Hello,
I just assembled my UMO, with the heated bed extension.
Now that everything is finished, I'd proceed to calibrate the Z axis. However, after stepping the Z motor upwards, when reaching the top ~ 10 mm, it always "slides back" a bit, as if the holding force of the motor would not be sufficient to keep it in place.
This only happens near the top (but still before reaching the end-stop switch which I'm about to calibrate). A few millimeters below, everything is very stable.
Did I mount something wrong?