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View Full Version : Moving Table vs Moving Gantry; Dremel vs Router



chuckknigh
04-30-2003, 11:32 PM
For a homebuilt unit, which is a more robust design? I can see benefits to both approaches...

My understanding of them is based, primarily, on photos of other people's machines, and of Cranky's 7th Sojourn and Routezilla designs.

Both look well engineered, and both would be excellent designs to emulate. (OK...copy) But which, for someone starting with a "blank sheet of paper" is the better design to emulate?

I *like* Routezilla better -- something about it appeals to me. But, my concern is the potential for the gantry to rack while the machine is under load.

Is this a real concern, or is it more of a theoretical thing? I'd be using twin rails -- one on each side with fully supported homemade linear bearings -- and a screw drive mounted in the center.

THANKS!

-- Chuck Knight

P.S. For the cutter head, would it be better to go with a Dremel/RotoZip, or a small router?

I already have both a Dremel and a trim router, so it's not a matter of using "what I already have."

And then there's this router:
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=44914

I've seen it on sale for $20 from time to time...a truly exceptional price. Something cheap that I could dedicate to this project, next time it goes on sale.

anoel
04-30-2003, 11:58 PM
I built the 7th Sojourn and liked it well. The table was a bit small for my specific needs. With a little help from John ;) I just finished up the mechanicals for a Routezilla sized machine. It's more of a hybrid of the Routezilla and Pheonix as I migrated the X and Y axis from the 7th to a moving gantry style machine. So far so good. I've not cut anything with it yet because it's going to need some faster speeds to cope with the large size of it. It's got a 28"x16" cutting area. I'm moving to 4v steppers and a 24v power supply in the next few days, which should prove to be much more powerful than what I've been using. I hope to get slightly better than 25" per minute with it. I cut all of the plastic parts and the gantry uprights with the 7th Sojourn and alignment was extremely good on this one. I can turn the lead screws very easily with my fingers and move any of the axis with less effort than I could on my all hand cut 7th. I'm pretty stoked. I can't wait to get my power supply. Where's that damn UPS man?

HomeCNC
05-01-2003, 12:02 AM
I never liked the moving table because the screw under the table is exposed at times, and it requires a larger floor/table space.

chuckknigh
05-01-2003, 12:13 AM
Why does it need higher speeds? Is it just a matter of practicality vs patience, or is there an actual reason to have the higher speeds?

To start out with, I'm thinking of getting "whatever" steppers I can find, adapting them through pulleys/gears to the torque I actually need, and then upgrading as better parts come available.

By driving it from a smallish shaft to a larger pulley, I should be able to increase the effective torque and resolution of "whatever" I can find. And, it doesn't seem to be too hard. It might make the machine painfully slow, but it should work...and suffice till better parts can be had.

I'm going to use that braided air hose coupling trick that was mentioned on the board -- good tips on here, and on the RC forum. I've already mocked up one of my screw drives, and it works just fine. Support bearing on each end, air hose coupler design, etc. Works great, even if it is only 6" long at this point. Like I said -- it' a mockup.

I have a computer flea market event coming up next weekend -- it's obvious what types of things I'll be hunting for. There's usually at least 1 guy down there with steppers and otical components...and another with broken LASER printers and Xerox machines. Both should prove to be good sources for steppers.

-- Chuck Knight

anoel
05-01-2003, 12:24 AM
Is'nt "Just because" the excuse our parents alwas gave us?

The need for speed is the fact that I need to route soft and hard wood. Too slow Feed rates cause the wood to get burn marks. 6 inches per minute on a 28 inch long axis would be dreadful, think about it. It'd take over 4 minutes to go from one end to the other. 12 inches per minute is almost as bad. I'll accept full length travel in a minute though, anything less would be like watching paint dry.

chuckknigh
05-01-2003, 12:35 AM
:-)

Anyway, seriously, I always wondered what the big deal was about speed. While there is a practicality aspect (1/2" per minute would be painful!), almost any speed is still workable.

In my case it's the precision, and not the speed that I'm interested in.

