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grbl setup issue

Discussion in 'CNC Mills/Routers' started by mel, Oct 2, 2017.

  1. mel

    mel Well-Known
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    I have one axis, the x-axis, I will build the others when I figure this one out.
    I am using a 200 step/rev stepper motor, 20 tooth drive pulley, GT2 belt in a loop, and Easy Driver with default stepping (1/8). I am also using Grbl 1.1 (The G-code sender screen says at the top v1.0.9). I do the calculations for $100 and the answer is 40 steps per mm. I checked the calcs with Grbl calculator (originally by DrRob and modified for GRBL 0.9j by the swarfer). I used a pitch of 2mm, 200 step/rev motor, x/y pulley teeth of 20, and x/y microsteps of 8.

    The carriage only moves about 3 inches when I tell it to move 10.0 inches. I have to set $100 at 127 in order to get the 10.0 inches. Any ideas? what am I missing?
    Mel
     
  2. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder

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    127 is one of those factors of inch to metric conversion, so lets check that.....

    Gcode can be either metric or imperial. GRBL supports both, even though all internal settings are in millimeters.
    send it the right code to put GRBL into the correct mode.
    G20 sets imperial mode (all distances in decimal inches)
    G21 sets metric mode (all distances in millimeters)
    so, make sure it is in the right mode.

    then check that your acceleration and max speed settings are not too high. it might be missing steps, though I think you would notice that as it makes strange noises and is not repeatable. ie doing G0 X10 then G0 X0 would not end up at the right place at both ends.

    I confess to being confused though. 3 inches instead of 10 inches is off by a factor of 3.
    are you sure about the belt pitch and pulley teeth, even motors steps per rev?

    maybe you can try this: (you may need to adjust other numbers for this to work, and disable soft limits if you have them set)
    1. disconnect the belt!
    2. set $100=1
    3. now issue
      1. G91 G21
      2. G0 X1600
    the motor should turn exactly 1 turn. 1600 is 200*8 and at 1step/mm that is one turn
    if not, your numbers for steps per rev and microstepping are wrong. (-:
     
  3. mel

    mel Well-Known
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  4. mel

    mel Well-Known
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    David,
    I hope this is the correct place to say thanks, so thank you for your help.
    I performed your test and the motor turned 1 rev exactly. So I knew my motor was a 200 step motor. I checked my belt again and it is a 2mm pitch belt. I counted my pulley and is has 20 teeth. So, I was back to the micro-step setting. I found that I did not understand the four options on the Easy Driver. Once I had it set on 1/8, everything fell into place. I can now run my X-axis in imperial or metric units and it works. So, THANK YOU!! Now I can buy additional parts from Openbuilds.

    Marvin
     
    David the swarfer likes this.

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