Respectfully, Ron, these are two separate points, are they not? Yes, a soundboard ( when built ) MAY support a full load without a rim. And this, I am willing to believe, can be amply demonstrated in the shop. But to presume that a board with no rim holding it inward would resist the downward pressure of strings, replete with climate variations, OVER TIME is just that -- a presumption. Unless, of course, you have already built a board, laid it on a table ( preferably with a concavity beneath ) and observed its deterioration over DECADES! And then compared it to an identicle board mounted in a rim. Respectfully, Thump --- Farrell <mfarrel2@tampabay.rr.com> wrote: > Ron N wrote: > > 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. > > Some ribs. ;-) > > > as is easily demonstrated that a > > soundboard assembly has crown, and will support a > full load without being > > anywhere near a rim. > > Excellent point. So simple, but I had never thought > to present this concept in these terms - but that's > it - you can load a board (positive crowned) > un-attached to any rim and it will have all the > support it will ever have. I've done this, just > playing with all these new things I am building, and > it's quite amazing!!! > > I think folks fall into this mental image of a 1 > meter radius domed structure attached at the edges > to a rigid rim. In such a case I am sure the rim may > well be some significant contributor to support of > the dome. But with the 2 mm to 10 mm (or whatever) > crown one may find in a soundboard, 99% of the crown > support is going to come from the ribs on a rib > crowned assembly or from the panel (at least for a > while - hopefully until it is sold) on a > compression-crowned soundboard assembly. > > Terry Farrell > > ----- Original Message ----- > From: "Ron Nossaman" <RNossaman@cox.net> > To: <oleg-i@noos.fr>; "Pianotech" > <pianotech@ptg.org> > Sent: Monday, July 21, 2003 10:15 AM > Subject: RE: soundboardinstal again > > > > > > >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 > _______________________________________________ > pianotech list info: https://www.moypiano.com/resources/#archives __________________________________ Do you Yahoo!? Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com
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