Ron: It looks like Mason & Hamlin did a fantastic marketing job with that little strip of spruce on the fixture with the business card! dave *********** REPLY SEPARATOR *********** On 7/21/2003 at 9:15 AM Ron Nossaman wrote: >>Ron, >> >>Me think (may be wrongly) that on the opposite, the fact that a so >>small dimension is involved show us the importance of a better joint >>(last news from the day !) > >It doesn't work that way. > > >>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. > >Again, it doesn't work that way. It's not tension you're putting in the >panel, it's compression. Modulus of elasticity and compression resistance >are not the same thing, and MOE is meaningless in this context. Soundboard >crown is still not an end supported arch, so buttressing the edges will >have no significant effect on the crown. In the example rib I used, of 36" >(915mm) and 60' (22M) radius, the outward thrust of the "arch" will be 40 >times the load it carries. This means that at 580psi fiber stress >proportional limit of cross grain compression of Sitka spruce, that rib >can >only hold up to 14.5 pounds load before the wood is crushed. It gets much >worse with shorter ribs. Once again, the rim has nearly nothing whatsoever >to do with the maintenance of crown, nor the retention of compression in >the panel. The ribs do that all by themselves. > >>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. > >Yes, I have also heard (or heard of) all sorts of folks saying all sorts >of >things. The physical fact is that this doesn't work. The physical >structural limits of the materials just don't make it possible. > > >>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 ? > >Yes, but it's not a view. It's a fact, as is easily demonstrated that a >soundboard assembly has crown, and will support a full load without being >anywhere near a rim. > >Ron N > >_______________________________________________ >pianotech list info: https://www.moypiano.com/resources/#archives **************** END MESSAGE FROM Ron Nossaman ********************* _____________________________ David M. Porritt dporritt@mail.smu.edu Meadows School of the Arts Southern Methodist University Dallas, TX 75275 _____________________________
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