Threaded rod alignement problem

Hi everyone,

I am just finishing settin up my MPCNC latest version and i am facing a problem with the Z assembly. I am using an 8mm threaded rod.

As soon as i put the threaded rod through the Z lower bracket (the one with the bearing inside), it puts a very very slight amount of force on the rod because the rod is not perfectly centered with the bearing center. Maybe by a half millimeter even less… but this slight force causes the rod to lock in place and not spinning anymore or with a huge amount of force that the Z motor cannot handle.

When i remove all the Z Axis and i put the rod inside the the middle assembly i constat 2 things:

  • when totally aligned i can spin it correctly (screw and unscrew)
  • as soon as i put a slight force with a single finger on the back of the rod then its impossible to spin it anymore (its the same direction needed to put the rods in the bearing axis when everything is in place)
  • if i put the same force (or more) on the front of the rod it always spin correctly

So is someone ever faced the same problem ? Did i assembled something wrong ? A known problem with 8 mm threaded rod or a part design issue ( nut lock off center) ?

Thanks for your help guys, hope that i can sort this out fast :wink:

It should be straight. The z lower bracket and the z bracket should be dead on. Do both of your have the same letter on them? Double check your z rods are parallel on a flat table, glass is nice for this.

Thanks for your answer but i was on holliday and had a huge ton of work to do when i came back home.

For the record, i solved the problem by changing the threaded rod coupler by a better one and slightly shorter and also changed the z motor coupler for a “rigid” aluminium one. Everything went back to normal and Z is moving correctly now.

Will move to a trapezoidal screw in the future cause it seems to be the way to go.