My dad bought one and it had a problem with breaking the flexable coupling that connected the stepper to the screw. When the second one broke I went and looked it over. We put an indicator on the screw and swept the locating boss for the stepper motor and found they were not on the same centerline. We fixed that and it works super now. Check and see if yours has the flex coupler and if the screw is on centerline with the stepper.