Having said that, though, I'll be overjoyed if I find some 450 oz-in steppers at that sale this weekend. :-)

Any particular devices I should look for, for scavenging big steppers? Big printers, old IBM typewriters, LASER printers, mainframe tape drives, copier machines. Anything else that would be a good choice? Last month I turned down an old IBM mainframe for $5. I'd have taken it for eBay, had I had any way to arrange for shipping. I'm telling you, *ANYTHING* technological can (and does) show up at this sale.

-- Chuck Knight

WOODKNACK
05-01-2003, 12:39 AM
Anoel,
Your machine looks very good! You did a nice job..

Did you use 1/4-20 threaded rod or something different?
You might be able to get a little more speed out of 1/2-13 threaded rod.;)

anoel
05-01-2003, 01:31 AM
I used 5/16" - 18Tpi threaded rod. It was the easiset to deal with without finding someone to turn the ends down. I did need to grind one end down to 1/4" to fit the motor coupling, but that was easy because I just needed to grind it down just till the threads were gone. Ginding down a 1/2" rod to a centered 5/16"/22mm to fit the thrust bearing would have been a bit more risky and if done wrong would cause binding and vibration. If everything works well I might jump in again and try 1/2" and have someone turn it on a lathe.

WOODKNACK
05-01-2003, 01:46 AM
I was thinking about turning some 1/2 rods down. Lucky for me I have acces to a lathe. What are you using for a board? John's board? I can't wait to hook my new xylotex board to a machine. I have to get the lead out of my a_ _ and get working on it. With spring here there is much to do around the house.. Sucky...

anoel
05-01-2003, 02:07 AM
Yeah, I'm using John's board. (or a 3 axis clone of it at least.)

WOODKNACK
05-01-2003, 02:11 AM
Well keep up the good work and keep us posted. Would like to see something you cut on that machine. Again nice looking machine....

WOODKNACK
05-01-2003, 11:12 AM
Anoel,
What size is the foot print of your machine? How much room does it take up?

HEY CHUCK,
I looked at that router at HF. Looks like an easy one to adapt to a machine with that square base on it. I wonder if you can get different collets for it. Like say a 1/8 collet so you could use dremmel tool bits.. You could buy a route speed control at say Wood Workers warehouse to control the speed of the router!!

anoel
05-01-2003, 04:38 PM
That HF router is not good as a CNC Spindle. The Spindle runout is pretty bad and the collet design is such that you'll not find a 1/8" collet for it. I bought the Homier equivalent, same router just a different color. It'd be fine to use for a hand held router but not for the CNC Machine. Step up to a name brand laminate trimmer that you know will give you good service and that you know you'll be able to get a 1/8" collet. I've been very happy with my Dremel Advantage and it's not very expensive and it's got a continuously variable speed contol built in.

balsaman
05-01-2003, 04:40 PM
I have heard that HF router takes an odd ball collet. Also lots of endplay in the collet.

Gantries are smaller for the same cutting area.

Eric

coherent
05-01-2003, 04:47 PM
my 4 cents worth...

Speed is an issue with larger machines. If you're getting 5-6 ipm with a homebuilt system with small steppers on a 12" axis, you may not mind. Put the same drive system on a 48" axis, and you're talking 8 min, just to move from one end of the table to the other in a straight line. Multiply that multifold for a design or lettering and it'll take forever to cut. You may say you wouldn't mind, but I guarantee you (ask anyone with a machince) that you will after a little while.
Moving gantry vs moving table has many arguments and both designs will suit a home build machine. The only real argument (other than the machines footprint if that's an issue) it that with a moving gantry, a piece of material can be in theory any length, and you could for example cut a sign 10 foot long sign by simply sliding it through the table and cutting in steps. A heavy piece doesn't have to be limited by the capability of a moving table either. Also, material clamping or a vacuum hold down system can be a simpler process with a stationary table, although simple t-nuts work well with either.
A previous post regarding speed in realtion to your cutter is an important one. If you can't control your cutting speed to some degree, than you need to be able to control your spindle speed to avoid burning or melting the material depending on what you are cutting.
Pulley, gears and all that stuff are great in theory, but keep in mind that even small steppers do a very good job of turning plain old 1/4 20 tpi threaded rod. And the torque you will get is normally more than sufficient to drive a small machine. A threaded rod is an inclined plane and the simplist way to get good torque to your table or gantry. There will be a tradeoff adding more mechanicals (gears, pullys etc) in a couple of ways... first, the more parts, the more play. And it can add up considerably if it's not precision fit/parts. Second, design such components carefully or you may find the initial added drag does not result in an overall torque increase.
Lastly, go with a small trim router or dremel, especially if you have a speed controller for it. The cheap routers at harbor freight seem to have more play side to side at the spindle bearings than your dremel or a good trim router. (I know, I bought one and tried it). Why build a tight machine that could cut to within 1/32 or less, then slap on a cheap router that after a week of use, has 1/8 inch of slop? Best bet is to make a differrent mount for each of your tools, and use what best suits the job.
Sorry for the verbosity
-Marc :D

