Fig. 1 shows the plan of a scroll, and wreath to stand over the curtail
step and winders. Divide N N into 9 equal parts. Make N 1 equal 5 of
these parts and draw the largest quadrant. To draw the remainder make
N 1, Fig. 7, equal N 1, Fig. 1; with N as centre and N 1 as radius,
strike the arc. Make 1 2 equal 1 of the 9 parts; from 2 erect a
perpendicular to cut the arc in 7. Join 7 N. Now with N as centre and
N 2 as radius, strike the second arc to cut N 7 in 8; draw 8 3 parallel
to 7 2. Again, with N as centre and N 3 as radius, strike the arc to
cut N 7 in 9; draw 9 4 parallel to 8 3. This process can be continued
as far as required. N 1 will strike the largest quadrant, N 2 the next,
and N 3 the next, and so on until the scroll is completed. The centre
and inside lines of rail will be struck from the same centres. Make the
joint at A, and draw the radius line from 2, which is the centre of
this part of the scroll; draw the tangent A B square to it.
Fig. 2 shows the elevation. Set up the treads and risers as they occur
on the centre line of rail, Fig. 1, and draw the centre falling line so
that it will finish level, about on the line N N, and at a height of
about 1 or 2 inches above the top of the first step. Make 3 7 equal the
stretch-out of the centre line of rail, Fig. 1 from A to C. Draw the
level line through the falling line at 7, and make 3 8 and 8 A equal
C B and B A, Fig. 1, and complete the development of tangents as shown.
Draw the joint at 7 square to the tangent A B. The scroll must be the
distance S S thicker than the thickness of rail, and the joint worked
to the bevel as shown.
Fig. 3 is the face mould for the top side of the plank. Make B F,
Fig. 1, equal 8 F, Fig. 2, and at Fig. 3 make C B F equal C B F and
B A equal B A, Fig. 2, and F A equal F A, Fig. 1. Draw C 11 and A 5
parallel to the horizontal trace F A, and make A 5 and C 11 equal A 5
and C 7, Fig. 1, and draw the major axis through 5 and 11. With 5 as
centre and 5 7, Fig. 1, as radius, strike an arc at 7; draw a line
through 11 and tangent to the arc. Now, if the drawing is correct, 7 11
will equal the height 3 C, Fig. 2. Make 5 4 3 1 6 7 equal corresponding
figures, Fig. 1, and complete the mould as usual. Notice O will be the
centre for sections D E R and C, and S S, Fig. 4, will equal the radius
1 D, Fig. 1. But for the section at the joint A, 2 will be the centre
and S S, Fig. 5, will equal the radius 2 A, Fig. 1. The bevels, &c.,
are got as usual. Make 3 4 5 6 7, Fig. 2, equal C R E D A, Fig. 1. Make
4 4 and 5 5 and 6 6, Fig. 2, equal 1 S and 1 O and 1 W, Fig. 3. Now,
the difference between 4 5 and 6 and the falling line is what each
section is out of the centre of plank.
Fig. 6 is the face mould for the under side of the plank.
[Illustration: PLATE 30.]