Stephen Lathrop on thu 16 sep 99
Brent Wheels that don't stop, the causes and solutions....
A Brent Foot Pedal is an electronic device (Rheostat). Electronic devices are
usually
notorious for changing over time and:
1.) They are sensitive to going out of adjustment from a bump, kick or ruff
handling.
2.) They are sensitive to moisture and local voltage changes or voltage
variability.
The result of a foot pedal rheostat out of adjustment is, either the wheel will
not stop
when the pedal is in the stop/closed/off position, or the opposite the rheostat
does
not send full power to the wheel when the pedal if fully depressed. In the full
power
case you may not know if your not getting full power, but you sure know in the
other
direction if the wheel doesn't stop. A wheel that doesn't stop can be caused
also
by the electronics getting damp. Moisture changes the resistance of lots of
those
little parts you can't see inside the wheel and that change in resistance
effects the
shut off point.
Fortunately in the infinite wisdom of the manufacturer these mechanical or
environmental changes can be accommodated with an adjustment to the pedal.
Your local conditions are either different from the factory or have changed from
what ever setting the factory made. So we/you need to make an adjustment to
optimize for both the wheel stopping and the wheel receiving full power. This
usually only has to be done once unless you move your wheel.
A bump, kick or ruff handling may have caused movement to the adjusting device
called a pot located inside the housing supporting to pedal. Moisture getting
into
the pedal or local voltage variations also can cause changes. Disregarding the
cause because the adjustment for both is the same. Although 3 years experience
in an electrical repair shop says my best guess is moisture is more likely the
culprit.
Lets face it clay is wet and we use water too. Despite how dry I try to throw,
with
porcelain it is a necessity, sometimes things just get messy. Possibly you like
me
have a damp studio. As for adjusting, the manufacturer installed a little
electronic
adjusting device called a pot inside the foot pedal. The adjustable pot is
accessible through a hole in the base plate on the bottom of the foot pedal.
The pot is adjusted by what appears to look like a screw in the center of a
piece of
plastic you may or may not be able to see much other than the screw. The screw
is
probably set some where in the middle of the full range of its travel
(adjustment). The
screw should only be adjusted with the pedal in the stop/closed/off position.
Moving
the screw in or out on the pot adjusts the voltage to a zero point (also called
setting
a null voltage). Pot screws are normally supposed to be adjusted with a plastic
screw driver. Now who has a plastic screw driver??? OK not many of us. I know I
didn't
get one when I bought my Brent. Some electronic pots are sensitive to metal and
it
effects the adjustment a little.
Another good reason for using a plastic screw driver, if you can get one, metal
around
electrical devices can create a shock hazard for the operator. So I am supposed
to
warn you to take reasonable precautions if you use a metal screw driver and use
your
only option and that is to turn the power off before adjusting the screw. I
should listen to
my own advice. After you insert the screwdriver into the screw make a mark on
the
base plate that lines up with the screw driver blade. It makes for a good
reference
now and for the future. Then turn the screw in any direction say maybe a 1/4
turn. Turn
on the power and see if the wheel is going slower, faster or maybe it stopped.
If slower
repeat and keep going further in the same direction until the wheel stops. If it
went faster
we have turned the screw in the wrong direction so now turn it back the other
way to
where you started and continue further in the opposite direction until the wheel
stops.
The optimum is achieved when you find that point where a small turn of the screw
starts
the wheel turning and a small turn back stops it. There is a trade off to note.
If you don't
get close to that optimum point you will not have full power when you move the
pedal
to full speed. So adjust the screw as close as you can to the point where the
wheel just
stops with a tiny additional adjustment. Unfortunately if there is a lot of
voltage variation
in your area the wheel might start turning again in the stop position when an
increase
occurs. If so you may have to go back one last time for a little additional turn
of the
screw to compensate. If moisture is your problem then you suffer like I do. The
last
two places I lived were dry but not so now.
My current tiny studio is in a damp sometimes wet basement. When I first moved
the
wheel into all that moisture it raised lots of trouble for me with the
electronics. It was
so bad at times my only option was to leave the wheel turned on all the time.
Electronics turned on produce a little heat. The heat actually helps to protect
them
a little by reducing the moisture absorbed and preventing a change in the
resistance
of some of those little electrical parts. If you have a moisture problem with
your wheel
it is possible to tell when the wheel is turned off. Then later when you turn
the wheel on
it begins to turn when it did not the last time you shut it off. It is much more
likely
after a relative long time off. If this occurs allow the wheel to run for say at
least an
hour and you may find it stops all on its own. If is stops after an hour or so
this is the
result of the electronics warming up and drying out. The dryer electronic parts
have
less resistance and changing the resistance is enough to cause the shut off
point
on the pot screw to be different. I now leave the wheel always turned on during
the
wet season to stabilize the electronics and thus prevent continual adjustments.
Here's wishing your Brent's adjusted and your happily throwing.
Steve
The Pirates Pottery in PA
Where any Day with Clay is a Good Day
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