<!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 6.00.2800.1226" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV> </DIV> <DIV style="FONT: 10pt arial">----- Original Message ----- <DIV style="BACKGROUND: #e4e4e4; 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><B>To:</B> <A title=pianotech@ptg.org href="mailto:pianotech@ptg.org">Pianotech</A> </DIV> <DIV><B>Sent:</B> October 02, 2003 12:28 PM</DIV> <DIV><B>Subject:</B> Re: RC vs CC again</DIV></DIV> <DIV><BR></DIV>  <P>Delwin D Fandrich wrote: <BLOCKQUOTE TYPE="CITE"><FONT face="Comic Sans MS"><FONT color=#000080></FONT></FONT> <BR><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 'Lucida Sans'; = mso-bidi-font-size: 10.0pt"> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT = face="Comic Sans MS" color=#000080></FONT><O:P></O:P></SPAN> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><SPAN style="FONT-SIZE: 12pt; FONT-FAMILY: 'Lucida Sans'; = mso-bidi-font-size: 10.0pt"></SPAN> <DIV class=MsoBodyText style="MARGIN: 0in 0in 0pt"></DIV> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt">Grin... now THATS = what I'm talking about !!...  Seriously tho... this is easy enough to = follow. Do you have a similiar formula for how much stiffness the assembly takes = on for panel compression ?..   </P></BLOCKQUOTE> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080>I do not know of any way to predict the panel stiffness = of a compression-crowned soundboard system. Even if a formula were developed = I suspect the many variables would degrade accuracy to the point of uselessness.</FONT> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080></FONT>  <BLOCKQUOTE TYPE="CITE"> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT = face="Comic Sans MS" color=#000080></FONT>  <P class=MsoBodyText style="MARGIN: 0in 0in 0pt">And.... well.. = you could always increase height of the ribs in a CC board as well... but = then... that wouldnt make much difference given that the ribs dont do a lot to = support the pannel. </P></BLOCKQUOTE> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080>Well, think about this a bit. What would be the effect = of a tall rib? Of course it would make a difference. It would limit the = development of crown and further increase the amount of compression within the = panel.</FONT> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080></FONT>  <BLOCKQUOTE TYPE="CITE"> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT = face="Comic Sans MS" color=#000080></FONT>  <DIV class=MsoBodyText style="MARGIN: 0in 0in 0pt"></DIV> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt">So.. what.... the = ribs function in a CC board is primarilly to force the panel into = compression ?? Why the choice of fat and not so high instead of lots of height... or something else... what determines your choice of rib dimensions in a = CC board ? </P></BLOCKQUOTE> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080>Since I no longer do them I don't have to make that = choice. </FONT> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080></FONT>  <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080>As to why they are wider than they are tall (and I've = now written this so often my fingers can find their own way around the keyboard with = no further input from my brain -- so repeat after me....)</FONT> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080></FONT>  <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080>THE RIBS IN A COMPRESSION-CROWNED SOUNDBOARD SYSTEM HAVE = TO BE FLEXIBLE ENOUGH TO BEND IN RESPONSE TO THE STRESS INTERFACE BUILT UP = BETWEEN THE EXPANDING SOUNDBOARD PANEL AND THE RIBS. THIS IS HOW CROWN IS FORMED IN = THE COMPRESSION-CROWNED SOUNDBOARD SYSTEM.</FONT> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080></FONT>  <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080>If the ribs are too stiff there will be little or no = crown. The wood fibers will still compress as they take on moisture but they won't = be able to develop enough force to create a crown in the system -- the wood's perpendicular-to-grain compression strength limit will be exceeded = before crown is developed. Selecting the right rib cross-section was probably an = empirical study in cause and effect.</FONT> <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080></FONT>  <P class=MsoBodyText style="MARGIN: 0in 0in 0pt"><FONT face="Comic = Sans MS" color=#000080>Del</FONT></P></BODY></HTML>