PLATE 26.
PLATE XXVI.
WINDERS IN THE QUARTER-SPACE, WREATH IN ONE PIECE, TO FORM ITS OWN EASING INTO STRAIGHT RAIL.
Fig. 1 shows plan with face of risers laid, and centre line of rail enclosed with tangents A B C.
Fig. 2 shows the development. Make Y Y equal stretch-out of centre of rail, Fig. 1. Set up treads and risers, placing the risers as they occur on the centre line of rail, Fig. 1; draw the centre falling line as shown. To development tangents make 1 2 C equal A B C, Fig. 1. Continue the tangent C B in a line with straight rail; make H R equal the distance between the line 1 and springing; join R B extended to cut the level line in F. Draw the joint line square to the straight rail, and R P square to the tangent; mark off along R P, R S to equal half thickness of plank.
Fig. 3 shows the face mould for the top side of the plank. Make R A B F and B C equal corresponding letters, Fig. 2, and F C equal F C, Fig. 1; draw C O and A O parallel to A B and B C; draw the major axis O M square to F C through the centre, with M as centre and M O, Fig. 1, as radius strike an arc at P; draw V L through the centre and tangent to the arc. Make M H equal M H, Fig. 1; draw Y J parallel to V L; make Y E equal H E, Fig. 1. Draw Y J parallel to M P, and J K square to major axis; join K E for section line; draw the short tangent from E square to K E.
Fig. 4 shows bevels, width of mould, thickness of plank. Get the levels by taking O, Fig. 3, as centre, and for radius open out to touch each tangent; transfer these distances to Fig. 4 for each bevel as shown, and complete the sections as usual; the section at each joint will be in the centre, but each of the others will be below. Make C E D, Fig. 2, equal C E D, Fig. 1. Make E E and D D equal P J and P O, Fig. 3. Then the difference between K D E and C and the falling line, is what each section will be out of the centre of plank.
Fig. 5 shows the bevels for the bevelled joint at R. Draw P P to the same bevel as the bevel for the shank, marked O O, Fig. 4; draw C H square to P P. Make C N equal 1 1, Fig. 4, make C S and C S equal S S, Fig. 2, and join S E and S P for bevels T and S. Cut the wreath out square through the plank as usual, except at this joint, which is worked across the top and bottom to the bevel T, the bevel S being for the sides. If the joint is worked true to these bevels, it will joint correctly to the straight rail. S S, Fig. 2, is what the face mould will require to be longer for the under side; this is shown by the shaded part on end of shank, Fig. 6, while R S on the shank of the top face mould, Fig. 3, shows the same amount shorter. It is presumed that the method of squaring the wreath is fully understood, and needs no further explaining here, as it can only be a repetition of what was described in the first few plates.
PLATE 27.