No.
Turning backwards is dangerous as well.

The threads must be clean - and the back ring. It seats for a flat
and mounts the chuck in precision.

Martin

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