Hi Ron, > There have been experiments, including making pins so tight in > waterproof pinblocks that you could barely turn the pin in with > three hands. Guess what. The super tight waterproof block pianos > still dropped in pitch over the long run. In my experience, tuning > stability gets better with decent scaling, rib supported boards, and > laminated bridge caps. Hence my answer. But has anyone ever looked for rotation in the pin? That is, were pin positions accurately measured/recorded, so that any migration in pin position (corresponding to magnitude of pitch drop) could be measured? If not, then the question wasn't answered. I can drive a 10 penny nail into a block of wood, and given conformational cycles in the wood, due to cycling humidity, etc., the nail can walk out when under no outward tension. I'm not necessarily saying it does, but that it can. I think you will agree that the fit of a nail in a block of wood is pretty tight! When there are repeated changes in conformation of one material against another, frictional effects are negated. All that is really required for the materials to walk is for the conformational change to be great enough to result in slippage. Now, if the pinblock cycles in thickness enough that there is the teensiest bit of slippage of pin against pin block in the longitudinal direction (and expanding wood can generate some pretty impressive forces!), the pin will start walking, bit by bit, in the direction of any forces applied to it, no matter how high the friction of the pin against the pinblock. The question of a moisture-impervious pinblock material is more interesting. However, I would suggest that many mated materials are going to shift against each other without the help of cycling humidity. For instance, there is the issue of thermal expansion. One material may expand more than the other when heated, hence slippage. There's also the effect of mechanical forces acting upon the two materials. As an assembly is torqued and vibrated back and forth, the parts can walk against each other. There may even be stochastic gremlins at play. Perhaps on a molecular level there are local, random conformational changes in the cellulose, as it mates with the metal of the tuning pin. Again, with time... Other examples of slippage can be seen in machinery. If two parts don't corrode together, if they aren't "stuck" together (e.g. with LocTite), and if they aren't locked with some sort of pin or lock washer (that digs into the metal), they can walk apart, even when they are first assembled under great tension. Fact. On a piano, the screw stringer design seems the most unlikely to walk. Inquiring minds still want to know... ;-) Peace, Sarah
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