Dave Finkelnburg on tue 27 may 03
Hi!
Randy's complaint about the power output of his pottery wheel, and
follow-up comments, reveals a severe limitation in how wheels are described
by wheel manufacturers. Frequently potters are told a given wheel will
center, "up to X-pounds(kilograms) of clay." That's not a good measure.
If you can center 5 pounds of clay on a wheel, you can center 50 on the
same wheel. It may take a little longer to center the box of clay than the
5 pounds, but you can do it. Shoot, any five-year old kid can center 50
pounds of clay on almost any electric wheel, given time and instruction.
It's not about strength, it's about technique.
Wheels should not be rated by something so affected by technique. There
is a better way to do this.
Pottery wheels should be rated by torque. For example, in the civilized
world the rating would be the kilograms of force per meter a wheel can
develop at a specific distance from the center of the wheel head, in the
plane of the wheel head. Here in the US the rating would likely be in
foot-pounds of torque.
Rating the power of pottery wheels on torque factors in horsepower and
the drive belt or gear reduction, removes a potter's technique as a
variable, and would allow an honest comparison of wheels based on power.
Good potting!
Dave Finkelnburg in sunny, unseasonably warm sunny, did I mention
sunny? Idaho!
Fredrick Paget on wed 28 may 03
I think that something is left out here.
Torque by itself doesn't tell how the wheel behaves. If you measure
torque with the wheel still - not rotating It does not tell the
story. My wheel , if I do that to it, blows a fuse - yet I have never
blown a fuse while throwing.
You need some sort of brake test where the torque can be measured at
different speeds as the brake is applied and a set of curves drawn.
The brake would have to be fastened to the wheel head for the purpose
of testing.
Fred
--
From Fred Paget, Marin County, California, USA
Chris Morgan on wed 28 may 03
I agree. This has been one of those issues that has always mystified me.
I was using a wheel that was "rated" for 100 lbs, but would bind while
using much less. Newton/Meters would be good. The only problem is no
one, my self included, would have a good idea how a measurement of torque,
in standard or metric, would translate into the capacity of the wheel. I
would guess that the current system, though misleading is an attempt to
bridge this gap. I have seen, btw a wheel that advertises umlimited
centering capacity. One wonders what their definition of "unlimited" is.
Chris Morgan,
With a brand-spankin' new BS in CompSci
On Tue, 27 May 2003 18:55:12 -0600, Dave Finkelnburg
wrote:
Pottery wheels should be rated by torque. For example, in the
civilized
>world the rating would be the kilograms of force per meter a wheel can
>develop at a specific distance from the center of the wheel head, in the
>plane of the wheel head. Here in the US the rating would likely be in
>foot-pounds of torque.
Bob Nicholson on wed 28 may 03
Great idea.
Maybe a few manufacturers will take the message from
ClayArt and start publishing torque measurements!
pdp1@EARTHLINK.NET on thu 29 may 03
Hi Fred,
Makes sense to me - I was thinking on this in that way as
well...some way to tell what the effective working torque
may be, and as it differ at various r.p.m.
It does not seem an easy matter to solve without rather a
lot of work, or having a practical method of 'drag' or
'brake' as you say, as can be measured.
One could adapt a Brake drum with internal expanding shoes
and backing plate, as from an automobile, to allow ( in it's
being mounted to a Wheel head with some 'universal' bracket
say) a fairly fine adjustment of 'drag' to be had by
increasing or adjusting the Hydraulic pressure against the
slave cylinder in the Brake mechanism.
And to this, to the backing plate, a lever is well attatched
as may from it's end, pull against a known spring-scale,
callibrated as a Fish weighing scale may be...and...with a
little Arithmetic, one may then tell maybe fairly
practically, what the effective Foot-Pounds may be at
different speeds on a given Wheel...
The longer the lever, the smaller or lighter the scale may
be...
The worst would be if a little too much drag...one would
blow a fuse, and a fairly sensitive fuse-box should be in
line as may defer to the particulat Motor a given Wheel has
for that reason. One could also have some electronic device
in the line, as tells of the draw so one could lessen the
drag before blowing a fuse, or, if you knew where she'll
blow to do so.
Anyway...that popped into my head...some method like that,
as a fellow can make without too much grief.
Fun thought...I gots too much to do right now tho'...!
Hmmmm...maybe later on, but how often would I get to use it?
Phil
lasvegas
----- Original Message -----
From: "Fredrick Paget"
To:
Sent: Wednesday, May 28, 2003 10:21 PM
Subject: Re: Pottery wheels--why not a common
rating--torque?
> I think that something is left out here.
> Torque by itself doesn't tell how the wheel behaves. If
you measure
> torque with the wheel still - not rotating It does not
tell the
> story. My wheel , if I do that to it, blows a fuse - yet I
have never
> blown a fuse while throwing.
> You need some sort of brake test where the torque can be
measured at
> different speeds as the brake is applied and a set of
curves drawn.
> The brake would have to be fastened to the wheel head for
the purpose
> of testing.
> Fred
> --
> From Fred Paget, Marin County, California, USA
>
>
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at melpots@pclink.com.
Clay Art Information on thu 29 may 03
Good afternoon,
The torque measurements of a 1/3 HP motor maybe around 90 oz-in, but
with mechanical advantage this may go up to 460 oz-in, torque around
this area and up are required for centering 100 lbs, with permanent
magnet motors, this will be a huge motor, but with brushless DC you may
achieve this feat depending on the poles and the way the motor is
constructed, most wheels out in the market has a 10 to 1 ratio,
boosting the torque, but unable to handle the centrifugal force at 250 rpm.
Best regards,
Arthur Morales
RK Whisper - Brushless DC motors
Shimpo Ceramics
Nidec-Shimpo America
(800) 842-1479
Dave Finkelnburg wrote:
>Hi!
> Randy's complaint about the power output of his pottery wheel, and
>follow-up comments, reveals a severe limitation in how wheels are described
>by wheel manufacturers. Frequently potters are told a given wheel will
>center, "up to X-pounds(kilograms) of clay." That's not a good measure.
> If you can center 5 pounds of clay on a wheel, you can center 50 on the
>same wheel. It may take a little longer to center the box of clay than the
>5 pounds, but you can do it. Shoot, any five-year old kid can center 50
>pounds of clay on almost any electric wheel, given time and instruction.
>It's not about strength, it's about technique.
> Wheels should not be rated by something so affected by technique. There
>is a better way to do this.
> Pottery wheels should be rated by torque. For example, in the civilized
>world the rating would be the kilograms of force per meter a wheel can
>develop at a specific distance from the center of the wheel head, in the
>plane of the wheel head. Here in the US the rating would likely be in
>foot-pounds of torque.
> Rating the power of pottery wheels on torque factors in horsepower and
>the drive belt or gear reduction, removes a potter's technique as a
>variable, and would allow an honest comparison of wheels based on power.
> Good potting!
> Dave Finkelnburg in sunny, unseasonably warm sunny, did I mention
>sunny? Idaho!
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
>
>
>
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