bearing, loose bridge pins leading to Wapin considerations

[Ron Nossaman]

>Ron,
>
>Didn't you show me some data at Reno that showed the Wapin bridge had the
>least amount of stress at some point?  You measured some sort of stress in
>relation to the angle of the bridge pin.  I apologize for not remembering
>any specifiics.  This whole line may be completely off topic.
>
>Tim Coates
>Wapin Co., LLP

Hi Tim,
I did.

String tension = 160lb.
Stagger angle = 10°
Downbearing angle = 1°
Downbearing load = 2.792lb
Coefficient of friction between pin and string = 0.53

				20° pin angle	0° pin angle
Side bearing induced 
downbearing load on bridge	9.503lb		0lb

Static resistance down 	4.335lb  	14.725lb

Static resistance up		23.34lb		14.725lb


Where it takes 23.34+2.79= 26.13lb to push a string up a 20° pin, it only
takes 14.3+2.79=17.52lb with a vertical pin. The cap will suffer less
crushing from bridge expansion with the vertical pin. Conversely, the
string on a vertical pin will be less likely to be seated on the bridge as
the bridge shrinks. The slanted rear pin(s) will help, but there will still
be a difference.
    
Ron N