of frog will be = ƒa. But if the backsight be taken on a point f· 2 (say 5 inches distant) parallel with the main track, the deflection will then be = - 8 f+s +8= Making the value of x, radius, g-m 2 Calling 81° 15', f= 6° 45', g = 4'70, m = 0·42, and g 4.28, we have sin. 4° : R :: 4·28 : x = 61.36ft. -m= When a double opening of a switch rail for a double turnout occurs, we have, sin. (+20): s Rg 2 x m: x = distance to nearest frog. The linear and angular opening of rail being the same, this table may be adapted to any other gauge by increasing the value of x as given in this table, and the length of radius of turnout 2 per cent. for every additional inch in the gauge. This is a little too much; the correction for a 6 ft. gauge being about 30 per cent. Thus 100 ft. chord of turnout on this track will give 130 ft. on 6 ft. gauge, and 1000 ft. radius will give 1300 ft. This is for a straight line. When on a curve going the same way as turnout, it is sufficiently accurate for practice to add rate of curve of main track to that of the table; but when going in opposite direction, subtract it; thus making relative departure from main track the same as on a straight line. EXAMPLE: Thus a 5° frog for a 4ft. 8 inch gauge gives a distance of 78.5 ft. curvature 4° 46'. If the main track were a 4° curve and going the same way, distance being the same, the rate of curvature would be 4° 46' +4° 8° 46', radius 653 ft.; but going the other way 4° 46' · 4° = 0° 46′, radius 7473 ft. TABLE Of distances on chord from opening of switch rail where the curve commences, to point of frog, radius of curvature and rate per 100 ft., calculated to every 15 minutes of frog angle, from 30 to 15o. Constant data: opening of switch rail 5 inches='42 ft., average angular opening say 1° 15', rails being from 18 to 20 ft. long. Variable data gauges of road. TABLE Of distances on chord from opening of switch rail to point of frog, radius of curvature and rate per 100 ft. |