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  1. #1
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    Steel Gantry Router

    Hi all,

    After a few years with my Shapeoko 3 XXL, it is time to build myself a more serious machine. I have done considerable reading on here and other sites over the last year or so and though I know what I want to achieve, I would like a bit of input into my design from those more experienced members.

    Mechanical:
    - Work area minimum 1250x1250mm. More is ok, but must fit a half sheet of plywood
    - Z-axis travel 150-250mm – I’d like the clearance to fit taller jobs in
    - Able to comfortably mill aluminium. This is always a contentious comment, my Shapeoko *can* mill aluminium, but not comfortably. I don’t expect it to cut like a tormach.
    - Steel frame, happy to use Aluminum for brackets & smaller parts.
    - Steel parts will all be welded. At this stage Heat treating is not feasible, So will weld 20mm sections evenly around the frame to keep temperatures and hopefully warping to a minimum
    - Hiwin linear rails all round - 20mm seems well suited.
    - 10mm strips of steel welded to beams on linear rail mounting points. Machined flat.

    Steel sizes:
    Gantry - 200x100x6mm RHS - 1500mm long - Now 200x200x6mm
    Side beams - 150x100x5mm RHS - 1500mm long
    Cross supports - 50x50x5mm SHS - 1350mm long
    Gantry/bearing plates - 10mm steel plate
    Z-Axis(when I get there) will be 16-20mm plate


    Electrical:
    - DMM 750w servos direct drive to (originally 2010) Now 2525 ballscrews. - Not settled on this setup yet - I’d like to avoid belts or any reduction if possible. Now 3:1 reduction. Not sure what rapid rates I should be targeting, maybe 6000-8000mm/min Now 25m/min with screw @ 1000rpm
    - There are substantially cheaper 750w AC servos on Aliexpress, at close to half the cost. Not sure if anyone has any experience with these, obviously DMM are better but I don’t want to blow the budget out
    - Centroid Acorn control board. Also now considering Mesa 7I77 and LinuxCNC
    - Power supplies yet to be decided
    - 3-4kw spindle – yet to be decided


    So I started drawing up the below design (first two pictures), I got the basic bed and gantry set up, I’m quite happy with this design so far. It seems quite sturdy and has the added benefit of keeping the rails and ballscrews well away from the bed and the majority of dust.



    I then started googling for router designs for some z axis ideas and realised that there are not a huge amount of machines designed like this, and most commercial designs have the linear rails at bed height or below, with a ‘gantry riser’ style of design. This doesn’t feel as rigid as what I have designed, but I whipped up a quick draft of how this might look. Don’t be too harsh it’s just a concept at this stage.

    Any thoughts on what might be the better option? I haven’t put a lot of time into the gantry riser design, It needs a lot more support on the ends of the gantry and on the riser-bearing joint. The first design is my preferred option, it just feels a lot more rigid, and the joint from the gantry to the Y rails is very solid.

    Thankyou for any input, much appreciated!
    Attached Thumbnails Attached Thumbnails R1.jpg   R2.jpg   flat 1.jpg   flat 2.jpg   flat 3.jpg  


  2. #2
    Community Moderator ger21's Avatar
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    Re: Steel Gantry Router

    Not sure what rapid rates I should be targeting, maybe 6000-8000mm/min
    That machine should be able to cut plywood at 10m/min. I'd be looking for 15m/min or more rapids.

    3000rpm motors would give you 30m/min, but you don't want to spin the screws that fast. A better choice would be 2525 screws with a 3:1 reduction. That gives you 25m/min rapids with the screw spinning at 1000 rpm.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  3. #3
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    Re: Steel Gantry Router

    3000rpm motors would give you 30m/min, but you don't want to spin the screws that fast. A better choice would be 2525 screws with a 3:1 reduction. That gives you 25m/min rapids with the screw spinning at 1000 rpm
    Thats awesome info, thank you. I didn't expect to need reduction as I didn't think those rapids would be possible. What sized pulleys and belts should I look at for that sort of torque/rpm? I'm digging into research now but would something like a 5mm pitch HTD belt of 20mm width work? and 20/60 tooth pulleys? or are GTx belts a better idea?

    Is there any guide of how far apart the pulleys should be to minimise belt length?

  4. #4
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    Re: Steel Gantry Router

    Gantry beam should be 200x200.

    The Z axis induces a torsional force on the gantry. The forces are not just in X, Y and Z.

    Add diagonal bracing within gantry beam. Close the gantry beam ends also.
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  5. #5
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    Re: Steel Gantry Router

    Add diagonal bracing within gantry beam
    Ok Cool, I'll bump it up to 200x200 and see how that looks. should I increase the thickness of the beam or is there not so much benefit in that?

    The design that I think I will go with (first 2 pics in OP) does have end plates on the gantry, that attach to the Y rail bearing blocks

    As far as diagonal bracing goes, I saw a build recently (that I can't find now) where the guy drilled holes in the gantry beam at opposing corners, he then welded in 20mm round bar and ground it flat. I'm thinking of doing that every 200mm and alternating the direction (as shown in attached primitive drawing).

    Would that suffice?

    *edit* I came across this post and am taking a few tips from it too. https://www.cnczone.com/forums/diy-c...ml#post1858440

    Still not sure if I leave the Y rails as the 2x 150x100 beams or build risers, I can't find anything definitive or any reason to go one way or the other

  6. #6
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    Re: Steel Gantry Router

    So I've continued on with the gantry on raised sides design, It looks the most rigid so I will run with it.

