On Fri, 21 Nov 2008 17:42:12 -0800 (PST), wrote:



This would keep chips from jamming the switch, and a defeat piece
would have to be purpose-built.
Too long, it won't go in, too short, it won't push the top plunger up
to trip the switch.

That's a lot more work, though!

For a tamper-resistant system that doesn't require much work you could
mount the key from a guard interlock switch on the chuck key. Both
mechanical and coded magnetic switches are available from several
mfrs. For example:

http://www.schmersalusa.com/machine_...sp?ProductID=5
http://www.schmersalusa.com/machine_...p?ProductID=32

--
Ned Simmons