Stuck between a rock and a hard place: Z axis conversion with manual control

Hello All,

I'm retrofitting a Bridgeport Series 1 clone (a machinist's dynapower, to be exact) and am
stuck on the z axis motion. The mill is in my father-in-law's shop, and while he's very
interested in CNC control, he desperately wants to keep full manual control of his mill as
well.

As far as the quill -

It seems logical mount a ballscrew and servo to the side of the quill and to grip on the
hard stop bolt/ring on the front of the head, but can that be done, while still keeping the
functionality of the hard stop? If that can be accompished, has anyone devised a way of
disengaging and re-engaging the ball screw/nut to switch to manual mode?

The other option would be to grip to the quill itself, like Jeff Davis' setup (http://
www.homecnc.info, but the mill is fitted with an Ultron Snap Change quill release tooling
system (highly recommended, by the way!) (http://www.snapchange.com), which requires
that the quill be retracted entirely into the head before the tool ejects.


As for the knee -

I've seen the acme screw replaced with a ball screw, and driven from directly inside the
knee, but maintaining manual control dictates that I have to use those damned bevel
gears, which have their problems with backlash (with air springs) or gravity (without). Has
anyone done a ballscrew knee retrofit and maintained manual control? If so, please post
pictures!

I'm feeling pretty stuck here! Thanks for any insight.

-Christopher