Cutting rib radii

[Ron Nossaman]

>> ..."But the shape of the curve wont' be an arc"
> I've heard that argument before.  I'm not so sure that is
> the case, and even less sure that it is of any consequence.
> 
> 
> Another method for scribing a large diameter arc is to
> convert the radius data to "rise" over a given distance,
> say 6'.  Construct a bow, as in an archery type bow, where
> the string is music wire secured by tuning pins at each
> end.  The frame is an otherwise straight wooden beam, bent
> by the tension of the string.  Adjust the tension until you
> measure the correct "rise" for the desired radius.  Trace
> along the edge to transfer the "arc" to the work piece.  Of
> course, bending the work piece itself has essentially the
> same result.

I am quite thoroughly sure this does not produce an arc 
segment, but haven't yet seen anything to indicate that any 
one crown contour is inherently superior to any other.
Ron N