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.
PLATE 29.
PLATE XXIX.
WINDERS STARTING FROM A CURTAIL STEP.
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.