Okay got it. I thought the rim, though strong, was flexing enough to effect crown and bearing due to the immense pressure from the strings. On Thu, Dec 31, 2009 at 10:54 AM, Ron Nossaman <rnossaman at cox.net> wrote: > Noah Frere wrote: > >> I find this confusing because I would have assumed that as soon as the >> soundboard starts pulling away from the strings, and negative bearing sets >> in, then the strings would be /pushing/ the soundboard down further, rather >> than pulling up. >> > > I don't see how. Positive bearing is what supplies down pressure. Negative > bearing would pull up. The string is under tension and trying to maintain a > straight line between capo and aliquot (or whatever). > > > > I imagine it this way: imagine a tunpperware container with a lid that's >> slightly convex - you push the sides together and it forces the lid up >> higher. (the equivalent of putting on strings). >> > > No. Putting on strings, assuming positive bearing, will push the board > down, not raise it up, and the rim has nothing to do with it. > > > > Now take the pressure off the container and push the lid down just enough >> to make it concave, reapply pressure, and the lid will continue its downward >> path. >> > > Again, you're manipulating the perimeter, which in a piano would be the > rim. The rim has virtually nothing to do with crown formation or support in > a piano. > > > > Visually this description reminds us of the soundboard, but i mean to >> apply it to downbearing. >> > > Then where is the downbearing in your illustration? There is none. > > > > That is, no matter which direction the crown is facing, the tupperware lid >> represents the board/bridges as a whole. However, being neither a >> physicist nor a rebuilder, i must have it wrong, >> > > Yes, wrong. <G> > Ron N > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20091231/46191c80/attachment.htm>
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