Vince Pitelka on wed 8 jun 05
> What I was told was that the ring/belt gets a depression in it if you
> leave
> it in an engaged
Kelly and Gayle -
It isn't quite accurate to say "ring/belt" above, since they are two
separate parts. The belt is of course the standard V-belt that connects the
small jackshaft pulley and the big wheelhead pulley (some later models don't
have a jackshaft). The ring is the hard rubber ring located on the
jackshaft that engages with the drive cone. In order to get adequate
traction, it engages with considerable force. If you leave the pedal
engaged when the motor is turned off, the cone is pressing very hard in just
one place, and the rubber ring retains a "memory" of that impression, thus
the "thump, thump, thump, thump" as the wheel is operating. When this
happens, the best thing to do is to turn the motor on, engage the wheel at a
fairly high speed, and leave the wheel spinning at that speed for a few
hours or until the thump disappears. The friction causes the rubber ring to
heat up, which encourages it to return to it's original shape. It might
only take ten minutes of running for this to happen. Othewise it can be
pretty unnerving if you are trying to throw while the wheel is going "thump
thump thump."
I learned to throw on Lockerbie kick wheels at Humboldt State, but we also
had several of the early Shimpos RK-1s, and those were coveted by the
advanced students. Frequently someone would turn one of them off with the
drive engaged, and then we would have to contend with the thump thump thump
for a while. When I built my faux-Shimpo around 1976 I copied one of those
RK-1s at Humboldt, but I used a double-pole double-throw switch. When the
motor circuit is turned off, another circuit is turned on, connected to a
micro switch on the pedal linkage and then to a loud buzzer. If I ever turn
the motor off with the pedal engaged, the buzzer goes off and I slap myself
in the forehead and return the pedal to the neutral position. So, in almost
thirty years of using this wheel, the only time I ever accidentally leave
the pedal in the engaged position is while moving the wheel around the
studio and accidentally bumping the lever. Since the wheel isn't plugged in
at those times, the buzzer circuit isn't hot. But when I do plug in the
wheel again and the buzzer immediately goes off I slap myself in the
forehead extra hard and leave the wheel spinning at high speed for an hour
or two to get rid of the thump thump thump.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
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