Salaam Mahmood,

I suspect your machine uses a stepper motor, or some kind of motion control, to set the z-axis position. My LPKF machine does it differently. It has a sort of threaded collar around the chuck/bit. The machine doesn't try to move the bit to a computer controlled depth. It simply lowers the chuck/bit assembly down until the collar rests on the surface of the copper clad board. The depth of cut is adjusted by threading the collar further up or down around the bit/chuck. This allows for very critical and consistent depth of cut control.

I don't know if you could easily implement such an approach on your machine, but you might give it some thought.

Joe