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  1. #41
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    Default Re: Need help - Fixed gantry design

    Alright. Quickly put together a couple more.

    So the one above out of aluminium not including uprights or internal angles weighs 41kg.

    The first ones below is a slight modification to NIC 77 design, main reason was I wanted to move the rails closer together so that the moving table didn't need additional support. I was also interested in how much it would weigh.
    In the end, comes in at 104kg. 200x100x4mm, 100x100x4mm RHS and 10mm plate is used. Main thing I don't like about this one is the upright height, which is 340mm, vs 220mm in the first one below.

    The second ones below, which is NIC 77 design, weighs 111kg all up (not including rails). All 200x100x4mm RHS. All plate is 10mm.

    Looks like you have the best design NIC 77!

    Attached Thumbnails Attached Thumbnails Need help - Fixed gantry design-06rev02-png   Need help - Fixed gantry design-06rev01-png   Need help - Fixed gantry design-05rev02-jpg   Need help - Fixed gantry design-05rev01-png  



  2. #42
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    Default Re: Need help - Fixed gantry design

    No.....I don't like any of them, except the last one.....the main reason is the 2 base tubes are not forming a rigid box frame with bolting and that will lead to misalignment in the 2 Y axis linear rails........they have to be dead in line.....not even a smidgeon out to one another across their entire length.

    Bolting them together will give you no end of trouble trying to get them to be both level along their length.

    This is one reason why in all build the Y axis rail seats are machined together to make them "perfectly" flat and level to each other.

    You would not have any reference to test if the rails are level to each other.

    My suggestion is, referring to the last pic........lay the base rectangular tubes down on their bigger side (without the mounting pads) and weld the two Y axis tubes onto them......the rest of the design is as per the last pic.

    I would also strongly suggest welding the 2 uprights to the bottom of the crossbeam, not bolting them.....this will give you just one complete assembly to bolt to the base frame.

    Once the base frame is complete the 2 linear rail seats and the side supports pads are all that needs to be machined.....that is, the main machining apart from the mountings for the stepper motor supports etc and a few tapped holes.

    Machining the base in one hit gives you accuracy.....the X axis assembly with the side supports can be "fitted" to the base by mating them to the base.....the X axis rail seats can be machined true to one another in 1 plane and square to the bottom of the side supports.

    You'll be able to get the two assemblies close to one another with the welding and final fitting, to give you 2 axis that are more or less square in 3 planes and just need final adjusting to make them good.

    Referring to the last pic, I would make the uprights from the same rectangular tube section as the base and cut them away for the width of the X axis tube to make them continue up the back side of the X axis crossbeam where they are welded back and bottom....this will give you a very broad based pair of uprights all in one piece.

    I think with a frame design like this you could get 200mm under the X axis for a 6040 build.

    You only have to get the two base/side support interfaces mated to one another to have a machine that is almost done.
    Ian. .



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    Default Re: Need help - Fixed gantry design

    Quote Originally Posted by handlewanker View Post
    No.....I don't like any of them, except the last one.....the main reason is the 2 base tubes are not forming a rigid box frame with bolting and that will lead to misalignment in the 2 Y axis linear rails........they have to be dead in line.....not even a smidgeon out to one another across their entire length.

    Bolting them together will give you no end of trouble trying to get them to be both level along their length.

    This is one reason why in all build the Y axis rail seats are machined together to make them "perfectly" flat and level to each other.

    You would not have any reference to test if the rails are level to each other.

    My suggestion is, referring to the last pic........lay the base rectangular tubes down on their bigger side (without the mounting pads) and weld the two Y axis tubes onto them......the rest of the design is as per the last pic.

    I would also strongly suggest welding the 2 uprights to the bottom of the crossbeam, not bolting them.....this will give you just one complete assembly to bolt to the base frame.

    Once the base frame is complete the 2 linear rail seats and the side supports pads are all that needs to be machined.....that is, the main machining apart from the mountings for the stepper motor supports etc and a few tapped holes.

