What would cause this? I’m printing 1mm deep with a total depth of 1mm using a .125" (.3mm) endmill. The cut in either linear or parallel at 1mm is flat, but then the bit raises and lowers for the outline (at the end of the gcode), and cuts a hair deeper.
Just another suggestion, last time I had that it was because my Z coupler was not well tightened. It just dropped down a little during the very last path. I had a hard time finding that…
Check also that your Z motor doesn’t miss step and that your Z axis rod can turn freely. It is more likely to stall during lifting, in which case it will go deeper and deeper.
I’ll second that. I was having issues exactly as you describe - The Z would end up going deeper that it should as the job progressed, due to missed steps on lifts. The solution, in my case, was to slow down the Z movements a bit and lubricate the threaded rob with some better grease. Since then it is spot on!