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Thread: My carbon fiber CNC gantry

  1. #37
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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by ack1 View Post
    Awerby, it is flexing side to side. Well front to back if you are standing in front of the machine.
    Is the gantry beam hollow and if so, what is inside it now?

    It goes to show that you can't always tell how sturdy something is from a pic. A thick-looking steel part could be made of thin walls welded together instead of being solid.



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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by ack1 View Post
    This is my machine when i got it.


    Side view of the gantry with the cap off. IF i remember correcly steel was about 8mm thick.



    Sometimes i do whole alu sheets of engraved pieces and if I go too fast (gantry makes a sudden change from forward to reverse or vice versa, in the Y direction) the gantry flexes just by its own. Specially if im in the middle of the table.
    The gantry span is somewhere around 2.3meter so its not surprising.
    These numbers are very small but you can cleary see what i mean. Look at number 7.
    Have you checked the g-code for the job, especially when it does the number 7? Sometimes CAM puts out crappy code... and sometimes the font, if translated from a Windows or Adobe font, can look "pixelated" even if it's a single line font. Sometimes on what appears to be a diagonal, CAM will spit out something like

    G1X0
    Y0
    X1
    Y1
    X2
    Y2

    and when you run this at speed it looks like it's a mechanical or electronics issue. Not saying that this is the case, but something to look at. Especially with some older machines.



  3. #39
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    Default Re: My carbon fiber CNC gantry

    check all the bolts of Router and Spindle motor..seems looseness..

    http://free3dscans.blogspot.com/ http://my-woodcarving.blogspot.com/
    http://my-diysolarwind.blogspot.com/


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    Default Re: My carbon fiber CNC gantry

    I think Louie might be onto something. Looking closely at the results you're getting, the oscillations are suspiciously regular. The number "1", for instance, wiggles exactly the same way each time. If this were looseness or deflection, as I originally suspected, the wiggles would be more random. Check your code, and see if it's in "exact stop" rather than "constant contouring" mode.

    Andrew Werby
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    Default Re: My carbon fiber CNC gantry

    Quote Originally Posted by louieatienza View Post
    Have you checked the g-code for the job, especially when it does the number 7? Sometimes CAM puts out crappy code... and sometimes the font, if translated from a Windows or Adobe font, can look "pixelated" even if it's a single line font. Sometimes on what appears to be a diagonal, CAM will spit out something like

    G1X0
    Y0
    X1
    Y1
    X2
    Y2

    and when you run this at speed it looks like it's a mechanical or electronics issue. Not saying that this is the case, but something to look at. Especially with some older machines.

    That's interesting. They use regular square and rectangle steel tubes. I was originally planning on using similar steel rectangle tubes for the gantry and frame on my build as they seemed to be relatively cost effective. I was unsure how thick the walls would need to be to deliver acceptable rigidity but I guess that it probably depends and few different things. That gantry looks fairly long in the pic.

    The good news with a hollow tube is that it can be filled to create extra stiffness. There is probably a lot of options that would help including more steel tubes to fill that cavity.

    If it were me, and I felt like experimenting, I would want to try reinforcing the center with strong steel bars and filling the rest of the cavity with a mix of epoxy granite (which apparently has a proven track record for creating rigid CNC bases with good vibration dampening) and a high shore hardness urethane rubber. I am sure others will have better advice that is based on actual CNC experience though.



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