Fig. 130. Development of Face-Mould for Wreath
Connecting Rail of Flight with Level-Landing Rail.
To draw the curve, the points or foci where the pins are to be fixed must be found on the major axis. To find these points, take the length of b k (which is, as previously found, the exact length of the semi-major for the inside curve) on the dividers; fix one leg at 2, and describe the arc Y, cutting the major where the pins are shown fixed, at o and o. Now take a piece of string long enough to form a loop around the two and extending, when tight, to 2, where the pencil is placed; and, keeping the string tight, sweep the curve from b to b.
Fig. 131. Arranging Risers in Quarter-Turn between Two Flights.
The same method, for finding the major and foci for the outside curve, is shown in the diagram. The line drawn from b on the outside of the joint at n, to w, is the semi-major for the outside curve; and the points where the outside pins are shown on the major will be the foci.
Fig. 132. Arrangement of Risers around Quarter-Turn
Giving Tangents Equal Pitch with Connecting Flight.