ger21
05-01-2003, 06:12 PM
If you try to gear your steppers to get more torque, remember that the faster they spin the less torque tey have. And it drops off pretty fast, as they have the most torque at very low rpm's. So you may not actually gain any torque this way.

Gerry

chuckknigh
05-01-2003, 06:17 PM
Thank you all for so much help! I can't tell you how much it's appreciated.

I think I'm going to hold off on the final design (is there such a thing?) of my router, till I find out what parts I have to work with. Like I said earlier, there's a surplus computer equipment flea market coming up on Saturday -- I'll see if anything promising shows up out there. (I hope, I hope, I hope)

If nothing else, I'll definitely pick up some old printers, or something similar, and rob them of their steppers.

Once I have some materials, I'll "finalize" my design as much as I can...maybe even draw it up and submit it for review.

As to my opinion of speed...faster is obviously better. I'd never argue that... My point was only that my intentions for this machine are to provide precision I cannot manage by hand. Slow is OK, so long as it doesn't end up burning the edges of the workpiece. (Thanks for the warning!) Like I also said above, it won't hurt my feelings if someone shows up at the flea market with 450oz-in steppers for $1 a piece. :-) I'm only half joking...

As to complexity, I definitely don't want to add complexity. However, if I'm using an O-ring to drive the allthread rod from the stepper, there will almost definitely be a difference is the 2 diameters of the shafts. That's the "pulley" system I was referring to...a smaller shaft driving a larger shaft WILL result in a higher torque and lower speed. The precise increase will have to be calculated, once I get the parts. I hope it's a 1:1 coupling...but I know that's probably not going to happen. I'm assuming that I'm not going to use a direct coupling to the driven shaft...but it's only an assumption.

Moving Gantry vs Moving Table. The racking I was concerned about doesn't seem to be a significant factor, based on some of the responses here. I'm delighted to hear this. Consequently, I think I'll focus my efforts on a moving gantry design, to start with.

Harbor Freight tools. I was not aware the bearings in the HF router were of such remarkably poor quality. I think I'll just stick with my trim router or Dremel tool...my thought was to have yet another tool (can you ever have enough?) that could be dedicated to this project. The price was DEFINITELY right...I'll see if they have something reconditioned by DeWalt, instead. My DW scroll saw and planer are top notch.

Thank you all, again. I really do appreciate it.

-- Chuck Knight

P.S. now...noone had any another suggestions as to what machinery to look for...big old impact printers, older LASER printers, copy machines, old IBM electric typewriters. Anything else have good sized stepper motors in it? This flea market is 100 miles from my house (in Dallas...I live in a small, country town) and I'll be going ONCE this month. My next chance would be the following month, so I want to get it right.

P.P.S. ANOEL, your machine looks fantastic. I'm envious that you've gotten to this stage already...but in my defense I've not been on this forum for very long. :-) I hope you and Cranky don't mind if I "borrow" a few ideas from it.

Thank you for the inspiration.

balsaman
05-01-2003, 07:03 PM
Hi, look for old HP LaserJet l, ll, or lll printers. They have 100 oz., 5 volt steppers in them.

You don't want 450 oz steppers. They use too much current and the driver board will cost you a fortune. Look for 50-100 oz 5-6 volt 1-1.5 amp steppers. They run great on unipolar driver boards and surplus 12 volt PC powersupplies. With 1/4" to 3/8" or even 1/2" threaded rod you will get 8 to 18 inches a minute.

