They certainly will want to bow up if not restrained. I came to tune a Steinway where the nose bolt had not been tightened. I happened to notice and when I did tighten it the plate pulled down some and the pitch went sharp. How much they flex when properly restrained I don’t know but it doesn’t seem like much. Were the plate to flex upward when you add tension then I would guess that the bearing changes anticipated with the calculated deflection characteristics of the soundboard would not hold. On the boards that I’ve built, they seem to. In addition, you would expect to see some change in the string heights, but you don’t. At least, if there’s any flexing of the plate up and down, it seems to be negligible. At any rate, to the question on which this supposition was made, I think it’s safe to say that the issue was soundboard rise and negative crown to begin with. That was verified by the change in measured crown in certain sections of the piano accompanied by similar changes with respect to the distance between the bridge and struts. The relationship seemed to be 1:1 according to my low tech measuring device. That suggests little if any contribution of plate flexing. On the other hand, when you add 40,000 lbs to a structure like that something is probably moving somewhere. Occam’s Razor, the best answer is usually the simplest one. Didn’t really mean to drive the discussion onto this tangent. The main point of the exercise was to look at the map of a soundboard that needs to be changed. The more important questions to ask are: What would be the minimum readings required in order to declare the board usable? With those minimum requirements what kinds of compromises would you have to make? How much downbearing is required and how much soundboard deflection do you need to provide adequate amounts of potential energy to the system. Which input might you have to change to get the system back in balance and produce an acceptable tone if two of the components are out of balance? What can you expect in terms of tone production as compared with the piano in its original condition. Those are the questions that one should be asking before you restring over a compromised but, perhaps, usable soundboard—at least, in my humble opinion David Love www.davidlovepianos.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Encore Pianos Sent: Thursday, June 23, 2011 5:04 PM To: pianotech at ptg.org Subject: Re: [pianotech] Soundboard Analysis On a Mason & Hamlin A a couple of years ago I had a nose bolt mounting block coming unglued from the beam and had to make a repair. The piano was strung and I was hoping to make the repair without letting down the tension. So I made a jig whereby I could restrain the upward movement of the plate strut when I loosened the nose bolt. I was able to observe and measure the strut rise as I loosened the nose bolt and the strut followed, until I engaged the restraint of its further movement. (I was able to break loose the mounting block and remove it, bolt and all). So I think it is reasonable to surmise that the plate will bow upward as tension is added to the strings, and relax that bend as tension is removed. If a nose bolt is very near the point of measure from the bridge top to the underside of the plate strut, then there would likely be little or no movement in your setting. If there is no nose bolt or it is some distance from the bridge, and the strut is long enough, then I would believe that there would be some bowing. How much would be a reflection of how substantial the plate struts in relation to the load they are carrying. But you could devise a way of measuring so that you could tell if it was occurring in your piano and quantify it in relationship to the bearing values and crown measurements. Will -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://www.moypiano.com/ptg/pianotech.php/attachments/20110623/a43f8535/attachment.htm>
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