Replacing Metal Bushings with J.S. Delrin Bushings
By Curt Altarac
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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