Well, if it's not Gertz's invention, why do so many ( all? ) old M&H's still sound like rolling thunder when the board is riddled with cracks and the whole thing is a dilapidated mess? Thump --- Phillip Ford <fordpiano@earthlink.net> wrote: > >All, > > > >Back in 1900, if the patents-office examiner had > been paying attention, > >Richard Gertz never would have got his patent. The > sound board of a real > >world piano does not push outward as downbearing is > applied. While the > >sound board shown in the piano diagram at Mason and > Hamlin's website > >(http://www.masonhamlin.com/crown/crown.html) might > push outwards, real > >pianos do not have the sound board ribs offset > higher than the cord-line > >as shown in their image (a jpeg conversion of the > M&H website image is > >shown below). > > Ron, > > Would you explain what you mean by the cord line? > > >... > >So yes, a substantial back beam configuration is a > good thing, but the > >Richard Gertz 'crown retention system' will be of > virtually zero assistance. > > > >Ron O. > > Unless it works in both directions, in which case > it's essentially doing > the same job as the back beams. It's not clear that > it does from the > diagrams on the M-H site (which diagrams are hard to > read, BTW, since they > chose to use red lettering on a black background). > I don't know if those > long bolts are a press fit in the holes in the rim > or not. There certainly > seems to be a gap between the bolt head and the > outer rim which would seem > at first glance to allow the bolt to move outward, > offering no resistance > to the inward movement of the rim. On older M-H > pianos the rods were > attached to tapered plugs in the inner rim which > were captive by the outer > rim. You can see drawings of this on the patent, > No. 783,781. I believe > that this assembly would form quite a rigid frame. > Those rods may look > insubstantial next to the large softwood beams > beneath them, but because > they are steel, each of them provides the stiffness > of a large softwood > beam. Assuming a 20 mm diameter rod and a modulus > for softwood of 10 GPa > and steel of 200 GPa, then each rod is equivalent to > a softwood beam of 63 cm^2. > Bump the rod up to 25 mm and it's equivalent to a > softwood beam of > 98 cm^2 (15.2 in^2 - roughly a 2.5 in. x 6 in. > beam), which I would > consider a fairly massive beam. It's my feeling > that if this device were > properly designed, then the wooden frame members > would be superfluous. A > property of the steel is that it is consistent in > strength and stiffness, > which is not the case with the softwood (for those > that value consistency > from piano to piano). A downside may be that this > type of frame would be > more expensive and heavier than the softwood frame, > but I wouldn't think > significantly so. Also, the centerline or line of > action of the 'spider' > could be closer to the centerline of the soundboard, > since the spider needs > less physical space. On the other hand, because it > has less vertical > depth, it's probably not very good at resisting > twisting of the rim, the > way a 15 cm deep beam would be. > > Looking at the M-H page that you mentioned I also > noticed a couple of other > things that I hadn't noticed before. They're > expecting not only the rim to > act against the soundboard panel to resist board > flattening, but the rim > acting on the end grain of the ribs to resist > flattening of the > board. They also make a point of mentioning that > the grain of the ribs is > perpendicular to the grain of the rim. I'm not sure > why they think that's > important, and I'm not sure how that can be the case > unless the ribs were > at 90 degrees to the rim at the points where they > intersect the rim, which > is almost never the case. They also seem to think > that white spruce is > stronger than Sitka spruce. > > Phil Ford > > > > > Phillip Ford > Piano Service and Restoration > San Francisco, CA > _______________________________________________ > pianotech list info: > https://www.moypiano.com/resources/#archives > __________________________________ Do you Yahoo!? Take Yahoo! Mail with you! Get it on your mobile phone. http://mobile.yahoo.com/maildemo
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