According to Chuck Sherwood :
with the VFD. For extreme cases (where you *really* need the higher
torque of the low speed, or the higher speed of the high speed), you can


I don't think that is the case. All 2 speed motors that I have looked
at have a much lower HP rating on Low speed than high speed. Usually
it is less than 1/2.

Since the horsepower is a function of both the torque and the
speed, this makes sense.

I would venture that a 2 speed motor runing on
high speed but slowed down with a VFD will actually have more
(or at least as much) HP as the same motor runing on low speed.

That sounds good -- as long as the winding for the high-speed
setting can handle the current at low speed operation.

So in my opinion you can wire the lathe to only use high motor
speed and then use the VFD to generate the low speed without
any loose in motor torque.

Excellent suggestion.

Once you use a VFD you will love it. For example I was facing an
8 inch diameter disc. I set the VFD for 20Hz and geared the lathe
for the speed I wanted for full diameter. As the toolbit
works it way towards the center, I gradually increase the VFD
frequency to increase the spindle RPM. It makes facing a big
object so much faster and better.

And -- if you're doing a lot of the same part, you might even
hook a rack gear on the cross-slide, and a pinion on a potentiometer, to
have a result of a constant SFM as you face. This can also help
eliminate chatter at certain speeds and radiuses.

Enjoy,
DoN.

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