<!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 6.00.6000.16587" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY>
<DIV><FONT face=Arial>John, this is one of the best descriptions I have read
here on "Traditional (CC) board construction. Very clear and concise. I have on
question with the RC&S board construction. Are the ribs curved or flat when
they are glued up?</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Al</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial>Al Guecia<BR>Allied PianoCraft<BR>PO Box 1549<BR>High
Point, NC 27261<BR>(336) 454-2000<BR><A
href="mailto:PianoTech@alliedpianocraft.com">PianoTech@alliedpianocraftcom</A><BR><A
href="http://www.alliedpianocraft.com">www.alliedpianocraft.com</A></FONT></DIV>
<DIV><FONT face=Arial>----- Original Message ----- </FONT>
<DIV><FONT face=Arial>From: "John Delacour" <</FONT><A
href="mailto:JD@Pianomaker.co.uk"><FONT
face=Arial>JD@Pianomaker.co.uk</FONT></A><FONT face=Arial>></FONT></DIV>
<DIV><FONT face=Arial>To: "Pianotech List" <</FONT><A
href="mailto:pianotech@ptg.org"><FONT
face=Arial>pianotech@ptg.org</FONT></A><FONT face=Arial>></FONT></DIV>
<DIV><FONT face=Arial>Sent: Saturday, January 26, 2008 7:58 PM</FONT></DIV>
<DIV><FONT face=Arial>Subject: Re: R,C&S question JD</FONT></DIV></DIV>
<DIV><FONT face=Arial><BR></FONT></DIV><FONT face=Arial>> At 23:17 +0100
26/1/08, Richard Brekne wrote:<BR>> <BR>>>Hi JD... What I see here is
that in an RC & S board under <BR>>>downbearing load at anything near
glue up MC, the ribs will be in <BR>>>the opposite condition with respect
to which half of the rib is <BR>>>under compression and which half is
under tension then traditional <BR>>>boards.<BR>> <BR>> Well, the
"traditional" board never experiences downbearing load when <BR>> the
moisture content is anywhere near what it was when the ribs were <BR>> glued
on because it relies on moisture uptake to form the crown by <BR>> internal
compression. At the time the ribs are glued on the <BR>> un-ribbed side
of the board is slightly stretched by being forced <BR>> into a dished table
by the curved ribs, but once the glue is set and <BR>> the assembly is
removed from the press this tension is at first <BR>> reduced and then
replaced by compression as the board takes on <BR>> moisture, vainly tries to
expand along the ribs and somewhat less <BR>> vainly tries to expand on the
unribbed side, so that by the time the <BR>> board has acclimatized the
various forces have increased the <BR>> convexity, or upward curve, of the
whole structure, the greatest <BR>> compression being at the glue line, where
no expansion is possible.<BR>> <BR>> Once the board is installed and the
piano strung, the crown is <BR>> pressed down by the force at the bridge and
the compression at the <BR>> top of the board is further increased.<BR>>
<BR>> <BR>>> The [RC&S] panel's probably reasonably
significant compression <BR>>>will be due string load forcing it (and the
ribs) down. So the <BR>>>panel will be in somewhat similar condition
to compression reliant <BR>>>assemblies... while the ribs will be in
opposite orientation.<BR>> <BR>> As I understand it the RC&S board is
subjected on glue-up to a <BR>> greater tensile force on the unribbed surface
but (a) since it has <BR>> been less dehydrated and (b) because it has been
forced round a <BR>> tighter radius against much less flexible ribs, some of
this tension <BR>> will either remain or be reduced to a point while the
assembly is <BR>> free. Compression at the glue line will exist, of
course. Once the <BR>> piano is strung, the downbearing will press down
the soundboard less, <BR>> because the beams (ribs) are more solid, and hence
there will be less <BR>> reduction in the curvature and less increase in
compression (or <BR>> decrease in tension) at the surface of the board.
Now those who <BR>> practice this art will be able to give actual rough
values to these <BR>> phenomena, but this method of construction seems to
have as one of <BR>> its aims the avoidance of anything close to the degree
of compression <BR>> to which a high-class traditional board is
subjected. The <BR>> specialists will correct me if I am wrong.<BR>>
<BR>> As you say, a lot of things are unclear, and these discussions often
<BR>> start off with some hope of providing enlightenment, facts and <BR>>
figures, and a statement of principles but all too often, almost <BR>>
always, deteriorate into a rather vague mish-mash, a bit of dogma and <BR>>
bye-bye. I try to limit myself to facts and experience and as much
<BR>> science as I can muster, which is not always much! Opinion is
<BR>> worthless -- and in my view excellent piano tone is far less a matter
<BR>> of taste and opinion than you have recently suggested. There are
a <BR>> number of measurable qualities in the sound of a good piano.
It's <BR>> nice to have a fairly good string scale but I could name several
<BR>> pianos that won gold medal after gold medal in the old days with
<BR>> quite outrageous stringing scales and took the prizes because the
<BR>> work they did on the belly was good. The belly itself produces
<BR>> nothing, but what it does with what it's given is what makes the
<BR>> difference between a "satisfactory" piano and something that sends
<BR>> shivers up your spine.<BR>> <BR>> JD<BR>> <BR>> <BR>>
<BR>> <BR>></FONT></BODY></HTML>