> On a five-foot span I get 0.63 inches of crown. >This seems excessive (isn't an unstressed new board supposed to have about >1/4" - 3/8" of crown in the middle?). Your crown height for 60' radius is right by my figures, but how long a rib do you plan on having in a piano? That's what cutoff bars are for. The compression crowned boards ended up averaging about XX crown at XX length (varying widely with material choice and methods) as a consequence of the crowning process rather than a design criteria. With rib crowning, you are granted the opportunity to make your own decision and build to a much closer spec. It's supposed to be whatever you find works to your satisfaction with all the other dozens of factors considered in your soundboard design, string scaling, bridge configuration, loading, etc. Nor is it particularly necessary or (to some builders) desirable to have the same crown radius throughout the rib scale. >Or is it that on the rib-crowned >board, you cut the rib to the aforementioned arc, glue it to the board in a >caul of the same arc, and when removed from the caul the naturally flat >board help the assembly to straighten out a bit to where it has the >"?normal?" 1/4" - 3/8" of crown? Panels are still dried down before assembly in a rib crowned board, just not as much as with compression crowning, so the panel is still under some compression, and still helps support crown rather than dragging it back down. >Am I making a boo-boo somehow with my drawing? > >Terry Farrell Nope, but there are a few assumptions behind it that you need to decide whether or not to accept. <G> Ron N
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