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IndustryArena Forum > Machine Controllers Software and Solutions > Mach Software (ArtSoft software) > Machines running Mach Software > My machine won't route exact circles. Does it look like there are still screws loose?
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  1. #1
    Join Date
    Jul 2017
    Posts
    57

    My machine won't route exact circles. Does it look like there are still screws loose?

    I had discovered some issues I was encountering on my machine which mostly were corrected after tightening up some screws, but I still see that though most cuts have improved significantly, my machine still doesn't cut an exact circle when I attempt to do so. So that you know what type of machine I have and what I am experiencing I will submit a brief summary of my machine, its electronics, hardware & software, include a picture of it, and include a picture of the result of the piece I just cut which is not perfectly round. Any assistance you might be able to provide using the information I have provided would be appreciated. I'm thinking it may still be some loose screws or that I possibly don't have one of the motors set exactly correct regarding steps/unit. I still have to go back and check the latter as I switched it once and attempted quickly to return it to the settings it had originally.

    I built my own machine. It has an ESS ((Smooth Stepper) motion controller connected to a PMDX-126 BOB. I’m running a three axis machine using Mach 4 controller software. The external drivers are all DM542T stepper drivers with dual 425 oz-in NEMA 23 steppers driving 2010 Ballscrews on linear rails. The X axis is a smaller torque NEMA 23 driving a 1605 ballscrew on linear rails and the Z axis is a NEMA 34 driving a 1204 ballscrew on linear rails. The frame is made of 80/20 aluminum extrusion (profile 3030). I’ll include a photo:

    0836764C-5E58-4547-B296-0A86E081EDA1.jpeg4032×3024 3.41 MB



    Attached Thumbnails Attached Thumbnails IMG_0196.jpg  

  2. #2
    Join Date
    Mar 2003
    Posts
    35538

    Re: My machine won't route exact circles. Does it look like there are still screws lo

    Yes, it looks like one axis has some play in it or backlash.
    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
    Join Date
    Jun 2010
    Posts
    4252

    Re: My machine won't route exact circles. Does it look like there are still screws lo

    Yep, a typical case of backlash.

    Cheers
    Roger

  4. #4
    Join Date
    Apr 2004
    Posts
    5728

    Re: My machine won't route exact circles. Does it look like there are still screws lo

    That looks a bit extreme for backlash, which is typically under a mm or so. If you've ruled out confusion in the units/mm settings, I'd suspect some mechanical issue, either loose screws or (more likely) loose pulleys. When a set screw develops some play in it, it's not always obvious; it only lets go at the extremes of motion, and then goes to the other end of its range. Try making a mark on the shaft and pulley with a Sharpie, and run your program again with a piece of scrap. Inspect your mark for discontinuity as the program progresses. If you find this is the problem, make a flat on the shaft so the set screw can't drag itself around to various positions when stressed. .
    Andrew Werby
    Website

  5. #5
    Join Date
    Feb 2011
    Posts
    5

    Re: My machine won't route exact circles. Does it look like there are still screws lo

    While i have zero real world build or use experience, as I have not yet jumped in....

    Shouldn't the first piece of troubleshooting be to use an extremely light cut in a soft material, or even chuck up a sharpie and draw on some paper? The results would be extremely telling...

  6. #6
    Join Date
    Jun 2007
    Posts
    3891

    Re: My machine won't route exact circles. Does it look like there are still screws lo

    There is an "issue" with mach and some drivers, where the drive will not catch some slow moving steps sent by mach - usually these are at the transitions of an arc.
    In mach3 the way you would fix this is by setting it to sherline mode, which changes the pulse pattern from tiny pulses, to half waves. I dont know if mach4 is the same

    This is the first place i would look if i was getting "backlash" like that that did not appear to actually be mechanically induced.

  7. #7
    Join Date
    Jun 2010
    Posts
    4252

    Re: My machine won't route exact circles. Does it look like there are still screws lo

    Oh, I agree entirely with Andrew: 'backlash' due to a very loose coupling or similar. Could be almost half a turn of the ball screw in fact.

    There is an "issue" with mach and some drivers, where the drive will not catch some slow moving steps sent by mach - usually these are at the transitions of an arc.
    For cases where a single pulse is being lost, this is usually solved by flipping the default state of the Step pin. Tyhe problem there is timing constraints in the power driver electronics.

    Cheers
    Roger

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