In Fig. 152, a bc is the plan of a line passing through the centre of the rail around the cylinder, as before, and the lines above it are a vertical section of steps, risers, and platform, with the lines for the rail obtained as in Fig. 144. Set half the width of the rail from b to f and from b to r, and from f and r draw fc and r d parallel to ca. At Fig. 153 the centre-lines of the rail jc and cl are obtained as in the previous examples, making jc equal jn of Fig. 152, ct equal ct of Fig. 152, and tl equal sl of Fig. 152. Make ci and ck each equal to ci at Fig. 152, and draw the lines im and kg parallel to cj; make le and lr equal to ne and nd at Fig 152 and draw dn and eq parallel to lc; also, through j draw og parallel to lc; then, in the parallelograms mnro and goeq, find the elliptic curves, dm and eg according to Art. 551, and they will define the curves. The line dp, being drawn through l perpendicular to lc, defines the joint which is to be cut square through the plank.

Fig. 152.