<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; = charset=iso-8859-1"> <META content="MSHTML 6.00.2800.1264" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black">From: <A title=Richard.Brekne@grieg.uib.no href="mailto:Richard.Brekne@grieg.uib.no">Richard Brekne</A> </DIV> <DIV style="FONT: 10pt arial">To: <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">Pianotech</A> </DIV> <DIV style="FONT: 10pt arial">Sent: Sunday, October 26, 2003 = 1:34 PM</DIV> <DIV style="FONT: 10pt arial">Subject: Re: Rib Support</DIV> <DIV> </DIV>  Cy Shuster wrote: <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. >>Yes, I mean like the third drawing.  Yes, the forces would add, but like vectors: the weak = spring resists bending by "x" amount; the strong spring bends by "10x"; so = the result is a bend equal to "9x". 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. >>I'm thinking of the case as = you've drawn it, where it's just the ribs and SB, out of the piano, not = attached to a rim.  In that case, there's no "common force".  The SB holds = the ribs down.      <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 ?      >> I don't think the cable's a good analogy, because as soon as the panel = bends, it will go slack.   <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.    >> Would you feel the = same if the SB and ribs were out of the piano, just sitting on a flat surface, = crown up?  If you take the rim out of the picture, then it seems to me = the ribs don't support crown, unless they have a strong "spring" action in = trying to straighten themselves.  Would you agree? --Cy--</BLOCKQUOTE></BODY></HTML>