With the benefit of having Mason & Hamlin in the neighborhood of the Boston PTG Chapter, I've had a chance to follow conversations between one of the Burgetts (Kirk? the one who lives in Haverhill -- I'm terrible with names!) and Bruce Clark with our chapter members, on the subject of flange bushing. Your description may be 100% accurate for all I know, but they did indicate "it an't as easy as you think", and that they had a very steep learning curve as other parts manufacturers held back "trade secrets." Eventually they got someone who was expert (presumably from long experience at other parts manufacturers) to help them over the hump. Maybe they can provide some commentary, especially as they have now gone beyond felt based bushings. Patrick Draine On Dec 1, 2010, at 8:53 PM, Fred Sturm wrote: > > 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).
This PTG archive page provided courtesy of Moy Piano Service, LLC