116 Designing and making stairs to current building regulations
Tapered steps and their shaped strings
Figure 6.45: Arrangements of tapered steps and
their inner wall- strings are best set out on a ‘rod’. As
described in Chapter 2, rods are full- size drawings of
elevational, plan or sectional views that develop and/or
display the details required. The plan- and elevational-
view of one of the developed wall strings seen below
was set out on sheets of hardboard that had been
painted with white emulsion.Directly above this, a cramping arrangement –
either of telescopic trench- props, improvised timber
struts with folding wedges, or (in large workshops)
permanent screwing jacks connected to an overhead
beam – must be in place to exert a downwards thrust
on the encased steps.
Once this is set up, only a minimum of pressure
is first applied, then the steps are eased open at the
unconnected joints between the back of the treads and
the bottom of the risers, glue is worked in, the joints
are brought back together and screws are power-
driven into previously- drilled shank holes.
When the complete flight of steps is screwed
together, the pressure is released from the cramp-
ing arrangement and the top string is removed and
replaced again after applying glue to the housings. The
reassembled flight is then carefully, but quickly turned
over, the dry- housed string on top is removed, glued,
replaced, and pressure (more than at the start) is reap-
plied from above.
The treads must be quickly knocked up tightly
into the housed nosings (with an offcut of wood – a
‘hammering block’ – taking the hammer blows);
then each of the tread wedges is glued and driven
in, followed by the riser wedges (after cutting off the
tread- wedge projections with a chisel and mallet).
To complete the operation, the riser wedges are
trimmed off by the same method – by inclining a
wide chisel, with its ground- and sharpened- edge
against the underside step- arris and striking one or
two blows.
Note that as the sides of the string- housings are
slightly bevelled (this being automatically achieved
by a shaped TCT router cutter), when the wedges are
driven in, a dovetail effect is achieved. It should also
be noted that some joiners prefer the wedges to be
more robust; say, instead of the tread- wedges being
10mm diminishing to 4mm, they may be 15mm to
9mm. But, remember – to avoid a mix- up of wedges –
the riser- wedges (and riser- template, if used) must be
to the same angle.
It should also be realized that the top riser and the
landing- nosing – because they are up against (or very
close to) the landing trimmer- joist – cannot receive
glued angle- blocks. For this reason, it is most impor-
tant that the site- fixer glues and screws this joint
with at least three so- called ‘pocket screws’. In Figure
6.44(c), the recessed niche for the pocket screw is
shown traditionally gouged out by an in- cannel scrib-
ing gouge, but, if preferred, suitable recesses can also
be formed by drilling shallow holes with a Forstner-
type bit of, say, 16mm Ø, prior to drilling the angled
shank holes.
Figure 6.45 This half- turn stair of tapered steps (taken from
Figure 6.27) was set out to full size on a painted hard-
board rod. First, the two newels were drawn in a central
position, so that nosing- lengths 10, 13 and 16 were equi-
distant to each other. Then the nosings were set at 30°, 60°
and 90° from the left, then the right, radiating from a central
point at the back of the newels. The quick, easy and most
accurate way to do this is to describe a semi- circle on the
rod (with a beam compass in the form of trammel heads) to
the flight’s width, radiating from the newels’ central back-
point. This semi- circle will look similar to the ‘deemed width’
line in Figures 6.6 and 6.23(b) – although those are only
quadrant shaped. Then set the compass to an intelligent
guess and make trial- and- error adjustments until three exact
steps fit around half the semi- circle, between nosings 10,
11, 12 and 13 – or between nosings 13, 14, 15 and 16.
Mark them and draw the nosing- lines back to the newel’s
radial point. Once the riser faces are set back and drawn
on the rod’s plan view, the points that touch the wall string
are extended out (as shown by broken lines) and the riser
heights added to plot the wide ends of the steps – which
produce the string shape.Wall-string development
from full-size setting out
of tapered stepsUp9101112 13
141516Wall-string development
from full-size setting out
of tapered stepsUp