On 2011-02-24, Karl Townsend wrote:
I'm taking the knee apart on my CNC mill and sending out for
rebuild...

I have an extra ball screw on hand that is perfect for replacing the
Acme hand knee lift screw. I'd then put a servo motor on the knee.

I did some preliminary layout for initial design of how to do this. it
will work best to rigidly mount the ball screw and spin the ball nut
with the nut located right at the bottom of the knee sitting on a
taper bearing.

Anyway, with this layout it would be all but impossible to change out
a timing belt. You'd have to take the knee apart. (There's always a
design weakness for maintenance)

Anyway, a #35 roller chain would make for a far easier and less
expensive installation. Given that the knee will only move slowly at
tool changes and always have downward force; is this causing another
problem that I don't see?

Karl

A good timing belt should last a very long time under these
conditions. I would expect the condition of the 1,000 lbs knee pushing
on the ball screw all the time, to be quite punishing for the ball
screw. If you have pneumatic support, it would help.

But please keep us posted, this sounds like a very interesting plan.

i