I find that the Z nut lock is a bit fussy. I thought I had it tight enough, but I noticed after a bunch of testing (with no tool mounted to boot) that it was starting to slipand the Z nut was starting to drop. The small nut was about 1/2 way out of the bottom of the Z nut lock. I had stopped tightening it when it seemed snug enough.
So I took it apart (just the Z nut lock) which was a joy, NOT!! But I was able to get it cleaned up, just in case I did the same thing someone else had done wrapping some tape around the big nut. Then pried the nut lock slightly with a flat blade and pushed everything back together. This time I really cranked down especially on the upper nut lock screw and it seems much improved, but I’m still uneasy with it not being supported at the bottom, and with it being a big pain to have to pull it apart if it starts slipping again.
I was even considering maybe very slightly scaling the z nut portion of the part down to make it a little snugger, but that’s a lot of work if you have an improved design in the wings.
I’m eagerly looking forward to the new middle (and Z Nut Lock). It looks like it will be much nicer, and since I will at some point be reprinting the middle pieces to resolve the bearing gap that I had due to a small amount of warping I might as well wait for the new design to be ready to print. If you need someone to give it a go I’m more than happy to kick of a print run as soon as the models are available.