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 > > > _______________________________________________ > pianotech list info: https://www.moypiano.com/resources/#archives > >
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