Manual of Purpose-Made Woodworking Joinery

Frame joints 25

Blind mortise and stub tenon joints

Figures 3.12(a)(b)(c)(d): One of the main uses for
blind (closed- end) mortises and stub- tenon joints
in joinery is in stair work, when jointing strings and
handrails to newel posts. Although such tenons are
often found to be mortised into newel posts by half
the post’s thickness, in good joinery practise the stub
tenons should be two- thirds the post’s thickness. The
main reason for this is that these joints (which cannot
be cramped together in the usual manner) rely on
wooden, so- called draw- bore dowels to pull- up the

shoulders – and by this process, the short grain created

on tenons of only half newel- thickness tends to shear,

making the cramping ineffective. The vertical division

of the cheeks of stub tenons used for joining strings

to newel posts is usually based on thirds. This gives

an upper and a lower tenon and a middle haunch, as

shown in Figures 3.12(a) and (b), for a stair with a

step protruding past the newel post. However, when

the riser- board of the first step does not protrude, but

is located in the centre of the newel post, the string

(as illustrated in Figure 3.12(c)) usually touches the

floor and the lower tenon loses its containment. To

overcome this, a haunched area of at least 38mm is

allowed at the base before dividing into thirds.

Short grain
Figure 3.12(d): Note that, to simplify the mortising of
newel posts, the ideal shape for oblique stub- tenons
used on stair strings and handrails would be rectan-
gular, but – although theoretically possible on string-
tenons – it would create weak ‘short grain’ on the
vulnerable triangular part of the tenon – as illustrated
in Figure 3.12(d). And on handrails, there would
not be enough tenon- material to create a rectangle.
Another point too, from a practical point- of- view,
is that newel- mortises can be cut square or sloping
with the grain – but they cannot be undercut, sloping
Figure 3.12 (a) Oblique, bare- faced stub- tenons showing against the grain.
draw- bore holes.

Figures 3.12 (b) and (c) Vertical division of thirds on centre- lines of^2 ⁄ 3 stub- tenon depth.

(a)

—^1

3

—^1

3

—^1

3

—^1

3

—^1

3

—^1

3

38 mm

(b) (c)