Last night I cut the lead screws to length, which sounds trivial but took a while.
Measuring 338mm accurately (which should give me 0.5mm of clearance) on a screw was tricky, because my largest calipers go to 300mm. I guess I could have stacked calipers but instead I measured the first screw against a long rule and turned it until I had a land that was aligned with 338mm and marked the land with a sharpie. Then I put it in a 5/16 collet (I don’t have metric 5C collets, but fortunately that’s close enough to 8mm) on my lathe, and used a razor blade along the edge of a cutoff tool to locate the cut to the right place on the sharpie mark.
Stainless work-hardens, so I had to be a little bit aggressive in feed rate. It still screamed a bit during the interrupted cut until it got through the thread, and I was using a carbide cut-off tool that deformed the edge of the thread instead of a HSS cut-off. I didn’t need the end to engage with a nut, it just needed to be able to be threaded through the nut without damaging the nut, so I filed off the first ⅓ or so of a turn of thread where it was deformed. Then I ran the lathe in reverse to relieve only the outer few turns of thread.
Then I filed it lightly to fit stacked into the top and bottom bearing blocks I made.
I used the first screw as a reference to cut each of the other screws, in order to avoid stacking errors. I used a square reference for the end, lightly engaged threads side by side, and used the reference screw to mark the next screw.
Now all the screws are threaded into the nuts, with pulleys installed, waiting for my next shipment to drop-in T-nuts to arrive so that I can install them. (The alternative would be to take apart the frame a little bit for the nth time to fit slide-in T-nuts, and I suppose I really should do that anyway, but I sure don’t feel like it.)
Next design task is an adjustable motor mount with idlers to drive the Z belt. So far, I have been trying to design this such that it could be built by someone with a 3D printer, common tools including a dremel, and easily-available parts. I’m trying to come up with a design for the motor mount that fits those design constraints. (I could have cut off the lead screws with a dremel, so even though I did use my lathe mostly for the fun of it, this fits my design constraints…)