encoding free leadscrew end?

Now that I have a linear encoder strip up on the Z axis of
my lathe, I'm thinking of putting a salvaged 500 cpr rotary
encoder on the crossfeed screw.

On the South Bend and similar lathes, the back end of the screw is
unsuported, so the slide can in fact simply be cranked off the back of
the machine. I'd like to put the encoder back there so as to not
interfere with the handwheel end.

The main thing I need to figure out is how to make a removeable
attachment to the end of the screw. There is a center hole that I was
able to get a drill into, and could probably tap - but runout would
I'm sure be excessive. Another idea would be to turn a brass sleeve
that would fit over the end of the screw, then reduce to go through a
small bearing and then the necessary thin shaft for the encoder wheel.
Thought about just gluing that on. Even if I do get it attached, I'm
not sure if there will be any issues with constraining the back end of
a screw that has been running free for 30 years and might well be
slighly bent. Any ideas?

Also, the rear cover/extension of the cross slide has to pass over the
top of all this, and the stock encoder housing is just barely too big.
Guess I'll have to make another with thinner walls.

Chris

--
Christopher C. Stratton, stratton@...
Engineer, Instrument Maker & Horn Player
(978)538-5179 work, (617)492-3358 home
30 Griswold Street Cambridge, MA 02138
http://www.mdc.net/~stratton