What radius is the section of track that curves away from the straight portion on an Atlas No. 6 Mark III Customline turnout? I inserted one coming off of a 30-inch radius curve (the points are in the opposite direct of traffic flow) and it appears to have a much wider ratio. Any suggestions?
There are two radiuses to consider: The first is the closure radius. The closure radius is the actual curve that is built into the turnout. The second radius is the substitution radius. This is the radius of the curve that would fit if you removed the turnout including the straight section in front of the points. For a standard number 6 in HO this closure radius is 42" and the substitution radius is 56" per John Armstrong. The dimensions of the Atlas Mark III may be slightly different, but you are correct that it is much broader than a 30" curve. A good trick for designing spiral easements is to use the substitution radius and length of a number 6 turnout before each curve. This provides a standard also makes it easy to splice a turnout into the start of a curve if you ever want to in the future.
