20 Joinery joints
In general joinery work, tenons normally have
two shoulders, one on each side- cheek – but, occa-
sionally, to position a mortise or a rail off centre
for various reasons, a tenon may have only one
shoulder and it is then known as a bare- faced tenon.
For example, on stair work, the string- board (the
outer string) that is tenoned into the newel posts
may have bare- faced tenons with offset (off- centre)
mortises in the posts – especially if the string has a
minimally finished- thickness of only 28mm, which
is quite common nowadays. In this case, the reason
for the bare- faced tenons is to create more shoul-
der depth on the step- side of the string, so that the
12mm deep tread- housings (that meet the newels
and run into the area for the tenons), do not cut
into – and possibly weaken – any part of the 16mm-
thick tenons.
Tenons with three or four shoulders (where the
tenons have been reduced in width as well as the
normal reduction in thickness that produces the
tenon’s cheeks and side- shoulders) are more com-
monly used in furniture- making, than joinery.
This reduction in the tenon’s width is done to
mask the entry point into the mortise and hide
any slightly- oversized mortising or mortise- chisel
damage. It also eliminates the risk of the mortise’s
entry- point being revealed if the tenon should even-
tually shrink in width. Such considerations appear
not to have been given to traditional – or modern –
joinery. But they could be; especially on hardwood
jobs.
be minimal, to a maximum of 5mm (as over- reduced
tenon- width reduces joint- strength) – and if the rail
is not in mid- frame area, but forms a corner angle (as
does the top rail of a door), then the outer edge of the
tenon must be reduced much more to conform to the
rules of tenon- reduction and haunching.Outer- edge tenon reductions
Figure 3.3(a)(b): Framed members such as rails and
stiles that form right- angles, acute or obtuse corner
angles, cannot be given a full width tenon. This is
because the tenon would not be contained (held in)
on the outer edge. If done this way, it would, in effect,
be a corner bridle joint (also known as an open mortise
and tenon joint) and would not be suitable where
common mortise and tenon joints were required.
Therefore, to hold the tenon in a closed mortise,
as opposed to an open slot, the tenon’s width must
be reduced. For example, the most common reduc-
tion on relatively narrow, top rails of entrance- doors
is usually one third of the tenon’s width. This is to
allow the mortise to be reduced by the same amount
so that the wedge can be safely driven- in near the
outer corner. The reduction of the tenon must be
enough to combat the pressure exerted on the so-
called short grain at the end, which can shear when
wedged (as illustrated in Figure 3.3(a) below). For
this reason, the tenon- reduction (and short grain
above the mortise) should never be less than 38mm;
(this having been traditionally established as 1½
inches). Usually (dependant on the actual width of
the top rail), the common practise of one- third reduc-
tion on wedged, through- tenons for top rails of doors
violates this old joinery rule. In fact, there is lots
of documentary and physical evidence that bygone
scribes and craftsmen preferred even greater reduc-
tion than the 38mm rule.
It seems that well- founded woodworking
rules, developed, established and passed down byFigure 3.2 (a) Single- shouldered (bare- faced) tenon;
(b) double- shouldered tenon; (c) triple- shouldered tenon;
(d) quadruple- shouldered tenon.
5 mm 5 mm5 mm(a) (b)(c) (d)
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2
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2
(a) (b)Figure 3.3 (a) Shearing of ‘short grain’ above wedged
tenon (b) 50/50 tenon- and- haunch division.In (c) and (d) above, where additional shoulders are
created, the reduction to any tenon- edge should only