<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <body bgcolor="#FFFFFF"> Ok.. Thanks muchly for your patience once again. This has been very instructive. I think I am pretty clear on what I was asking about. It will be easier reading the two texts at this point, knowing better what I am after. <p>Cheers <br>RicB <p>Delwin D Fandrich wrote: <blockquote TYPE=CITE><style></style>   <blockquote dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000080 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 href="mailto:Richard.Brekne@grieg.uib.no" title="Richard.Brekne@grieg.uib.no">Richard Brekne</a></div> <div style="FONT: 10pt arial"><b>To:</b> <a href="mailto:pianotech@ptg.org" title="pianotech@ptg.org">Pianotech</a></div> <div style="FONT: 10pt arial"><b>Sent:</b> August 29, 2003 1:57 PM</div> <div style="FONT: 10pt arial"><b>Subject:</b> Re: Compression Question</div>    A few days back you said <blockquote><i>"If the degree of compression is beyond what the wood can handle--i.e., it is stressed beyond its proportional limit--the wood fibers will crush immediately. If it is compression stressed below its proportional limit compression-set will work to reduce that compression stress slowly over some period of time. In both cases there will be forces at work to reduce compression, in the first situation it simply happens faster."</i></blockquote> So.. given what you say above, am I to understand that a rib crowned board ribbed when the panel is about 6.5 - 7 % MC will not suffer enough compression set during its lifetime... say 30 - 50 years  , to cause any real compression / compression related problems ?</blockquote> <div dir="ltr"><font face="Comic Sans MS"><font color="#000080">No. Some compression set will occur any time the MC of the panel goes substantially above the MC at which the panel was ribbed. It is a matter of how much compression set can reasonably be expected to occur. In a perfect world the amount of compression set will be reduced to a level that will not seriously impair the wood's tensile strength at the lowest MC that it will be reasonably expected to survive. In the real world the possibility still exists that the wood fibers might be damaged to some extent but the chances this happening to an extent that will result in visible damage to the panel have been reduced considerably. In addition, if the soundboard's rib system has been properly designed any cosmetic damage that does appear will be just that--cosmetic. Crown and stiffness are born by the rib system not compression within the panel. I could deliberately cut slots periodically across the surface of the panel (longitudinally with the grain) through to, but not into, the ribs and it would not affect the acoustic performance of the system. (Except, of course, for some acoustical coupling between the top and bottom surfaces.) And, indeed, this has been done. By Vose, I think. In other words the panel is now functioning almost completely as a radiating surface, not as a load-carrying structural member.</font></font></div> <p dir="ltr"><font face="Comic Sans MS"><font color="#000080">Del</font></font></blockquote> <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.broadpark.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>  </body> </html>