[George777]

The mill has been working fine but now there is something wrong with the z stepper motor. When sitting at idle under Mach 3
the z stepper motor will occasionally lurch or make a very short movement without a command input. When a file is run under Mach 3 the z axis is all over the place and does not follow the G-code.

[lsces]

You do not say what electronics you are using? The taig/microproto controller, or some third party unit?
I would be starting by checking the wiring between the computer and the controller, but an easy option to help pin down where the problem is would be to swap a couple of motors over and change the Mach3 pin settings. This will identify if the problem remains with the motor and driver or is something to do with the current 'Z' output on the computer.

[George777]

Found the problem….. Talked to the nice people at Taig and they suggested re-installing Mach 3. Mach 3 was slightly corrupted or whatever; the re install fixed the issue.