Z axis binding at top

I know this issue has appeared in various forms and in several discussions already. But in my case, after all the checking, double-checking, triple checking v wheels, belt tension, pulley tightness/position, delrin nut free-ness, and potentiometer settings… I discovered that my Z axis is actually not plumb.

Specifically, the ACME rod is closer to the makerslide at the top by the bearing than it is at the bottom. This would most certainly cause the binding only at the top of travel. I believe this is causing the delrin nut to wedge the ACME threads and cause enough extra friction to keep the motor from turning.

How in the world would I go about fixing this? It is off by almost 1mm according to my ruler. Even though I do have an ACME wobble, this is not causing the pinch at the top. Should I take it apart and flip over the makerslide and tap the other end (and hope that the threads settle in a better position)?

If you’re saying that the ACME rod is closer at one end than the other then it means that either your ACME rod is bent or that the bearing in the Z-axis plate is not seated flush.
If your ACME rod is bent then you should be able to see the wobble. I’d check the bearing on the Z-axis. Check also that the Z-axis plate is sitting correctly on the top of the makerslide.

My X-Carve has a slightly difeerent design for the ACME rod is that there’s a bearing top and bottom of the rod.

The ACME rod is bent for sure. There is a noticeable wobble. It just doesn’t cause a problem until it gets to the top inch of travel. I flipped the makerslide end for end and tapped the screws for the motor/bearing plate. One of the screws was not exactly straight in the original configuration and the plate moved back and forth as I unscrewed it. There is quite a bit of movement possible just due to the positioning of these screws. I put everything together again (the bearing is definitely flush) and tested the movement. This only gained me an extra 1/2 inch before it starts to bind again.

The delrin nut may also be an issue. I turned that around and it changes the positioning of the rod. That means that the delrin nut is not threaded at perfect center.

It looks like I should replace both.

I really like your Z-provement Geoff. I may end up doing something similar.

Not my improvement, it’s standard on the Australian XYZ-Carve.

Apparently, this is a known issue at Inventables. There is a certain percentage of ACME rods that were bent from the supplier. It is also necessary to replace the delrin nut. They sent me a new ACME kit today. I will post my results when the new parts are in place.

Installed the new ACME rod and delrin nut. Everything works perfectly. All the Z axis issues are gone.