"Ned Simmons" wrote in message
...
On Thu, 31 Jul 2008 12:56:31 -0700 (PDT), "Denis G."
wrote:

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.

Hydraulic duplicating (tracer) mills and lathes were once common. Last
I knew a customer of mine was still using a tracer mill to duplicate
molds for shoe counters for which there was no CAD data available.
Google True-Trace or Mimik and you may find some info.

Sinker EDM rams were often servo-hydraulic, but, I think, not so much
for coordinated motion as for smooth motion at very slow speeds

Small point, but the primary reason was that hydraulics could handle the
quick reversals -- often several times per second -- involved in the EDM
servo motion, and do it with relative simplicity. They just used a
voltage-sensitive valve switch. DC servos didn't have enough "first-pulse"
torque to do it until some advances came along in servo drive controllers.
The first ballscrew-driven servomechanisms for EDMs that were successful
used stepper motors.


All the large planers I've seen were hydraulically driven, though
that's more for brute force rather than controlled motion.

--
Ned Simmons

Production milling at one time was mostly a pass-through operation, a lot
like planers. Before CNC, production parts were, wherever possible, designed
so that you didn't have to precisely control the start and stop positions of
the axis traverse.

--
Ed Huntress