Ballscrew installation issues

My plans for lathe conversion are progressing.

I've determined that the 1" square nuts for 5/8" screws will nearly
fit. However I'll either have to mill a little bit of metal out of
the channel in the carriage to clear the lower corners of the nuts, or
find a way to grind? a radius on the bottom corners of the nuts.
Unless anyone knows an economical source of round rather than square
nuts for 5/8" screws.

5/8" does seem on the small side, however there should be more strength
in a ballscrew of this size than the existing acme screw, plus I'll be
preloading some tension on the screw with bearings at both ends,
compared to the single end support present now. So the only real
question on loading is what the balls themselves can take. Chances
are if I'm overloading them, they just won't last as long. But for
$20 a nut, I can afford to replace them after a year of light use.

McMaster only sells right hand screws/nuts. Anyone know a cheap
source of the left hand ones? Having a lathe with a backwards
crossfeed would be somewhat annoying - almost enough that I'm tempted
to put the handwheel on an encoder rather than on the screw and always
use the motor to move the crosslide even for manual work, probably
with a simple circuit to generate step/direction when the computer is
off.

Will I be able to machine the screws with carbide insert tooling?
Hardened linear shafting machines like a charm this way, and I was
doing some extremely interrupted cuts on mild steel the other day
without breaking the inserts, albeit with fine feed. So if I feed
slowly and carefully, can I turn the ends down or groove them to make
it easier to clamp on?

Is there any standard trick for making up double preload nuts from the
single ones? I was thinking of making two pieces to thread onto the
end of the nuts that could somehow be rotated in relation to each
other to set preload and then clamped. Should there be a spring of
some sort in there, or just the springiness of the metal involved?

What size (series/pitch) timing belts are people typically using?
With a .200 lead screw and a 200 step/r motor I need 2:1 reduction
just to get steps of .001, but am planning on going for .0005 or
.00033 if I use a 10 tooth driving a 60 tooth. I'm thinking of buying
a single 470-oz/in or so stepper to try on the crosslide and
eventually leadscrew. If it turns out to be too small, I'll save it
for converting my mill and get a bigger motor for the lathe.

Thanks for any ideas,

Chris

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