All.
The math to calculate curves is not particularly difficult. Spiral curves (what model railroaders incorrectly call easements) are somewhat more complicated. Just keep in mind that if any two elements of a curve are known, all other elements can be calculated.
The radius of a 1 degree chord definition curve = 5729.65'
The radius of a 1 degree arc definition curve = 5729.58'
To obtain the radius of a 5 degree curve, simply divide the above radii by 5, a 15 degree curve by 15 etc. Then all other elements can be found. (including stationing).
During my career, I have put many design curves (albeit arc definition curves) onto the ground by "walking the curve" which required the survey instrument to be moved along the center of the arc at 100' intervals (or intervals divisible by 100), and calculations performed to set the next centerline point(s). I have also staked curves with the survey instrument located at the P.C., P.T., and P.I. of design curves, and calculations performed to determine points on the center of the arc at varius intervals. As I said, these calculations are not difficult, but a basic understanding of the math involved must be learned. Your scientific calculator, or PC is not going to teach this.
These methods can also be used with a protractor (not a high end farming impliment) and rule directly on the layout surface, without need to locate the radius point of the curve. This is in fact how I lay out curves on my layout.
As a note of clarification, the standard surveyor's chain was 66' long and had of 100 links 7.42" long. Many railroad engineering forces had chains 100' in length, with 100 links 12" long. These chains were VERY heavy, and cumbersome to use. They were suseptable to expansion and contraction due to temperature variation, thus correction calculations were frequently required. They were intended to measure horizontal distances, thus had to be used "level" to acheive their highest degree of accuracy. This could prove very difficult in steep terrain, and "breaking chain" was often required. These two factors may go a long way in explaining why a certain chain was 3% long as noted in one post above.
Jim J.
