In 1979 my very first machine related job was in a production shop.
We used
Die Heads all the time.
Way back then, the die head had an adjustable rod that would hit a stop
to snap it open at the appropriate time. Those old turret lathes
were running with a flood of cutting oil on the chuck and the chuck was
never stopped. It was air operated, opened and closed with the flip of a pneumatic valve.
When a part was finished you would grasp it loosely and open the chuck. When you felt
it was slowing down you would pull it out of the cutting oil flood, jam the next piece in
and hold it loosely while engaging the chuck to begin the machining process again.
You couldn't really see what was going on at the chuck because of the cutting oil constantly
running. Every now and then, an unseen chip would become stuck behind the work piece
so it didn't go as far back into the chuck as it should have and the die head would shoulder
out before the opening rod hit it's stop. That would bring the office guys running out to
check for injuries and machine damage. I worked there for less an a year and did that
three times! :-[
The tapping heads we used were very similar.
They were fitted with the same simple mechanical rod that would hit a stop
reversing the the chuck. You still had to keep a bit of manual pressure on the
carriage or it would stop as the tap exited destroying the entry thread.
Rick