WINDERS IN THE HALF-SPACE, WITH A STRAIGHT FLIGHT ABOVE AND BELOW,
WREATH TO FORM ITS OWN EASING.
Fig. 1 shows the plan with face of risers laid down. It will be noticed
that the winders commence at the springing at the top, while they are
brought past the springing at the bottom; this causes the rail to be
high at E and, therefore, safer for any one coming down the stairs
with their hand on the rail; and by bringing the winders below the
springing it makes a better easing into the straight rail. This will be
understood by referring to Fig. 2, where the centre line and tangents
are developed. Set up the treads and risers as they occur on the centre
line of rail, Fig. 1; also draw the springing and the centre line W.
Draw the centre falling line resting on the corners of square steps top
and bottom, and continue it up over the winders as shown by the dotted
line. To develop the tangents make the distance between 1 2 3 4 5
equal A B C D E, Fig. 1. From where the falling line cuts the centre
line square out a level line to cut the line 3 at C. Continue the top
tangent down in a line with the straight rail to cut the line 4 in D.
Join D C extended to cut the line 2 in B. Now make the joint below the
springing, as near to it as possible, so that it will be clear of the
easing. There being no ramp on the straight rail, the joint should be
well clear of the easing and into the straight so as to avoid any signs
of a cripple when the wreath is jointed to the straight rail, which
there would be if the joint was made in the easing. Square out a level
line from the joint P, and make P R equal the distance between the line
1 and the springing. Join R B, this has cut the line 1 at A. From A
draw A W level. From R draw the joint square to the straight rail, and
R P square to the tangent A B R. Make D F, Fig. 1, equal 4 F, Fig. 2,
and join F E for the horizontal trace of the top wreath. Make B S,
Fig. 1, equal 6 S, Fig. 2, and join S A for the horizontal trace of the
bottom wreath.
Fig. 3 shows the face mould for the top wreath. Make C D F equal
C D F and D E equal D E, Fig. 2, and F E equal F E, Fig. 1. Draw from
E parallel to D C and from C parallel to D E to meet at the centre
O. Draw the major axis square to the horizontal trace F E. With M as
centre and O M, Fig. 1, as radius strike an arc at N; draw V L through
the centre and tangent to the arc, and complete the mould as usual; M S
will equal M S, and T J will equal S J, Fig. 1.
Fig. 4 shows the sections. S S will equal the radius of centre line of
rail, Fig. 1, and for bevels place one foot of the compasses on the
centre O, Fig. 3, and open out to touch each tangent, then transfer
these distances to each section, Fig. 4. To find what each section is
out of the centre of the plank, make E J K, Fig. 2, equal E J K on the
centre line of rail, Fig. 1. Make J J and K K, Fig. 2, equal N H and
N O, Fig. 3. Now the difference between E and the falling line is what
the section is below the centre at the springing, and that between J
and the falling line is what the section is below the centre, and that
between K and the falling line is what the section on the minor axis K
is above the centre; the sections at both joints are in the centre of
the plank.
Fig. 5 shows the bottom face mould. R A B will equal R A B, and S B C
will equal S B C, Fig. 2, and A S will equal A S, Fig. 1. Proceed as
usual to get bevels, sections and width of mould. Now, as the tangent
A B is not in a line with the straight rail, and the joint being
square to the latter, the end of shank must be bevelled so as to joint
correctly to the straight rail. Draw P P, Fig. 7, to the same bevel as
that for the shank marked O O, Fig. 6. Draw C D, Fig. 7, square to P P,
make C N equal 2 2 at section A, Fig. 6, draw the level line through N
to cut P P in E and C D in D. Now, at Fig. 2 mark off along R P, R S to
equal 2 2 or 1 1, Fig. 6. Make C S and C S, Fig. 7, equal S S, Fig. 2,
and join S E and S D for bevels T and S. Apply the bevel T as shown and
S as shown at Fig. 8. The face mould for the under side will be S S,
Fig. 2, longer, and that for the top side the same amount shorter.
[Illustration: PLATE 23.]