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 From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of David Love Sent: Thursday, June 23, 2011 6:52 PM To: pianotech at ptg.org Subject: Re: [pianotech] Soundboard Analysis They do? The change in distance from the struts to the bridge when I let off tension corresponded pretty well with the change in downbearing. In other words, the soundboard moved up, the plate didn’t. 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 3:06 PM To: pianotech at ptg.org Subject: Re: [pianotech] Soundboard Analysis Now, that’s an explanation further worth exploring. The plate struts certainly rise when tension is added. Some struts have nose bolts to restrain that upward movement, others don’t. Next time you teardown a piano David, measure that upward or downward movement at the same time you are taking your bearing and crown readings. I think it is a better explaination than the one I offered. Will Truitt From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Albert Picknell Sent: Thursday, June 23, 2011 5:21 PM To: pianotech at ptg.org Subject: Re: [pianotech] Soundboard Analysis --- On Thu, 6/23/11, David Love <davidlovepianos at comcast.net> wrote: When I took pressure off the board by letting down the tension and saw an increase in bearing (soundboard rise) and a change in the distance between the bridge and the struts (which I didn’t include below), and then crawled under to check the crown it was still not positive. *************** The plate drops when you let off tension. Because the string plane is below the plate struts, the struts rise when you put tension on the strings, and drop when you release that tension. It's like stringing/destringing a bow. This would at least partially account for the increase in bearing, as well as the decrease in the distance between the bridge and the plate struts. Cheers, Bert -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://www.moypiano.com/ptg/pianotech.php/attachments/20110623/0de197e9/attachment.htm>
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