<!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><FONT face=Arial>Oops! This note was not finished - it was = supposed to go to my outbox for completion later. I deny having anything whatsoever to = do with this post!</FONT></DIV> <DIV><FONT face=Arial></FONT> </DIV> <DIV><FONT face=Arial>Terry Farrell</FONT></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"><B>From:</B> <A title=mfarrel2@tampabay.rr.com href="mailto:mfarrel2@tampabay.rr.com">Farrell</A> </DIV> <DIV style="FONT: 10pt arial"><B>To:</B> <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">Pianotech</A> </DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> Sunday, October 26, 2003 = 9:31 AM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Rib Support</DIV> <DIV><BR></DIV> <DIV><FONT face=Arial color=#800000>Hello Richard. I know some = have express some disenchantment with your persistant theoretical explorations = of soundboard crown, but I am rather enjoying it. It's a good mental = excercise. And I also understand that even though you may well never build a = soundboard, it is still a great thing to try and understand how they might work. = There are not very many authoritative references available to find answers to = these questions.</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>So with that in mind, let's = proceed to do the best job we can leading each other into an advanced state of = total confusion............ </FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>Comments interspersed = below:</FONT></DIV> <DIV><FONT face=Arial color=#800000></FONT> </DIV> <DIV><FONT face=Arial color=#800000>Terry Farrell</FONT></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"><B>From:</B> <A title=Richard.Brekne@grieg.uib.no href="mailto:Richard.Brekne@grieg.uib.no">Richard Brekne</A> = </DIV> <DIV style="FONT: 10pt arial"><B>To:</B> <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">Newtonburg</A> </DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> Sunday, October 26, = 2003 5:47 AM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Rib Support</DIV> <DIV><BR></DIV>Hi List <P>I wanted to try and better explain why I am having difficulty in accepting that the ribs in a CC board do not support crown against = down bearing. Please follow the following reasoning and diagrams and you = will see where I am stumped. <P>First is a panel that is simply bent across the grain and held = into place with a cable appropriately attached on the ends of the panel. = Obviously, when down bearing is applied, the outward pressure on the cable is increased. This entire situation is going to be the same if one = first dries out the soundboard, then securing that same cable tightly, let the = panel take on enough MC to form the same crown. <P><IMG height=305 = src="cid:002801c39bf5$cd432b90$b9b52341@youro0kwkw9jwc" width=482> <BR>  <P>Replacing the cable with a piece of wood doesn't really change a = whole lot conceptually.  The rib will  be under the same amount = of tension as the cable was, though the amount of physical strain may differ.  Pressing down on the panel is definitely going to be = resisted by both the panel and the rib. If the assembly is only resting on = supports at the edge, down bearing might even result in some downwards = bending of the rib.. but I will have to try this to see. Still, the panels edge = will <<bend>> in a downwards direction, and there might be = some reaction in similar direction by the ribs. In any case, the assembly = as a whole will resist any down bearing for the same basic reasons as = above. <P><IMG height=174 = src="cid:002901c39bf5$cd457580$b9b52341@youro0kwkw9jwc" width=472> <BR>  <BR>  <P>Now if the rib is secured to the panel such that it bends a bit = in the same direction as the panel, (i.e. glue say about 10 inches in on = each side)  then the only thing that has really changed is that the = rib bends upwards a bit... as in the below drawing. Yet the same basic = condition exists. Downwards pressure in the panel increases the outwards = pressure, yet this is resisted just in the same way as in the previous two = examples, so in response both panel and rib will feel an increased stress and will = strain against that stress until one of the pieces fail, which of course = will be the panel. <P><FONT face=Arial color=#800000>Keep in mind here that stress = and stain, although related, are two very different things. Stress is a force = that is applied to an object - or an object's ability to resist deformation. = Stain is the deformation. With the soundboard, I suppose stress is = delivered to both panel and rib, but strain is negligible for the rib, and orders = of magnitude larger for the panel. I've searched for numbers that = describe this relationship, but have found none.</FONT> <P>But until that point is reached, the entire system will resist = down bearing vigorously. No doubt the rib will straighten at some point, = and the relative tension/compression on the top and bottom sides will = equalize, but it will have to experience an increase in overall tension for this = to happen, which it will resist. The panel will also straight out at somepoint... but nobody believes for one second that it wont be = under stress when its flat.. So why should the rib be any different ? Opposite = side of the same coin. Both will physically strain against the stress, the = panel a good deal more then the ribs, but the stress levels are the same on = both. <P><IMG height=319 = src="cid:002a01c39bf5$cd457580$b9b52341@youro0kwkw9jwc" width=506> <P>The only thing that remains is to simply glue the entire rib to = the soundboard, but I cant see that that changes anything. If the above = three steps hold, then it seems in error to say that the only thing that = supports crown in a CC board is compression in the panel. The entire system, = panel and ribs alike will strain against down bearing. <P>Ok... so this seems to make perfect sense to me, and though ribs = are not acting as beams in their support, they can neither be said to be = purely fighting crown. Quite the opposite. The fact that the rib is bent in = the process, and of course resists this bending can be said about the = soundboard as well. But I dont see that simple bending of either describes = their condition adequately. <BR>  <BR>  <P>Cheers <BR>RicB <P>-- <BR>Richard Brekne <BR>RPT, N.P.T.F. <BR>UiB, Bergen, Norway = <BR><A href="mailto:rbrekne@broadpark.no">mailto:rbrekne@broadpark.no</A> = <BR><A = href="http://home.broadpark.no/~rbrekne/ricmain.html">http://home.broad= park.no/~rbrekne/ricmain.html</A> <BR><A = href="http://www.hf.uib.no/grieg/personer/cv_RB.html">http://www.hf.uib= .no/grieg/personer/cv_RB.html</A> <BR>  </P></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>