Soundboard tension & compression

[Richard Brekne]

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