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IndustryArena Forum > Laser Engraving and Cutting Machines > Laser Hardware > Can't eliminate backlash, please help
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  1. #1

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    Jun 2021
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    Can't eliminate backlash, please help

    I built the Further Fabrication laser and I can't seem to get rid of the backlash on the longer axis. It makes my circles look like crap, check out the attached photo. I have been chasing this problem for months, I have tried many different configurations of the drive on this axis to eliminate any slop, and I've aligned the laser countless times.

    Is a 1.5 meter loop of 9mm wide timing belt(3m total length) just too much length on the belt? Do I need to get some kind of stiffer drive system? Am I just not aligning the laser to the level of perfection required? If I didn't have so much money sunk into this machine I would've gave up by now.
    Attached Thumbnails Attached Thumbnails lopsided circles.jpg  

  2. #2
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    Re: Can't eliminate backlash, please help

    X axis is right left and Y axis is forward backwards as you stand in front of the machine. So if the photo were orientated top bottom of the page to X+ and X- then the X axis appears delayed.
    Assuming this is belt driven, you don’t have to have tight belts. Just snug should do. Also shafts in pulleys need to be tight with no play when you twist them by hand.
    What resolution do you have on your stepper drives? Can you go to the highest setting?
    You need to change the machine configuration if you mess with these settings or you dimensions will all be wrong.


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  3. #3

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    Re: Can't eliminate backlash, please help

    I have checked the belts and pulleys a million times and played with levels of tightness from rubber band to guitar string. I will check the step resolution and try turning it up

  4. #4

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    Re: Can't eliminate backlash, please help

    Ok i tried doubling the steps per rev from 6400 to 12800. sadly it doesn't help. i'm beginning to convince myself the belt is no good. checked the tension again, it's good

  5. #5
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    Re: Can't eliminate backlash, please help

    Ok good that’s now set. I think it a good idea to try posting the circle some other way.
    Process it with different gcode or something. Don’t know if your using a DSP controller, Laserburn or what.
    Check what happens if you take the cut in the opposite direction.


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  6. #6

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    Jun 2021
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    Re: Can't eliminate backlash, please help

    I'm using a ruida controller with lightburn and rdworks, tried them both, they both have the same problem

  7. #7
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    Re: Can't eliminate backlash, please help

    I would advce to find out the root of the error.
    what is accuracy and repeatability of axis positioning? That's the point to start from.

  8. #8
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    Re: Can't eliminate backlash, please help

    Just to see what happens when i loosen up the X axis belt by about 10mm. So it was loose but the teeth were still engaging on the pulley.
    then cut a 75mm circle. I compared it to a circle cut with a tight belt (the circle is very round as I can spin it in the wood) and found the loose pulley circle to be distorted slightly.
    I'd say about a half mm in the two sections as shown on the attached photo. So I'm not getting what you are seeing. I don't think the problem is mechanical.
    Click image for larger version. 

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  9. #9

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    Re: Can't eliminate backlash, please help

    Dean448, that's very interesting, I wonder what the problem could be then. I remember seeing a post about a stepper setting that can cause you to lose a step when you change direction but I didn't think that would make enough of a difference to be visible. Now I'm wondering if it could be a software problem. I'll try to find the post again.

    https://lightburnsoftware.github.io/...ringRuida.html

    I found it but on a second read it looks like it produces skewed engravings so I'll test that when I can but I don't that that's it. Are there any common laser test patterns that help diagnose mechanical problems?

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