PLATE XXV.
QUARTER-SPACE LANDING, WREATH IN ONE PIECE, TO FORM ITS OWN EASING INTO THE STRAIGHT RAIL.
Fig. 1 shows the plan laid down exactly the same as in [Plate XXIII].
Fig. 2 shows the elevation. Make Y Y equal the stretch-out of centre line of rail, Fig. 1, and set up one step above and below as shown. Draw the centre falling line resting on the corners and passing through the centre at the height of half a riser above the landing. For development of tangents, make 1, 2, 3 equal A B C, Fig. 1. Square out a level line from the lower joint H, and make H R equal the distance between the line 1 and the springing; join R N; then A B C will be the tangents of face mould. From R draw the joint line square to the straight rail, and R P square to the tangents.
Fig. 3 shows the face mould. Make R A B S equal R A B C, Fig. 2, and S C equal the diagonal on plan, and B C equal B C, Fig. 2. Draw C O and A O parallel to A B and B C, make C N equal C N, Fig. 2. The bevel A and C will be the same, as both pitches are the same.
Fig. 4 shows the sections at the two joints, and the section on the minor axis will be in the centre of the plank. But section A will be above, and that at C below the centre. The distance between C and the falling line is what the section at C will be below, and A above the centre. It will be seen one corner of the rail is cut off at these sections; this makes no difference so long as the moulding of the rail will work it out.
Fig. 5 shows the bevels for the joints to be worked off to, so as to make them joint to the straight rail. Draw P P to the same pitch as O O, Fig. 4; draw C H square to P P; make C N equal 4 4, Fig. 4. At Fig. 2 mark along R P, R S to equal 4 4, Fig. 4; make C S and C S equal S S, Fig. 2, and draw S E for the bevel T to be applied across the end of shank and along the tangent. Join S D for the bevel S, to be applied through the end of shank and along the surface of the stuff; this bevel must be held parallel to the tangent across the joint, that is, square through the plank. Notice that in all these bevel joints if the tangent is steeper than the straight rail, the bevel T is applied so that the ends of shank diminish towards the inside, while if the tangent is flatter, the end of shank will diminish towards the outside. This will be understood by referring to Fig. 3 in this plate, and Fig. 5, [Plate XXI].
Fig. 6 shows the face mould for the under side; the shaded part N S shows the extra length required; this will equal S S, Fig. 2, the other end R S will be the same amount shorter. This mould is reverse to Fig. 3.
Fig. 7 shows the wreath cut out square through the plank, before the moulds are put on. The application of the bevels is seen here.