In article ,
Ignoramus25542 wrote:

The cleanup of the lathe is basically done all around, the VFD is
wired the way I want and things are cookin'.

Got something else going on...

If I try threading, the half nuts would not stay engaged, they lose
this engamenent in a second or so. If I hold the engagement lever,
they they do stay engaged, but I feel the lever kind of bumping.

What would be the typical cause of this?

Wear and/or maladjustment. How much backlash does the closed half-nut
have? (This ordinarily does not matter unless one is making very
accurate and long screw threads, but is used to gauge wear.)

Joe Gwinn