HELP! Z axis zero position drifting upward

[firebeard]

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)

[ken_rychlik]

I would unhook the z motor and check for smooth movement of the Z slide. Make sure the springs are carrying most of the weight so the motor is not working to hard. Sometimes the bit slips in the collet, so you can mark the bit and make sure it is staying in the same place. By the way, check the things you think are good better. Something is not good. It could be your settings are to aggressive in the file design, as in asking it to go up and down at a rate that the machine can not handle.

[firebeard]

I would unhook the z motor and check for smooth movement of the Z slide. Make sure the springs are carrying most of the weight so the motor is not working to hard. Sometimes the bit slips in the collet, so you can mark the bit and make sure it is staying in the same place. By the way, check the things you think are good better. Something is not good. It could be your settings are to aggressive in the file design, as in asking it to go up and down at a rate that the machine can not handle.
I went back and double checked everything you mentioned this morning. Also slowed my speeds to a crawl, same issue. I'm not sure what to check next.

[coryatjohn]

If you have similar motors on other axises, swap them and see if the problem persists. If it moves to a different axis, then you likely have a failing motor. If it persists on the same axis, it's probably the software, controller or a wiring issue.