Hi Keith: I still think you were right originally. The teflon does not change except as a result of the surrounding wood affecting it. As a shank fork takes on moisture, the hole for the bushing enlarges. I know that this seems contrary to our experiences with regard to loose and tight tuning pins, but the principle is the same. Moisture causes wood to swell. This swelling takes place more across the grain. In the case of pinblocks, it is the wood swelling between tuning pins which causes the pins to be tighter. In the case of a shank fork, there is no restraining force of neighboring wood to force the grain to impinge upon the tuning pin. In the case of the tuning pins, when the block is dry, the wood between the neighboring tuning pins shrinks and therefore less pressure is exerted upon the tuning pins. At first, all this sounds counter intuitive. I have written on this before on this list, and I still have a maple board in which I had drilled a 1" diameter hole. It was carefully measured. After soaking the board in water, the hole enlarged in the direction across grain. The enlargement along the grain was imperceptible. You must understand that this was just one hole in one board. If there had been multiple laminations restricting the board from getting wider as is the case with pinblocks, then the holes would get smaller due to the swelling of the wood between the holes. In hammer shanks, there is no restraining force from cross laminations, hence the holes do get larger and the teflon which doesn't swell is relieved of pressure and thereby rattles. During the dry cycles, the shank fork shrinks and applies more pressure cross grain and the teflon in turn squeezes the center pin tighter and we then have tight flanges. Jim Coleman, Sr. On Thu, 4 Mar 1999 kam544@earthlink.net wrote: > I'll submit to both Jon and Avery. > > FWIW: In one of Steinway's publications (around 1990) on the teflon > bushing, it states under General Comments: > "While teflon is an inert substance, the wood surrounding it remains > sensitive to climate. It is a curiouis fact that if clicking is present, > it will be obvious in a damp climate and may disappear when it is dry." > > This almost supports the demonstration you mentioned, and at the same time, > declares the inertness. Odd. > > No wonder the bushings were so misunderstood. And here I've held the > belief they remained stable, while the wood fluctuated. All these > years..sheesh! > > Thanks for bringing it up. > > Keith McGavern > kam544@earthlink.net > Registered Piano Technician > Oklahoma Chapter 731 > Piano Technicians Guild > USA > http://www.ptg.org/1999/conv/ > PTG Convention, Kansas City, July > > >
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