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  1. #1
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    Jun 2016
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    Circle problems

    Hello,
    I have build CNC, when I calibrate it with gauge indicator (10mm lenght, 0.01mm resolution) for example: go 3mm Y or X axis, gauge indicator shows 3.01-3.02mm. then go -3mm, indicator shows 0.01 or 0.02mm. Z axis is more accurate, resolution and repeatability is less than 0.01mm. For X axis I use 2 motors and two SFU 2005, Y axis same SFU 2005 ballscrew, for rails I use linear block rails. When I mill squares or corners, everything looks good, but when I mill circle - It looks awfully. there is pic of circles: https://imgur.com/a/lJfTn circles diameter 5 and 7 mm

    While CNC is milling circle, X and Y axis half of circle start moving with velocity and almost stops, then again start with velocity and stops. So as you can see in the picture, circle consists of two parts. I use mach 3, I try a lot of different cad's and cam's, but I have same problem. Any thoughts?

  2. #2
    Community Moderator ger21's Avatar
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    34659

    Re: Circle problems

    You have a lot of backlash, or your screw or nut is loose.
    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: Circle problems

    when measuring with gauge indicator backlash is 0.02mm, so 20um. I bought new ballscrews. Sad, I will need to buy new ones. But that circle milling per two half's, how I can make that circle mills without any stops at half way?

  4. #4
    Community Moderator ger21's Avatar
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    Re: Circle problems

    when measuring with gauge indicator backlash is 0.02mm
    from the look of the cuts, I'd say you measured wrong, or something came loose.
    Can you post the g-code you used?
    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)

  5. #5
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    Apr 2005
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    Re: Circle problems

    backlash or losing steps on the Y, but with the flattened section and the ends not meeting most likely as Gerry has said backlash
    I'll get it finished sometime after I start it.....

  6. #6
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    Re: Circle problems

    hello,
    I think I found problem, today I will try to fix it and then I will post results.

  7. #7
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    Re: Circle problems

    Thanks for help, after ger21 say about backlash I started to search where can it be. And I found it, ball screws support bearings were not fixed correctly , so I fix it and results: https://imgur.com/a/EElbO

  8. #8
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    Re: Circle problems

    Quote Originally Posted by Patuc View Post
    Thanks for help, after ger21 say about backlash I started to search where can it be. And I found it, ball screws support bearings were not fixed correctly , so I fix it and results: https://imgur.com/a/EElbO
    excellent, well done
    I'll get it finished sometime after I start it.....

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