Rails on curves are usually laid with square joints. The inner rail gradually gains the lead over the outer rail on a curved track. The excess length D, which the inner rail gains over the outer rail for a length L of the circular curve is calculated as follows (Fig. 13.21).
(i) Difference in circumference of outer rail and inner rail (i.e., gain):
= for BG and for MG 1000 1654
where L is the length of outer rail of the circular curve, R is the radius of outer rail of the circular curve, D is the degree of curvature of outer rail, and G is the dynamic gauge (i.e., gauge + width of rail head), which is 1750 mm for BG and 1058 mm for MG.
Fig. 13.21 Cutting rails on curves
Normally, when the inner rail of the curve leads over the outer rail by an amount equal to half the pitch of the fish bolt holes, the inner rail is cut by an amount equal to one full pitch and another hole is drilled for fastening the joint with a fish plate. The number of rails to be cut for a particular curve is worked out depending upon the degree and length of the curve and the pitch of the bolt holes.