Z stepper motor hangs up

After manual level-printer is one yr old-I raise the z axis, set up print, heat bed and extruder print starts extruder moves x axis y axis but while lowering to hit z home, the left stepper jams-makes loud humming/grinding noise. If I hit the z end stop-motor stops. If I give all-thread bar a little twist z continues to lower. If I raise z up near top, the z motor hangs up about 3/4 in from bed. No issue any higher than that. I have taken the carriage and by hand raised and lower to be sure there are no areas where is binds. I don't dare lubricate anything until someone tells me OK to do so. right stepper seems ok.
Something I can do or has stepper stepped out on me?
-mark}

 

Mark,
I just ran into this, too. Did you ever get it fixed?
Ryan

 

Ok, yes I know I've awakened a sleeping thread, but perhaps this will be useful. It was simply the fact that the two z steppers were binding because the carriage was totally out of parallel. I simply rotated the right z threaded rod as I slid the extruder carriage across the x axis rails until the distance between the extruder nozzle and the bed looked to be about the same. Ran a part thru with no probs at all.

 

Yes -originally Robo3d sent me new couplers, but that didn't help much, I still couldn't get them tight enough to stop the thread from spinning. So I used a thin 2sided tape and wrapped it around the threads that are inside the coupler and solved the problem . Now no slippage . It lasts quite awhile too.

-mark

 

I'll add that to the list of upgrades. Thanks, gents!