"Martin Rost" rostmartin @ hot mail . com wrote in message
...
At a recent club meeting the following statements were made, and I'm
interested in comments/corrections.

It is torque, not horsepower that cuts the wood.
I can accept that as torque is a measure of rotational force.

With a Reeves drive at low rpm you gain torque over high rpm.
This is what I learned riding 10 speed bikes and driving a standard
transmission.

With electronic variable speed you lose torque at low speeds, this is why
the bigger lathes have 3 hp motors, to make up for the lost torque.
This one I don't buy, but I don't know if it is right, wrong or
partially correct. From posts in rcw, I though with DC motors you lost
torque at low speeds, but AC (3 phase) motors maintained torque at low
speeds.
SNIP ..........
==========================
Martin,
Torque and horsepower are intertwined functions. Horse power is defined as
to performing a given amount of work in a set amount time. The original
rating was set by having draft horses lift a weight with a pulley. So the
pulling (turning) force is adjusted for the amount of time applied. If you
look at automotive engines, they have both torque and horse power ratings.
The two ratings occur at different locations in the RPM range. The torque,
or kick in the seat, usually rises quickly and peaks in the midrange
(3000-3500 RPM typical in US cars). Then due to air intake restrictions, cam
specs, exhaust, etc., the torque starts to drop. However, since the HP is a
function of Torque X RPM, the horsepower continues to rise on into the
higher rev range (4500-6000 RPM depending on tuning). Transmissions and
differential gearing increase torque applied to the ground. A single gear
ratio would severely limit the versatility of the auto, either limiting the
top speed of the car, or causing a very long acceleration time.

All this can be applied to the lathe. A low HP rating means you have to have
a wide range of gears or pulleys to prevent bogging it down. A 3HP machine
will allow you to cut at a much faster rate (depending on your skill level)
than a 1/2 HP unit. A three phase unit has an inherent advantage over a
single phase drive due to the power applied over the AC line frequency
curve. If you overlay the single phase sine wave with the 3 phase wave
forms, you'll see that the 3 phase applies power at a higher average level
and has a much lower fall-off in between pulses. This gives you a much
smoother power application, as well as better torque. Variable Frequency
Drives on 3 phase systems can pay games with these factors by utilizing
various sensing circuits to monitor speed, current draw, etc., and adjusting
the power application accordingly.
Hope this helps some.

Ken Moon
Webberville, TX