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 a Reeves drive at low rpm you gain torque over high rpm.
True.
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. If you had a 1 hp motor, also rated at 1750 rpm,
you would only be getting 1/4 hp at 437 rpm which doesn't allow you much of
a cut. Having a Reeves drive or step pulleys allows you to adjust the speed
of the spindle while keeping the motor at full speed or near full speed,
thereby maintaining motor horsepower output.
An interesting feature of variable speed AC electronic drives is that they
can run the motor at over the typical rated speed. So a 1750 rpm rated
motor can be run at 3500 rpm in some cases. Generally the motor is fully
capable of being run at this amount of overspeed. In this case, the motor
runs at the same horsepower from 1750 rpm to 3500 rpm. So this means that
the motor torque drops off to half the torque at 3500 rpm that is has at
1750 rpm. The useful feature of this capability is that you can get full
horsepower over a wide range of speeds without changing pulleys. For
example if the motor has a 3" pulley and the lathe spindle has a 6" pulley
and the controller runs the motor down to 10% of rated speed and the motor
is 3 hp with a rated speed of 1750 rpm, you could have spindle speeds of
1750x3/6x10%=88 rpm to 1750x2x3/6=1750 rpm. Between 875 rpm and 1750 rpm
spindle speed you have 3 hp. At 88 rpm you have 10%x3hp = 0.3 hp. If you
had used a 3 hp motor with a rated speed of 3500 rpm, you would have to use
a 12" spindle pulley and a 3" motor pulley to get the same range of speeds.
Then you will have 3500x3/12x10%=88 rpm as a low speed. However, you
probably don't want to run this motor at 7000 rpm, so if you leave it at max
of 3500 rpm then your high speed is 875 rpm. So a motor with a high rated
speed gives you less flexibility.
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