HALF TWIST STARTING FROM A SCROLL, AND A SIDE WREATH STARTING FROM A
NEWEL.
Fig. 1 shows the plan of a stair starting with a scroll. Make D E equal
about 4 times the width of rail, which divide into 9 equal parts; make
D I equal 5 of these parts; this will be the radius for the largest
quadrant of the rail. To find the radius for each of the remaining
quadrants, make D 1, Fig. 5, equal D 1, Fig. 1; make 1 2 equal one of
the 9 parts, with D as centre and D 1 as radius; strike an arc from 2;
square up a line to cut the arc in A; join A D with D as centre and D 2
as radius; strike an arc to cut A D in B; from B draw B 3 square to
D 1. Continue the process as far as required to complete the scroll,
D 2 will strike the second quadrant and D 3 the third, and so on. The
face mould is seen at Fig. 3. Draw C B A at right angles and make C B
equal C B, Fig. 2, and A B equal A B, Fig. 1. Make A R equal radius of
centre line of rail C 1, Fig. 1, and complete the mould as usual. The
scroll itself will only require to be the thickness of the rail, as it
is level. All the sections in the wreath will be in the centre of the
plank.
Fig. 6 shows the plan, and Fig. 7 the elevation of a side wreath
starting from a newel. Make A P, Fig. 8, equal the radius of centre
line of rail, Fig. 6, and draw V L through P square to A P. Make A E
equal A E, Fig. 6, draw E 8 square to A E, and make E 8 equal B D,
Fig. 7. Join A 8 extended to cut V L in O; then O will be the centre
and A O the major axis. Make A B and 8 C equal A B and E C, Fig. 6.
Join C B, which is the tangent, and if the drawing is correct, this
will equal C B, Fig. 7. The tangent A B being level is of course the
same length as on plan. All the sections will be in the centre of the
plank; these are seen at Fig. 9. The short shank A N is to let into the
newel; A being the face of newel.
[Illustration: PLATE 29.]