Soundboard tension & compression

[Richard Brekne]

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Delwin D Fandrich wrote:


>            Richard Brekne writes:
>
>      And I just KNEW this was exactly where things
>      were going to happen. I guess thats a positive
>      sign anyways.. :) It seems obvious that all the
>      confusion, or dissagreement, or whatever it is,
>      is centered right at this exact bit here... the
>      presumed tension in the outside of the panel.
>      The confusion starts exactly the moment we
>      release the assembly from the caul then. Until
>      that point, everyone seems to be in aggreement
>      that there in tension in ribs (panel side) and
>      outside of the panel itself, and compression on
>      the inside of the panel.
>
>      What is not clear is WHY, (i.e. what the
>      mechanisim is and how it works)  the tension in
>      the ouside of the panel somehow reverses to
>      compression when the panel is released from the
>      caul. One is quite liable to think that whatever
>      tension was there would simply be halved
>      (assuming the assembly returns aproximately half
>      way to its origional flat state). Actually, one
>      could be tempted to think that this was the
>      whole point of the process... to pre-tense as it
>      were, the outside of the panel so it could take
>      on crown without so much compression.  And if
>      one DID assume that, then the rest of the logic
>      that follows would seem to make perfect sense.
>
> Well, Richard, it may not be clear to you but it is to
> many, if not most others. I should hope very few would
> actually tempted to believe that whatever exceedingly
> slight tension the top of the panel started out with would
> simply be halved. You're off considerably on the scale of
> the various movements involved. There must be compression
> -- quite a lot of it -- to hold the ribs in a crowned
> condition.
>
>

Well, gotta admit Del, the halved thing just came straight
from an assumption from this text of Junnhann, which
evidently is not held in much esteem by any of the
contemporary designers. But then I should think that many
would actually draw this conclusion without knowing more
about the subject. You say yourself how many tears you have
shed over the level of knowledge folks have coming out of
woodworking schools. And you mention your own experiences
with many others getting confused on exactly this point.
But, you've got me finnally jagged on reading up on this
subject matter too, so as I said in my last post I have my
Christmas reading cut out for me.


> I keep telling you that it would do you some good for you
> to devise little experiments to illustrate these things
> but you seem some averse to this approach. So, I've done
> it for you. But the file is some 3.5 or MB large (there
> are a couple of pictures). If you're interested I'll send
> it on.
>
>

No nono... I'm not adverse to it at all... just so many
hours in a day as I am sure you know, and I simply have to
spend at least a couple in the evening relaxing in front of
my puter... and believe me it has done me tons of good
reading and corresponding with you all these past years...
tho to be sure much remains (and always will) to be learned.
I would love the file and appreciate your efforts more then
perhaps I am able to convey. And, now that I have gotten a
few "biggies"  on my personal goals list out of the way this
past couple years,  I certainly promise to carry out a few
experiments in wood working this comming year. I have DSL
lines so  3.5 MB is not a problem.

>
> Regards,
>
> Del

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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