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<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">Pianotech</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> November 23, 2002 12:14 =
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: S&S D =
Duplex</DIV>
<DIV><FONT face="Comic Sans MS" color=#000080></FONT><FONT
face="Comic Sans MS" color=#000080></FONT><BR></DIV>
<BLOCKQUOTE TYPE="CITE">
<P>I'm not at all sure what you mean by "natural" crown. If it is =
some
<BR>factory's doublespeak for compression-crowning, the process is =
anything
but <BR>natural. <BR> </P></BLOCKQUOTE>Natural crown is an =
older English
(British) term which seems to rougly equate your term Compresson =
Crowning.
Junghanns text discerns between straight ribs on a flat panel, vs a =
panel
pressed into a dished caul. In both cases we are talking about a =
thoroughly
dried board, ribs across the grain. And in both cases crown is =
achieved by
allowing the finished glued assembly to take on moisture. Where he =
notes
differences are
<P>1) The dish cauled assembly will immediatly become stressed when =
released
from the call, where as the flat panel will not. <BR>2) An asymetrical =
spherical curvature which is desirable can be easily achieved with the =
dished
cauled assembly and practically impossible with the flat panel. <BR>3 =
The
crown achieved with the dish cauled assembly will be stronger and more =
stable
then with the flat pannel. <BR>4 The dish cauled assembly is more =
sensitive to
being over stressed by too much downbearing. </P></BLOCKQUOTE>
<P dir=ltr><FONT face="Comic Sans MS" color=#000080>I would take =
issue with #3
and #4. Assuming the ribs start out flat and are not machine crowned in =
any way,
ultimately both are compression-crowned and depend on the ability of the =
wood
fibers to resist the force of compression. It doesn't matter if the =
force comes
from having been pressed in a dished caul or from taking on moisture =
after
having been dried to some very low moisture. It is still compression and =
the
wood cell structure reacts the same way. </FONT>
<P dir=ltr><FONT face="Comic Sans MS" color=#000080></FONT>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">
<P>He (Junghann) also states that both these, plus the forementioned =
will
expererience an increase in cross grain pressure and crown as the =
panel takes
on moisture. And with the flat ribs / flat panel all crown is entirely =
a
result of taking on moisture. </P></BLOCKQUOTE>
<P dir=ltr><FONT face="Comic Sans MS" color=#000080>Well, to some =
extent all
soundboards experience an increase in across-grain pressure as the panel =
-- the wood cells -- takes on moisture regardless of how they =
are
crowned. The question is how much tolerance does the wood have to =
resist
structural failure because of that pressure . If the fibers are already =
stressed
-- compressed -- to a point close to their maximum fsl (fiber stress =
limit) due
to the compression-crowning process there will be little tolerance =
for any
further stress and the fibers will begin to crush. If the soundboard =
panel is
essentially neutral and it begins to take on moisture the fibers -- not =
being
close to their fsl -- still have a lot of resilience and will remain
intact.</FONT><BR> </P>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">
<BLOCKQUOTE TYPE="CITE">> ....Steinway is about as careful as =
anyone
could be with this process. Their controls are really quite
good.</BLOCKQUOTE><FONT face="Comic Sans MS" =
color=#000080></FONT><FONT
face="Comic Sans MS" color=#000080></FONT>
<P><BR>Well, I have to take your word on that I suppose. Tho there has =
been
quite a bit of fun poked at the NY plant for total lack of humidity =
contol on
this very list recently. Another common comment going around is that =
the
pitfalls of this method are not as well understood by craftsmen today =
as
earlier.... because specialization in such "arts" is dissapearing. I =
have
absolutely no idea as to the validity of such claims myself. =
</P></BLOCKQUOTE>
<P dir=ltr><FONT face="Comic Sans MS" color=#000080>To the first =
point -- that
would be in the factory itself. Not in the soundboard conditioning room. =
As far
as I know the soundboard ribbing process is quite well controlled. =
</FONT></P>
<P dir=ltr><FONT face="Comic Sans MS" color=#000080>To the second =
-- I have no
specific knowledge on which to make a judgment other than by looking at =
the
finished result. </FONT></P>
<P dir=ltr><FONT face="Comic Sans MS" color=#000080>I do know it =
is not
possible, in today's labor market, to come up with workers who =
understand wood
and woodworking as the result either of their upbringing or as the =
result of
their education in our school system. I am nearly brought to tears =
interviewing
people coming out of what passes for a wood shop education these
days.</FONT></P>
<P dir=ltr><FONT face="Comic Sans MS" =
color=#000080></FONT> </P>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">
<P>"As todays manufacturing is hardly able to use such changed of =
humidity
deliberatly, this methods seems no to promise success. However, the =
authors
(Junghanns (I guess)) seems to be different as he says the following.
<BLOCKQUOTE>
<DIV>"An equal radius of the rounding of all ribs is desirable. If =
this is
not achieved then the finished assembly will be under unequal =
stresses, a
condition that should be avoided at all =
costs."</DIV></BLOCKQUOTE></BLOCKQUOTE>
<DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>And all that =
trouble I go
through to create all those unequal stresses ... what shall I do? But I =
do
understand the theory. It is based, I think, on the notion that the =
response
characteristic of the soundboard should be uniform across its span, or =
surface.
At the risk of starting the Great Soundboard War all over again, if you =
will
consider the soundboard as a series of overlapping loudspeaker =
drivers you
will see why this is not desirable. You need a tweeter in the treble and =
a
woofer in the bass. Their response characteristics are not -- should not =
be --
similar.</FONT></DIV>
<DIV dir=ltr><FONT face="Comic Sans MS" =
color=#000080></FONT> </DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px">
<DIV>Fenner goes on to say then that Junghann further states that for =
this
same reason the bridge had to be fitted to the crown of the =
soundboard, and
that this is contadictory to what is found in older texts, and he =
(Fenner, I
believe) agrees with the older texts. </DIV></BLOCKQUOTE>
<DIV dir=ltr><FONT face="Comic Sans MS" color=#000080>And =
my bridges will
still go on flat.</FONT></DIV>
<DIV><FONT face="Comic Sans MS" color=#000080></FONT> </DIV>
<DIV><FONT face="Comic Sans MS" color=#000080>Del</FONT></DIV>
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