[greybeard]

Just a thought based on an old memory.
When building a crude wood carving machine to make rocking horse bodies on a copying lathe type set-up, we used a piece of hard wood as a lead screw nut.
The compressibility of the wood averaged out any localised innacuracies in the lead screw.
Perhaps you could bootstrap your leadscrew accuracy by a simillar method.

John

Edit - no backlash, either !