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.
Classic case of worn half-nuts. But, take the whole mechanism
apart, there may have been a detent mechanism that has gotten
gummed up or worn. If not that, then it is likely due to wear
of the half-nut threads that are now pushing the nuts apart.
It could also be a misalignment of the nuts to the leadscrew,
swarf packed into the half nuts preventing them from fully closing
or something like that.

Jon