MakerBot Industries

My guess is that you just have to adjust the potentiometer on the stepperdriver board a little to give it more torque.

I hope you did try to move the nuts all the way along the rods before you installed them, to make shure there are no bruses/dents in the thread that could block the nuts. You could maybe remove the z-stage, use repG to set the z-axis moving, hold the nut just with your finger and let it run up and down to just to make shure there is no mechanical problem (You should feel it pretty well with your fingers if the nut isn't gliding smoothly).

Something i did before assembling my bot is to clean the z-rods thoroughly before i mounted them in the cupcake and oiled them. There was a lot of dirt and residue in the threads, probably from the machining process where the threads were cut. Removing the metal flakes and all the dust before you lube the rods is definately a good idea.

If bumping up the driver current doesn't help, check that the set screw that holds the pulley to the motor axle hasn't come loose.

The holes in most stepper motors are straight through tapped holes only having 4-5mm of use-able thread in the hole. The rest of the hole is filled with the screw from the other side of the assembly holding the stepper motor together.

Checks to try.
1 Check that the Stepper will turn easily without the belt or being connected to the controller.
2 Check the controller can turn the stepper without the belt.
3 Add some torque with your fingers.

File a small flat on the spindle of the stepper for the pulley screw to tighten on to this guarantees the pulley can not spin/slip.

4 Check that each z rod spins freely and that you can finger turn the assembly with the belt on and the stepper dis-connected from the stepper controller.

1 Will show if the Stepper is miss-aligned. (due to being dropped)
2 Will show the connections to the stepper are correct.
3 Will demonstrate that the power drive is enough.
4 Will show if it is a mechanical alignment problem.