QUARTER-SPACE LANDING, WREATH IN ONE PIECE, TO FORM ITS OWN EASING INTO
THE STRAIGHT RAIL.
Fig. 1 shows the plan laid down exactly the same as in Plate XXIII.
Fig. 2 shows the elevation. Make Y Y equal the stretch-out of centre
line of rail, Fig. 1, and set up one step above and below as shown.
Draw the centre falling line resting on the corners and passing through
the centre at the height of half a riser above the landing. For
development of tangents, make 1, 2, 3 equal A B C, Fig. 1. Square out
a level line from the lower joint H, and make H R equal the distance
between the line 1 and the springing; join R N; then A B C will be
the tangents of face mould. From R draw the joint line square to the
straight rail, and R P square to the tangents.
Fig. 3 shows the face mould. Make R A B S equal R A B C, Fig. 2, and
S C equal the diagonal on plan, and B C equal B C, Fig. 2. Draw C O and
A O parallel to A B and B C, make C N equal C N, Fig. 2. The bevel A
and C will be the same, as both pitches are the same.
Fig. 4 shows the sections at the two joints, and the section on the
minor axis will be in the centre of the plank. But section A will be
above, and that at C below the centre. The distance between C and the
falling line is what the section at C will be below, and A above the
centre. It will be seen one corner of the rail is cut off at these
sections; this makes no difference so long as the moulding of the rail
will work it out.
Fig. 5 shows the bevels for the joints to be worked off to, so as to
make them joint to the straight rail. Draw P P to the same pitch as
O O, Fig. 4; draw C H square to P P; make C N equal 4 4, Fig. 4. At
Fig. 2 mark along R P, R S to equal 4 4, Fig. 4; make C S and C S equal
S S, Fig. 2, and draw S E for the bevel T to be applied across the end
of shank and along the tangent. Join S D for the bevel S, to be applied
through the end of shank and along the surface of the stuff; this bevel
must be held parallel to the tangent across the joint, that is, square
through the plank. Notice that in all these bevel joints if the tangent
is steeper than the straight rail, the bevel T is applied so that
the ends of shank diminish towards the inside, while if the tangent
is flatter, the end of shank will diminish towards the outside. This
will be understood by referring to Fig. 3 in this plate, and Fig. 5,
Plate XXI.
Fig. 6 shows the face mould for the under side; the shaded part N S
shows the extra length required; this will equal S S, Fig. 2, the other
end R S will be the same amount shorter. This mould is reverse to
Fig. 3.
Fig. 7 shows the wreath cut out square through the plank, before the
moulds are put on. The application of the bevels is seen here.
[Illustration: PLATE 26.]