O rings wont work as a belt drive. You need toothed (timing) belts or direct drive. I would go direct. You already get a lot of mechanical advantage in your threaded rod/leadscrew.

Gantries are more complex than moving table designs. If you want cheap and simple and accurate and learning, keep it easy. Build a movable table. easier to calibrate too.

K.I.S.S.

Eric

ger21
05-01-2003, 08:08 PM
Chuck, what kind of driver are you going to drive your steppers with? That has a lot to do with what motors you can use.

Gerry

Max
05-01-2003, 08:42 PM
Chuck,

I'd look for an old line printer ... that prints on fanfold continuous forms. They are dinosaurs now and will have not only a stepper motor but the gearing and belt to hook up to your threaded rod. Also, there will be a power supply for the stepper. Depending how cheap you can bargain down, you may be able to cannibalize the thing for good use.

> micro-switches for your limit stops. Most have a hinged arm so that the frame of the moving table will push against it and press in the switch.
>Then there's those little multi-conductor wire connectors to put the wiring harness together and make it easier to replace an item if need be.
>Flexible wiring harness "loom" sleeves to protect the wiring.

I can think of all sorts of "what-not's" to fill a shopping basket for usable parts.

Happy shopping ....

coherent
05-01-2003, 09:08 PM
I don't want to spoil the fun of finding parts in old machines... I bought and had fun tearing apart a few old printers and a couple of copy machines... but to be honest, 99.9 percent of the parts are still in a box. I ended up getting the best deals on steppers on ebay. It's fairly common to see 2, 3 or 4 matching (matching can make things a bit easier) stepper motors for under $50 for the package deal. After all is said and done it's not only cheaper, but the steppers were more powerful than those found in most office machines. If I had it all to do over again I think I'd go with a xylotec 3 axis controller board (last price I saw was $125), and then track down some cheap steppers on the net or ebay and go from there. That controller is a true "chopper" controller and will control bi-polar and uni-polar motors, so any 4, 6 or 8 wire lower voltage steppers will work, and it has pots on the board so you can adjust power to the motors without messing with resistors. I don't have one (went with a stepperworld fet-3 board) but it's my next controller for a hobby machine. Don't get me wrong... if you're goal is to build cheap from scratch and time is of no concern, hit the swap meets and take your time and you'll eventually get the parts u need. If you're lucky maybe even fairly soon.
-Marc

chuckknigh
05-01-2003, 10:19 PM
Hi, look for old HP LaserJet l, ll, or lll printers. They have 100 oz., 5 volt steppers in them.


Darn it -- I recently gave away a HP LJII printer, working perfectly. I upgraded to a used HPLJ4.

HP laserjets frequently turn up down there -- often IIP and IIIP models. Since they're the "small" units, would they have the same size motors in them?

And, how many steppers will I find in these printers? i.e. Can I buy only 1 printer and get enough steppers, or is it 1 per unit, or what?

(In other words, do I need to take the car or the truck?)

BTW: Do the NEC LASER printers have big steppers in them, too? If so, I have a "half" dead one in the garage -- it needs a $200 part to make it work right. Perfect to cannibalize.


O rings wont work as a belt drive. You need toothed (timing) belts or direct drive. I would go direct. You already get a lot of mechanical advantage in your threaded rod/leadscrew.

I'll see what I can do about finding a cheap way to make the interface. Sounds quite managable, overall. I really don't anticipate much trouble with this aspect of the design, but I could be wrong. It wouldn't be the first time...

While in Dallas I'm going to hit quite a few stores, including a machine parts store, and of course Fry's. Amazing what you can find in the VCR repair parts aisle.


K.I.S.S.

KISS to a point. True KISS is me, cutting clock gears, using a handheld jeweler's saw, and just toughing it out.


Chuck, what kind of driver are you going to drive your steppers with? That has a lot to do with what motors you can use.

I intend to build my own, based probably on the L297/298 chipset. By hooking the 4 outputs of each driver chip to sufficiently large power transistors, I should be able to drive practically any load.

