Stephen Birkett wrote: > .... 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. > > 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. > > >... 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? > > 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 -------------------------------------------------------------- Stephen, In a pure compression-crowned soundboard, the ribs actually resist crowning. That is one of the reasons why ribs on these boards tend to be a bit wider than they are tall. Whatever their shape, they would really prefer to remain flat. So, if the ribs are not supporting crown, what is? As Sherlock Holmes would say, "Once you have eliminated the impossible, whatever remains, no matter how improbable, must be the solution." About the "pre-cracked" soundboard: I worked on one of these a few years ago, although it was not in a Steinway. In this particular case the crown was machined into the ribs. It wouldn't have to be though. It would be quite possible to "compression-crown" an assembly even if the panel was not "solid." It might put a bit of additional strain on the wood fiber and on the glue joints, but it would crown. Assuming that the wood strips were dry enough when the ribs were glued on, that is. Del
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