## TRACK MODELING DETAILS

SPIRAL EASEMENTS-EASY METHOD FOR DETERMINING THEM There has been a lot of discussion on this and the railraod list about calculating spiral easements, so I'd like to throw in my two cents worth. First of all, unless you love math, and are doing it for the pure joy of filling pages of note paper with chicken tracks, there is no need to do any calculations for building easements. Here is the method I've used on my own layout and on our club layout. 1. Calculate the maximum radius you can get into the space where you want your curve. 2. Subtract 2 inches. (as the ads all say, HO of course) 3. Layout the tangent (straight) track. 4. Off set the beginning of the curve 1 inch inside the tangent at each end. 5. It's actually easier to do the track laying than the drawing. If you are doing a drawing, sketch in the easments connecting the "true curve" with the tangents. If you're building the curve, just lay the sub-grade and sound deadening board for the tangents, cut the curve subgrade to the desired radius, and install 1 inch off center towards the inside of the curve. When you lay the roadbed or track, if you connect the tangent track to the curve and allow the flex track to form a natural spiral, and nail it down, it's done. The joint on the subgrade at the junction of straight and curved will not be the best looking thing you've ever seen, but that's what scenery is for. (someone else does scenery, I never touch the stuff) Bill Meiners

For those interested I transcribe from "Building and Repairing Railways" a supplement to "The Science of Railways" by Marshall M. Kirkman, published by the World Railway Publishing Co.- 1902- pgs. 601, 602: "Elevation-The elevation (in inches) of outer rail upon curves will be made in accordance with the following table:## TABLE OF ELEVATION OF OUTER RAILS ON CURVES

De- |---------------Rate of speed in miles per hour.-----------------| gree 15 20 25 30 35 40 45 50 60 of |-----------------------Superelevation---------------------------| curve ins. ins. ins. ins. ins. ins. ins. ins. in 1 1/8 1/4 7/16 9/16 13/16 17/16 21/16 13/8 19/8 2 5/16 1/2 13/16 19/16 13/8 17/8 43/16 53/16 19/4 3 7/16 13/16 5/4 7/4 39/16 25/8 4" 79/16 7.06 4 9/16 17/16 13/8 19/8 13/4 67/16 85/16 101/8 .... 5 3/4 21/16 33/16 3" 4" 21/4 107/16 .... .... 6 7/8 25/16 39/16 57/16 77/16 51/8 .... .... .... 7 17/16 29/16 23/8 33/8 45/8 .... .... .... .... 8 19/16 17/8 53/16 75/16 13/2 .... .... .... .... 9 21/16 19/8 59/16 85/16 .... .... .... .... .... 10 3/2 21/8 33/8 95/16 .... .... .... .... .... 12 7/4 25/8 79/16 43/8 .... .... .... .... .... 15 35/16 63/16 99/16 .... .... .... .... .... .... 18 21/8 75/16 .... .... .... .... .... .... .... 20 47/16 21/4 .... .... .... .... .... .... .... "The greatest elevation must not exceed six inches unless otherwise directed. "The elevation of outer rail on curves must necessarily be adapted to speed and other local conditions with due regard to safety, comfort and economy of track maintenance, for all classes of trains. "The elevation on mountain grades should not exceed that required for 25 miles per hour. "The elevation of outer rail must not be continued beyond the tangent point, but should decrease uniformly along the easement curve from point of maximum curvature to tangent point. "To ascertain the elevation required at points on easement curves, trackmen are required to use a cord of standard length, the middle ordinate of which will be equal to the proper elevation, as follows: Speed. Length of cord. 20 mph 31.74 ft. 25 mph 39.68 ft. 30 mph 47.61 ft. 35 mph 55.55 ft. 40 mph 63.48 ft. 45 mph 71.42 ft. 60 mph 79.35 ft. "This method is applicable to all curves, and aids in maintaining true alignment, as all ordinates should be equal on full centered portions of curves, and ordinates must decrease uniformly on easement curves from full elevation to zero at tangent point. In using the cord to ascertain elevation, it should be stretched and firmly held at both ends against the inner face of rail on inside of curve. The middle ordinate will then be equal to the required elevation and can be measured by a foot rule, or by attaching a short piece of graduated tape to the cord at it's center." Hope this is useful to some of you. Ron Dugas## © S.A. McCall