I think Allegro has a nice chipset, too...and they're known to give samples in qty 4. :-)

Of course, like everything else, this design will probably change once I have some real parts in my hands.

-- Chuck Knight

drrogla
06-09-2005, 08:15 AM
As far as I know printers usualy have two steppers in them...
One for moving the printer head and one for moving the paper...

Božo

Kammo1
06-09-2005, 08:54 AM
Hi would these steppers work for the machine like Anoel's on this thread
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=26209&item=7522025756&rd=1 Kammo1

Marc
06-09-2005, 10:02 AM
Unless I'm mistaken, that's only 45 oz of torque. What are you planing to cut ?

Marc..

Kammo1
06-09-2005, 02:26 PM
Hi I would like to build a machine that will have a cutting envelope of about 30-32 inches X 18 inches and a Z height of about 3 inches. I plan on cutting small decorative signs as well as maybe inlayed pictures and 3D shapes as well. I have seen the Hobby CNC kits and the Xylotex kits but as these were cheap I thought that they might do but if that is the only torque it will deliver it might not be suitable. I plan on using 1/2 acme rod but again what TPI should I get??? I also plan on using a small router like a Rotozip as well as a small Dremel for light delicate work such as inlays. The machine will be 3/4 MDF and a pipe and bearing set-up for all axis.
Also without getting into a A versus B scenario what would be a simple kit to start with
Hobby CNC or Xylotex?? bearing in mind I am a total novice and what something thats easy to build and use, for some strange reason I am tempted to go for the Hobby CNC but again any help in getting it right would be greatful. I must say that since I have visited this site some of the machines you guys have built are superb and this has inspired me to finally now take the plunge and get started but would like to build the machine around parts that I can get easily and also that are going to work. Kammo1

Marc
06-09-2005, 04:03 PM
Kammo1
Personaly I would go for the Hobby CNC kit, I think it's your best option and I heard good things about it

Don't forget pictures

Marc..

Kammo1
06-10-2005, 06:19 AM
Hi does Dave at Hobby CNC sell the circuit board already wired up so I haven't got to do this myself ? sure would make my life easier if it is all done. Also I found this driver whilst searching the web, would this be suitable to control a 3 axis machine with 200oz steppers. http://www.hobbytron.net/product574.html If I am not misunderstood is this like the Hobby CNC but all in one box ?? and the price indicates to me that it may not be up to Dave's quality but worth some comments. Kammo1

Marc
06-10-2005, 10:09 AM
does Dave at Hobby CNC sell the circuit board already wired up so I haven't got to do this myself

I don't beleave so


Also I found this driver whilst searching the web, would this be suitable to control a 3 axis machine with 200oz steppers.

The price sure looks good but I never heard of it

Marc..

Pete Stenabaugh
03-25-2007, 12:43 PM
I am surprised at what some of you fellows are talking about here.....Anoel you have yourself listed as a machinist, yet you talk about grinding down a threaded shaft to make the coupler fit? The coupler alignment must be accurate and concentrice or else the shaft will not likely run true and at high speed it will create lot of problems.

As far as speeds go, you fellows likely realize that these small dremels and zip routers etc, all run at very high speeds, but they do not have much power (torque). You need to use a regular variable speed router, like a Hitachi or a Bosch etc. If you plan on trying to route wood at speeds of 5, 12 ipm or so, you are really out of touch with what is required. To properly route soft wood like pine, cedar etc, or even into hard woods like oak, maple etc, you need to have feed rates in the range of 50 to 60 inches per minute, or you risk burning the wood with the high speed routers. Even the variable speed units need to run at least about 15,000 rpm, so trying to slow the router down doesnt help either.

As far a stepper motors go, you need to realize that stepper have their highest torque at 0 rpm when they are stopped. The faster they run, the less torque they have, and then you run into the risk of having them loose steps if they hit anything that tends to jam them up. With the lower torque available at the high speeds, this is easy. Keep your stepper motors to a max of about 250 rpm for cutting, but you can go a bit higher for rapid speeds, if your machine is nice and free moving.

