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<DIV class=OutlookMessageHeader dir=ltr align=left><FONT =
face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> =
pianotech-bounces@ptg.org
[mailto:pianotech-bounces@ptg.org]<B>On Behalf Of </B>Richard
Brekne<BR><B>Sent:</B> February 04, 2004 1:46 PM<BR><B>To:</B>
Pianotech<BR><B>Subject:</B> Re: Soundboard
stiffening<BR><BR></FONT></DIV>Delwin D Fandrich wrote:<BR>
<BLOCKQUOTE =
cite=midNCBBLPIFHEMDJHENPLOAAENICHAA.fandrich@pianobuilders.com
type="cite">
<BLOCKQUOTE type="cite"><PRE wrap="">Now, wait a minute here. =
Who said "the ribs are doing nothing but trying to
straighten out the panel."? With or without crown, and regardless of how
crown is obtained, the ribs are going to add stiffness to the assembly. =
That
does not preclude their resisting being bent in the compression-crowned
soundboard assembly.
</PRE></BLOCKQUOTE></BLOCKQUOTE>
<DIV>You guys do ! And quite frequently. Ok...in the context of =
rib
supporting crown. But forgive me... I am a bit foggy on how it is that =
ribs
that in that context do nothing but resist crown and offer no support =
against
downbearing, can at the same time not only make the panel stiffer =
(which makes
it harder to press down.. hmmmm ) and not only that but makes the =
system
increasingly stiffer (even harder to press down) as more downbearing =
is
applied.<SPAN class=171045715-05022004><FONT face="Comic Sans MS"
color=#0000ff> </FONT></SPAN></DIV><FONT face="Comic Sans MS" =
color=#0000ff></FONT>
<DIV><BR>I am just sure I am crossing Z's with Ø's here... but these =
two
positions seem a bit contridictorary to me.<BR><SPAN
class=171045715-05022004><FONT face="Comic Sans MS"
color=#0000ff> </FONT></SPAN></DIV></BLOCKQUOTE>
<DIV><SPAN class=171045715-05022004><FONT face="Comic Sans MS"
color=#0000ff>So, let's see. We're not only supposed to figure =
out how to
explain a principle in words you can't possibly dissect and render
other, unintended meanings to but we're also supposed to figure out =
how
to do this in a way you can't possibly take out of context and =
render
other, unintended meanings to. OK. I think I've got it. Of course, =
you
realize that does limit both the ability and the desire to communicate =
with
you.</FONT></SPAN></DIV>
<DIV><SPAN class=171045715-05022004></SPAN> </DIV>
<DIV><SPAN class=171045715-05022004><FONT face="Comic Sans MS" =
color=#0000ff>No.
there are not two positions. There is one unified theory of operation =
and it
contains no contradictions. The whole system works
together. </FONT> <FONT face="Comic Sans MS" =
color=#0000ff>Think of it
as having more than one thing going on =
simultaneously.</FONT></SPAN><BR><SPAN
class=171045715-05022004><FONT face="Comic Sans MS"
color=#0000ff> </FONT></SPAN></DIV>
<DIV><SPAN class=171045715-05022004> </SPAN></DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px =
solid">
<BLOCKQUOTE =
cite=midNCBBLPIFHEMDJHENPLOAAENICHAA.fandrich@pianobuilders.com
type="cite"><PRE wrap="">No one talks about "the panel trying to =
straighten out the ribs" because it
doesn't work that way. Have you ever handled an edge-glued spruce panel?
Sure you have. Just how much straightening is that thing going to do?
</PRE></BLOCKQUOTE>
<DIV>What I see is two pieces of wood that are forced into a curved =
condition
against their better judgement... and both... would return to being =
flat if
they had their ditthers about it. Why would the rib be pulling =
on the
panel to straighten it out, and not the other way around in equal
amounts?</DIV></BLOCKQUOTE>
<DIV><SPAN class=171045715-05022004><FONT face="Comic Sans MS" =
color=#0000ff>Oh,
think about it! Because the rib, longitudinally, is quite stiff and =
resists
being bent with some vigor. And the soundboard panel, cross-grain, is =
quite
flexible and bend readily. So readily, in fact, you have to handle it =
gently
until those nice, stiff ribs get glued on.</FONT></SPAN></DIV>
<DIV><SPAN class=171045715-05022004><FONT face="Comic Sans MS"
color=#0000ff></FONT></SPAN><BR> </DIV>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px =
solid">
<BLOCKQUOTE =
cite=midNCBBLPIFHEMDJHENPLOAAENICHAA.fandrich@pianobuilders.com
type="cite"><PRE wrap=""></PRE>
<BLOCKQUOTE type="cite"><PRE wrap="">I would suggest that the =
ribs are not bent simply because the panel is
taking on moisture... but because they are made to resist any panel
expansion at the interface between ribs and panel. It seems only half a
truth and one that easily leads to less then half truths to simply say
the ribs are bent by the panel, and do nothing more then resist crown.
</PRE></BLOCKQUOTE><PRE wrap=""><!---->
I think you're getting the idea. In the compression-crowned soundboard
assembly, the ribs are indeed bent because of the stress interface =
between
them -- they really don't like to stretch along their grain -- and the
expanding soundboard panel. (At least the panel would be expanding if it
were not constrained by the ribs glued to it.) And the panel is =
expanding
because it is taking on moisture. That is how a compression-crowned
soundboard assembly works.
</PRE></BLOCKQUOTE>
<DIV>Well heck there Del... this much has been clear all along... and =
of
course we dont want the ribs to actually strain along the grain... but =
that
doenst mean they dont feel the increase in stress in that direction. =
If they
strained or failed... then crown would disapear as well.<SPAN
class=171045715-05022004><FONT face="Comic Sans MS"
color=#0000ff> </FONT></SPAN></DIV></BLOCKQUOTE>
<DIV><SPAN class=171045715-05022004><FONT face="Comic Sans MS" =
color=#0000ff>Of
course the ribs are going to strain along the grain. At least a little =
bit. That
is a natural effect of the stress interface built up between the top =
surface of
the rib and the bottom surface of the soundboard panel in which we've =
created
some level of compression that we have glued together. As the soundboard =
panel
takes on moisture and tries to expand it forces the top of the rib to =
stretch
slightly. Simultaneously the bottom of the rib to compress =
slightly. This
is what happens when you force a bend into an otherwise straight piece =
of wood.
And being strained in this way it wants very much to return to its =
neutral
state. So it pulls against the crown. Continually. That pull is resisted =
by its
being glued to the soundboard panel. The rib does not have to fail for =
crown to
dissipate, all it takes is for there to be a loss of compression within =
the
soundboard panel. At which point the rib returns to its neutral position =
(which
is what it was trying to do all along) and is no longer
strained.</FONT></SPAN></DIV>
<DIV><SPAN class=171045715-05022004><FONT face="Comic Sans MS"
color=#0000ff></FONT></SPAN> </DIV>
<DIV><SPAN class=171045715-05022004><FONT face="Comic Sans MS"
color=#0000ff>Del</FONT></SPAN></DIV></BODY></HTML>