The American Stair-Builders' Guide. E-book. Formato PDF - 9780243786947

Make A B (figure 1) the long diameter or major axis, and C D half the short diameter or minor axis of the required ellipse. From the point D as centre, with C B as radius, describe arcs, cutting the major axis at 2 and 3; at the points, place pins; around the pins, place a cord so fastened at the ends that it shall reach around g de; place your pencil inside the cord and describe the ellipse A D B R. Dare should be taken to keep the cord to an even tension. Suppose the elliptic curve A D B to be the centre of a mould required for a wreath, set off each way from D half the width of the rail, and draw the dotted lines D 2 and D 3. From the points S and H draw lines parallel to D 2 and D 8 to intersect the major axis. At the points thus found, place pins and describe the outside and inside curves. To draw two elliptical curves parallel to each other, set ofi' from R to J, equal to B N, from the point J as centre, with C N as radius, describe ares, cutting the major axis at A and B, the points for the pins to describe the curve required.