Hi Stephen. Please pardon the nested chevrons, I'm trying to provide a modicum of continuity. Comments wedged between. At 11:04 PM 1/3/98 -0500, you wrote: >Jim wrote (a while back): >> When one considers a piano soundboard with many splits and there is >> still downbearing, one might think that indeed the ribs are supporting >> the downward force of the string bearing. ... >> >I would say your analysis is absolutely correct here. The ribs provide >the upward force that balances static downward string forces. The panel >can be irrelevant...read on > Irrelevant, no, I don't believe that... read on. >> ... However, when one also >> considers the fact that as humidity increases, the soundboard rises and >> increases the tension on the strings, one might think that the board is >> the crown supporting member. It is well known that the ribs do not >> lengthen any to speak of when the humidity increases, but the soundboard >> certainly does swell and rise with humidity increases.... >> >Agreed again, but the panel simply forces the ribs to take on a different >shape. The forces involved in differential wood movement are sufficient >to allow the technique to be used for stone-masonry, pyramid building >etc. so it is understandable they can deform the shape of the ribs. This >doesn't mean the panel is "supporting" the crown though. > Given positive downbearing, if the crown was initially formed by gluing a thoroughly dried panel to straight ribs against a flat caul and letting rehydration of the panel bow the rib, then the panel is the ONLY thing supporting the crown (whatever crown there is), regardless of the cracks. If the panel was initially dried and glued to ribs with a crown machined into them, then the fact that the board moves with humidity proves that the panel is supporting at least a PORTION of the crown. In neither case is the panel even remotely irrelevant. >A small line of pianos that Steinway produced in the 1940s illustrates Jim >Snr's point to a tee. On these the boards were made with the individual >panels separated by a small distance, ca 2 mm, i.e. they were pre-cracked >along every glue-line. The boards behaved as normal boards do. >Unfortunately the line was short-lived, since the pianos were >un-saleable...they were deemed to be broken coming from the factory. > If you are saying that the panel is superfluous to maintenance of crown here, I disagree. The discontinuity of a soundboard panel along the length of the ribs (gaps, intentional or otherwise) does not mean that the ribs alone are supporting the crown. Again, the soundboards in these pianos would react to humidity swings very much like any other boards because most of the panel/rib relationship is functional. >>... Perhaps we can >> gain a little more insight from the harpsichord builders who have to >> work with much fewer ribs and funny wavey things that go on with the >> soundboards. >> >What are funny wavy things? Yea, by the way, what the heck are funny wavy things? And why do harpsichord builders get all the fun? > >Stephen > >Stephen Birkett Fortepianos >Authentic Reproductions of 18th and 19th Century Pianos >464 Winchester Drive >Waterloo, Ontario >Canada N2T 1K5 >tel: 519-885-2228 >email: birketts@wright.aps.uoguelph.ca > Now, a question or two for you. By what reasoning would a crack, cracks, or intentional gaps at what should be the glue joints mean that the crown is being supported solely by the ribs, instead of a combination of the ribs (stiffness, I'm talking about) and the compression in the panel? How is it possible for such a board to rise and fall with humidity swings unless the panel was part of the equation? If the panel is merely, as you said, "simply forcing the ribs to take on a different shape" instead of partially supporting the crown, what's the difference? We aim to serve... and volley. Ron Nossaman
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