Whew! Sorry it’s taken so long to update, folks, but Real Life just kept taking away all my opportunities to work on this. But I finally got the Z axis swapped out for a new unit.
As you can see, the old screw (on the right) had definitely started to come loose from the motor. In fact, I was able to push the screw shaft back into the motor using about 10-15 pounds of force and my bare hands… which probably means that it would just drift loose again over time if I ever put it back into service.
I’ll also note that the new motor has a socket, where the old motor was hard-wired. A definite improvement, I’d say. The motor is also a bit more compact.
The anti-backlash nut assembly is interesting:
The spring goes inside the brass bushing, and the small black nut actually has two flats on it that mate to flats on the interior of the brass bushing. Both the “disc” end of the bushing and the nut are threaded, which would seem like it’s asking for some cross-threaded situation, but I’m guessing that the nut has enough “float” to avoid that. When properly assembled, the nut seems to fit flush in the face of the brass bushing. The old one came apart as I pulled the lead screw out, but the new one held together on its own so I didn’t have to worry about tolerances. I just spun the anti-backlash assembly off the lead screw, set it in the circular depression machined for it in the bottom of the X carriage, then dropped the new lead screw down through the top of the carriage and spun it (carefully) into the anti-backlash assembly until the motor was just about resting on the top of the X carriage. After that, I started threading in bolts.
I will say, getting those bolts in and out was a NIGHTMARE, at least for someone as ham-fisted and carpal-tunneled as I am. The right-side bolt in the anti-backlash assembly and the two rear motor-mount bolts were the next best thing to inaccessible. Jorge (blessings upon his name), linked me to a low-profile ratchet that they apparently use for this at the C3D shop, and it turned the job from impossible to merely very painful. If you ever have to do this, get the ratchet, and get some 2.5mm ball-end allen wrenches. And some long needle-nose pliers.
The issue with those three (out of the 6) bolts is that, even when you get a tool on them, the motor and/or vertical shafts block your “swing” of the wrench almost completely. I kept getting one “click” out of the ratchet, but then I had to pull it out, rotate it one more click by hand, and then re-insert it. If you can find some sort of flexible-driveshaft thing for your Allen keys, USE IT. You’ll be glad you did.
Still, not nearly as nasty a repair job as some cars or household appliances I’ve worked on. Just be forewarned of what you’re getting into with these screws.
I still have to finish re-routing the cables and buttoning the whole unit back up, but I did fire up the Nomad and successfully zero’d all the axes (the collet nut can reach the tool sensor – I did not know that). So, I think I’m pretty much in the clear (fingers crossed).