Manual of Purpose-Made Woodworking Joinery

124 Designing and making stairs to current building regulations

triangular fretwork completed, the bullnose end of

the riser containing three of the holes had to be bent

to shape. This further challenge was overcome by an

experimental mixture of traditional techniques involv-

ing saw kerfs and staving. Vertical, saw- kerf grooves

were cut across the backsides of the three ring- bands

• and these 6mm- wide grooves were made slightly
  v- shaped in width. Their depth removed four of the
  five cross plies to expose a 4mm width of face ply. The
  idea was that this would act as a pliable veneer and
  allow the plywood to bend easily. As illustrated above,
  to strengthen the exposed portions of bent face- veneer
  (and reconsolidate the 9mm ply), 4mm × 8mm timber
  inserts (staves) were glued into the vertical grooves
  when cramping up.
  After the usual glue- setting period, the slightly
  protruding staves were cleaned up on the concaved
  face of the riser and one of the 18mm ply, shaped
  back- supports was glued and screwed into its top
  position. The sash cramp was then released and the
  staves that were exposed in the openings of the fret-
  work were carefully removed with a fine, sabre- type
  keyhole saw. The half- framed riser was then glued
  and screwed to the underside of the scotia board
  (that had been previously glued and screwed to the
  underside of the bullnose tread) and – to complete
  the bottom- step assembly – the second hockey- stick
  shaped back- support was glued and screwed to the
  base of the riser.

String details

Figures 6.53(a)(b)(c): The three strings in this staircase

are technically described as 1) the inner (wall) string;

2) the outer (return) string; and 3) the outer (wreathed)

string. The first two were developed on rods, as shown

in Figure 6.49(b) and (c) and – because of material

availability – they were comprised of 30mm- thick

plywood that I built- up by bonding 18mm- and

12mm- thick pieces together. Partly to conceal the

edge appearance of the plywood and partly to create a

wider surface for the balusters on the outer string, the

top edges of both strings were lipped with 7mm- thick

round- edged capping; the round edge was flush on the

wall string, but projected by 7mm from each face of

the outer string. The capping’s minimal thickness of

7mm enabled it to bend to the curved easings of the

two strings’ top edges.

Regarding the wreathed (coiled, spiral- shaped) string,

I chose at the outset to simplify this from that shown

on my original drawing (Figure 6.47) and it became a

simple floor- standing quadrant shape of solid, two-

piece timber that was joined (by dowelling and gluing)

to the extended, square sections of the adjacent newel

posts.

circular band around the 64mm Ø holes that

accounted for the other two divisions. These bands

created the radial triangles that were removed by the

jigsaw. The challenge in setting out was in getting the

rows of circles to finish with a full banded circle at

each end of the varying riser lengths. And this was

achieved by allowing the linkage bands between the

circles (which had to be less than two bands, anyway,

to achieve structural linkage) to overlap by a slightly

greater or lesser amount on each riser.

The bottom riser required nine banded 64mm Ø

holes and, after these had been drilled out and the

Figure 6.52 (c) As illustrated, the straight portion of the
riser was temporarily supported by a 100mm- wide par
board on each side, held by screws fixed through the
open fretwork, then the 4 × 8mm timber inserts (staves)
were positioned into the glued grooves and the end
bent up and held with a sash cramp; and (d) the internal
shape of the step was tested (during the cramping) with
one of the two hockey- stick shaped and drilled back-
supports previously prepared for the riser from 18mm
plywood (shown in Figure 6.51(b)).

(c)

(d)

Figures 6.52 (a) and (b) Part elevation and plan
showing the 15 saw- kerf grooves that were required in the
backside of the bottom riser. Note that the un- kerfed end
on the left was for the step’s square entry into the front of
the newel post.

Backside view of bullnose-end of bottom riser

Plan view of saw-kerf grooved riser

(a)

(b)