricating with MDF. The aluminium is ordered and should be with me tomorrow so I will have no excuses not to get things moving again.

A little update on the controller - the new interface board is installed but because the pins are tied the opposite way to the previous board, the device made to register individual drive faults had to have its signal inverted. This is way beyond my expertise (though I do understand the logic - (pun intentional) and my electronics friend produced the goods, I installed it and now everything is working just as it should. Just need to change the mini power supply now to the new one from Arturo Duncan. This is slightly more tricky as the new one is a commercial item with long mains leads and I need to install it inside the cabinet.

More anon,

Mike

Another update on the controller.

Mini power supply is now installed, supplying the 12v to the charge pump and cooling fans and 5v to the interface board, relay board, drive fault indicator and inverter (mentioned in previous post)

With four fans operating at 12v, the noise from them was quite significant and the volume of air shifted enormous. I figured that the fans did not need to run flat out at all times and found they would run quite happily at 3.5v, still moving enough air to do a reasonable job. However, my electronics friend made up a controller board for the fans that alters the voltage depending on the temperature of a sensor. The sensor is attached to the Geckos so if they start warming up, the fans will increase in speed and provide more cooling. The circuit varies the voltage between 3.5v and 12v with both the gain and lower voltage being adjustable. On testing, it works brilliantly, thanks Mike.

It will be interesting to see how often the fans need to increase their speed as, after quite a lot of testing, the geckos barely get warm. Perhaps, once I start cutting material and experimenting to see what the machine is capable of, it will put the Geckos under a little more stress. We shall see.

Mike

Would your friend be willing to post a schematic of the fan controller?

or after a quick Google search (what did I do before Google???)

http://www.heatsink-guide.com/content.php?content=control.shtml

Is this similar?

Randyf1965,

The solution Mike (my electronics friend) came up with is more complex than the one you found as there were a couple of complications he needed to sort out. The circuit is designed to take either a 12v regulated supply or anything up to 40v unregulated. The reason for this was that the original mini power supply from CNC4PC had a 25v unregulated supply we could tap into or we could have used the regulated 12v supply from it. To get round the unregulated supply, Mike built in a switch mode regulator that is more efficient than a simple, linear regulator. Mike explained that the heat that would have had to be dissipated had he used a linear regulator would have been too much and it would have been very inefficient. As it turned out, with the new power supply from CNC4PC, I now only have a12v regulated supply.

I don't pretend to fully understand how the circuit works - but I do trust anything Mike does.

Mike has agreed that I can supply the schematic for the circuit and if you require any more details, do ask. Apologies for the quality but the Zone kept asking me to reduce the size.

Mike

Apologies for the quality but the Zone kept asking me to reduce the size.

ZIP the original schematic and post the ZIPPED file instead of the graphic. ZIP files posted on CNCzone can be up to 8.58MB whereas everything else has a 500KB limit.

Keep up the good work!

Despite being in the middle of the January examination season, I had quite a productive day today and the Z axis is progressing nicely.

Cutting aluminium on the small Isel machine in school was a fairly slow affair and demonstrated the limitations of such a machine. However, I am hoping it has been accurate enough to produce good parts. The holes for all the bolts were only centre drilled on the Isel machine. I then used a bench drill to drill through the correct size. I then replaced the part in the small CNC and counterbored the holes for the bolt heads. You can just make out the counterboring on the vertical tie on the left of the picture.

Being able to use even a small CNC has been invaluable in terms of accuracy. I would not have relished marking out all those holes by hand.

Not too much more to do before I have all three axes working :)

Mike

Hello Mike you are a brave man ! , All i seem to do is collect the parts for such a project but never get round to starting one. As for motors and drives I would recommend Step and direction ac servo drives and motors try Kollmorgen , API or Parker. ebay good place to look but can take up a lot of time Good Luck. Mike

Technojunkman