"Ignoramus11200" wrote in message
...
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

You're probably missing the delightful experience of trying to remove a
threaded chuck after it's been on a while! :-) Some have had to take a
parting tool to the back plate to get their chucks off the spindle. I had a
South Bend with a broken back gear tooth, most likely a result of someone
trying to remove the chuck. My 13" South Bend had a D1-4 Spindle that I
much prefer to threaded spindle.

RogerN