Ulf,

Calculating the diverging route curve would be very dependent on the uniformity of the curve(s), and also the use of a straight vs. a curved frog. You can however, layout the 'straight' section along your 100cm outer curve - and then marking the centerline of the resulting diverging curve.

Take a ruler and draw a straight distance of 1cm just touching the curve centerline points. At the midway point (50mm) carefully measure to the curve offset (location of the curve at that mid-point).

This is the mid-cord ordinate. The offset can then be plugged into the formula for determining the resulting curve radius:

L= Length between curve points (base)

z = Max Offset ( ~1/2 base to intersect)

r (effective radius of the curve) = (L^2) / (8z) + z/2

Thus if the offset is say 2.6mm (EXAMPLE VALUE ONLY):

r = (100^2) / ( 8 * 2.6 ) + (2.6 / 2)

r = (10,000) / ( 20.8 ) + (1.3)

r= ~ 482.07mm (or close to 19" radius)

If the offset is only 1.5mm at the mid point along a 100mm cord you'll end up with about a 33" (836.33mm) radius.

Note: That's NOT the answer - just an example - the actually measured offset would need to be put into the formula. You can see that the measured mid-cord ordinate offset will be very small and getting good accuracy in measuring is important for reliable results.

_________________

-ed mccamey-

COSLAR RR -

http://www.coslar.us/NMRA Standards and Conformance Department

PROTO & FINE Scale Coordinator

I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.