----- Original Message ----- [link redacted at request of site owner - Jul 25, 2015] To: "Pianotech" <pianotech@ptg.org> Sent: Sunday, April 13, 2003 2:23 PM Subject: Re: Killer Octave Question > Del, > > I think we were talking about the crown of the bridges not the ribs. > > John Well, both I should think. If a particular soundboard assembly looses whatever initial crown it had rather quickly how could its attached bridge end up with any crown, whether real or hypothetical, via compression set? To take on compression set a wood member has to have some strain--it has to be physically bent. Most, but not all, purely compression-crowned soundboards do lose their initial crown rather rapidly. So in most cases the bridges would not be forced into any kind of curve long enough to become bent by the action of compression set. There are exceptions, however. Occasionally we encounter a soundboard in an older piano of a make that we know was originally compression-crowned and that still does have adequate, if not great, residual crown. My post was simply an explanation of how this could happen. And why we might see the phenomena in some instruments and not in others even though they were ostensibly built the same way. Personally, I don't see how we can tell if the long bridge was originally crowned or not. It is not apparent from height measurements--if the bridge was hand-planed to height in the piano after the piano was bellied then bridge height is a function of many disparate variables and is no longer a reliable indicator. Neither is a visual examination. Most of the old bridges I've removed are all curved--I've never done a Banana Piano--and when I lay them on a table they exhibit all kinds of odd and inconsistent curves and twists. Even including those from relatively recent Baldwin pianos that I know were milled dead flat prior to installation. Incidentally, these dead flat bridges conform rather nicely to the crowned soundboard as they are glued on, neither impeding nor assisting soundboard crown. Del
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