| Replacing Metal Bushings with J.S. Delrin Bushings |
| By Rich Zimmerman |
|
There are several types of fastening methods for holding flute pads in
their cups. If the flute is a closed hole instrument the pads may be
secured in place with a metal washer and small screw, a plastic spud
that fits over the inner collar, a threaded post and washer, or in the
case of an open hole flute, a friction fit circular bushing that fits
inside the chimney of the pad cup. This article will concentrate on the
workings of the open hole flute pad bushing and the improved design of the
J.S. Delrin bushing.
Delrin is a plastic that has many of the same characteristics of
materials such as brass, aluminum, zinc, and stainless steel. Its
properties include stiffness with a higher degree of flexibility then
most metals, an ability to maintain a prescribed dimension, impact
resistance and structural strength. These properties make Delrin the
ideal material for machining bushings that must be strong but still have
a certain amount of flex to seal around the edges of the pad cup chimney.
The purpose of a friction fit bushing is to secure an open hole flute
pad in its pad cup while creating an air tight seal around the edges of
the pad cup chimney. Traditional metal bushings have certain
disadvantages that cause leaks, damage pads and, at the very least, make
padding a flute more difficult. A metal bushing does not give and can be
bent even when extreme care is taken when removing it. A bent
bushing may damage the pad, the pad cup chimney or cause leaks. J.S.
Delrin bushings slide on and off the inner wall of the pad cup chimney
more easily, forming an air-tight seal yet allowing removal without damaging
the pad, the chimney or the bushing.
Installation of a J.S. Delrin bushing
is the same as a conventional
bushing: First remove the key from the instrument. Then pry out the old
bushing using a thin metal slick that has an even, flat surface
containing no burs. If you see that your slick has a sharp edge or bur
left over from the manufacturing process remove it with a file and
sandpaper. Place the slick between the top portion of the bushing and
the pad skin. Using a gentle prying motion carefully pry around the
circumference of the bushing, utilizing the pad cup's edge as a fulcrum
for your slick. To fit the J.S. Delrin bushing measure the flute pad cup
chimney and use a Delrin bushing that is .1mm (.004") smaller than the
outside diameter of the pad cup chimney. This will allow the Delrin
Bushing to seal completely around the inside diameter of the cup
chimney. With the back of the pad cup on a flat surface carefully press
the Delrin Bushing into place with your fingers. Iron the pad as
necessary and reinstall the key on the instrument.
When overhauling an open holed Flute, consider changing all of the
Bushings to J.S. Delrin Bushings. J.S. Delrin Flute bushings are simple
to use and less likely to damage the instrument or the pads. Because
they seal better than metal bushings the J.S. Bushing will improve the tone
and projection on any open holed flute. |
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