Fanned ribs (was Soundboard grain angle)

[Ron Nossaman]

>Ron,
>Do your ribs fan out from a point on the bent side, like the ones shown on 
>the sketch
>sent out by Del a couple of days ago?  Why do you feel you get better 
>results with a
>fan arrangement rather than parallel ribs, varying their spacing and 
>properties?
>
>Phil F

Yes, pretty much. I didn't see the sketch, but my rib configurations are
similar to his. A given panel thickness and a given rib dimension can make
a panel more or less stiff in different directions by the orientation of
the rib to the grain. Perpendicular orientation of the rib to the panel
grain gets you stiffest cross grain, and most flexible along the grain. As
the angle between the rib and panel grain narrows, the assembly gets
stiffer along the panel grain, and more flexible across it. Look at the
sketch and see the relationship between panel grain and rib angle in the
bass, tenor, and treble. Also, I don't consider the bridge to be a rib
that's supposed to flex, so I want my flexibility control (ribs) at some
angle far from that of the bridge. 


Ron N