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X axis movement issue (OX)

Discussion in 'CNC Mills/Routers' started by Psibernetix, Mar 1, 2018.

  1. Psibernetix

    Psibernetix Well-Known
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    Hi everyone,

    I am having an issue with my X-axis movement. See the video below.

    I am unsure if this is a setting issue (which I don't believe it is) a stepper motor issue, belt tightness issue or something else. If anyone has had a similar issue and managed to solve it please let me know as this is putting the machine out of commision and I have loads of stuff I need to get started.

     
    Chillimonster likes this.
  2. Chillimonster

    Chillimonster Veteran
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    I Dont think it will be belt tightness.

    It will be 'microstepping' related.

    From the way i understand it (and someone will be along with a LOT more knowledge tha i have) microstepping tries to force the stepper motor to split a full step and its an approximation.

    I reckon if you had the controller on full steps the results would be spot on and repeatable, but you would lose accuracy.

    there is a good explanation of the issues here
     
  3. Psibernetix

    Psibernetix Well-Known
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    I would be happy to lose a little accuracy if I can get it moving a lot closer than I have it now! ill give changing the step pins a move around and see what I get from that. After running some more steps it's like the drive moves and gets sorta stuck (but not physically) and stops the step halfway through for the 2 smaller steps and then when it's not stuck tries to catch up with the final step. ill give it a go through and see if that helps.
     
  4. David the swarfer

    David the swarfer OpenBuilds Team
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    what are your
    belt sizes
    pulley size
    microsteppping settings

    on my OX I have 2mm pitch belts with 20 tooth pulleys, and the drivers are set to 8x microsteps.
    this gives 40 step/mm or 0.025mm per step.
    This means that if I try to step 0.01mm it simply cannot do it and will do what you see, some small steps and some large steps as it adds up 0.01 till it gets to 0.025 and can do an actual step.

    I also tried to calibrate with a dial indicator and found that using a good 300 or 500mm long metal ruler to be more accurate.
    Use a magnifying glass to read the scale and beware of parallax errors!
    You will need to do the calibration a few times to refine the numbers and it will all depend on the tension of the belts.
    I used a spring balance to set the tension to 6kg so that I know that they are all the same. 6kg is arbitrary, 4kg seemed a bit loose (-:

    formulas for calibration
    https://openbuilds.com/projectresources/howto-calibrate-your-cnc-machine-for-mach3-or-grbl.145/
     
  5. Psibernetix

    Psibernetix Well-Known
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    @David I am running the same as you by the sounds of it.

    GT3 Belts and Pulleys and the GT3 pulley is 20 tooth with Nema23 steppers 8x microstepps.

    I am moving in 0.1mm increments but I get the same issue moving in 1mm increments and 3mm increments if I move 1mm steps up to 3mm the third step catches up to the 3mm step then if I try to move back I get a backlash loss of 0.5mm and the same issue two smaller than 1mm steps and then the third step catches up to the 3mm although it will only total 2.5mm of movement as I lose the 0.5mm of movement. I have tightened and loosened the belts thinking that there was backlash but to no avail, I still lose the 0.5mm movement in the X and have the issue's with the steps not being correct. and it's repeatable! I machined a hex with 5 holes in different places and all of them came out oval! and the overall size of the part in X was wrong yet the Y was perfect (same motors, belts and pulleys in Y as well) all settings in UGS are the same all pin settings and voltage settings are the same as well.

    I purchased the OX CNC Full Kit | Everything For A Hobby CNC Machine for further info the 750x750 kit
     
  6. David the swarfer

    David the swarfer OpenBuilds Team
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    check the set screws on the X pulley. they have a habit of coming loose.
    make sure that one of them is tightened on the flat spot on the motor shaft.
     
  7. Psibernetix

    Psibernetix Well-Known
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    I may have solved it. I got it working from 0-200 movement fine but as soon as I started doing smaller steps back like 20mm or so it was still losing 0.5 on the return so only getting 19.5 movements back yet if I went from 200-0 it was fine! this made me think that the settings in GRBL were fine at it was more of a hardware issue.

    I switched one of the Y motors to rule out the motor (same issue) I switched the pulley wheel as I had a spare to rule out that. (same issue) which was leading me to think that it was a board issue until I hit one of my limit switches and had to turn off and move the machine off the switch by hand. noticing that it seemed a lot harder to move in the X than in the Y. So I checked the Belts were not too tight loosened it completely and still noticed that it seemed tight so loosened the Wheel tension slightly and fingers crossed this may have been the issue. I attached a Pen to see if it looked ok and it seemed to give better results but the proof will be in the pudding when I cut something tomorrow. and will let you know how it came out.

    Thanks for all the suggestions though. If this has solved the issue I hope that if anyone else has the same issue that they will now have an answer to the problem.
     
    Chillimonster likes this.
  8. Psibernetix

    Psibernetix Well-Known
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    This does seem to have fixed the issue.

    I need to correct the X movement now in the GRBL settings but it is moving MUUUCH! better! I did also change it to 1/4 movements in X as well but this doesn't seem to be affecting the accuracy too much! I may change it back to 8th steps at some point but currently it is working considerably better the wholes are not oblong anymore they are pretty close to round now and it sounds much better now as well.
     

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