    Machining the base in one hit gives you accuracy.....the X axis assembly with the side supports can be "fitted" to the base by mating them to the base.....the X axis rail seats can be machined true to one another in 1 plane and square to the bottom of the side supports.

    You'll be able to get the two assemblies close to one another with the welding and final fitting, to give you 2 axis that are more or less square in 3 planes and just need final adjusting to make them good.

    Referring to the last pic, I would make the uprights from the same rectangular tube section as the base and cut them away for the width of the X axis tube to make them continue up the back side of the X axis crossbeam where they are welded back and bottom....this will give you a very broad based pair of uprights all in one piece.

    I think with a frame design like this you could get 200mm under the X axis for a 6040 build.

    You only have to get the two base/side support interfaces mated to one another to have a machine that is almost done.
    Ian. .
    So pretty much this. You're right about have the base frame as one welded unit, otherwise every time the base is moved the x rails would have to be realigned.

    Attached Thumbnails Attached Thumbnails Need help - Fixed gantry design-0702-jpg   Need help - Fixed gantry design-0701-png  


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    Default Re: Need help - Fixed gantry design

    Yes, now that looks so good.....I think that's as simple and easy to construct as you'd get.....it'll look good when it gets a 2 pack paint job.

    I would make it all from the same sections.....3mm wall would be adequate, but as lot would depend on the actual size you want to make it, so you might have to go to 5mm..... and once you've got the plan and layout to a size you want, all it takes is a cutting list ....7 pieces in all.

    Close all the tube ends to make them a box and less flexible.....3mm plate would do.

    I dealt with Dandenong Steel Supplies, just off Greens road, and they charged a small fee to cut the tubes etc......cash in hand works wonders etc.

    I bought full lengths and worked out the size combinations to get the tube cut by them in approx. four 2 meter lengths.....the main cutting was done at home on my small power hacksaw.

    I would suggest an investment with a Hare and Forbes bandsaw would make life easier.......the $450 model would do the trick even if very basic, but the more expensive model would be better for the long haul.....EBAY has them too, probably the same models at half the price.

    Now you have to decide on the table.......a slab of aluminium would cost a bob or two.

    I think a 10mm thick steel plate would be more than adequate and not break the bank.

    A light grind all over with an angle grinder would make the top very presentable.

    Then you could glue an MDF board on it etc.

    I wouldn't bother about Tee slots.....tapped holes would be ever so simple, and you don't need too many of them.
    Ian.



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    Default Re: Need help - Fixed gantry design

    Quote Originally Posted by boltzzz View Post
    So pretty much this. You're right about have the base frame as one welded unit, otherwise every time the base is moved the x rails would have to be realigned.
    The bolt together design is more work to make, but way easier to move into tighter spaces, and to work on individual pieces, for example, when drilling the holes for your rails. The design I proposed has 16 bolts holding the bottom four pieces together. Torqued with lock washers, this would never move when assembled. You could bang on it all day long as hard as you can with a rubber mallet and never get it to shift. Sure, it would take a bit of alignment work if you take it apart and put it back together, but how often would that happen? Not really a problem IMO.

    The vice on my mini mill is held in place with two bolts. It's not going anywhere.

    You could weld the gantry tube to the uprights or have the uprights welded to the base, but you'll want to have it bolted on 4 bolts per side either at the top or the bottom as a minimum (as opposed to 8 bolts per side bolting at both the top and bottom). The way you have it drawn there is space for two bolts at the bottom as the plates don't extend at the back. Otherwise what you have drawn so far could work very well so long as you can move it where you need to.

