Dear Pianogeometrical Wizzes: Greg Newell is causing me problems. He is making his first soundboard, and he caused me to lay awake half the night diagramming 60-foot arcs, fire-hose air clamps, clamping tables, etc. Geesh! Don't people ever think of the ramifications of their actions? Anyway, using my CAD program to draw some arcs for making rib clamping cauls, I drew an eight-foot long arc with a 60-foot radius (common arc for a soundboard). Looking at the crown of such an arc over an eight-foot span, I get 1.6 inches of crown. 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?). 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? Am I making a boo-boo somehow with my drawing? Terry Farrell
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