Compression Question

[Richard Brekne]

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Delwin D Fandrich wrote:

>
> > Do I understand correctly that the rib crowned board will sooner or later
> also
> > surcomb to more or less the same self destruction, but that essentially it
> will
> > just take much more time for it all to happen ?
>
> Sigh. It depends on the MC of the soundboard panel at the time it is
> ribbed. If it is 4%, yes, the panel will still self-destruct even if the
> ribs are crowned. But the system will still retain most of the crown that
> was machined (or otherwise put) into the ribs. If the MC of the panel was
> up around 6.5% or 7% when it is ribbed it will still be possible to damage
> the board by leaving the piano in a semi-truck trailer somewhere in
> Tennessee during a summer heat wave for two weeks (every day well above
> 100º F) while the driver goes on vacation but it is far less likely that
> the panel will be damaged during anything resembling normal climate
> conditions.
>
> Never is a long time and even wood beams stressed in thier longitudinal
> direction will undergo some creep or compression set. At least in theory.
> But, assuming a normal string load, after some initial settling it will not
> be all that noticable over the lifespan of the piano or its owner.
>
> Del

Just trying to put different things said in diffferent discussions into
perspective whilst reading Del.  A few days back you said

     "If the degree of compression is beyond what the wood can
     handle--i.e., it is stressed beyond its proportional limit--the wood
     fibers will crush immediately. If it is compression stressed below
     its proportional limit compression-set will work to reduce that
     compression stress slowly over some period of time. In both cases
     there will be forces at work to reduce compression, in the first
     situation it simply happens faster."

So.. given what you say above, am I to understand that a rib crowned board
ribbed when the panel is about 6.5 - 7 % MC will not suffer enough compression
set during its lifetime... say 30 - 50 years  , to cause any real compression /
compression related problems ?

RicB

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html


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