Wrong X Y in G1 movement


I modified my 3d printer to use also an laser for engraving.
To control it I have an raspberry pi with software octopi on it.
When I engrave something the printer prints fine but sometimes it seems that it gets wrong coordinates. So for example it gets a line completely through the think I want to engrave, even outside of the space I want to engrave and then it gets back to the next real point to engrave. For me it looks like it is getting a wrong X or Y Value. Sometimes it even looks like it forgets a point. So it directly engraves to the next point, then for example an edge is missing.

The wrong points are definetly not In the gcode file. I checked it with a gcode viewer. And if printing it twice the faults are not at the same place.

Any idea what this can be?
I am using the actual OctoPi version and the actual repetier firmware, not the development...


  • It can be communication errors not detected. You could enable echo and log the session. Echo will write what it thinks you send while log also contains what you really have send. If it differs that is the problem. Firmware will not add moves on it's own. And I'm quite sure Octoprint also only sends what you give.

    Normally the checksum prevents this but if you send
    N8833 G1 X100 Y120 *67
    and firmware gets
    N8833 G1 X10 
    0 Y120 *67
    It will execute G1 X100 as a separate move and triggers an error for next line which it will ignore for missing line number I guess. Just an example of how com errors might cause unexpected moves. But better first compare in log as described.
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