HELP! Z axis zero position drifting upward
I just replaced my Z axis motor and driver on my 2006 PRT Alpha. I updated to the newer system shopbot is using now (from ASD to the ARD style driver). I got my stepper values set and the axis is moving accurately. I can consistently move it precise distances multiple times using the keypad with no issues. However, when running a file, the Z axis seems to drift upward about 1/8" each time the machine plunges. So after a few plunges the machine will show that the Z zero point is now far above the material surface. I have tried different files, same issue. I have run the same file multiple times with consistent results as well. Any advice would be greatly appreciated. (by the way, the pinion gear isn't slipping and the tool is firmly in the collet)