I have had bits move with 2 different routers.  Both of these routers didn't 
have a collet as such.  Rather, the bit was helled
directly by the armiture of the motor.  A proper sized hole was drilled into 
the end of the armature to hold the bit.  Next, a slit
was cut lengthwise across some threads.  A farrel nut was then threaded onto 
the end of the armature.  As the nut was tightened,
down, the end of the armiture would get squeezed making the sides of the 
armature clamp onto the bit.  Unfortunately, this doesn't
create equal force on all sides of the bit's shaft.  Also, the bit is only 
gripped at the very end near the cutters.  This allows
the bit to vibrate.

A collet works more like a drill chuck creating equal force on all sides of the 
bit.  As the collet is tightened it is forced
deeper into a cone.  The cone forces the fingersto squeeze the bit as the 
surface area gets smaller.  Being is that there are 4
fingers, the bit is gripped equally on 4 sides.  The bit is also gripped along 
more llength of the shaft.

So, I guess I should ammend my statement.  If I am using a router with a 
collet, I'd feel very comfortable in snugging down the bit
and making the cut.  If I am using a router wwith out one, I'd torque the thing 
as hard as I could.

Terry

On Fri, 9 Jan 2009 10:34:59 -0500 (EST)you write:
>Terry wrote:
>
>> Likewise.  If a collet is over-tightened it will eventually have to be 
>> replaced.  Snug is good.  Torqued isn't.
>>
>Hmm, that probably explains why bits have been sticking in my router, and 
>why I probably need a new collet.  I crank the hell out of it when 
>tightening in a new bit.  I've heard many stories about bits walking out, 
>ruining a nice piece of wood, or your whole damn day if it fully comes 
>out.  So, I always tightened my bits in super tight.  Guess I can ease off 
>a little.
>
>-- 
>Blue skies.
>Dan Rossi
>Carnegie Mellon University.
>E-Mail:        [email protected]
>Tel:   (412) 268-9081
>

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