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GRBL Scaling Issues

Discussion in 'CNC Mills/Routers' started by jeffxclark, Mar 3, 2019.

  1. jeffxclark

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    So, I have an OX, with a Gradus M1 Pro controller, running GRBL 1.1. I have been having a frustrating problem calibrating the machine, and my googling abilities have failed me on this one.

    When setting the steps/mm, it seems to vary from small distances, like 50 mm or so, to larger, like 300 mm by almost a mm. According to the calculations on the belt/pulley, the setting for larger distances is a lot closer, and I have to increase the steps for the smaller distance to be correct.

    Aside from this issue, the machine is consistent, and pretty rigid. With the steppers locked, there is very little play to the spindle (definitely not a mm)

    Mathematically, the only reason I could imagine why I am having this problem, would be issues calculating acceleration, as a step should be a constant, but messing with that setting didn't change the situation. I cannot find anything about this, does anyone have any idea what might be going on?
     
  2. Gary Caruso

    Gary Caruso OpenBuilds Team
    Staff Member Moderator Builder

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    Hi Jeff, so after calibration you are off by a mm? not sure what you are saying in your description.
    Can you post your $$ grbl settings?
    could be a backlash issue, wheels too tight, pulleys with the setscrews not on the shaft flat or loose and slipping, belts too tight or too loose.
    There are a lot of grbl cal video's like this one from Ooznest
    Cheers
    Gary
     
  3. jeffxclark

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    Hi Gary, thanks for the reply,
    I have followed those procedures, but the issue is I can either calibrate it for 2 inches of machine travel, or 8 inches. so for 8 inches, it would need to be 26.6ish steps/mm for it to be 8 inches, and 2 inches would have to be 26.8ish to be 2 inches. Same issue for x and y.

    As far as the machine goes, the wheels will all still spin independently of the slots decently easily. I got tired of the set screw on the pulley issue, so they are glued to the steppers with structural adhesive, and I am aware of the play in the belts required to not bend the shaft of the stepper from over-tightening, but it's not as much as the travel distance varies.

    Here are the settings currently running:

    $$
    $0=14
    $1=255
    $2=0
    $3=3
    $4=0
    $5=0
    $6=0
    $10=3
    $11=0.010
    $12=0.010
    $13=0
    $20=1
    $21=1
    $22=1
    $23=0
    $24=100.000
    $25=1000.000
    $26=44
    $27=2.000
    $30=27000
    $31=4000
    $32=0
    $100=26.750
    $101=26.680
    $102=397.870
    $110=7500.000
    $111=7500.000
    $112=500.000
    $120=50.000
    $121=50.000
    $122=10.000
    $130=1300.000
    $131=1290.000
    $132=70.000
     
  4. Gary Caruso

    Gary Caruso OpenBuilds Team
    Staff Member Moderator Builder

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    Jeff,
    When calibrated for 8" how far off is 2"?

    Gary
     
  5. jeffxclark

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    Gary,
    Its about 25 thou less.

    Thanks,
    Jeff
     

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