Soundboard question

[David Love]

I would seriously question whether a controlled "compression set" is
possible.  Compression set implies damage to the panel at the cellular
level.  Whether, to what degree and where in the panel that it experiences
compression set is idiosyncratic and will depend to a large degree on the
specific characteristics of each one of the flitches that make up the entire
panel.  Also, damage to the wood panel at the cellular level doesn't mean
that the panel will be less reactive to changes in RH.  The wood will still
take on and lose moisture.  Even if it did, introducing compression set
uniformly across the board would not be possible.  The panel may lose its
ability to expand against the forces that otherwise constrict it such as the
force of the bent ribs or the downbearing, but why you would want to
purposefully cause that type of damage so as to simply weaken the structure?
I can't think of any good reason to begin the process which ultimately leads
to panel failure in advance.  There's plenty of time for that later :-).  As
far as I'm concerned, the idea is to avoid damage to the panel and create
greater stability by reducing the potential for compression set with, at
least, a hybrid design of ribs with a preformed radius and a lower EMC
during the ribbing process or a completely rib supported structure with
virtually no compression crowing at all. 

David Love
davidlovepianos at comcast.net 
www.davidlovepianos.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Richard Brekne
Sent: Tuesday, August 19, 2008 10:17 AM
To: pianotech at ptg.org
Subject: Soundboard question

I didnt say that was what compression set was. I said (in question 
format) that it was my understanding that reduced reactiveness to RH 
swings was one consequence of compression set. In any case, a controlled 
compression set is certainly quite doable.

Cheers
RicB


    Why would forcing a controlled 25% compression set (even if it were
    possible) reduce the tendency for the board to expand and contract
    with humidity changes?  That's not what compression set is.

    David Love