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IndustryArena Forum > WoodWorking Machines > DIY CNC Router Table Machines > Circles aren't circles, but I don't think it's backlash!
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  1. #1

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    Post Circles aren't circles, but I don't think it's backlash!

    Hello!

    Just finished up my DIY router build and having a few issues, every time I cut circles, they are coming out squashed along the Y axis (Picture attached)
    I've checked all of the usual info I could find on the forums, its running pretty square and I've checked and double checked any slippage or backlash?

    Does anybody have any ideas before I strip it down any further looking for a loose coupling somewhere or a loose belt?

    I'm generating the code in Aspire and using MAck3 into a PoKeys57cnc

    Thanks for your help!

  2. #2
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    Re: Circles aren't circles, but I don't think it's backlash!

    I think you have already narrowed the search to the likely culprits;belts would be more likely than couplings but its worth checking both.Depending on the feed speeds you are using and the depth of cut it could be the gantry or the spindle mounts flexing.Have you tried locating a dial indicator against the collet nut and pushing with your hand to see how easy it is to deflect the needle?Try it both in X and Y to see if there is a difference in the force needed to achieve the same deflection.

  3. #3
    Community Moderator ger21's Avatar
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    Re: Circles aren't circles, but I don't think it's backlash!

    You're getting flex somewhere in the Y axis.
    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)

  4. #4

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    Re: Circles aren't circles, but I don't think it's backlash!

    Quote Originally Posted by ger21 View Post
    You're getting flex somewhere in the Y axis.
    Brilliant, Thanks!
    Can you explain what you mean by flex? This is just a pen stuck to the spindle mount so there should be very little force involved that would cause flex?

  5. #5

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    Re: Circles aren't circles, but I don't think it's backlash!

    Quote Originally Posted by routalot View Post
    I think you have already narrowed the search to the likely culprits;belts would be more likely than couplings but its worth checking both.Depending on the feed speeds you are using and the depth of cut it could be the gantry or the spindle mounts flexing.Have you tried locating a dial indicator against the collet nut and pushing with your hand to see how easy it is to deflect the needle?Try it both in X and Y to see if there is a difference in the force needed to achieve the same deflection.
    Thank you, I tried at multiple different feeds, and still the same result every time.
    Will try the indicator today!

  6. #6
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    Re: Circles aren't circles, but I don't think it's backlash!

    ...X and Y following error not the same? This can cause out of round circles. Tune your drivers by doing a feedmove and adjust the Signal Gain

  7. #7
    Community Moderator ger21's Avatar
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    Re: Circles aren't circles, but I don't think it's backlash!

    Can you explain what you mean by flex?
    When the motors start moving, but the machine is lagging behind, also known as backlash.
    When your Y axis gets to the top and bottom of the circle, and changes direction, there's a slight delay before it starts moving in the other direction. It could be just about any mechanical part in your machine causing it, from the drive system, to the frame actually flexing.
    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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