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Prototype Rack-n-Pinion 4'x8'

Discussion in 'CNC Mills/Routers' started by Mike Campbell, Nov 29, 2020.

  1. Mike Campbell

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    Mike Campbell published a new build:

    Read more about this build...
     
  2. Mike Campbell

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    Tried to make this build a little bit bigger this week and hit a snag. I've re-worked the OB spindle mount specs to accept a full size router and even cut one on the machines at work to test. The good news is the mount works great. The bad news is this frame design, as it is, won't handle a big router. There is just too much deflection on the gantry beam to be usable. I don't see why this mount wont work on the new "LEAD1515" gantry setup, so I'll clean it up and share the file here soon.

    I did manage to get the X axis motor mount made and installed though. All that's left is to make is the custom swing arms for the rack and pinion drive on the XY and start wiring.
     

    Attached Files:

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  3. jeffmorris

    jeffmorris Well-Known
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    Try making another motor mount and put the mounts at top and bottom of the carriage, holding the motor at top and bottom. I think that the router motor may be too heavy.
     
  4. Mike Campbell

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    I think I follow what you're saying here, a second spindle mount wouldn't hurt. And the weight of the router can be overcome by adding a spring loaded return without much trouble which is pretty common.

    The real problem here is the lateral flex in the "C-beam" gantry rail. The OpenBuilds team has addressed this issue pretty well on the LEAD series by stacking the C-Beam extrusions and doubling up on the axis plates. Since I'm cobbling this machine together with off the shelf parts and plates from older builds, it has certain limits.

    Good thing I can use it to improve itself though.
     
  5. ljvb

    ljvb Well-Known
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    Interesting.. for something that wide... I would go with a much taller setup on the x axis. quad c beams.. maybe that is overkill.. but 2 butted up edge to edge and double that up.. lose the wheels and go with linear rail. I think even with a regular spindle you are going to see torsional flex due to the width.. You could also try balancing it.. place a counterweight to offset the router and the weight of the Z axis...
     
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  6. Mike Campbell

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    I like where your head's at, but this build is kind of a Frankenstein's monster using parts and resources already on hand versus buying and designing all new. It will be fine, as is, to dial in the new drive system and even fabricate parts for it's own replacement down the line.

    MC
     
  7. Mike Campbell

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    Just about got her all wired up and ready to test over the holiday. Had to drop back and order some other wire and a few bits of hardware to complete everything, so another week in limbo.



    1.jpg 2.jpg 4.jpg 5.jpg 8.jpg 9.jpg 6.jpg 7.jpg
     
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  8. Mike Campbell

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    Machine is 100%. Here's a quick vid of the first motion test. Full speed/random jogging by way of the game pad. More to come...

     
    #8 Mike Campbell, Jan 13, 2021
    Last edited: Jan 14, 2021
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  9. Paul Amelang

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    Hi Mike,

    This looks fantastic. Do you happen to have a CAD file of this? That way I could see what you are doing without pestering you for a bunch of little details.

    Where did you source the rack and piston parts?

    I need a 4x8 CNC for my startup business but don’t have the funds to drop $15k on a prepackaged solution. I have a 4x8 set up right now using the Openbuilds platform, but it lacks precision and repeatability due to my lack of experience building CNC’s.


    Thanks so much,
    Paul
     
  10. Mark Carew

    Mark Carew OpenBuilds Team
    Staff Member Moderator Project Maker Builder Resident Builder

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    Well done Mike! first cuts turned out really nice
     
  11. Mike Campbell

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    Thanks for the kind words guys, it means a lot. Still working on putting the CAD files and parts list together but will post them here when I can.

    The gear racks were custom cut at my day job and have been tested on a couple of builds there for about a year. This machine was built to kind of show them off a bit and let me start making them for others at home. I'll post more info on that soon, but am happy to answer any questions until then.
     

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