John Baymore on sat 18 apr 98
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=3Cclip=3E
I'm having problems with my approx. 20 year old, not used much until
recently, wheel. ................. The wheel doesn't want to spin and
once it starts going it stops easily with pressure. It has gotten
progressively worse. If I let it spin for a while it seems to warm up and
do better. By the end of the day it does fine. If I put it on a fast
speed quickly it doesn't engage and won't go. Any ideas of what the
problem could be or how to adjust it?
=3Csnip=3E
Yahoo. This sounds like the =22classic=22 Shimpo ring / cone drive getting =
old
syndrome. Anyone who has had a lot of experience keeping these wheels in
operation in an institutional setting probably knows it well.
The (old constant speed AC drive) Shimpo wheels get their =22connection=22
between the constant speed AC motor and the wheelhead via a tapered =
=22cone=22
of metal attached to the motor shaft, and a rubber =22ring=22 bonded to a =
metal
disk which is attached to the wheel shaft. By moving the motor to change
the position of the cone, the cone engages the disk to transfer the power
to the wheelhead. That's why the foot pedal on the Shimpo RK's feels so
much like you are moving a lot of mass...... you are=21 And also why you =
get
that jarring =22clunk=22 when you disengage the drive.... the mechanism is
highly mechanical.
The point along the length of the cone touching the ring determines the
speed of the wheelhead. This has to do with the ratio of the circum. of
the point of cone touching the fixed circum. ring. Simple physics........
basic pulley stuff. Smaller circum. touching ...... the slower the
wheelhead turns..... the larger, the faster.
The transfer of power (torque) comes from the friction between the hard
metal cone and the soft rubber ring. With aging, the rubber gets harder
and harder. Makes no difference if the wheel is used a lot or not.... it
is simply the aging of the rubber compound. So the rubber gradually loses
its =22friction coefficient=22. It also shrinks in physical dimensions. So
the transfer of power gets poorer and poorer. Eventually it fails. First
it only works with centering 25 lbs.....then 10 lbs..... then 5 lbs......
then 2 lbs, and so on.
So why does it seem to work when it is used more? As the cone transfers
motor power to the ring, it is not perfectly efficient .... it creates heat
out of the energy not effectively transfered. So the heat transfers into
the rubber ring and the metal cone. Also, as this transfer gets poorer,
the cone spins a bit more against the rubber ring. This creates even more
loss which creates heat. The heat makes the cone and ring expand a little
creating more pressure between them. The heat also softens (and the
slipping wears away) the rubber, and it gets more =22friction-y=22, so the
wheelhead engages and gets =22tighter=22 transfer of the power the hotter it
gets. So the wheel works poorly (or not at all) when the ring is cold, but
sems to get better when it gets hot (friction softening the rubber).
The longer you run it like this the faster the ring is deteriorating and
the worse it will get.
The thing that keeps it from turning when you just hit it on =22fast=22 when
the rubber is cold, is that the cone is probably also misalligned a bit and
the tensioning of the cone against the ring is very light (due to ring
wear, drying shrinkage, and/or the misallignment). So the cone really just
sort of misses the edge of the rubber ring mostly, and there is not enough
friction to engage. (This also comes from wear of the ring over time.....
accentuated by the wearing away that occues as the cone slips on the ring.)
When the rubber is hotter it has swelled up a little, and the cone then
gets enough purchase on it to make it turn.
If you leave the cone running on one spot on the ring without the wheelhead
turning, you can cut a little =22bump=22 into the ring, that will cause the
wheel to run rough and jerky. Also it is bad to shut off the wheel power
with the motor in the engaged position. That can compress the ring and do
the same thing.
The repair is simple, and requires a new ring from Shimpo. Replace the
cone while you are at it.... it may have been damaged from the friction
also. You take off the old one and put on the new one. Adjusting the
tension between the cone and ring is a little trickier, but still simple.
Look carefully at how the motor moves and you'll see the adjustment points.
It is a nasty space to work in, though. Bruise your knuckles a bit, I bet.
Shimpo can step you through the basic repair. Call them.
Of course, it is possible that age isn't all that is involved here.
Someone may have =22glommed up=22 the ring/cone area with some sort of
lubricant at some point, causing it to slip too. Liberal application of
WD-40 or oil or grease, or whatever in the wrong places will cause this
syndrome too =3Cg=3E. Same replacement suggestions in this case.... =
although a
little cleaning of the ring and cone would certainly help until the part
arrives.
So... basic Shimpo RK wheel repair. Hope this is of help.
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40Compuserve.com
George Mackie on sun 19 apr 98
John - thank you for your insightful analysis of Shimpo Ring Disorder
(SRD) - everything you say RINGS true. I love my old Shimpo but
it is a bitch to get the cone pressing against the ring just right a real
knuckle bruising feat as you note. This explains a puzzling thing I
found- we actually won this wheel in a pottery show back in 1969 and got
three extra rings with it. When SRD strikes, I have tried replacing the
ring with one of the ones from 1969 but funnily enough they dont seem to
help much. It hadnt occurred to me that they would age and harden just
like the ones in use. Brilliant! You must be a rocket scientist or
forensic pathologist. Are you any good on cardiac pacemakers? i have a
minor problem there too. George
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