    Also, the way I drew it (the uprights for the gantry) with a box section on it's side and a plate welded over the front is easier to make. You could weld plate over the back as well, which I did not show. The way you have it drawn now requires the upright tubes to be cut exactly the same and exactly square. If your cuts are off by 1mm, now your gantry will be 1 mm lower on one side. Also, if they are not welded at 90 degrees exactly, or the ends are not cut perfectly square, now you will have some strange twist in the gantry / upright tube structure. I would not make it this way because there are easier ways to make it without the same potential alignment problems during construction.

    I'm still thinking about your original idea having the pieces cut from sheet aluminum.



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    Default Re: Need help - Fixed gantry design

    Hi......welding the side tubes to the base is not an option.......you need to have the base frame clear on top to be able to machine the two linear rail mounts and the pads that the side rails get bolted down to.

    I proposed that the 2 side supports be welded to the bottom of the X axis beam as this then becomes one entity and is easier to align.

    You can machine the faces of the linear rail seats on the X axis beam in one hit to make them both in line and level.

    The base of the two side supports can also be machined in one hit and squaring and aligning them to the face and overall length of the X axis prior to machining is easy as so little has to be machined off the bottom faces of the side support pads to level them
    Ian..



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    Default Re: Need help - Fixed gantry design

    Quote Originally Posted by handlewanker View Post
    Hi......welding the side tubes to the base is not an option.......you need to have the base frame clear on top to be able to machine the two linear rail mounts and the pads that the side rails get bolted down to.
    I'd prefer not to weld the side tubes to the base either. It's not a good idea.

    Quote Originally Posted by handlewanker View Post
    I proposed that the 2 side supports be welded to the bottom of the X axis beam as this then becomes one entity and is easier to align.
    And I disagree that this would make it easier to align or to build.

    Quote Originally Posted by handlewanker View Post
    The base of the two side supports can also be machined in one hit and squaring and aligning them to the face and overall length of the X axis prior to machining is easy as so little has to be machined off the bottom faces of the side support pads to level them
    Ian..
    I stared at this for a few minutes trying to make sense of what you're saying. Still not sure I understand.

    So you're proposing that he weld the side tubes to the gantry, and then machine the entire structure, gantry (which I believe you are calling the x axis) and side tubes (risers)?

    So weld it all together and then machine the plates at the bottom of the risers?

    Goodness! How is that easy? Does he have access to a huge horizontal mill? For the size of the piece, not many machine shops are going to have anything that could do that, and if they did, $$$. Not the type of thing I'd want to try doing with an angle grinder and a flapper disk. It wouldn't just need to be flat, but also square and parallel to the rail mounts.

    Sure, he could build it and make it work, perhaps with some conformal shimming (epoxy) or other tricks, or just being really careful about the measurements and square of it.

    I personally would bolt the uprights onto the base before welding the gantry on if I were going to do it that way. Then I would use a bunch of clamps and measure and remeasure the square and parallel between the gantry and the base before tacking it in place. There would be no machining after the fact. And I would design the uprights differently to make it easier, as I have already said.

    I don't see anything easy about the actual "machining" you're talking about unless you have access to a huge machine and a guy who knows how to use it. Actually, not certain I understood what you wrote, but I'm still fairly sure I disagree with whatever it was.



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    Default Re: Need help - Fixed gantry design

    Hi, having been in heavy and light industry as well as fitting in the field, I tend to think that it's easy, but the methods I proposed are all valid as that is how it can be done with credible end results.

    I agree that you "could" machine the end faces of the uprights first, and then bolt them onto the base pads...... then align and square the cross beam to the Y axis rails......and weld the uprights to the bottom of the crossbeam, but welds being welds do tend to create some distortion or leave stress in the bolted state......unbolt them and the parts will spring out of square.

    BTW.....as I mentioned before, I weld in the cold state......that is, I don't allow the structure to gather heat and so expand in any direction........short welds, check for alignment.......cool the weld with water.......do some more welding......check etc etc.

    If you go at it like tomorrow must be today........the heat build up will make you cry when you wonder how the distorted members are going to be straightened.

