Quite an Unusual one

[Jonathan]

Brings back memories...



Anyway. How have you ensured alignment of the Z-rails - both their spacing (parallel to Y) and parallelism? I can't see any features for alignment, so either you milled reference edges in after assembly, spent time with a DTI and straight edge, or (I doubt) didn't do it? It almost looks like the spindle is just clamped by the plates with the arc-section cutout? If so I'd be a bit concerned about maintaining the accuracy of the rail alignment.

Then as we spoke it became clear that 1 ball nut assembly is ok, especially if fit with double ball nut.It also became clear that maybe i will not use at all the hammer but make separate machine.

I've probably mentioned this before, but I'm not convinced that a double not would actually work better than 1 nut here. In a double nut system the nuts are preloaded against each other, so a force is applied the load on one nut decreases whilst the force on the other nut increases. For any force above the preload force, all the force will be transferred to one nut.

Either way, as you implied, in general it's more economical to use a larger ballscrew (or larger rails) than multiples *unless* the spacing of the linear bearings is such that racking is an issue. I mentioned it here regarding rails and stiffness, but similar reasoning applies to ballscrews.