"Tim Wescott" wrote in message
...
Wayne Lundberg wrote:

"mac" wrote in message
oups.com...

I just became the owner of a 13" LeBlond regal lathe the the number on
the ways is B 9860. The lathe seems to be in good shape, came out of a
trade school, everthing seems to be tight and the

---snip---

First thing... LeBlond was among the best of the best. Second thing: HP
labels have changed since then. I'm not sure, but I believe HP in the
days
of your B9860 were calculated at 1,700 rpm and today's electric motors
calculated at 3,600? so it may be that your 3/4 HP is equivalent to
today's
inflated 2HP or more.

It's not the speed that affects the horsepower. An induction motor can
be built to operate just shy of the line rate (60Hz = 3600 cycles per
second), or just shy of 1/2 the line rate, or just shy of 1/3 the line
rate, etc. So a two-pole two-phase induction motor will spin around
3500 RPM, a four-pole two-phase will spin around 1750 or 1700, etc.

Back in the day, however, motors tended to be rated _very_
conservatively, because everything was done with a slide rule and paper.
To make sure they were telling the truth they way over designed
things. This is why an older 3/4HP is "better" than a newer one.

I think it's harder to tell on a lathe or a drill press when to change the
motor than in an application with a fixed load, though. I have a 58 year old
single phase 3/4 HP motor on my SB 10L and I think it slows down and stalls
too easily. If it was running a compressor I'd put an amprobe on it and see
what it was trying to pull at full load. However I don't have any simple way
of putting a known 3/4 HP load on it. Most motors will continue to spin at a
lower load even after their prime, for example, if you lower a compressor or
pump setpoint a marginal motor will keep going for a while.