At 6:34 AM -0500 11/14/01, Clyde Hollinger wrote: >Well, now we got this thread going on glue, too! :-) Your response >raised a question in my mind. What kind of glue was used in the old >uprights to glue in the jack flanges? The ones that on some pianos come >loose because they've lost their holding power? Is that hide glue >"attacked by mold," or something else? This is simply due to swelling and shrinking in changing humidity conditions. The jack falnge relies more on a press fit than a proper glue-line for adhesion since it is glued against end-grain in the lever body. The glue pressed out round the edges helps to provide support but if the piano is exposed to lengthy periods of low humidity the glue will dry out and the flange work loose. The glue itself does not deteriorate. Two sorts of adhesion are at work with hide glue: mechanical adhesion and specific adhesion, which works due to the 'polarity' of the wood and the glue. For every 90 year-old piano that has a problem with loose jack flanges, I'd say there are at least 20 with no problems at all, at least in our climate, but put any furniture in a centrally-house with concrete floors and warm it up enough and any glue joint will fail as both the wood and the 'hooks' of glue holding things together shrink or break. JD
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