Summary

I got sick of my Huxley's Z couplings working loose, so decided to design one that didn't make use of rubber hoses. This version should stay on without any major problems, although there's no provision made for Z-wobble, so make sure that your frame is totally straight and aligned, otherwise Bad Things can happen.

Instructions

Print it out.

Insert an M3 nut into the rectangular slot in the end with the round hole - this will lock the grub screw against the output shaft.

Fit two M5 nuts to the end of your Z-axis threaded rod, with a spring washer sandwiched between them. Do it up as tight as you can, while keeping the nuts aligned with one another - it should be possible to get it pretty tight without too much alignment trouble.

Heat the rod so it's hot enough to deform the plastic, and then insert it into the hex end. Once it's set, Wind the rod back into the Z carrier mounts, and insert the stepper output shaft into the small round hole on the opposing end of the coupling.

Screw the grub screw in to the captive nut, and tighten up to lock the output shaft in place.

Printing it with two solid layers, and 0.2 infill should be sufficiently strong, since the walls are pretty close together on this design. Support material isn't 100% necessary, but I tend to indulge, just because I'm a little bit paranoid about deformation.

Revised Huxley Z coupling