<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <body bgcolor="#FFFFFF">   Cy Shuster wrote: <blockquote TYPE=CITE><style></style> 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.</blockquote> 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. <blockquote TYPE=CITE> 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.</blockquote> 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.     <blockquote TYPE=CITE>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.</blockquote> 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 ?     <blockquote TYPE=CITE>  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?</blockquote> 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.   <blockquote TYPE=CITE>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 </blockquote> -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway <A HREF="mailto:rbrekne@broadpark.no">mailto:rbrekne@broadpark.no</A> <A HREF="http://home.broadpark.no/~rbrekne/ricmain.html">http://home.broadpark.no/~rbrekne/ricmain.html</A> <A HREF="http://www.hf.uib.no/grieg/personer/cv_RB.html">http://www.hf.uib.no/grieg/personer/cv_RB.html</A>   </body> </html>