If you think you can get lots of torque out of a stepper by gearing it down (by having a small pulley on the motor and a larger one on the leadscrew) this is also false thinking because to get the speed you need on the lead screw, you need to run the stepper very fast, so it looses torque as previously mentioned. You can get away with this to a degree, but if you plan on doing that then get a BIG stepper that has lots of extra torque right out of the gate.

The BEST way to get high feed rates, with only having your stepper run slow to maximize the torque is by using a rack and pinion drive. This is what the professional units use. Just think, a pinion gear that has a pitch diameter of 1" such as a 12 dp gear - the circumference of this gear, at the pitch line is 3.14", so if this gear turns at 100 rpm, then the resultant feed rate is 314 inches per minute.....that is how you get high feed rates out of steppers. The only draw back is that the resolution is lower, at about 0.001" per step, if you use the Xylotex controller and gear the stepper 2:1 to the pinion gear, but that is fine for wood working (200 steps x 8 = 1600..........then gear it 2:1 gives you 3200 steps on the pinion. The pinion is 3.14" diameter, so 3.14/3200 = 0.00098" per step).

Get your steppers from www.homeshopcnc.com this is likely the best and the cheapest place to deal. A very good reliable place to shop, Rick is a good guy. Dont use steppers that are under 500 oz in. you are only wasting your money and fooling yourself. These are not expensive motors, get the big ones. I use the 1780 oz in, which he has now replaced with even bigger ones, but you cant run these on a Xylotex.

Pete

delstanton
03-25-2007, 11:59 PM
I see a large disadvantage in size with an X-Y table versus an X table gantry machine, with Y and Z on the gantry.

Suppose you machine must cover a 4 x 8 foot panel. With the X-Y table you will need 4 x 8 foot motion of the table - a BIG machine. You have a 4 x 8 ffot workpiece that you need to move 4 feet one way and 8 feet the other way, a 8 X 16 foor envelpe. Of course this is disregarding the structures necessay to support the X and Y axis, outside that envelope.

Also the structure to support an X-Y table is more complicated. Looking at large metal workinjg machines there is no such thing as a large X-Y table milling machine, the large machines are all gantry types. I believe as you proceed with design of an X-Y table machine you will appreciate the superiority of the gantry approach.

You design the gantry to be as stiff as required to maintain accuracy. Looking at successful gantry machines will give you a good sense of what is required.

Del



For a homebuilt unit, which is a more robust design? I can see benefits to both approaches...

My understanding of them is based, primarily, on photos of other people's machines, and of Cranky's 7th Sojourn and Routezilla designs.

Both look well engineered, and both would be excellent designs to emulate. (OK...copy) But which, for someone starting with a "blank sheet of paper" is the better design to emulate?

I *like* Routezilla better -- something about it appeals to me. But, my concern is the potential for the gantry to rack while the machine is under load.

Is this a real concern, or is it more of a theoretical thing? I'd be using twin rails -- one on each side with fully supported homemade linear bearings -- and a screw drive mounted in the center.

THANKS!

-- Chuck Knight

P.S. For the cutter head, would it be better to go with a Dremel/RotoZip, or a small router?

I already have both a Dremel and a trim router, so it's not a matter of using "what I already have."

And then there's this router:
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=44914

I've seen it on sale for $20 from time to time...a truly exceptional price. Something cheap that I could dedicate to this project, next time it goes on sale.

lgroulx200
03-27-2007, 08:04 PM
I am surprised at what some of you fellows are talking about here.....Anoel you have yourself listed as a machinist, yet you talk about grinding down a threaded shaft to make the coupler fit? The coupler alignment must be accurate and concentrice or else the shaft will not likely run true and at high speed it will create lot of problems.

As far as speeds go, you fellows likely realize that these small dremels and zip routers etc, all run at very high speeds, but they do not have much power (torque). You need to use a regular variable speed router, like a Hitachi or a Bosch etc. If you plan on trying to route wood at speeds of 5, 12 ipm or so, you are really out of touch with what is required. To properly route soft wood like pine, cedar etc, or even into hard woods like oak, maple etc, you need to have feed rates in the range of 50 to 60 inches per minute, or you risk burning the wood with the high speed routers. Even the variable speed units need to run at least about 15,000 rpm, so trying to slow the router down doesnt help either.

