Z axis calibration question

Hi, I am almost finished with a 500x500 build. ACME screw and Nema 23 motors.

I am unto the ‘calibrate’ stage of the instructions, testing direction of the stepper motors.
X and Y work as expected, however Z is skipping steps or binding (going in correct direction).

I have yet to set the homing switches and voltage but I have the pots at 12 o’clock for all 3 axis for now.

I have read the forums and have done the following:

  • Checked/adjusted Z belt tension
  • Ran the delrin nut up and down with a power drill (now smoother)
  • Switched the Z motor wires to X terminal block mounted to carriage to make sure it wasn’t a problem with gshield connections on the Z controller
  • Loosed off the retaining nut on the top of the ACME rod.

I do not detect any major resistance when I turn the ACME rod manually with a spanner, motor spins freely when not connected to belt.

I will check the screws holding the rod bearing are not too tight tonight (although, if it moves OK by hand I doubt it is a problem)

What is an ideal voltage pot position for the Z? Should I turn it up, or do I risk overheating?
I guess the Z needs more voltage due to resistance in the screw drive compared to the other axis, but how much is too much?

Here’s a good video to explain it. I had to turn up my Z pot for the same reason. My Z motor runs pretty warm while all of my other ones don’t heat up at all. If you turn the pot too high the motor will get too hot and run into thermal shutdown (and you’ll lose steps) but you should be fine to increase it a bit to see if it solves your problem.

Thanks Corey, I watched your video the other night and thought I would go through them steps for all 3 axis once I had finished the calibration stage of the instructions.
I was just concerned if I crank up the Z voltage it is covering up another possible issue I have with my Z?

Maybe someone else can comment but I think you’ve covered everything pretty well. Luckily it’s very unlikely if you turn the pot up too high they you could immediately damage something. If you get it too high it will just overheat and then just turn itself off. You can try bumping it up a bit and see how the Z movement reacts. Run it up and down a few times and make sure you’re not losing steps and feel the motor to see if it’s room temp, warm, or hot. As long as it’s not hot you should be good.

(I believe @RobertA_Rieke made the video, not me)

OK, Thanks Corey. I will give it a go tonight. Hopefully finish the calibration in the instructions (homing switches etc) and then I will fine tune the pots as described in the video.

I ended have up having the Z pot at about 2 o’clock for now and after a bit of running through the process of elimination found loosening the 2 bolts attaching the durlin nut to the z carriage resolve the binding (most notable near the top of the z travel). If nothing else, removing the bolts will tell you if the binding is in the z carriage/rail or not.
Thought I would add my solution just in case it is helpful.