The spline dovetail is a joint that
can be used both for strength
and decoration. It looks especially
attractive on small carcases and is very
popular with boxmakers. It's simple to
make, and the only tools needed are a
router fi tted with a dovetail cutter, and a
tilting arbour table saw. However, you do
need to make a simple jig fi rst. This can
be modifi ed to suit your particular router/
guidebush combination. The design here
uses a 24mm guidebush.
Start by making the jig as shown in the
picture and drawing. Use 18mm MDF for
strength, and make sure that the included
angle is exactly 90 degrees to ensure
stability. The sizes given are advisory,
though keep the top plate as large as
possible for maximum router support.
The dovetail splines are inserted through
an already assembled mitre joint, so the
fi rst step is to assemble the joint and glue
it up. It's a good idea to use biscuits to
help hold the joint in alignment.
1] Clamp your assembled mitre joint in the
bench vice so that it faces upwards
2] Mark out the dovetail spacings across
the joint. Start about 10mm in from each
edge for the outside pair, then divide the
space in between equally across the joint
3] The clearly marked-up workpiece is now
ready for machining. Fit the router with a
guidebush and dovetail cutter
4] Make a setting bar to help you set up
your jig accurately. This should fi t snugly
in the guidebush groove and have its
centre clearly marked
5] Insert the setting bar through the jig and
line it up on the fi rst of the marked lines
on the joint below
6] Clamp the jig in place so it fi ts squarely
over the mitred workpiece. Check its
alignment again with the setting bar
7] Stand the router on the jig and plunge
the cutter until it touches the joint. Set the
depth 10mm below this. Pull the router
back, plunge to full depth and lock it down
8] Start the machine and run it through
the joint. Switch off without releasing the
plunge lock. Re-set the jig and repeat for
all the marked positions across the joint
9] After machining, the joint has an evenlyspaced
series of cleanly-cut sockets
10] Remove the dovetail cutter from the
router and set a sliding bevel to match its
cutting angle
11] Transfer this angle setting to your table
saw. The crown guard has been removed
for clarity here, but must always be fi tted
when using the saw
12] Set the rip fence a little wider than the
base of the dovetail, and rip down both
sides of your timber to make the splines.
Prepare a long length; trim it to size later
13] To adjust the fi t, lay the timber on its
side, and with the blade still tilted, take
shaving cuts off the bottom until the piece
will just fi t into the dovetail sockets
14] Cut the splines into short lengths, apply
a little glue and gently drive one into place
in the fi rst socket with a hammer
15] Repeat the process for the other
sockets and put the joint aside to allow
the glue to set
16] Trim off the waste with a fl exible
pullsaw. This allows you to trim right up to
the edge without damaging the workpiece
17] Finally clean up the surface of the joint
with fi ne abrasive paper
18] The fi nished joint, with the dark
splines contrasting well with the paler
wood of the workpiece
DeadFire
