Making basic mortise- and- tenon joints 31taught and practised in training establishments and
detailed in text books. And although hand- mortising
methods vary, I believe that my innovative – but not
unorthodox – way of doing it is relatively fast, efficient
and accurate.
As mentioned previously for tenoning, because
there is a separate chapter in this book covering setting
out and marking out the joints with a try square and
mortise gauge, etc, the procedure explained here starts
after the marking out has been done. However, I will
mention that the allowance for wedges, outside of the
pencil- squared mortise- lines on the back edge of the
stile, should be one third of the tenon- thickness. After
these ⅓rd allowances are pencil- squared – usually by
judgement rather than measurement – the eventual
mortise- gauge lines extend each side to include them.
Mortise- chopping
Figures 3.21(a) to (j): To make a good job of hand-
mortising, concentration and attention must be given
to sighting the verticality of the mortise chisel prior
to striking a blow with a mallet. If you can achieve
this with every blow and apply it to a good chopping
technique, you might be surprised by how fast a good
mortise can be produced. Chopping techniques vary
from orthodox to unorthodox methods – and one
of the latter that uses a series of drilled holes and is
pared out, as opposed to being chopped and reamed
out with a proper mortise chisel, should only be used
on site-carpentry work, or if a mortise is wider than
the largest mortise chisel available. The following is a
simple variation on the orthodox, traditional method,
which personally evolved many years ago. My way,
as detailed and illustrated below from (a) to (j), is as
follows:
(a)(b)(c) Position the mortise chisel between
the gauge lines in the middle area of the mortise,
leaning it at about 110° away from the flat underside
of the chisel and strike a light blow. Turn the chisel
around and place it at about 10mm from the first cut,
leaning it the opposite way and strike another light
blow. Both of these actions aim to produce a small
V- shaped incision with the short- grain fibres broken
away between the cuts. Keep repeating the procedure,
with more powerful mallet blows, working away from
the last cuts by about 6mm on each side, widening
and deepening the V- shaped mortise with each cut.
The angle of chisel will need to reduce to about 80°
and the V- shape should now be looking more like a
U- shape. After each action the chisel is removed by
levering downwards carefully to ream the sides of
the mortise and remove the wood chippings. Stop
the action when you are about 5mm away from the
mortise lines at each end, as any leverage beyond this
will cause exposed bruising. At the same time, make
sure that the deeper chisel work, at the inverted apex
of the mortise, has approximately reached half the full
depth.
(d)(e) Turn the work over and repeat the whole
procedure again. When nearing completion, you will
sense a feeling and a sighting of breaking through in
the depths of the middle area. When this happens,
enlarge the break- through point slightly to check on
the side- alignment of the upper mortise to the lower
one.
(f )(g) Now hold the chisel upright in both vertical
planes, positioned off centre in the deep part of the
mortise and start chopping estimated mid- depth cuts,
in about 6mm steps, with the flat side of the chisel
working towards yourself and the finishing line of the
mortise. Repeat this procedure on each side of the
mortise.Figure 3.20 (a) A heavy- duty mortise chisel; (b) a sash
mortise chisel.
(a)(b)Figures 3.21 (a) and (b) Initial stages of mortising tech-
nique.110º(a) (b)(c) (d)80ºFigure 3.21 (c) Chopping angle; (d) Work turned over.