On Dec 1, 2010, at 9:48 AM, Don Mannino wrote: > So to clarify, I don't believe the low friction causes the tone > change so much, but the lack of control in the bushing that low > friction can cause. That's why I mentioned earlier that I like the > sound of well fitted Teflon actions. They can have almost no > measureable friction, but still sound great. I concur with Don, that it is firmness of the bushings that leads to the tonal impact of repinning more tightly, not the friction. I think it is important when pinning to keep those two aspects in mind at all times: we measure our pinning by friction, but that is by no means the whole story, and possibly not the most important part of the story. Let me illustrate by two center bushing scenarios. First, what the factory does (and Don, please correct me or amplify as needed). They start with bushing felt of a decent density, strip it and pull it through the holes in the flange or shank. The stripping and pulling process "unfelt" the wool to a considerable extent, though the fibers are still pretty well aligned to one another. They install a sizing pin and dip into a wetting agent, of which the active ingredient is water. The water is absorbed by the wool fibers, which swell. Because they are confined between the sizing pin and the wood, they are compressed together. When they swell, their scales are lifted from their surfaces to some extent (anyone have electron microscope photos of swollen fibers? I have only seen photos of them dry). These scales interlock to some extent, so that when the bushings are dried, the wool has become more densely compacted, fairly permanently. If it is exposed to higher humidity, the fibers will swell, and if dried they will shrink, but the interlocking structure will stay the same. Then the sizing pin is removed and parts are pinned together (and there may be intermediate steps involving burnishing or a second sizing and wetting, and Don can elucidate if he wishes). Second scenario, tech in the field rebushes a flange. Again felt of a reasonable density is stripped and pulled through a hole and cut. The result is a bushing that is "too tight" (too high a friction). Reamers are used to remove some fibers until the target friction level is reached. The parts are pinned together. They have a "correct friction level" but they are unusably spongy. After the part has been played a good bit, it needs to be repinned up a couple full sizes. This is to illustrate the problem of looking at bushings from the perspective of friction. A couple other scenarios: verdigris. Too much friction. Remove pin, ream a bit to achieve target friction, repin parts. Result: correct friction but knocking bushings. "Asian flu": frozen joint. Remove pin, ream and possibly burnish without adding lubricant. Result: to get target friction, you end up with a spongy joint. My own solution, which I have written about earlier on this list, is to burnish vigorously enough to produce heat and (at least I think so) felt the wool relatively permanently "iron" it. In this case I am taking flanges that are too loose and all need to go up a half size. But just putting in the half size larger gives too much friction. Since we are talking about a .001" difference in pin size, I assume the target is about .0005" different, that where I am is midway between the two pins. Or, looked at another way, if I can compress the felt by .0005", I will achieve the friction I want and have denser felt than I started with, by a little bit. The alternative is to remove felt. If I remove felt, I might very well remove a little too much, and after a little play the flange would return to its original condition. And since that is what I had found several times after doing a repinning job (thinking I was doing great work), I prefer the notion of compacting that little bit, if possible. If not, I remove the absolute bare minimum of felt fibers. Lots of vigorous burnishing, very little reaming. I am more concerned with felt density that with hitting a specific target friction level (though I do want to hit a window that is functional). Regards, Fred Sturm fssturm at unm.edu
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