RC vs CC again

[gordon stelter]

Hi Terry,
    Just to confuse things more: Let's not forget that
the rim will change dimension with humidity swings,
and eventually deform somewhat:
     And getting back to the "War of the Orifice"
which occured here about a year ago ( "Does a tuning
pin hole narrow, or widen, with increased humidity?" )
     How about the case itself??? Does it offer more
resistance to the soundboard's outward push under high
humidity, or flee from it? What about in the Southern
Hemisphere ?????
     Inquiring minds want to know....
     Thump

 --- Richard Brekne <Richard.Brekne@grieg.uib.no>
wrote:
> 
> 
> Farrell wrote:
> 
> > I don't deny for a moment that I may be missing
> the ball here entirely
> > - I'm really just trying to kick this around, I
> think much like
> > yourself. That being said ...... When you have a
> CC soundboard with no
> > load on it, the rib is stressed in that it is
> trying to straighten out
> > at all times. The panel is compressed - that is
> what makes the rib
> > bend, panel compression. When a load is applied to
> the top of the
> > soundboard downward, the panel compresses more and
> the rib is returned
> > to a state closer to straight and thus lessens
> stress on the rib.
> 
> Hmm.. I think we need to take a closer look at just
> whats happening
> where with this  "When a load is applied to the top
> of the soundboard
> downward, the panel compresses more"  bit. Why does
> it compress more ??
> Because there is something holding it in place...
> namely the ribs.  If
> the panels concave side becomes more compressed...
> then the convex side
> of the ribs simply MUST be experiencing more tension
> from the panel...
> its the other side of the same coin.
> 
> Its easy to see this exact thing happening when
> crown is formed to begin
> with... panel expansion stresses the top side of the
> ribs... causeing
> compression in the bottom half (at least) of the
> panel and tension in
> the top of ribs.... why should it be any different
> when downbearing is
> applied ?
> 
> Pushing the panel flatter increases all  the
> stresses involved... not
> just the half the the panel posseses.
> 
> 
> >  I don't understand the logic of "...the underside
> of the panel will
> > want to expand when down bearing is applied...".
> What leads you to
> > that conclusion? Why would the underside of the
> panel want to expand?
> > The entire thickness of the panel would compress I
> should think.
> 
> It is the same logic that always applies to a bent
> peice of wood. Just
> because its bent one way or another doesnt change
> that the convex side
> is stretched compared to the convex side. Since we
> are dealing with a CC
> crowned soundboard, its probably more correct to say
> that the Convex
> side is less compressed then the convex side... but
> the basic picture
> remains the same... and when you press down on the
> panel...then this
> condition will want to reverse. The downward
> pressure will put a
> compressing stress on the convex side of the panel,
> and tensioning
> stress on the concave side of the panel.
> 
> Since the ribs resist this tensioning force, The
> state of overall state
> of compression in the panel will no doubt increase
> as you point out...
> but exactly because that happens... the ribs must be
> being met with a
> stretching force from the underside of the panel.
> 
> 
> 
> > Maybe I'm all wet here, but that's what makes
> sense to me. Anyone else
> > care to chime in? Terry Farrell
> 
> Well...grin.. I shore dont know whos all wet...
> doesnt really matter...
> all that matters to me is that in the end I get to
> understand whats
> what. Besides !!.. the journey is kinda fun... that
> is if you ask me.
> 
> Cheers.
> 
> 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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