If you recall my earlier post, the apron interlock pin was bent in my
lathe, and after straightening it out, it would not properly engage
with the lock arm. I thought that maybe I did not do a good job
straightening it, etc.

Finally I guessed that the root cause of it was 1) bending of the pin
by some unthinking user when it was intelocked and 2) the cam on the
half nut shaft not being seated where it should be. So the travel
range of the interlock arm was wrong.

After checking this guess, it turned out to be correct. After turning
the cam a bit (loosening the setscrew etc) the range of travel of the
lock arm is now correct, and the interlock system is working. I can
now see that this pin is very fragile. The bottom line is that I can
only operate the half nut lever very gently, with my pinky finger, and
never apply any force to it.

The apron seems to work completely properly and I am reinstalling it,
along with the cleaned leadscrew, etc.

i