Manual of Purpose-Made Woodworking Joinery

Designing, setting out and making stairs 107

Main stair components required

Treads

Nowadays, 18mm MDF (medium- density fibreboard)

is often used for treads, but it is prone to short- grain

delamination when grooved near its nosing edges to

receive the tops of risers and tends to split on its back

edges when receiving screws from the riser fixings. On

better- class work, treads are of timber (mostly soft-

wood, but hardwood stairs are also popular), usually

varying in finished thickness between 18 to 28mm.

Risers

Traditionally, these were also of timber boards (and

still may be if the stair is to be made in hardwood),

usually of 16 or 18mm finished thickness. In the

1970s, 9mm- or 12mm- thick plywood was used quite

effectively – but nowadays, this appears to have been

mostly displaced by the use of 9mm or 12mm MDF

(which is cheaper) – although there is evidence that

plywood is also still in use.

Strings

These are the load- bearing, pitched on- edge boards that

house and carry the ends of the steps on each side of

a stair. For obvious reasons, one is named a wall string

(or inner string) and the other is named an outer string.

The width of these boards can vary to suit the size of

the steps and the size of the ‘margin’ below the string’s

top edge (explained further on). However, the common

minimum width of string is usually ex 225mm (220mm

finish) – although ex 250mm (245mm finish) gives

a more generous margin. The common minimum

thickness is usually ex 32mm (28mm finish) – and

more substantial stairs (usually in Category 2 or 3; or

Category 1 Stairs with cut and bracketed strings), can

require strings of ex 38mm or more.

Joints between treads and risers

Figures 6.33(a)(b)(c)(d): If a cutting list of all the

required components of the staircase is to be produced

(usually required if the work is split between joiners

and machinists), giving details of length, width, thick-

ness, etc, it will be necessary at this stage to establish

the method of edge- jointing to be used between the

treads and risers. Four methods are shown below and

although method (a), with a plywood riser is common

practice and has a good rating in first- class softwood

stairs, theoretically, there is no allowance for tread-

shrinkage. When using softwood (or hardwood) boards

for risers, methods (b) and (c) are regarded as the best

methods to combat the possible effects of shrinkage.

Practical dividing method

Figure 6.32: Traditionally, this sum was arrived
at more tediously. The total rise was marked on
a storey rod (a timber batten) and the rise was
stepped out with a large pair of carpenter’s dividers
(Figure 6.32) by a trial- and- error method of repeated
mini- adjustments, until the exact division of risers
was determined. This practical method of division
was quite accurate, but relatively time- consuming.
However, it must be mentioned that the division of a
total rise of 2.688m (used above) was in fact approx
8ft 9¾ inches in pre 1973 imperial measurements.
Even though the feet could be easily converted into
inches, most divisions required the inches to be
converted into fractions. For example, the rise (used
above) of 192mm would be approx seven inches and
thirty- five sixty- fourths of an inch. Knowing how
people generally feel about fractions, might explain
why a practical method of division evolved in yester-
year before metrication and calculators!

250 mm

Figure 6.32 A pair of wrought- iron dividers with wing- nut
adjustment, used traditionally by carpenters and joiners for
setting out. Note that the usually dull points of the divid-
ers were easily filed with a mill file, or saw file until sharp
points were produced.