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.

Any corrections or clarifications to these three statements would be greatly
appreciated.

Thanks
Martin
Long Island, New York

On Fri, 22 Apr 2005 10:22:26 -0400, "Martin Rost" rostmartin @ hot mail . com
wrote:

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.

Any corrections or clarifications to these three statements would be greatly
appreciated.

Thanks
Martin
Long Island, New York


hmm... time for a diesel powered lathe?


mac

Please remove splinters before emailing

"Martin Rost" rostmartin @ hot mail . com writes:

It is torque, not horsepower that cuts the wood.

True. Horsepower lets you cut the wood *faster* though. Imagine a
lathe with a worm drive instead of gearing. The wood would only turn
at a few RPM but it would be pretty much unstoppable.

I can accept that as torque is a measure of rotational force.

Torque is foot-pounds. For a given torque, the closer to the axis you
are, the more linear force is available for cutting.

With a Reeves drive at low rpm you gain torque over high rpm.

True. Torque is foot pounds; you can change torque with gearing.

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.

A given motor can generate UP TO a given horsepower. Speed controls
can only REDUCE the amount of horsepower. An ideal controller/motor
combo would maintain peak horsepower, but vary only the frequency.
Unfortunately, because the coils in such motors are inductors, lower
frequency means less resistance, so you have to reduce power at low
speeds to prevent burnouts. This means less horsepower. I suspect
that at lower frequencies you have to run the motor at a lower
magnetic offset angle, which reduces the torque the magnetic fields
apply to the armature, but I'm just guessing on that one. A really
smart motor/controller combo would detect the amount of torque needed
to maintain a given RPM, and adjust the angle and power accordingly.

The gearing determines the ratio of horsepower to torque, which is why
big lathes still have step pulleys.

Big lathes have bigger motors because you want the motor to overpower
the wood, and still provide usable torque at the largest supported
diameters. Big lathes allow heavier and larger diameter wood, hence
bigger motors.

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.

"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

That's right. You can take the same amount of material per revolution
either way. But at 4x the speed (given the same pulley setup) you can
remove 4x the wood per time period. Of course, there are certain
non-linearities in the way controllers work, but that is the basic
proportion. For an understanding of the practicality of how horsepower
works, watch a Mike Mahoney video and see how fast he roughs a bowl with his
3 hp Vicmarc lathes. Yes, horsepower really does cut the wood, as does
torque!

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.

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

I turn with a 1 hp variable speed DC motor and I love the variable speed,
but I sure know what I'm missing in the horsepower...

"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

Not sure how they work (I'm not a motor engineer), but in the last few
years routers have come to market that ramp up speed on startup, and
the manufacturers claim they compensate for larger loads by "sensing" a
slowdown and automatically increasing power, to maintain nearly
constant speed.
Do any of the lathes out there do this?

Yes, they do. We are using the Cutler Hammer sensorless vector drives.
They detect slippage and will do what they can to make up for the
problem. The method is different from that used with the universal
motors on routers but the effect is very much the same.

Bill

wrote:
Not sure how they work (I'm not a motor engineer), but in the last few
years routers have come to market that ramp up speed on startup, and
the manufacturers claim they compensate for larger loads by "sensing" a
slowdown and automatically increasing power, to maintain nearly
constant speed.
Do any of the lathes out there do this?

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.


Odd, I use a gouge to cut the wood.

Torque determines if you have enough rotational FORCE to sever the wood
against the gouge. Horsepower determines how much WORK you do, or in our
case how many cubic inches of shavings you remove, per unit time.


hope this helps, Dan

Dan Bollinger wrote:
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.


Odd, I use a gouge to cut the wood.

Real turners use a skew! G,D&R)

....Kevin
--
Kevin Miller
http://www.alaska.net/~atftb
Juneau, Alaska

"Martin Rost" wrote: (clip) It is torque, not horsepower that cuts the
wood.(clip)
^^^^^^^^^^^^^^
Let's play with this a little. Suppose you were using a lathe that
developed enough *torque* to cut the wood, but did so at 1 RPM. It's true,
the torque would be cutting the wood, but you would be wishing for some
*horsepower" so you could finish and go in to dinner.

"Kevin Miller" wrote in message
...
Dan Bollinger wrote:
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.



Odd, I use a gouge to cut the wood.

Real turners use a skew! G,D&R)
===================
Kevin,
Do you want to demo that on the inside of a bowl?!
Or are skews there different than in the lower 48? {:-)

Ken Moon
Webberville, TX

Let's play with this a little. Suppose you were using a lathe that
developed enough *torque* to cut the wood, but did so at 1 RPM. It's
true,
the torque would be cutting the wood, but you would be wishing for some
*horsepower" so you could finish and go in to dinner.


LOL! That's what I said, but you said it with less words and more humor!
Dan

"Kevin Miller" wrote in message
...
Ken Moon wrote:
"Kevin Miller" wrote in message
...
Dan Bollinger wrote:
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.


Odd, I use a gouge to cut the wood.
Real turners use a skew! G,D&R)
===================
Kevin,
Do you want to demo that on the inside of a bowl?!
Or are skews there different than in the lower 48? {:-)

Uh, yeah. We use a special 'bowl skew'. It's only got one bevel and
sorta curves up on the sides. Works a treat! ;-)
==================
Y'all think up all sorts of things driving up the Alcan!!

Ken

Thanks to all that replied with explanations, examples and an equation. You
have all made this issue crystal clear to me. As has been said before,
you're a great bunch of people here at rcw.
Thanks
Martin
PS Could a few more of you look at my other post "Survey - Club Lathes"


"Dan Bollinger" wrote in message
news:8iPae.16139$r53.14374@attbi_s21...
Let's play with this a little. Suppose you were using a lathe that
developed enough *torque* to cut the wood, but did so at 1 RPM. It's
true,
the torque would be cutting the wood, but you would be wishing for some
*horsepower" so you could finish and go in to dinner.


LOL! That's what I said, but you said it with less words and more humor!
Dan

On Sun, 24 Apr 2005 08:41:25 -0800, Kevin Miller
wrote:


It is torque, not horsepower that cuts the wood.


Odd, I use a gouge to cut the wood.
Real turners use a skew! G,D&R)
===================
Kevin,
Do you want to demo that on the inside of a bowl?!
Or are skews there different than in the lower 48? {:-)

Uh, yeah. We use a special 'bowl skew'. It's only got one bevel and
sorta curves up on the sides. Works a treat! ;-)

...Kevin

that sounds like a good way to skew up a bowl..


mac

Please remove splinters before emailing

Ken Moon wrote:

==================
Y'all think up all sorts of things driving up the Alcan!!

Ken

Well, nights are long here in the winter! But springs here, the salmon
are moving in, I just scammed on a couple pickup loads of logs for bowl
blanks (alder) and I need to do some light maint. on the boat so I
probably won't have much time for any more thinking for a few months.

That might be A Good Thing...

....Kevin
--
Kevin Miller
http://www.alaska.net/~atftb
Juneau, Alaska