On Fri, 19 Jul 2013 08:39:56 -0700, wrote:

On Fri, 19 Jul 2013 05:33:17 -0500, Karl Townsend
wrote:

...
How is the CNC drawbar engaged? (curious) I thought drawbars were
just glorified, dual-threaded long bolts which engaged the bit from
the top, drawing it into the tapered spindle hole.

power drawbars have splined ends with points on the end of the
splines. There's a female mating spline on an electric impact wrench
and an air cylinder to drop it in place.



Deep 7/8" impact socket and pneumatic impact wrench, Karl. Use a
large diameter hose and high pressure air for maximum torque. Try it
both ways to rule out left-hand threads. Maybe wedge an old bit in
the collet to slow down the turning if it slips on you.

Wish I'd ask you BEFORE I broke it

Karl
Greetings Karl,
I have an old Index mill that uses the same type of power drawbar.
Even though the splined ends are pointed they would sometimes not
engage the female spline proiperly and the impact wrench would just
spin while trying to knock off the points on the ends of the spline.
So I installed a switch in the common wire to the impact wrench that
would only close when the splines were mated properly. Since then the
power drawbar setup works very well.
Eric
Now, THAT'S a good idea. I occasionaly grind a pound. Mine happens
when I'm overdue for a shot of air tool oil in the airlines to the
unit.

Karl