Splitnut for taig lathe, revision 2

The new splitnut consists of three main parts - a "stationary" half, a "mobile" part and a cam. The stationary part is permanently attached to the carriage with two 10-32 screws (the two threaded 10-32 holes are the only modifications to the stock lathe required by this design). The mobile part slides along the stationary one in one dimension. That is acheived by milling a T-slot in the stationary half, and a corresponding shape in the mobile part, so the two fit snugly together. When the nut is open, the leadscrew is positioned roughly in the middle between the threaded parts of the splitnut halves, almost, but not quite touching them. When the splitnut is closed, the mobile part moves closer to the stationary one, pushing on the leadscrew and deflecting it slightly (under 1/8") until both of the threaded sections fit snugly around the threaded rod. Yes, deflecting a leadscrew is a big no-no. However, in this case this rule can be bent. The leadscrew is only a 1/4" threaded rod, and deflecting it by as much as 1/8" over a 20" length will not damage it one bit. Neither will such a deflection introduce a measurabl error in the linear motion along the lathe bed. The cam keeps the splitnut in the 'locked' position. All parts except for the cam body were made using the "I have a plan in my head and eyeball all dimensions" technique. The cam body was CNC-milled.

all parts

splitnut body (two halves) assembled

cam assembled

Assembled and ready to install