Make a soundboard--Measurements

[Crashvalve@aol.com]

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In a message dated 11/1/03 12:53:13 AM, RNossaman@cox.net writes:


> No, it won't. It will be curved more in the middle and less at the ends. I
> used two straight edges. Starting with a line representing the anticipated
> maximum length of a rib of that particular radius, I computed the height of
> the arc segment represented by that chord at that radius. Then I drove pins
> in the points at the ends of the chord, and the center of the arc segment
> at the computed height above the chord. Placing the two straight edges one
> each on the pins at the ends of the chord, and overlapping above, but both
> touching, the pin in the center, I tacked them together. Placing a pencil
> in the shallow V produced at the intersection of the straightedges, I slid
> the straightedge assembly on the three pins so that the pencil went from
> one end of the chord to the other - describing the arc segment.
> 
> Realistically, the exact shape of the described arc isn't anything like
> critical to the ultimate performance of the assembly. The chosen radii and
> rib dimensions, balanced against the anticipated bearing load and resulting
> deflection are significantly more important.
> 

believe this two straightedges method is shown in fine woodworking magazine, 
and the formula for rise of segment/arc of a circle is in machinery's 
handbook. I am not strong on math but I presumed I had solved correctly when I did 
Wolfenden's suggested radius and it came out exactly .625 or 5/8 inch. My 
question is:   why express these rises of arc in such an arcane fashion as radius of 
a HUGE circle? Is it because of the need to be uniform despite the length of 
arc required ?
Glenn C.

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