Print plate scratched when canceling print during priming line
Just experienced something weird here.
I have been printing stably for many months at a Z-level of -1200.
Today, I canceled a print as it was starting the purge line. Before the printer stopped, the print head dragged the nozzle across the plate to where the actual print would have begun and left a sharp thin scratch in the plate.
Subsequent prints (at the same Z-level) as well as a test calibration print showed that my Z-level hadn't changed and that -1200 was still perfect.
Is it possible that in canceling during a purge line, the head suddenly lowered a fraction of a millimeter resulting in a scratch?
Is it possible that there is a firmware bug lurking here?
It also isn't clear why it didn't stop immediately but instead continued to move the print head towards the start of the model, rather than stopping in place.
RE:
Note that usually the head is raised to 0.6mm (from 0.2mm) when traveling from the prime line area to the start of the print.
I wonder whether the cancel occured before the 0.6mm height raise but somehow the firmware still told the head to return to the center of the plate -- but now it was at 0.2mm which due to imperfect bed level could lead to a scratch during the high speed travel from the prime line to the model...
Indeed the usual behavior during a 'cancel' is for the print head to stop later motion immediately and just raise the print head about 20 mm.