Stepper not locking

Strange issue here - i didnt’ think this is possible, but…mpcnc works fine. All motors runing great. But I just found that one stepper from X axis pair is not holding position when active. It is making the same squeaky sounds as the second one from pair, is runs hen it should be running - but is not “locking”

any ideas what could cause this?

I checked cabling and it seems to be ok - at least enough ok for normal routing operations without having isssues with skips, square-breaking etc.
Anyway, will redesign the cabling from scratch in near futur because I hate those stupid dupont connectors.

Swap X1 and X2 at the control board and run a test. If the issue is with the same motor, then it is likely a wiring issue or remotely a stepper motor issue (which is exceedingly rare). If the issue moves to the other stepper, then it is likely a driver issue. You don’t say what control board you are running. If the stepper drivers are removable, and if it appears to be a driver issue, you can swap drivers on the control board and retest.

Make sure the control board is powered down before making any wiring or stepper driver changes.

Based on forum posts, the odds are on this being a wiring issue.

To be honest, I have banged my head over bad DuPont connectors many times. Replacing the connectors on the faulty motor is not a bad idea. Swapping motors is even better because it can rule out bad internal motor wiring as well.

I swapped the axis, changed stepper driver, but still the same. all motors lock position except this one. So the motor seems to be faulty - or there is a wire issue on the preinstalled cable, probably not in the connectors as those were checked thoroughly and also swapped between axis.

What connectors would you recommend?

I thought about using

  • 9pin d-sub on the side of my electro box, because you can simply add more wires for the same axis output if needed, than you have very simple life when reconfiguring the machine
  • self-locking “micro-fit” connetcors on the side of the steppers (and possibly other low-voltage addons) - like those:

For cabling, I thought about pvc covered and shielded 4x0,5 (AWG20) fire resistant cable - for some reason, it is cheaper than unshielded variant:

I spent some more time with testing. I looked for any kind of electrical issue, checked stepper resistance, stepper controller, switched stepper axis - everything was normal.

Now, it is the right time to introduce myself - I’m the dumbest of all creators, king of stupidity.

Solution was so simple - two locking worm screws, that should hold stepper axis to pulley, got loose and fell out. During movement, when both paired motors turned same direction, friction was enough to move both carriages correctly, pretending everything is in normal. But when motor should stay locked, movement freedom was obvious.

So - no motor fault, no wiring issue, simple locking screws I forgot to loctite correctly in place.

Ah ha. The infamous grub screws strike again!!


I’ve been right where you are, went through all the trouble to take apart my axis to get to motor because I couldn’t see that side well. God damn grub screws.

I know your pain.