As far a stepper motors go, you need to realize that stepper have their highest torque at 0 rpm when they are stopped. The faster they run, the less torque they have, and then you run into the risk of having them loose steps if they hit anything that tends to jam them up. With the lower torque available at the high speeds, this is easy. Keep your stepper motors to a max of about 250 rpm for cutting, but you can go a bit higher for rapid speeds, if your machine is nice and free moving.

If you think you can get lots of torque out of a stepper by gearing it down (by having a small pulley on the motor and a larger one on the leadscrew) this is also false thinking because to get the speed you need on the lead screw, you need to run the stepper very fast, so it looses torque as previously mentioned. You can get away with this to a degree, but if you plan on doing that then get a BIG stepper that has lots of extra torque right out of the gate.

The BEST way to get high feed rates, with only having your stepper run slow to maximize the torque is by using a rack and pinion drive. This is what the professional units use. Just think, a pinion gear that has a pitch diameter of 1" such as a 12 dp gear - the circumference of this gear, at the pitch line is 3.14", so if this gear turns at 100 rpm, then the resultant feed rate is 314 inches per minute.....that is how you get high feed rates out of steppers. The only draw back is that the resolution is lower, at about 0.001" per step, if you use the Xylotex controller and gear the stepper 2:1 to the pinion gear, but that is fine for wood working (200 steps x 8 = 1600..........then gear it 2:1 gives you 3200 steps on the pinion. The pinion is 3.14" diameter, so 3.14/3200 = 0.00098" per step).

Get your steppers from www.homeshopcnc.com this is likely the best and the cheapest place to deal. A very good reliable place to shop, Rick is a good guy. Dont use steppers that are under 500 oz in. you are only wasting your money and fooling yourself. These are not expensive motors, get the big ones. I use the 1780 oz in, which he has now replaced with even bigger ones, but you cant run these on a Xylotex.

Pete

Hi Pete,

I agree with many of the points you have made. But you can still make a DIY router with small steppers, threaded rod etc. and still have a excellent working machine. Do you have any pictures of your machine?

Larry

Pete Stenabaugh
03-27-2007, 09:48 PM
Larry, no I do not have any photos yet, it is still in the design stage, using solidworks. I do have the partial assembly model, but there is not too much detail to be seen yet.

Unfortunately there are too many other things in my face right now to be able to spend much time on it. I hope to be able to get back on the design in the next couple of weeks.

This is going to be a very rigid and heavy duty machine, capable of anything the commercial units can do, although I have limited the length to an 8 foot table, due to space limitations in my garage. It will be able to cut 49" wide by 78" long, so if a person wanted to increase the cutting lenght it is only a matter of a longer frame, and some more rack gearing to make the frame 9'-6". I really wanted to do this, but in reality I think if I need to cut more than 78", I will have to move the material. The table is designed to handle up to 49" wide material (mdf) at any length.

If you are interested in something like this, keep in touch. If you contact me off the group and send my your personal email address, I will email you (and any others that are interested) a pdf of what I have designed so far. I think you will be impressed. I got the basic idea from a web site that was selling plans, but I did not llike some of their design ideas, so I took it up a few levels to make it a true "Peter-built" machine.

You are correct about the smaller DIY routers. They are quite adequate with small steppers etc., but the same problem exists with feeds and speeds. Fellows that build these units typically mount small dremel or similar tools on the gantry, due to the limited size of the machine. With these small high speed tools, there still exists the issue of feed rate as I mentioned before, however if a person is doing small detailed work, engraving, filgree details etc, then the high speed router is fine with small diameter cutters. With this type of engraving then you should still try to attain at least 20 to 30 ipm of feed. If you are only getting feed rates around 10 or 15 ipm, you will have trouble with your cutter burning and getting overheated. The other issue that exists is that with the slow feed rates, it is more difficult to get the material to clear the cutter, which again causes overheating and melting of materials like plastic and foam. If you do this type of thing, only use single or maximum 2 flute cutters, and use ones that are designed for cutting plastic, or for engraving. Regular machining end mills are not ground the same, and do have the high helix required for this type of work. Get cutters from "Engraving" suppliers, and you will have better success.

Pete