Whilst adding a plastic chip guard behind my SC3 mini lathe apron I decided to strip and improve the half nut mechanism. In the case my 'Super C3' (SC3) it's more a case of a 'half of a nut' mechanism in fact as only the lower half of the usual pair of half-nuts is present because the new leadscrew guard doesn't leave any room for the upper one. It still seems to engage and drive the saddle ok, but I found the engaging lever would often stick so I wanted to improve it.
I also noted the usual mini-lathe problem with the dovetails and gibs making poor contact so I expected to make some marked improvements by lapping them to a better fit.
However, the more I study the mechanism the more I think the manufacturers need to redesign it from scratch. It's quite a surprise it works at all as far as I can tell. Virtually all the dovetail in contact with the half nut is missing on one side where a circular recess has been cut for the cam type (?) mechanism that the handle turns, and on the other side the gib is held in place by two screws+washers. It looks like a total bodge and I suspect any minor attempts to improve it may stop it working by what ever mysterious means it currently functions. Are there any articles out there about this issue and ways to resolve it, because I can't find anything beyond a mention that the mechanism includes a gib?