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  1. #1
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    Oct 2018
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    Weird artifacts in cutting process

    Hello!

    So we built this CNC machine our self. Huge, 2x3m cutting area, first build, most of it manufactured in my workshop. And now we are in the process of dealing with weird bugs that we cannot really sort out anymore.
    In some areas, I tend to notice, in diagonal directions we get these artifacts. What the hell is going on? Rack and pinion is our drive mechanism. Backlash is not enabled. Chinese drives and Nema 34 motors.

    Sometimes it happens more, sometimes less, circles are more or less okay, but weird curves and ovals tend to be worse.
    Those artifacts also did not appear with one Hardcore cut. That was 3 multiple passes with a finishing repeat. So it means it is bloody following that artifact pattern.

    In the video you are also able to see when this "shaking" is happening. I cannot find any correlation between speeds and depths of cut. At least not yet.

    Could it be clearance between rack and pinion?

    Help guys!




    https://scontent.fosl3-2.fna.fbcdn.n...bb&oe=5E955B03

  2. #2
    Community Moderator ger21's Avatar
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    Re: Weird artifacts in cutting process

    What control software are you using? The shaking looks to be from the control software.

    The steps in the curve are from your rack and pinion. Is it direct drive, or belt or gear reduction?
    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: Weird artifacts in cutting process

    Quote Originally Posted by ger21 View Post
    What control software are you using? The shaking looks to be from the control software.

    The steps in the curve are from your rack and pinion. Is it direct drive, or belt or gear reduction?
    UCCNC software, perhaps some settings are screwed?

    Rack and pinion direct drive with NEMA 34 1600oz single shaft motors, there is a chance that the clearance might be too big between the pinion, we could try to reduce that.

    Initially I disregarded that idea, since the gears are constantly moving in one direction for the arc, so there should not be any backlash issues?
    And not all arcs and circles have those "steps", they come in "Certain"conditions and as seen on the other picture, not even on arcs all the time, but also just diagonal movement.

  4. #4
    Community Moderator ger21's Avatar
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    Re: Weird artifacts in cutting process

    I'd say it's a combination of the 1600oz motors, and direct drive rack and pinion.
    I don't think you'll ever get good results with a direct drive rack and pinion. You want at MOST to have 1" or 25mm travel per stepper revolution. Half that would be better.

    Loosening up the CV error tolerances may get it running a bit smoother.
    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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    Re: Weird artifacts in cutting process

    So whats the opinion of adding these in between? Would be an easy fix, would just have to throw some money at the problem.
    If that does not help, maybe go to 1090oz motors?
    Although the costs start adding up, so would like to be more sure of these expenses somehow.
    https://www.shop.cncdrive.com/index.php?productID=996

  6. #6
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    Re: Weird artifacts in cutting process

    Quote Originally Posted by MikeTerasT View Post
    So whats the opinion of adding these in between? Would be an easy fix, would just have to throw some money at the problem.
    If that does not help, maybe go to 1090oz motors?
    Although the costs start adding up, so would like to be more sure of these expenses somehow.
    https://www.shop.cncdrive.com/index.php?productID=996

    So the idea would be to increase the resolution by 5 times and if the issue persists then with smaller motors should be able to keep the torque high through gearboxes and the motors running with higher speed. Since currently with the direct drive they are running quite slow.
    What would the drawbacks be?

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