Fig. 1 shows the plan with the centre line enclosed with tangents.
Having laid down the risers on plan, keeping the narrow ends of winders
as near as possible half a step, then with one baluster on each they
will be the same distance apart as on the square steps which have two.
This is not intended as a fixed rule but merely as a guide. The risers
must be placed so as to get a good falling line, and this can only be
ascertained by developing or unfolding the centre line and tangents on
a board.
Fig. 2 shows the development of centre line and tangents. Set up all
the treads and risers as they occur on the centre line of rail, Fig. 1.
Draw the springing through A and E. Draw the centre falling line
resting on the corners of square step at bottom and 4 inches above the
landing at top. It is better for the falling line to be a little higher
over the winders, especially near the top. To develop the tangents make
the distance between the lines 1 2 3 D E equal A B C D E, Fig. 1. Draw
D E level. From the centre joint on the falling line square out a line
to cut the line 3 at C, join D C extended to cut the line 2 in B. From
where the falling line cut the lower springing, square out a line to
cut the line 1 in A; join A B; then A B C will be the tangents for the
lower wreath and C D E for the top. Decide where the joint is to be
below the springing, and draw a line parallel to the tangent A B, and
tangent to the curve of the falling line where the joint is to be. The
joint must be square to this line. It will be necessary to have a ramp
here to ease into the straight rail, this is shown by the dotted lines.
In the next plate is shown a method of easing the wreath into the
straight rail without the aid of a ramp.
Fig. 3 shows the bottom face mould. Make C B F and B A equal C B A
and B A, Fig. 2, and F A equal F A, Fig. 1, and complete the mould as
usual. To find what each section is out of the centre of the plank,
make W 4 5, Fig. 2, equal C 4 5 on the centre line of rail, Fig. 1;
make 4 4 and 5 5, Fig. 2, equal N O and N H, Fig. 3. The difference
between the falling line and 4 is what the section 4 on the minor axis
is above the centre; and that between 5 and the falling line is what
the section 5 is out of the centre. The section at both joints is in
the centre, but at the springing A the falling line is a little above
the centre, as it cut the springing above the level line A W, which
is the height of the centre of the plank there. Get out the mould for
the opposite side of the plank in the usual way, by laying Fig. 3 on a
thin piece of stuff, and transfer the tangents and section lines on to
it. Stick a bradawl through A 5 4 C and mark off out to it A 7 5 8 and
5 9, and C 10 and C 11, only on the opposite side. Work the inside and
outside off first with a gig-saw, as before described. The shaded parts
of sections at Fig. 4 show the superfluous stuff there is to come off
the top side.
Fig. 5 shows the face mould for the top half. Draw C D E at right
angles, and to equal C D E, Fig. 2. To see what the sections are out
of the centre, make E 3 2, Fig. 2, equal E 3 2 on centre line of rail,
Fig. 1. Make 2 2 and 3 3, Fig. 2, equal S R and S L. The difference
between 2 and the falling line is what the section 2 is below the
centre of plank, and that between 3 and the falling line is what the
section 3 is below the centre. And that between E and the falling line
is what it is below there.
Fig. 6 shows the sections, and the shaded part shows the superfluous
stuff there is to come off the top at each section, after the inside
and outside have been cut off.
Fig. 7 shows the wreath after the inside and outside have been cut off;
the dotted lines show the wreath cut square through the plank.
[Illustration: PLATE 22.]