    Heat is your worst enemy.....expansion goes hand in hand with heat......welding an expanded member to another will make you cry when it cools down and contracts.

    With the method I proposed the base of the side frames can be finally machined on a mill by turning the head on it's side.....even a Bridgeport can do that......that would probably be the only area that you'd want to send out.

    Some form of machinery is needed, but you could hand fit the side frames to the base without much drama.

    All it takes is to reveal the high spots by rubbing one face on the other and work them down progressively......the base pads act as a reference as they are already machined flat and true....... 4 points of contact per square inch was the accepted contact area for structures hand fitted in the field when I was fitting and that was done with an air powered angle grinder.

    With this build I would machine the 2 plates for the side frame bases separately and bolt them onto the base frame pads........then place the cross beam with the welded on side supports onto the plates and tack weld them on the bottom corners.

    If you now do short welds the bolted on plates will remain flat and the crossbeam and side frames alignment and squareness will not be affected by the base welding.
    Ian.



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    Default Re: Need help - Fixed gantry design

    Some interesting discussion. Just goes to show that there's more ways to skin a cat!!!

    Quote Originally Posted by handlewanker View Post
    Now you have to decide on the table.......a slab of aluminium would cost a bob or two.

    I think a 10mm thick steel plate would be more than adequate and not break the bank.
    I was thinking of going a 600x300x25.4mm ATP-5 plate. Around the $200 mark on my doorstep. Was thinking of using ATP-5 plate for the x, y and z plates.



    Quote Originally Posted by NIC 77 View Post
    The bolt together design is more work to make, but way easier to move into tighter spaces, and to work on individual pieces, for example, when drilling the holes for your rails. The design I proposed has 16 bolts holding the bottom four pieces together. Torqued with lock washers, this would never move when assembled. You could bang on it all day long as hard as you can with a rubber mallet and never get it to shift. Sure, it would take a bit of alignment work if you take it apart and put it back together, but how often would that happen? Not really a problem IMO.
    The more I thought about the two (welded base vs bolted), the more I thought welded is the way to go. The footprint of the base is only 840x600mm, so I think size is not the issue. I liked the fact that moving 4x 20kg sections is easier than 1x 80kg base frame, but I think it would be so annoying having to realign the frame every time I move it. I would like to do it properly once, not have to realign when moving.
    Also, the additional 10mm plates on each section added weight and meant more surfaces had to be machined flat which meant more work and stack up of tolerances.

    It's not really visible in the drawings, but my last design had 200x100x4mm tubes everywhere except for the uprights. The uprights are 150x100x4mm so that the gantry can be moved further back. I was also thinking of using this for the bottom two section too to save weight.



    Quote Originally Posted by NIC 77 View Post
    You could weld the gantry tube to the uprights or have the uprights welded to the base, but you'll want to have it bolted on 4 bolts per side either at the top or the bottom as a minimum (as opposed to 8 bolts per side bolting at both the top and bottom). The way you have it drawn there is space for two bolts at the bottom as the plates don't extend at the back. Otherwise what you have drawn so far could work very well so long as you can move it where you need to.
    I thought of that issue just after I posted it. Then I thought I could have two bolts at the backside on the inside of the upright tubing. A long extension would have to be used to get access to these bolts from the gantry top (through the 45° cutout section of the uprights).
    The issue that I have with this build, is because it's only 300mm cutting area in X (base rail direction), moving the gantry any more forward will increase the base frame dimension in X direction (as the spindle isn't positioned at the mid point).
    Having the uprights as you drew them initially is a better design I think. The only thing going against it is the back support of the gantry. I know notching out the uprights will be annoying in my latest drawing, but I do like how it supports the back of the gantry.


    I do love the idea of a bolt/rivet together aluminium flat pack design, but I think it will be too complex. The more parts you have to align, the more issues and the stack up of tolerances.
    Let me know if you do have anymore ideas on this aluminium design!!!

