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DoN. Nichols DoN. Nichols is offline
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Default Dangerous chuck mounting? 12" South Bend chuck

On 2009-05-21, Ignoramus11200 wrote:
Look at this pictu

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.

It is probably the most common style of chuck mounting around
for lathes. The various other systems were produced as improvements for
just such reasons.

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

It would not be a great experience -- but consider that the
machines which use these are typically not supplied with a gear-driven
headstock. Instead, they are belt driven (except in back-gear, where
the speed is too slow to pose a problem, except when doing a deep cut
in reverse).

And the South Bend lathes tended to use flat belts, so the slip
on plug reverse and the like is much greater -- offering a safety

Also -- in the home they are often fitted with single phase
motors, so plug reversing is not an option anyway. :-)

That said -- a friend who used to be a machinist in the Navy
plug reversed a lathe with a *big* chuck and a big workpiece, and it
started to unscrew. He quickly re-plug reversed it which caught up with
the chuck -- but made it *very* difficult to remove that chuck later. :-)

Note that some chucks -- for example some for the Myfords which
are screw thread spindles -- come with provisions to tighten a clamp on
the register of the spindle to allow turning in reverse without the
excitement of a chuck going walkabout.

But you have identified one of the reasons why I converted my
Clausing from 2-1/4x8 threaded spindle to L-00 (by replacing the spindle
with one from eBay.)


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