I’d suggest the following:
- Take the ACME rod off and use a hand drill to run it up and down a dozen times or so. (Breaks in the delrin nut)
- Reassemble the Z axis, making sure everything is flat and square. Leave the screws holding the delrin nut a little loose. (Helps diagnose if an offset due to the nut is the problem)
- Leave the V-wheels loose.
- With the power supply off, find the high and low stops for your Z axis potentiometer and set in the middle of the band. Be gentle when using the pot.
- Power it up and use the computer to raise and lower the Z axis a few times.
- Assuming it worked, tighten up the delrin nut and try to raise and lower it a couple times.
- Assuming it worked, tighten up the V-wheels to where you can’t spin them with one finger, but you can with two.
- Assuming it worked, carry on to calibration and setting your pots (I made a few videos on them (thanks @CaseyKookla!), you can find them in this thread: X-Carve Maintenance/Troubleshooting Videos - Add Your Own!)
If that doesn’t work, try swapping the motor out with one of the other motors and try again. That will help you diagnose whether the problem is the motor or the power going to it.
Good luck, and let us know what your results are!