----- Original Message ----- From: "jolly roger" <baldyam@sk.sympatico.ca> To: <pianotech@ptg.org> Sent: May 08, 2001 9:01 AM Subject: Re: Re: Spurlock shimming method. > > >I know what a buttress does, and the ribs are the constraining element. > >Once again, the assembly is crowned and will support a considerable load > >before it is ever put into the rim. The rim does not support crown - the > >ribs and panel compression do. > > > > Hi Ron. > Interesting hypothesis, you trying to say that there will be > no difference with the board supported at the perimeter, or not. > Well I suggest you put a 100lb weight in the centre of of an unsupported > board and measure the movement of crown, then do the same with the board > glued into the piano, and let us know the results. > Roger > --------------------------------------- I know, I know...I'm not Ron. But some time back when I was writing the original piece for the Journal I did just this. Actually, it was more like 230 lbs -- don't ask -- but the results were the same. I put the board in the piano loose -- i.e., without it being glued to the inner rim and loaded it. Then put it in with glue and loaded it again. The results were similar. I won't say exactly the same because of the difficulty of measuring and my unwillingness to spend a week setting up a more precise experiment. There are two problems with applying the Roman arch concept to the piano soundboard structure. The first is that the arch radius (i.e., crown radius) is much too large, especially after the soundboard bridge is loaded by applying a fairly substantial amount of string downforce. The second is that the material we use (wood) is not rigid enough to support crown in this manner. Even if there were some initial stiffening effect from the arch it would soon dissipate as the wood goes through its cold flow process. Regards,] Del
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