carves first cut then zero changes and over carves letters
i have done several of these and never had a problem
Looks like you are loosing steps. Maybe check your belts.
usung a yora 3018 no belts screw drive
If the bit is not going back to where it started you are loosing steps somewhere.
Loosing steps = stalled stepper and/or mechanical issues like binding etc.
A stepper will stall if the cutter forces exceed the available torque of the stepper motors.
The faster a stepper go (RPM) the less available torque you have.
If you go with a too large bit, going too fast and/or too deep you´ll exceed the machine capability and they will stall out.
Another possible cause for loosing steps is overheating of the drivers. If they get too hot, the go into a brief thermal protection shutdown. The stepper wont perform its intended steps during this time and position is lost.
A stalled stepper will make a grinding noise during stalled state
An over-temp shutdown will make stepper silent.
Time to trouble shoot, go shallower and work yourself up from a known good configuration.