Soundboard 60-ft. Arc

[Greg Newell]

Terry,
    I'm looking through some posts from the last weeks and I'm wondering if I
might be able to see these drawing you're talking about.

Greg

Farrell wrote:

> 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

--
Greg Newell
mailto:gnewell@ameritech.net