The pressure of using the spur or other drive is enough to seat it in the
headstock. The pressure of using the drill tends to seat the Jacobs chuck in
the tailstock but most are eqippped with threaded hole for 1/4" all thread
to secure it in place with a nut on the other end. This is called a draw
bar.

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God bless and safe turning
Darrell Feltmate
Truro, NS Canada
www.aroundthewoods.com