This is GRBL-related. I have a laser-engraver type machine, Chinese, ~550 mm X axis, aluminium extrusions, 2mm-pitch T belt, Nema 17H3430 motors, one mechanical homing switch for X, Arduino-based.

The X-axis accuracy is not up to par. When I make a mark on the X axis and jog to that mark (after homing), depending on the day, the position varies within ~4 mm or so. Sometimes I have to use G00 X-418, others G00 X-422.

I checked the belt tension, it seems OK, not too tight, not too loose. Is there something else I should check?

Another idea I have: put a homing switch on the other end of the X-axis, then home both ends of the X-axis, measuring the difference in machine position, then modify the steps/mm value for each session to force the command that puts me on the mark to be constant (e.g. G00 X-420). Any other ideas? Thanks.


This seems to be either a case of either belt slop or missed steps or it is a case of the accuracy of the limit switch.

If the limit switch moves even a little into either direction, you have to account twice that as the maximum error. So the 4 mm error could come from 2 mm into either direction from the 0-position.

However, there is a silver lining: Laser engraving, just like CNC, usually first dials in the 0 regarding the workpiece instead of the 0 of the machine. As long as the machine's movement is ok, you should be fine even without tightening the mounting of the X-endstop. I suggest to run the following test to find out what kind of error actually hounds you though:

  1. Mount a waste piece
  2. Go to a position on the workpiece
  3. Run the laser for a split second
  4. X10
  5. Run the laser for a split second
  6. Repeat 4&5 till you have 10 points
  7. Measure the real distances between the dots engraved

If the distances are always the same but short, you have the wrong steps/mm set and need to adjust them accordingly. If the distances are inconsistent, you have either lost steps or a sloppy belt. To fight lost steps, carefully up the signal to the motor a little. If the results don't change from that, tighten the belt a little - it should sing like a guitar string.

  • $\begingroup$ Thanks, I'll go through the steps. By "signal to the motor", I assume you mean the current on the drivers (TMC2130), which I set according to a formula I found for them. BTW, the motors are very quiet (as expected) and move evenly. $\endgroup$ – MrSparkly Oct 21 at 14:20
  • $\begingroup$ @MrSparkly yes, upping the current can sometimes help to counter lost steps. $\endgroup$ – Trish Oct 22 at 8:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.