We've seen some engineering stuff as it pertains to a 3-phase motor and
VFD combination. But, what it feels like is really the test. A
properly set-up system senses the motor WANTING to slow down as the load
increases and will make up for it seamlessly. It will also drive the
motor at above its rated torque for a time if it feels it is safe to do
that.

That said, you still need the mechanical advantage given by properly
designed pulley ratios and that is the very thing which is missing when
one goes to any direct drive system.

Once you have turned on a well designed VFD-based system, there is no
going back -- I don't think that anyone can argue with that.

Bill

Martin Rost wrote:
"Derek Hartzell" wrote in message
...

It is torque, not horsepower that cuts the wood.

Part true/Part False. Both torque and horsepower cut wood. For a given
horsepower there is a certain speed where you can take a certain depth of
cut with a certain tool in a certain type of wood. A 3 horsepower can

take

basically 3 times greater cut than a 1 horsepower if both are running the
same speed. Another factor is that having excess horsepower helps keep

the

speed of cut consistent, which improves the quality of the cut.

Horsepower = Torque x RPM / 5252



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.

False. When you turn down the speed, you are turning down the horsepower.
So a high horsepower motor allows you to have good horsepower through a

wide

range of speeds. If the rated speed of a motor is 1750 rpm, then you

will

get the full horsepower rating there (for example a 3 horsepower motor

will

deliver 3 hp). At 875 rpm motor speed, the motor gives 1 1/2 hp. At 437
rpm, you only get 3/4 hp.


Thank you Derek,
As you turn down the speed, the horsepower decreases linearly from your
example, and thus the torque is constant from the above equation. If I
understand all this right, I can take the same heavy cut (amount of material
removed per revolution) at full speed or 1/4 speed, I just have to adjust
how fast I move the tool along the tool rest. Just to be clear, I'm still
talking about electronic speed control here.

Thanks
Martin