Fig. 3 shows the face mould for the top wreath. Make C D F equal C D F and D E equal D E, Fig. 2, and F E equal F E, Fig. 1. Draw from E parallel to D C and from C parallel to D E to meet at the centre O. Draw the major axis square to the horizontal trace F E. With M as centre and O M, Fig. 1, as radius strike an arc at N; draw V L through the centre and tangent to the arc, and complete the mould as usual; M S will equal M S, and T J will equal S J, Fig. 1.
Fig. 4 shows the sections. S S will equal the radius of centre line of rail, Fig. 1, and for bevels place one foot of the compasses on the centre O, Fig. 3, and open out to touch each tangent, then transfer these distances to each section, Fig. 4. To find what each section is out of the centre of the plank, make E J K, Fig. 2, equal E J K on the centre line of rail, Fig. 1. Make J J and K K, Fig. 2, equal N H and N O, Fig. 3. Now the difference between E and the falling line is what the section is below the centre at the springing, and that between J and the falling line is what the section is below the centre, and that between K and the falling line is what the section on the minor axis K is above the centre; the sections at both joints are in the centre of the plank.
Fig. 5 shows the bottom face mould. R A B will equal R A B, and S B C will equal S B C, Fig. 2, and A S will equal A S, Fig. 1. Proceed as usual to get bevels, sections and width of mould. Now, as the tangent A B is not in a line with the straight rail, and the joint being square to the latter, the end of shank must be bevelled so as to joint correctly to the straight rail. Draw P P, Fig. 7, to the same bevel as that for the shank marked O O, Fig. 6. Draw C D, Fig. 7, square to P P, make C N equal 2 2 at section A, Fig. 6, draw the level line through N to cut P P in E and C D in D. Now, at Fig. 2 mark off along R P, R S to equal 2 2 or 1 1, Fig. 6. Make C S and C S, Fig. 7, equal S S, Fig. 2, and join S E and S D for bevels T and S. Apply the bevel T as shown and S as shown at Fig. 8. The face mould for the under side will be S S, Fig. 2, longer, and that for the top side the same amount shorter.
PLATE 23.
PLATE XXIII.
QUARTER-SPACE LANDING, WREATH IN ONE PIECE.
Fig. 1 shows plan of centre line of rail enclosed with tangent A B C. Draw risers, landing, and starting half a tread from B. This will cause the tangents on face moulds to be the same pitch as the straight rail. This arrangement answers very well if the rail is small, but if the rail is a wide one, say 4 inches or more, the inside has a crippled and awkward appearance.
Fig. 2. Make R S equal stretch-out of the quadrant, Fig. 1. Set up one tread and riser above and below, as they occur on the centre line of rail, Fig. 1. For development of tangents make C 2 1 equal A B C, Fig. 1. Square out a level line from the springing at S to cut the line 1 at A. Join A C for tangents, which will be the same pitch as the straight rail.
Fig. 3 shows face mould. Make C B S equal C B A and B C equal B C, Fig. 2, and S C equal the diagonal of the square on plan. Draw C O and B O parallel to A B and B C. Draw sine major axis and sine minor through O. Notice the major axis is parallel to the diagonal from A to C, and the minor axis is the other diagonal. Both pitches being the same throws the horizontal trace parallel to the diagonal from the centre to B. One bevel will do for both shanks, as the pitches are the same. The falling line will be in the centre of plank at both ends and at the minor axis.