Butterfly Draw Bar
 

I've been thinking about picking up a new 10x54 knee mill to be
supplemental to the CNC mills in my shop. I have come to recognize it
can do many things the machines I have can't, but I have gotten spoiled.
My bigger bed mill (9.5x18 work envelope) and my two main mini bed
mills (6.6 x 11.6 work envelope) all have quick change tools. I push a
button and the tool holder falls out in my hand. I insert a new tool,
release the button, and press start. The other small machine in the
shop just gets used for engraving so I never change the tool. Even my
CNC kne mill has quick change tooling, although not quite that fast. I
change the tool, place a setter on the (part/vise/table) raise the knee
until it zeros, remove the setter and press start.

Anyway, the idea of placing a wrench on a draw bar and maybe a spline
wrench with use of my shop ladder just appalls me at the thought of
wasted time. Even if I crank the handles or use the power feed. The
time wanking on that thread just sounds like it will annoy me.

I've been thinking about throwing together a butterfly impact drawbar
like so many others have done with either a solenoid or a small air
cylinder to compress the springs. Because this will be a manual mill I
fully intend to use the quill, so the typical loose fitting air cylinder
squeezing a stack of belleville washers used on so many small bed mills
is not really a good solution. I want something that except for what I
want to move stays firmly bolted in place without moving around. I can
do that. I've even thought of a quick simple way to engage the quill
spline so there is no risk of spinning the quill with the impact and
cutting myself. Well the risk of cutting myself is always there, but
not from that particular thing anyway. It seems like a pretty decent way
to tackle the problem. I should even be able to turn the head without
worrying about it.

I'm curious what problems there could be. I'm sure there is the obvious
one of a cheap impact failing quickly. I'll look around for something
above the level of a Harbor Freight Central Pneumatic. A long time ago
I might have picked Ingersol Rand, but my last couple IR tools/parts
have been a little disappointing. To be fair my 1/2 IR impact is pretty
much bullet proof. The other issue I see is speed. What other problems
do you see?

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