"Jon" wrote in message
news:hhpkk.500$aA5.361@trnddc05...
We have an older NC lathe, "Sheldon Tape Lathe" that uses Moog
proportioning valves.

IIRC The valve needs a 0-20 mV signal to operate.
Our resident electronical guru made us a pair of boards that turns +/-10V
servo control signal into the signal that makes the Moog valve happy.

We retrofitted using a galil dmc740 motion controller.

This works great for really big iron.

Unless you NEED it, I'd try to avoid hydraulic servos.

Oops, I missed a detail in the original post, the sheldon tape lathes use
hydraulic motors to drive ballscrews.
However, as later posts have described, technology marches on, and high
precision is feasable using cylinders now.
But still, it usually is saved for applications requiring high forces



"Denis G." wrote in message
...
Sometime recently I read about someone who acquired an older milling
machine that had hydraulic feed on the table. I wondered about how
these tables might be controlled and if any lathes have been designed
using hydraulics to move the carriage or crossfeed instead of lead or
feedscrews. (After all, there are mechanical, hydraulic and pneumatic
linear actuators.)
I don't know if you could control hydraulics as precisely as
feedscrews (with respect to headstock spindle rotation) for cutting
threads, but you'd never have to worry about worn screws and metric/
inch conversions. I imagine that the big problem is in designing the
feedback system and getting it to respond well.
I've seen descriptions of hydraulic systems made by companies like
Enerpac that control the balancing of bridge sections to keep them
level while being positioned with cranes. I know that hydraulics can
be controlled with electronics and proportional or servo valves.
Probably it's difficult to beat mechanical feed and leadscrews because
it's a simple and accurate system, but I was just curious.