<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <body bgcolor="#FFFFFF">   <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 18, 2003 10:38 AM</div> <div style="FONT: 10pt arial"><b>Subject:</b> Re: More on soundboard crown</div>   <p><br>Now correct me if I am wrong.. but I understand this to mean that a CC board will be stiffer, both unstrung... and increasingly so when downbearing is applied.  Assuming that is correct,</blockquote> <div dir="ltr"><font face="Comic Sans MS"><font color="#000080">Which it is not.</font></font></div> <br> </blockquote> <p><br>Please refer again to the statement made by Ron <blockquote>"Given a panel crowned assembly with a severely dried  panel, and one rib crowned with a non dried panel, both to identical crowns  at room EMC, the one with the higher panel compression level will have the steeper spring rate gradient, and will be stiffer."</blockquote> Under the qualifiers that we are talking about boards with same amounts of crown at the same RH. If then I've misunderstood the above quote... then it would be nice to hear what was really meant here. <blockquote>  <div dir="ltr"></div>  <blockquote dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">and putting aside all other compression damage discussion for a second or two... I have a question about this long term so called compression set.</blockquote> <div dir="ltr"><font face="Comic Sans MS"><font color="#000080">By this are you implying you don't believe the phenomena exists? Check The Wood Handbook (USDA) and Understanding Wood (R. Bruce Hoadley).</font></font></div> <br>  <div dir="ltr"></div>  </blockquote> <div dir="ltr">Jimmenees guys.... I was not under the impression that the term "so called" implied anything at all. Of course I recognize the validity of the phenomena.</div> <blockquote> <div dir="ltr"></div>  <blockquote dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">Given the absolute ideal climatic conditions over many years... would a soundboard subjected to uniform compression set take on a permanent stiffness as a result of that, or is it exactly the woods resistance to being compressed that causes the stiffness ? Seems to me I also read something in one of Johns posts that hinted in this direction. That a CC board <<properly treated>> will eventually be pressed into a very stiff and permanent condition.</blockquote> <div dir="ltr">No. Compression set continues until some neutrality is reached. I.e., the point at which there is so little compression left within the panel that in practical terms the wood fibers no longer deform. At this point compression and crown and stiffness will be at their minimum point.</div> </blockquote> <div dir="ltr">AH !!... Thankyou... That was what I was after. So.... stiffness then is in a sense a function of how much compression there is in the board, but if the degree of compression is beyond what the wood can handle it will loose both ?</div> <blockquote> <div dir="ltr"></div>  <blockquote dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">On the side of this... and please forgive whatever lack of knowledge I display in the asking,  if compression from ribs being glued cross grain to the panel is such a problem...even in RB boards.. is there no way of contriving a rib such that it is a bit less constraining ?</blockquote> <div dir="ltr"><font face="Comic Sans MS"><font color="#000080">I don't understand any part of this paragraph:</font></font></div> <br><font face="Comic Sans MS"><font color="#000080">    -- What compression from the ribs? In a compression-crowned soundboard system the compression is in the soundboard panel, not the ribs. The rib-crowned system uses an entirely different technology that has been described in infinite detail numerous times in print and on this list.</font></font> <br><font face="Comic Sans MS"><font color="#000080">    -- Compression from ribs is not a problem.</font></font> <br><font face="Comic Sans MS"><font color="#000080">    -- Ribs, in a rib-crowned system, can be contrived to do just about anything you want them to do.</font></font> <br><font face="Comic Sans MS"><font color="#000080">    -- What do you mean by "less constraining?"</font></font> <br><font face="Comic Sans MS"><font color="#000080"></font></font> </blockquote> <font face="Comic Sans MS"><font color="#000000">Thanks for asking for a clarifier Del. Kind of you. I meant that it is the ribs constraint upon the panel that cause the panel to either compress or become tensioned depending on what the MC was when the ribs were glued on and what it is at any other given time. If RH brings MC below that starting point the board becomes tensioned right ?? And when RH causes MC to rise above that starting point there will be some compression. So assuming that Climatic conditions can get over stress even an RC panel... I just was musing if there was some way of contiving a rib that gave crown support, but was a bit less constraining to the panels tendancy to expand and contract across the grain.... sort of sliding ribs if you get my meaning...Probably a silly question I know... but I was just curious.</font></font> <div dir="ltr"><font face="Comic Sans MS"><font color="#000080"></font></font></div> <p dir="ltr"><font face="Comic Sans MS"><font color="#000080">Del</font></font> <br>  <p>Thanks for clearing up most of it for me... I am still a bit foggy on what Ron meant in the first part tho. I suppose he will bring out his mace and try and smash it into my skull for me :) <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.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>