soundboardinstal again

[Danny Boddin]

Excuse me, what is the meaning of  the 'MOE' ?
Danny.
----- Original Message -----
From: "Delwin D Fandrich" <pianobuilders@olynet.com>
To: <oleg-i@noos.fr>; "Pianotech" <pianotech@ptg.org>
Sent: Monday, July 21, 2003 7:39 PM
Subject: Re: soundboardinstal again


>
> ----- Original Message -----
> From: "Isaac sur Noos" <oleg-i@noos.fr>
> To: "Pianotech" <pianotech@ptg.org>
> Sent: July 21, 2003 2:30 AM
> Subject: RE: soundboardinstal again
>
>
> >
> > The inserting under tension of the soundboard seem the only way to
> > have some tension in the panel, in the rib direction (across grain)
> > the modulus of elasticity is said to be 3 Kg cm2 vs. 100 Kg cm2 in
> > direction of grain.
> > So if we wish to have some tension in the panel that looks like a
> > convenient method, more than compression crowning.
>
> Do you mean tension as in "a pulling force, or stretching something
tight?"
> Or compression as in, "pressing together by an applied force?"
>
> Generally soundboard panels are under tension only after some period of
> having been subjected to compression-set and then finding themselves in a
> very dry environment.
>
>
> >
> > Stephen have forced back some boards with shims on the straight side
> > with good results he say, when we see the dimensions involved, that
> > looks like a possibility.
>
> The problem with this practice is that it works--but only very
temporarily.
> The physical structure of the wood we use for piano soundboards and ribs
is
> simply incapable of resisting the stresses created with these techniques.
> Entire theories have been built based on the assumption that wood is a
> perfectly rigid and non-compressible material. But it is not. Even along
> the grain it is a fairly readily compressible material.
>
> The mechanical characteristic involved here is actually compression
> parallel to grain, not the MOE. This value, for spruce (it varies with
each
> specific species) is approximately 5,600 psi to 6,000 psi (36 000 - 40 000
> kPa). This is not very much considering the small
> cross-section--approximately 0.25 in2 (160 mm2)--of the typical
> feathered-out rib end.
>
>
> >
> > The panel is said to be shaped with 1 cm more than the internal size
> > of the rim, was said. If possible a soundboard that should be pinched
> > in the rim should work better from an acoustical point of view (a very
> > good joke to future rebuilders !)
>
> A good joke on the builder as well, I think. Make a sketch of a grand
piano
> rim, sketch in the ribs and the soundboard grain angle and then think
about
> the stresses involved with the proceedure you describe. Compare those
> stresses with the known physical qualities of wood and you'll see what I
> mean.
>
>
> >
> > Idem on the belly rail, while some brands have stopped the insertion
> > there (Seiler for instance).
> > But I seem to understand that in the actual conception in the USA the
> > soundboard assembly is viewed as an auto supported device is not it ?
>
> In the end they are all auto-supported devices regardless of how they were
> installed. A few years of compression-set insure this.
>
> Del
>
>
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