Z Axis Grinding

My Lulzbot Mini has started to grind when Z Axis goes up and down. Almost as if it is out of align. I originally noticed a louder then normal vibration that progressively got worse over time until it just stopped. So here is what I have done so far to attempt to fix it.

  1. Removed all Z Axis rods and worm screw and used White Lithium Grease. Reassembled… Still the grinding sound.
  2. Used calipers and a bubble level to ensure Y Axis carriage was level… Still the grinding sound on Z axis.
  3. Tightened bolts on both stepper motors on the Z Axis worm screw… Still grinding.
  4. Tightened the couplers that hold the Y Axis Carriage to the Z axis worm screws…Still grinding
  5. Ordered a new stepper motor for the right side Z Axis as this is where the vibration was… Installed…Still Grinding
  6. Removed the Z axis rod and worm screws and rolled them on a table to ensure they are straight and not bent…Seems pretty straight to me with no visible warping.
  7. Installed latest firmware from Lulzbot website via Cura Firmware flash. Still grinding.

If I manually in Cura, try to move the Z Axis 10mm, while it is grinding, if I grip the Stepper motor coupler that attaches it to the worm screw and give it some manual assistance it seems to help, but it jams again shortly after. This is the same behavior with the old stepper as well as new stepper motor.

X and Y axis move smoothly without issue. I have had the Lulzbot Mini for 9 months and now is the first I have had an issue. Not sure what to check next on how to get Z Axis to move smooth again without grinding. Trying to eliminate either Stepper, Mechanical or Electrical from the equation.

Did you check the bearings at either end of the leadscrews? If one of those has failed, that would cause a grinding noise? Another possible cause can be a wiring fault. If one of the pins on the motor has failed or come loose, only half the magnet set will engage.

If you remove the X axis entirely (which is what attaches to the Z axis leadscrews) and run the motors, is the grinding noise still present? If so, if you remove the motor from the leadscrew causing the grinding, does it still grind?

It could possibly be debris in the leadscrew nut as well.

removed the X axis from the equation and ran the motors for Z axis…motors spin fine without grinding.

Any chance an adjustment to the X rod positions on either X end caused a pinch condition? Maybe try reassembling it with the rod anchor bolts loose and run it up and down and see if it still behaves. Grinding will also occur if the Z carriages/X ends are off even half a turn offset from one side to the other. Most conveniant place to check that is the height from the upper face of the lower bearing to the bottom of the leadscrew nut. it should be identical on both sides

Be sure that the lateral fan (the one refrigerating the electronics box) is working. The connectors some times get loose and if it is not working the printer could develop a behaviour similar to the one you are describing.

Thanks for the tips. I will take a look at all your suggestions.