Offset problem with 2 passes

I have a problem with the offset on a second pass.

  • If I choose 1 pass and the laser returns to the starting point and I make 1 pass again (manually), no shift is noticed.

  • if I choose 2 passes in automatic, there is a shift noticed on the start of the 2nd pass.

I’m on a cnc laser in grbl M3 (1.1 or earlier) + 15W laser module


Your machine is bouncing a lot:

If you click ‘Save GCode’ and then run that GCode in an online simulator, does it also show the offset? If not, the issue is the machine itself, probably losing steps.

I test with these all the time:

Thank you for your prompt return
I’m in a belt drive, maybe that’s why there are waves.
But apart from that why on 1 pass the square is correct and why on the 2nd pass I have this offset.
For information, the square in the photo was created with LightBurn and engraved immediately without using any other software.

I will try to see with the 2 links you gave me.

Thank you

I do not know, which is why I suggested verifying that the GCode is correct as a first step. If it is, then the problem is with the machine. If you run the job twice, and the machine returns to the home position before the 2nd pass, it might be over-shooting and stopping when it hits the limit switches, and then the 2nd pass would end up in the correct place.

I checked the G-code with your links and it looks correct.
The problem only appears if I choose 2 passes in the menu .image

If I choose 1 pass and it comes back to its point 0 and restarts the engraving, I don’t see any problem.

If I had a belt problem, the problem would appear on the first pass.

I will look at it in more detail tomorrow.

Thank you

I forgot to mention that for the moment I have not installed a limit switch.

and I solved my problem by choosing image
Now I can choose 2 passes and it works fine. :+1:

Thank you

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