Wierd problem. Please help

So i converted my CNC to arduino and grbl. The problem i have is that on short distance x and y travel are of by a few mm.

Lets say on 60mm it cuts 64mm, but on a 120mm cut, its dead on120mm.

If it was the other way around id understand. Makes no sense to me…

  • $132=200.000 (z max travel, mm)
  • $131=200.000 (y max travel, mm)
  • $130=200.000 (x max travel, mm)
  • $122=10.000 (z accel, mm/sec^2)
  • $121=10.000 (y accel, mm/sec^2)
  • $120=10.000 (x accel, mm/sec^2)
  • $112=500.000 (z max rate, mm/min)
  • $111=1000.000 (y max rate, mm/min)
  • $110=1500.000 (x max rate, mm/min)
  • $102=1030.000 (z, step/mm)
  • $101=120.390 (y, step/mm)
  • $100=120.390 (x, step/mm)
  • $27=1.000 (homing pull-off, mm)
  • $26=250 (homing debounce, msec)
  • $25=500.000 (homing seek, mm/min)
  • $24=25.000 (homing feed, mm/min)
  • $23=0 (homing dir invert mask:00000000)
  • $22=0 (homing cycle, bool)
  • $21=0 (hard limits, bool)
  • $20=0 (soft limits, bool)
  • $13=0 (report inches, bool)
  • $12=0.002 (arc tolerance, mm)
  • $11=0.010 (junction deviation, mm)
  • $10=3 (status report mask:00000011)
  • $6=0 (probe pin invert, bool)
  • $5=0 (limit pins invert, bool)
  • $4=0 (step enable invert, bool)
  • $3=2 (dir port invert mask:00000010)
  • $2=0 (step port invert mask:00000000)
  • $1=25 (step idle delay, msec)
  • $0=10 (step pulse, usec)
  • $$

With the shield the microstepping is set using the jumpers, based on the microstep setting, the calibration of movement is set via the $100,101,102 settings. So if its 7% off at 60mm, then it would also be 7% off at 120mm, so im a little confused how it could be spot on at 120 and that far off at a shorter distance…

Here is the method for calibration, but i prefer the calibration wizard built into openbuilds control software personally.

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Yupp… A thought just struck me… It could be the Mill bit? Inch to mm isnt my strong side… Damnit need to go home and check :slight_smile:

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If that’s correct, I’d say you have a mechanical issue. More details on your machine will be helpful.

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