Lathe threading disengagement set-up

[Frank S]

Meed pictures of the set up.the video just shows the limit sw
Anytime I ever had to thread right up to the flange I preferred to thread out instead or thread in.
to do this I ran the lathe in reverse with the cutter inverted. this way I could start right next to the flange the only relief or under cut as you called it was the depth of the cutter.