On Feb 24, 7:28*am, 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

I'm interested in CNC, but I don't know a lot about it. Probably I'll
go down that road in a few years, but two things come to mind. It
seems that you would be worried about backlash and want to keep it at
a minimum. 1st: Could you use a tensioner on the chain to reduce it?
(Similar to the ones found on car engines.) 2nd: Since you will
probably have an encoder, doesn't the software take into account the
backlash and compensate for it (assuming that you're measuring the
movement of the table and not the servo or stepper)?