PLATE XX.
HALF-SPACE LANDING, WITH THE RISERS IN THE SPRINGING.
Fig. 1 shows the plan of a half-space landing with the centre line of rail struck with a 9-inch radius, and the risers starting and landing placed in the springing. As the steps are only 10 inches it is very evident that if the tangents A B and D E were the same pitch as the straight rail the tangent across the well would pitch the wrong way, which of course would not do. To obviate this the tangent A B must only rise half a riser over B, and the tangent D E only fall half a riser over D, and the tangent across the well level and the joint on the end of shanks must be bevelled so as to joint square to the straight rail.
Fig. 1 shows the plan with the risers in the springing.
Fig. 2 shows the elevation. Make S N equal stretch-out of centre line of rail. Set up one step above and below and draw landing; also draw the centre falling as shown, this line must pass through the centre at the height of half a riser above the landing, and make a good easing into the straight rail above and below the springing. For development of tangents make F B equal A B, Fig. 1, and draw from B to the joint below the springing; draw R P square to the straight rail, which will be the joint, and R N square to the tangent A B.
Fig. 3 shows the face moulds. As the tangent B C is level draw A B C at right angles; make R A B equal R A B, Fig. 2, and B C equal B C, Fig. 1, and complete the mould as usual. It will be seen that the sections will be in the centre of the plank at both joints. For section P, make F H, Fig. 2, equal A P, Fig. 1, and H J, Fig. 2, equal H J, Fig. 3. The difference between J and the falling line is what the section is out of the centre of plank as shown at Fig. 4. The difference between the tangent A B and the falling line at the springing shows that the section A is out of the centre. The stuff must be thick enough to get this section out as required. Make R Y, Fig. 2, equal half thickness of plank. Add Y C to the end of shank of one face mould and reduce the other to the same amount, as shown by the shaded parts.
PLATE 21.
PLATE XXI.
WINDERS IN THE HALF-SPACE AND LEVEL LANDING AT TOP.
Fig. 1 shows the plan with the centre line enclosed with tangents. Having laid down the risers on plan, keeping the narrow ends of winders as near as possible half a step, then with one baluster on each they will be the same distance apart as on the square steps which have two. This is not intended as a fixed rule but merely as a guide. The risers must be placed so as to get a good falling line, and this can only be ascertained by developing or unfolding the centre line and tangents on a board.