Delwin D Fandrich wrote: > > It's probably not covered at all in "the literature." Who writes the > literature? Historically it's been the folks who get in there and design or > build the pianos. I expect then, like now, they pretty much dealt with the > more-or-less practical and the more-or-less reasonable. At least as it > seemed to them at the time. > Oh... its just that this ribs supply no support argument was being based on published knowledge like Hoadly's book... I thought. Not just a piano builders experience. > > > > I do have an experiement in mind tho... that should tell me just how much > >(if at all)I can expect the rib to be elongated. I'll take a few pictures > and post > > them when I get it together. > > We're waiting on pins and needles.... > Grin.. I doubt that... but I am interested... and hey.. its you who encourages us to experiements. I thought you'd be pleased. > > See... what I dont get is why the ribs are simply being treated as if they > were > > just being bent, yet the soundboard is treated as being bent AND stressed > > horizontally. > > I don't treat the soundboard as if it is bent and stressed horizontally. > Across-grain the soundboard panel has so little stiffness it can reasonably > be ignored as a practical force. It's not until it is shrunk down and glued > to the ribs and allowed to attempt to swell up again that the assembly > takes on the additional stiffness contributed by the resulting crown. The > components assembled together take on properties none of them have > individually. > I meant by "bent and stressed horizontally" horizontal stress from the ribs restricting the panel in swelling leading to crown. In anycase... these two things happen to the panel, yet for some reason the rib is just being bent... just as I could bend it in my hands. What happened to the tension on the rib ?... does it all go into simply bending the rib ?? > > The only real difference is the direction of the grain. > > This is a pretty significant difference! Well sure... but it doesnt change the amount of stress aplied to the rib/panel interface... on both the rib and panel equally. > > > > ...If one can declare the compresion in the soundboard is > > what supports crown, then why is any tension in the ribs not doing the > same > > thing ? Its just two sides of the same coin... or what ??? > > Because by themselves the ribs want to lie flat. Coupled with an expanding > soundboard panel they are physically bent out of their equilibrium > configuration and they want to get back to that configuration. They are > going to fight being bent every step of the way. The soundboard panel is > also trying to reach equilibrium -- that equilibrium determined by its > changing moisture content. It is being restrained by the ribs. It is only > the effort of the soundboard panel to reach equilibrium that is forcing in > the crown. > I see this much... I just dont see why the reverse is not also true, i.e. ---- The panel wants to lie flat, coupled with a restricting rib it is physically bent out of its equilibrium configuration and wants to return to that configuration. It is going to fight being bent every step of the way. The ribs are also trying to remain at equilibrium ... that equilibrium being determined by the changing moisture content of the panel. They are prevented in this by the panel. It is only the resistance by ribs to the panels expansion that forces crown.... ... actually...I dont see why its not working both ways. Sigh... no need to persue it further tho... obviously I just need to think it through more to see the sense in what you are saying. I'm not really trying to argue with you here... just attempting to illustrate where I am confused. Thanks for your thoughts Del RicB > Del -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway mailto:rbrekne@broadpark.no http://home.broadpark.no/~rbrekne/ricmain.html http://www.hf.uib.no/grieg/personer/cv_RB.html
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