Re: ballscrews...

> Chris & Pete,
>
> I've got a 14-1/2" SB as well, also with taper attachment. My nut is worn,
> and my threads are a little "pointy" in the middle of the screw. I was hoping
> to put a ballscrew in the same place as the old leadscrew. I made a drawing
> of the screw at one time and I'll try to dig it out, and post it somewhere.
> My machine is probably going to stay manual as I can't figure a good way to
> mount motors without butchering the lathe pretty bad. I don't have enough
> room behind the lathe for an outboard screw.

I finally made a screwdriver big and strong enough to get the slothead
bolts holding the carriage to the apron out, so my carriage is now
fixtured on the mill to enlarge the screw channel. The channel is
currently around 1.1" diameter, and the Nook 5/8" nuts are 1" sq with
1.2" diameter rounded corners, so I simply need to take off about
.050" on each lower corner, which doesn't seem like it will reduce the
strength of the machine that much, especially as it will stay rounded.
I did a test cut with a ball endmill, and it machines fine. Now if
the local Nook distributor would call me back...

I'm replacing the whole front bushing assembly for the screw that
threads into the carriage with one having bearings for the ballscrew.
It will be about an inch longer, which lets me simply hang a stepper
under it on an aluminum bracket that will clamp around the bushing
body. I prototyped that mounting method a while back on a 9" south
bend and it looked like it would work well.

The idea is that if I need to, I can dissasemble the front bearing,
unbolt the ballnut holder from the crosslide, and pull the whole thing
out the back of the lathe so as to be able to reinstall the acme screw
assembly.

(if you don't mount motors, you'll probably need some sort of brake to
keep cutting forces from backdriving the screw)

> I wonder if math functions such as the ones Chris has on his page that
> describe the curves of a horn bell could be added to RS-274, rather than
> approximating them with short line segments and single radius arcs.

An interesting idea. I keep planning to downgrade to RH 5.2 on my
shop machine and install EMC to at least start playing with, maybe on
my sherline mill. I have no experience with CNC programming other
than little hacking of PCB drill files. For actually making my horn
bell mandrels, the software requirements are minimal, and I might
simply end up writing my own program that would simply 'power feed' in
one direction (possible with a simple geared DC motor) while cranking
the crossfeed as appropriate for the calculated curve at current
position as determined by the linear DRO. Then step in a small amount
and do it again...

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