That's the old style mount. When you had shaft drive with overhead
pulleys there was not any fast breaking or reverse so no problem. But a
quick reversing motor will certainly send it across the room. I've seen
it done with a 6" 3 jaw on a Sheldon Lathe. It's not QUITE as bad as it
looks: the longer you use it on one setup, the tighter is sets itself on
the spindle.

Ignoramus11200 wrote:
Look at this pictu

http://yabe.algebra.com/~ichudov/mis...Chuck-4545.jpg

This is a 12" lathe chuck for South Bend lathes.

My question is that the mounting seems to be a simple thread. There is
no "lock" like there is on L type mounts, or on camlock chucks etc.

So, it could happen that the big chuck would unscrew itself during
stopping if RPM was too high, the brake was applied too vigorously, or
something broke inside the gearbox. The chuck weighs about 100 lbs, so
having it bounce around the shop would not necessarily be a great
experience.

Am I missing anything?

i