YOU are probably not doing anything wrong. I looked at your file, no problems that I could detect.
But your machine is probably having an issue, which could be lots of things. With what you wrote the very first thing that would come to my mind is electrical interference. When a machine goes on the warpath like you describe it is not usually a matter of losing a few steps here and there. Besides, your depth of cut is very shallow and on work of that type the Z axis does not get a workout that would expose the usual suspects.
IMHO, not a software problem or operator problem.
Just looked at your gcode, no problem there either. The deepest move on Z that I could find was Z-.120, which is what you programmed. Ya got a machine problem.
Last edited by TReischl
on Sat Jun 15, 2019 1:42 am, edited 2 times in total.
Low Profile CNC Router Vise