Fig. 128.
On the board draw a straight line which will be the center line of the well, and on any convenient point placing the leg of the compass (which will be set at the required radius), describe a semi-circle, which will represent the diameter of the well given in the plan in [Fig. 121]. Now from the semi-circle draw lines parallel to the center line, which will represent the outside stringer of the stair and the casing on the landing. [Fig. 129] shows the development thus far.
The rail is to be 1¼ inches wide and the balusters to be ½ inch square. The side of the balusters which come on the outside of the stairs comes even with the stringer, and the rail is to be placed so that the balusters are on its center.
From the line which is already drawn to show the part which is parallel to the landing, draw a line for the center of the rail, and on each side of the center line lay out half the width of the rail. On the other half, which represents the outside stringer (the incline of the twist), draw the center line of the rail for the straight part; then draw lines for the width of the rail as on the other half. Now, to obtain that part of the ellipse required, take the pitch-board [E, Fig. 122], and place it on the drawing as shown in [Fig. 130]; then draw lines from points X, Y, Z, perpendicular to the center line. Now set the compass to the distance A, B, and mark the distance A, B, on each side of the point Y. This gives the width of the piece required for the twist on the center line.
Fig. 129.
Describe the ellipse. The major chord would be 2 (E, F,) for the outside ellipse, and the minor chord is G, H, for the inside.
Fig. 130.