RC vs CC again

[Delwin D Fandrich]

----- Original Message ----- 
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: October 07, 2003 9:55 AM
Subject: Re: RC vs CC again


> >
> Let me ask you this... say the panel was steam bent into permant curved
shape
> instead of "crowned" per se.... same shape tho.. no drying out of the
panel.. .
> THEN you glue these same flat ribs into place. Now THERE I can see the
ribs
> doing nothing more then pulling down on the board. I can see them
willingly
> helping any downbearing because there is no stress in the interface
between the
> wood and rib that goes the other direction.

Have you ever picked up an un-ribbed soundboard panel? Steam bending would
be a meaningless gesture. You couldn't steam-bend the thing in any way that
would create enough cross-grain stiffness to pull the ribs into any kind of
bend. No, it is only the combination of a deliberately shrunken panel
creating a stress-interface between itself and the ribs as it un-shrinks
itself that creates the crown. Without that stress interface you simply
have a flat rib/panel configuration.

To better visualize what the rib is actually wanting to do all this time,
go back to that little experiment I described and carefully remove the
cross-grain portion of your sandwich. What happens to the longitudinal
piece, i.e., the rib? It does exactly what it has wanted to do all along -- 
it returns to it's rest (or flat) configuration, doesn't it? Now, what on
earth makes you think it wasn't wanting to do that all the time? Why would
the wood fibers suddenly lose their memory just because they get pulled out
of equilibrium by the expanding cross-grain panel and the resulting
stress-interface? Wood technology doesn't change just because some of us
don't want to acknowledge its rules. For the time your sandwich was being
held in a crown by the stress-interface between the longitudinal rib and
the cross-grain top piece do you suppose it somehow -- miraculously -- lost
its desire to get itself straightened out? I can't conceive how. That bent
rib is a spring, what are its lines of force?

Ponder this stuff as you will, I'll get excited when I see how these
hypothetical questions actually provide meaningful information that will
help me design a better sounding soundboard system and a better sounding
piano. Right now, however, I can't conceive how they will.

Del