    I do think this latest design is the simplest and I believe that simple will mean accurate in this case.



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    Default Re: Need help - Fixed gantry design

    Hi, the main problem in any design is alignment.....one reason to have an all welded base and machined linear rail seats and side frame support pads all in one..

    If you don't have a large marking off table that is known to be flat, the bolt together version will not be anything like accurate where the Y axis linear rails need to be dead level in 2 planes.

    Once the all welded version is machined on the linear rail seats and the side frame support pads nothing will go out of wack if you disassemble the mqachine for any reason, and knowing that those areas are as accurate as the machine that machined them takes all the worry out of that aspect.

    However, if the base frame is flimsy and prone to flexing from bad design, nothing will save it from the scrap bin as it will never perform as it should......so adequate forethought in the design of the base is needed to get to that end.

    I state that a truly flat base is the most important factor in the equation because everything hinges on it being flat for the table to run on and the X axis to reference to......linear rails are not at all flexible and need to be kept in line to one another.

    Machine building is not easy but also not impossible, and lack of 100% perfection is not something to lose sleep over, but reliability for the long run is paramount.
    Ian.



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    Default Re: Need help - Fixed gantry design

    A little late here, but have you guys noted that the design in post 43 has the entire fixed gantry mounted to tubular bells?
    Certainly nothing solid there. I would rather see the gantry beam extended and the uprights bolts to the the bottom on the base tubes with perhaps and additional plate under it. Then into the side of the tubes that support the table rails.
    That would yield a far more solid design than what I see here.
    Even if they are intended to be filled afterward, the supports mounted to 4 points is far better than just two.



    Lee


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    Default Re: Need help - Fixed gantry design

    Found while image searching 'fixed gantry cnc' and/or 'welded cnc'

    Need help - Fixed gantry design-23-jpg

    Diversified Machine Systems(DMS)



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    Default Re: Need help - Fixed gantry design

    Better for sure. Still more complicated than it needs to be.
    The third beam for base support that the gantry gets bolted to should be similar to the other two, but longer. 45 degree angles cut so that the gantry uprights can be bolted down there. Then blocking on the sides to bolt there too. You can eliminate the angle bracing then.
    Just spit balling here. I have not built one like it.

    Lee


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    Default Re: Need help - Fixed gantry design

    The problem I see with the layflat design, though I reallly like the simplicity of it all, is I feel the rails should be more towards center. I was thinking +/- 1/3 the gantry width. Without any dynamic modeling at hand, it just feels like the should be closer supporting the center where most videos show parts mounted.

    On the other hand, outboard of the rails is overhang, will more flex occur there?



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    Default Re: Need help - Fixed gantry design

    Well that is one aspect that most don't seem very focused on. That is the strength of the table itself. If it is designed stout enough, you will not need to worry too much about the overhangs. I think a short torsion box type of table would likely do well as a base and then you add spoil boards, t-slot tables vises etc depending on what you are doing.

    Lee


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    Default Re: Need help - Fixed gantry design

    Hi, before we go to the ultimate rocket science design and tie ourselves in knots with assembly and welding techniques that need expertise where simplicity would do the job as adequately as is needed........I think, if the design that was posted in #43 was made, nothing short of a stick of gelly would make it deform under cutting loads.

    The design that was posted in #43 is simple but sturdy, so what more needs to be added?

    One design aspect that could be indulged in would be to have the two bottom tubes placed between the two side tubes instead of underneath the bottom......this would make a far more rigid base frame with mitred corner joints all welded

    I think I would go a step further and go to the extreme to produce a more rigid frame work and consider having two tubes side by side to produce the same ross section size and weld them together to form one tube instead of a single tube as in #43.

    This will give you a potential double rib in the middle of the tube section instead of a single hollow large box tube........same overall tube cross section but with double the mass, a steel section that you can't buy off the shelf.

    OK, so it means a lot more welding to produce the centre ribbed cross section shape but the mass increase will make it that much more able to resist deflection as opposed to a single hollow tube section.

