PLATE XVIII.
FROM THE LEVEL TO THE RAKE.
The principal thing to consider in planning stairs of this kind is to place the riser starting, so as to get a good falling line. Fig. 1 shows the plan with the centre line enclosed with tangents A B C D E.
Fig. 2 shows the elevation with the centre falling line and development of tangents. Make R N S equal stretch-out of centre line of rail, Fig. 1. Draw the landing and the level part of falling line 4 inches above it to cut the centre line at H. Draw H E to pitch of pitch-board and complete the falling line from E to J; set up the height of a riser above the landing on the right, and draw the top of step to cut the line H E for position of riser. Make E P, Fig. 1, equal S P and draw face of riser starting on plan. This riser must be slightly curved, so as to get it the same width on the end as the others. For development of tangents, make 1 2 3 4 E equal A B C D E, Fig. 1. From 4 square down a line to cut H E in D; from where the falling line cuts the centre line, square out a level line to cut 3 in C; join D C extended to cut the line 2 in B; draw A B level. Then A B and B C will be the tangents for the bottom mould, and C D and D E for the top mould; make E F, Fig. 1, equal W F, Fig. 2, and join F C for H trace.
Fig. 3 shows the face mould for the upper wreath. Make E D F equal E D F, Fig. 2, and F C equal F C, Fig. 1, and D C equal D C, Fig. 2. Draw the major axis through the centre square to F C. With S as centre and O N, Fig. 1, as radius, strike an arc at N; draw V L through the centre and tangent to the arc. For section marked 3, make N H equal O H, Fig. 1, draw H J parallel to V L, make J 3 equal H 3, Fig. 1. Draw J P parallel to S N, and P L square to major axis, join L 3 for section line.
Fig. 4 shows the sections, width of mould, &c. The process of getting the bevels being the same in every case, it would be useless repetition to describe it every time. The shaded parts of sections show the superfluous stuff to come off the top side of wreath at each section.
Fig. 5 shows the face mould for the other side of the wreath. In applying these moulds care must be taken to get the twist the right way.
Fig. 6 shows the face mould for the lower wreath. As this one has only one pitch, draw A B C at right angles and make A B and B C equal A B and B C, Fig. 2. With A as centre and A O, Fig. 1, as radius, strike an arc, draw V L through the centre and tangent to the arc; make H S equal O S, Fig. 1; draw S 4 parallel to V L, make 4 2 equal S 2, Fig. 1. Draw 4 5 parallel to A H, and 5 6 square to major axis A O; join 6 2 for section line.
Fig. 7 shows the sections for this wreath. The section at the joint C will be in the centre of plank, but that at A and 2 will be below the centre. The difference between O H, Fig. 6, and Y J, Fig. 2, is what the section on shank will be below the centre; and that between O 5, Fig. 6, and 5 6, Fig. 2, for section 2. Draw the sections below the centre as shown at Fig. 7.
Fig. 8 shows a sketch of the bottom wreath with the inside and outside worked. The shaded parts show the superfluous stuff to come off top and bottom.