In article ,
jim rozen wrote:
In article , DoN. Nichols says...

I would suggest that for machines which have only steps in their
speed selection (e.g. gears or belts and step pulleys), the VFD is
preferred, while for those with variable speed pulleys, and for running
multiple machines at a minimum initial investment, a home-built rotary
converter (built around a larger three-phase motor, some capacitors, and
some voltage-sensitive relays) would be the better choice.

At the face of it this would seem to be the case,
but the really odd part is, folks who have some
machines like the monarch 10EE, or the lathe with
the variable speed drive that everyone dislikes
(I think this is either a rockwell, or a delta,
or maybe it was both) seem to say, the varispeed
drive is a major pain,

I've seen a lot about the problems with the hydraulic variable
speed lathes produced by Clausing. It seems that they are just getting
to be old enough to have problems with the hydraulics by now.

My Clausing is a 1957 one with the step pulleys. And there are
times when I would like to be able to reach out to a knob and tune the
speed without interrupting the cut. I also would like the ability to
reverse the spindle without having to wait for the motor to coast down
to near a stop (when I'm tapping with the turret), hence the desire for
a three phase motor, and a VFD (with the reversing being done by
commanding the VFD to reverse, not by switching the motor windings. I
can get away with that with the vastly oversized (e.g. 30A) VFD which is
currently running the 1HP motor on the Nichols horizontal mill, but I
could not do so with a VFD which is a closer match to the motor's
horsepower.

As for the Monarch 10EE -- that is because the electronics for
the older ones is getting to be rather expensive to keep going
(replacing the big old thyratrons to drive the motor), and some of the
newer replacement electronics is showing up as rather fragile. Probably
the best in terms of long-term service is the old motor-generator style,
which I used to use at work.

A friend in the local metalworking club (CAMS) has recently done
a marvelous job of marrying a three-phase motor to the original gearbox
in his 10EE -- to be driven from a VFD, of course.

and they always retrofit
with a VFD. But the folks with step belt machines
like southbend or the older hardinges, seem to
get along fine with step belts.

If it were not for the turret tapping work, I could probably do
without the upgrade, but I must admit to not always selecting just the
right speed for a given operation, thanks to having to squat down to
access the motor lever and belt for the changes. :-)

Where the VFD really shines though, IMO is in a
drill press. Just *so* handy for getting the right
speed.

That is something which I need to do some of these days. But I
also have a hefty permanent magnet DC motor and a matching speed
controller, which I may use for the purpose instead.

Enjoy,
DoN.
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