    Two tubes with radiused edges placed side by side will automatically have a vee down the middle for deep penetration welding,
    Ian



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    Default Re: Need help - Fixed gantry design

    Can't help feeling that open-ended box sections are going to a risk. The Y axis beam looks especially prone to deflection under load.
    If you were to fill in every open end with a small plate, the structure would be a lot stiffer. More or less as Lee suggested.
    If you put a hole in each end-plate so you could fill the tubes up after welding ... VERY stiff. OK, maybe double up the verticals?

    Now, if you put an A-axis RT on the end of the table and made the spindle support into a B-axis (aka a nodding head), um ... yes.

    Cheers
    Roger



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    Default Re: Need help - Fixed gantry design

    Thanks for the further discussion guys.

    This is where I'm now at.

    Pretty much finished building the electronics controller box. Using a ESS smoothstepper ethernet card with the G540.

    I've only just started looking at the design again.

    My latest iteration is the same at post #43 except it's all bolted together as NIC 77 suggested in post #19. I have changed the gantry uprights to Misumi welded stand-offs as used in wade-o-design. They just bolt been the top of the base and the bottom of the gantry.

    All 200x100x6mm colded rolled RHS. Still deciding on gantry beam between 200x100x6 RHS or 250x150x9mm RHS.

    Here are my reasons:
    I spoke to a very good machinist I know and he recommended all joints doweled and bolted in lieu of welded due to heat deformation.
    In addition, having smaller pieces as in post #19 allows machining of each part, which is why NIC 77 recommended his design.
    After a lot of consideration, I'll be buying a mill to machine all these parts. A HM46 with DRO or a used Bridgeport.

    So with the latest discussion, you're recommending to move the two base pieces of RHS common to the linear rails a little inboard to allow the gantry uprights to go all the way down to the bottom cross RHS (the one that runs in line with the gantry beam). Then the uprights are bolted to both the top of the bottom RHS and the side of the top RHS?



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    Default Re: Need help - Fixed gantry design

    It seems like alot of work to buy a mill to do the machining for your build. Personally, I would use an angle grinder with a sandpaper flapper disk and some cosmetics to make the surfaces flat if affordable machining wasn't available, and perhaps some stainless shim tape and jb weld or other epoxy.

    I am looking back over this and wondering how it could be made better and if the advice I gave was any good.

    I think you may consider even some epoxy granite filling, although with the heavy steel tubes and short spans, probably isn't necessary, and may make things too heavy to move about. Also some ribs, I welding some inside my own very long gantry tube using a stick welder taped to a broom handle and did a good enough job of it.

    I'm really not certain it was right for us to steer you away from your initial idea of using aluminum plate. I've been thinking about it more, and designing a bolt together machine from aluminum plate to be filled with epoxy granite is still on my list of things to do. The design I'm thinking of could be cut from a large 3/8" or 1/2" plate on a big router. But there would be cost in that as well.

    The steel tube design is by far the cheapest (as long as machining costs, buying extra machines to make it etc, don't wreak you) and would work well.

    I'd say, get an inexpensive second hand stick welder, a good variable speed drill press, and some square tubes and plate from the scrap yard, and and angle grinder, and just give it heck, see what you can do.

    Either that or revisit this design again with the idea of using aluminum plate.

    Doweled joints is getting too complicated / expensive for a machine like this IMO.



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    Default Re: Need help - Fixed gantry design

    Doweled joints is getting too complicated / expensive for a machine like this IMO.
    I will respectfully disagree here.
    In fact, doweled joints are probably the biggest bang for buck you could get here. You can even put them in with a pistol drill IF you buy a tapered drill bit and the matching tapered dowels. Two small ones per joint is probably all you need, to LOCATE the joint. The bolts will provide the holding power. Tap in place and optionally tap out to disassemble.

    Cheers
    Roger



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