Fig. 1 shows the plan of the rail, with the top riser placed in the
springing and the level rail 4 inches above the landing, so that when
the rail is raised to its proper height, 2 feet 8 inches above the
treads, measured vertically over the face of the risers to the top
of rail, it will be 3 feet from the landing to top of level rail. To
get the radius of the centre line of rail, make B H, Fig. 3, equal 4
inches; then A B will be the required radius. At Fig. 2 set up one
step and landing. Draw the centre falling line resting on the corners,
also draw the level rail 4 inches above the landing. Make N C equal
the stretch-out of the centre line of rail, Fig. 1, and complete the
falling line from A to C, as shown.
Fig. 4 shows the face mould. Draw A B C at right angles. Make A S equal
A S, Fig. 2, and A B equal A H, Fig. 3, and B C equal B C, Fig. 1, and
C P equal C P, Fig. 2. From A draw A O parallel to B C, and from C draw
C O parallel to A B. Then O will be the centre, A O the semi-minor
axis, and O C the semi-major axis. To get points in the curve and draw
section lines, take O C, Fig. 1, for radius and C, Fig. 4, for centre;
strike an arc on the left; draw V L through the centre, and tangent to
this arc; draw from C square to V L. Say there are to be two sections
marked 5 and 6, Fig. 1. Make C 2 1 equal C 2 1, Fig. 1. Draw from 1 and
2 parallel to V L to cut O C in 3 and 4. From 3 and 4 draw parallel to
A O, and make 4 5 and 3 6 equal 1 6 and 2 5, Fig. 1; then 5 and 6 will
be points in the curve. From 3 and 4 draw square to and cut V L in 7
and 8; from 7 and 8 draw square to and cut O C in 9 and 10; join 9 5
and 6 10 for section lines. To get bevels, width of mould, &c:--On a
piece of board draw two parallel lines, at a distance apart equal to
radius of centre line of rail, as shown by the lines R R, Fig. 5; also
draw the width of rail, as shown by W W. For the section at C, make
1 2, Fig. 5, equal O C, Fig. 4; draw section of rail; draw E F parallel
to 1 2, to cut the top corner of section of rail. Then O C will be half
thickness of plank and E C F the width of mould. For section 5, with O,
Fig. 4, as centre, strike an arc to just touch the tangent from 5; make
3, 4, Fig. 5, equal this distance. Make O 5 equal half thickness of
plank and draw R N parallel to 3 4, then R 5 N will be width of mould
on this section. The process of getting bevel and width of mould for
section 6 is the same, always squaring out the line from the centre of
section of rail and setting off half thickness of plank, and drawing
the top or bottom side of plank parallel to the bevel line through the
centre of section. To complete the face mould make C E and C F equal
C E and C F, Fig. 5. For section 5 make 5 R and 5 N equal 5 R and 5 N,
Fig. 5. For section 6 make 6 S and 6 P equal 6 S and 6 P, Fig. 5. The
section on the minor axis requires no bevel, as was explained in Plates
XII. and XIII. This line never exceeds its plan, therefore on this line
the face mould never exceeds the width of rail. Complete the face mould
as shown.
[Illustration: PLATE 15.]