---------------------- multipart/alternative attachment Cy Shuster wrote: > Ric, Thanks for spending the time to do the diagrams. It really helps > the discussion. I'm going to take a wild stab, based only on > intuition, so I won't even bother with a flame suit. It's supposed to > snow today, anyway -- we could use the heat! It seems like it's a > matter of degree. A force can exist, but be so small as to be > negligible. The Moon has a gravitational pull to be sure, but the > Earth's is so much stronger, it's irrelevant. A soundboard decal > undergoes stress when a board is crowned, but it's irrelevant. Grin... The moons gravitational pull is very very very far from irrelevant. Ever heard of tides ? And a soundboard decal has no function that relates to structure or physics to begin with... so of course its irrelevant. Tho the thought DID bring a smile. > The situation seems more like a stronger force overcoming a weaker > one. The weaker one subtracts from the stronger one, and then the > situation is in equilibrium. I'm thinking of a small leaf spring, > like for pedals, about 6" long, say curved in an arc of one foot > radius. It resists being straightened. If you take a stronger > spring, of thicker metal, same length, but curved to a 6" radius, and > nest the two so the stronger's on the outside, the thinner spring will > resist a bit, but the vector of its force is overwhelmed by the > stronger spring. Hmmmm.... Not sure where you are at here... if you mean nesting like my third drawing... then I would suppose their affects become additive. I dont see that the ribs are exerting a stronger force then the soundboard... if that's what you mean... I dont even see one as having a separate force from the other. Or at least.. I dont see that as being what yields and supports crown. I see that the ribs are holding, and the soundboard are pushing against a common force. > Same with the soundboard and ribs. If the force of the SB absorbing > moisture is so strong as to bend the ribs, then they're irrelevant > after that point, it seems. I keep hearing this one... but turn the reasoning around a bit... if the SB absorbing moisture is so strong as to bend the panel then its irrelevant, or if the Ribs are so strong as to force the panel to crown then they are irrelevant.... I could go on. Its this irrelevancy that I am questioning. Who says the ribs are irrelevant... ? and what reasoning can back that up...? and what set of physics principles for that matter ? And how does any of this explain the basic <<cable holding the panel bent>> that was my first example ? Are you suggesting that the cable in that example doesn't support the <<crown>> against a downward pressure ? How could that be ? and if not... why would the wooden ribs bending, in anyway relieve it of that same duty ? How could that be ? > > The material used seems to matter. If the ribs were spring steel, and > were initially flat, then of course they'd continue to want to > straighten out, forever. What does wood do? Hmmmm... if you used spring steel straight out like the cable example... does it not support crown ? The only difference I see between that and attaching it to the whole width of the panel is that you are more or less stringing together a continuos set of very short panel widths and rib lengths. I can't see that we can escape from the fact that pushing down on the soundboard is synonymous with exerting an outwards pressure on whatever is holding against that outward pressure. And if something is holding against that pressure... well that's spells support as far as I can see. > If the SB were stronger than the ribs to begin with (after coming up > to normal humidity), wouldn't it always stay stronger than the > ribs? --Cy Shuster--Rochester, MN -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway mailto:rbrekne@broadpark.no http://home.broadpark.no/~rbrekne/ricmain.html http://www.hf.uib.no/grieg/personer/cv_RB.html ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/bf/6e/6e/11/attachment.htm ---------------------- multipart/alternative attachment--
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