PLATE 19.
PLATE XIX.
FROM THE LEVEL TO THE RAKE—continued.
The plan, elevation and falling line, and position of risers in this case are the same as in [Plate XVII]., but show a different way of getting out the wreaths. This may not be such a correct method as the former one, as the centre joint will be vertical instead of square to the tangent across the well as was the case there, but nothing could be more simple than the method here described. Having the plan and elevation drawn, square out a bevel line from C, to cut the springing in R. Make R F equal E D, Fig. 1; say the joint is to be at S on the right, join S F, draw the joint S P square to the straight rail, and draw S N square to the tangent F E S.
Fig. 3 shows the face mould. Draw S E D C at right angles, make S E D equal S E F, Fig. 2, and C D equal C D, Fig. 1. To complete the mould, make O N and C N equal E R and F R, Fig. 2. Draw V L through O N; make C R and P H equal C R and R H, Fig. 1. As will be seen, the straight rail is not in a line with the tangent, and as the joint must be square to the straight rail it cannot be square to the face of the plank. Therefore, the face mould for the top side will require to be a trifle longer, while the mould for the bottom side must be the same distance shorter. To find out how much the joint will require to be bevelled, mark off along S N, Fig. 2, S J to equal half thickness of plank; then the distance between the two lines S P and S N at J is what the joint will be out of square to face of plank through half its thickness. The shank of top face mould must be increased, and that of the bottom reduced to this amount as shown by the shaded parts. The face mould shown at Fig. 3, being for the under side, is reduced.
Fig. 5 shows the application of the face moulds; as there is no bevel on the shank E S the joint will only be out of square to face of plank and not to the tangent. Fig. 6 shows the bottom half; this having no twist can be struck with the compasses, the same as the plan. It must be the distance C H, Fig. 2, thicker than the rail. The shaded part shows how the superfluous stuff must be taken off top and bottom.
Fig. 7 shows the pair in position after being squared.
PLATE 20.
