Soundboard tension & compression

[Tony Caught]

Hi Rick

 > Is what you wrote.  >> indicate what Del wrote. >>> indicate what you
wrote to Del.     Indicate what I write. Then when you resend.    Is what
you wrote. > Is what I wrote. etc

If the panel was secured at  cross grain edges then dried out by 8% moisture
content, you would then have two panels.

Regards

Tony Caught
Darwin Australia
caute@bigpond.com


----- Original Message -----
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: Wednesday, November 27, 2002 8:45 AM
Subject: Re: Soundboard tension & compression


> Delwin D Fandrich wrote:
>
> >
> > >
> > > WHAT IF ??... you took a panel at 12 % MC and secured its
> > > cross grain edges so they couldnt budge... and then dried it
> > > out to 4% MC.... and proceed back down that bunny trail ?...
> > > just for edification mind you :)
> > >
> > > Cheers
> > >
> > > RicB
> > >
> >
> > You figure it out. It will assist in the edification process and the
numbers
> > are readily available. The amount of wood fiber shrinkage that would
take
> > place, the relative weakness of spruce/pine under tension cross-grain,
etc.
> > Wood Technology 101.
> >
> > Del
> >
>
> Well, assuming wood reacts basically the same (but opposite) when tensed
thus, I
> would imagine you'd put the panel under about 1.5 to 2 % internal tension.
And I
> would suppose that this would be just as much over the safety line as it
would
> be for similiar compression levels. That being said you'd only leave it
this way
> for just a short while so'st you can get the ribs clued on. Ok so you glue
flat
> ribs on with the panel in this state, let cure and pop out of the device
> restaining the cross grain edges and what happens... ? I'm not really
sure...  I
> would imagine the panel would try to de-tense, and the ribs would fight
that,
> and there would be a slight tendency towards reverse crown. But then just
how
> much I dont know because the panel has been "stretch dried" as it were,
and as
> long as the humidity is the same then.... ??  Allowing it to take on
humidity
> back up to 12 % MC... the panel would crown as usual and seemingly end up
in a
> state of neither compression or tension...
>
> Now I just KNOW that has got to be wrong.... but I also know I wouldnt be
alone
> in reasoning thus. So lets have the real story :)
>
> Cheers
>
> RicB
>
>
>
> --
> Richard Brekne
> RPT, N.P.T.F.
> UiB, Bergen, Norway
> mailto:rbrekne@broadpark.no
> http://home.broadpark.no/~rbrekne/ricmain.html
>
>
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