    There is 290mm from the bottom of the gantry beam to the cross beams on the bed, I'm thinking of putting a 10mm steel plate as the base then a sheet of phenolic as the wasteboard which will bring it up to around 260mm - the Z-travel will allow a 1/8" endmill to hit the wasteboard, and a 50mm endmill to clear the bottom of the gantry. - the exact locations of the linear bearing carriages will be adjusted when I confirm spindle choice/dimensions

    Still working on the ballscrew locations, Z-axis lwill likely change a little to accomodate the ballscrew. I'm thinking I will just weld plate under the Z rails then machine flat to increase the space in there to fit the ballscrew & nut.

    The two Y-axis ballscrew mounts look a bit flimsy to me so I will likely make them more rigid by increasing plate thickness or putting a perpendicular brace in there.

    I'm not commited to electronics yet, I like the versatility of MESA card + LinuxCNC, but UCCNC and Centroid both seem pretty turnkey and a bit easier to set up

    Still a ways off ordering anything but I'm comfortable with how the basic frame is looking.

    Questions:

    1. Any comments on how rigid the Z-axis is? I plan to make both plates out of 10 or 12mm steel plate, thicker is no problem.
    2. Would it be better to weld the braces on the XZ carriage or drill, tap and bolt them on?
    3. Is there any major benefit to placing the X Ballscrew between the rails, or would sitting it on top of the gantry close to the carriage be acceptable?

  7. #7
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    Re: Steel Gantry Router

    Hi Stuart- You won't need the internal bracing in the gantry tube, anything inside your gantry tube is wasted effort . So far your designing a very rock solid machine. To match the stiffness of your machine you will need a very thick Z axis plate something like 1" to 1.25" or use a heavy channel or use a 1" plate but screw webs either side of it say 50-100mm high. 12mm steel plate for the Z axis is not near stiff enough to match the rest. Peter

    https://buildbotics.com/ consider this controller/driver/ all in one box. Seems to be very good.

    2. If you weld the flanges to the bearing plate it will change shape and need to be machined. If you can machine it then all good. If not then edge bolting is your next best option. Or find a large SHS or RHS and cut it down. Maybe these some large channel out there?
    3) either is fine. In between is slightly better but makes the stack higher. So the spindle will be outboard further.

    Re: welding if you have oxy welding equipment and are competent with it then bronze welding or brazing is a better plan. It normalises as you go because of the larger heat zone and because you don't melt parent, distortion and stresses are minimised.

  8. #8
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    Re: Steel Gantry Router

    That’s good info thank you Peter, I will see what plate I can source for the Z, I remember seeing some guys use thick steel tooling plate that’s been ground or machined on both sides, I will look into that. I intend to buy a manual bench top mill (meted DM45) for this project so will be able to square up the ends of beams and mill plate. I’ll also look into heavy channel. Even something huge that I can mill down a little may work.

    Do you mean webbing as I have in the last post? The X-plate has 100mm and the Z plate 75mm, is that what you are referring to? Just a thicker gauge?

    The Buildbotics looks like a good controller, but it doesn’t look like it supports running Servos the way I’d like to. I intend to run the DMM servos in Analog, with encoder feedback to both the driver and to the control (I know a lot of guys do this with LinuxCNC) part of this is to have very accurate motion control, part is because I want to learn how to do it.


    At the moment I am planning to go with standard Chinese rolled ballscrews, i understand this will be a weak point but ballscrews are an easy upgrade, and I will blow out the budget going with ground screws straight up

  9. #9
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    Re: Steel Gantry Router

    Hi Stuart there is a large discussion here about belts.

    https://www.cnczone.com/forums/linea...84496-cnc.html

    and I've just spent a few months working thru a similar machine. Look at

    https://www.cnczone.com/forums/austr...ml#post2312728

    cheers Peter

    also as a thought, its advantageous to be able to slide the entire Z axis assembly off an end or both ends if possible. So look at the ends and Z plates to see if you can do this. Saves a lot of work sometimes vs pulling the Z apart piece by piece to get deep into it somewhere.

  10. #10
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    Re: Steel Gantry Router

    Send buildbotics a note, they respond very fast and being the designer and builder they know their stuff really well. But didn't think to look if it will run servos....Peter

    Re Z axis - The z axis is a really good place to use aluminium. A 25mm thick steel plate say 200mm wide weighs 39kg/m yet a 36mm thick aluminium plate is the same stiffness yet weighs 19kg/m which is a huge advantage in moving it around. Since your getting a mill maybe a large chunk of aluminium is the go for the Z axis plate. I'm near Byron Bay so were about as far away as we can get in OZ. Peter

  11. #11
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    Re: Steel Gantry Router

    The buildbotics looks interesting, Though I can't find anywhere what type the controller is: Mach/LinuxCNC/GRBL/proprietary etc.Also I don't like the web based interface, it's an interesting concept nonetheless.

    You make an Interesting point about using aluminium, I may cost some aluminium just to get an idea and go from there. 450x200x36mm (or closest size) is not likely to be cheap, but I will check it out. As far as I can tell weight savings on the XZ-carriage are a bonus, though cost will be the deciding factor.

    That is some excellent info on the belts too, thankyou - I had searched on here for any belt-related posts but didn't come up with much. There is plenty of reading for me to do there.

    I am actually based in Armidale NSW, I moved from Perth around a year ago. So not too far away! Can you recommend any good suppliers for metal, linear motion or electronics that I can get some quotes from? at this stage I'm using local guys for steel and ebay/aliexpress for linear motion & electronics, but happy to travel to Sydney, Brisbane or between to save a few bucks or acquire the right gear.

  12. #12
    Community Moderator ger21's Avatar
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    Re: Steel Gantry Router

    I think it might be based on the TinyG, as that's the only hobby controller I know of with S Curve acceleration.

    If you want to run analog servos, that limits your options to LinuxCNC, KMotion, or Mach4 with one of the few Analog controllers that work with it.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

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