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Sliding Dovetails
Author: Warner
There are a lot of applications for router
cut sliding dovetails. They can hold a drawer together, join a cabinet door, fasten
table legs and rails, and lock a shelf in the sides of a cabinet, (Figs. 1, 2,
3 & 4). They can also be used with jigs and fixtures where sliding stops
and such need more purchase and interlock to keep them from slipping under load.
Though the dovetail bit inventory (industry
wide) is substantial there are gaps. And as such the ideal dovetail bit for
a given task may not exist. For example, the longest production made dovetail
bit is only 1-1/4", most are less than an 1". Consequently, there
is not a lot of penetration possible. Furthermore, the flare (taper) of the
dovetail is such that one socket (especially in square legs) may cut into another
(Fig. 5). Notwithstanding, a little woodwork when applied in the right place
can more than compensate for most of the compromise in cutter design (Fig. 6).
The router cut sliding dovetail is no match for the likes of mortising machines
and tenoners, but it is a viable connection and can play an important role in
cabinet and furniture construction.
Due to safety and practicality, the
dovetail ways (pathways) in this exercise will be cut with the hand router when
across grain and on the router table when down (with) the grain. All the tenons
will be cut on a platform jig with an edge-guided router.
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| (1)
The sliding dovetail in this drawer front is stopped. The side is centered
13/16" from the end of the front, leaving room for the slide. |
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(2)
Should you tire of the look of cope and stickery you can always dovetail
a cabinet door together. The dovetail is a bit wide in this one. |
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(3)
The table under this sample is held together with the same interlocking
dovetails. |
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| (4)
I used one dovetail shelf to help square up this open beech cabinet |
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(5)
The leg & rail dovetailed joint. |
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(6)
The short dovetails in this sample are reinforced with a corner brace, bolts
and steel-cross dowels. A connection of this sort can easily withstand the
stress of nursery schools, libraries and even prison riots. |
MATERIAL PREPARATION
It is wise to begin the joinery process
with acceptable (not heroic) and ordinary material preparation. Ignore this and
expect some joints to fit, some to jam, and some to be sloppy loose. Not only
is joinery dependent on good milling, but all woodworking processes (shaping,
drilling, sawing, sanding, etc.) demand it for consistency, safety and expedition.
Routing dovetails will require you to reference the work from its ends, faces,
and edges. Moreover, to center the cut you will have to remove equal amounts of
material from both sides of equal thickness stock. If the stock is tapered, unsquared
or otherwise misshapen, your jigs will index the work differently from stick to
stick and you can expect nothing less than a cascade of havoc as you proceed through
the stages of your project.
Better to head for the jointer
first to flatten one face, then straighten and square one edge of your boards. Don’t
hesitate to the planer for thicknessing, and lastly to the table saw to rip
to width and chop to length. The interested reader is invited to read a chapter
on material preparation specific to router joinery in "The
Router Joinery Handbook."
With milled, dry sticks in hand you
are ready to cut some dovetails. Let’s start with the sliding dovetail for
a drawer side to drawer front connection. To simplify the joint we’ll cut only
one cutter diameter dovetail way (socket). Cutting only one diameter renders
this sex of the joint constant. The tenon fixturing will therefore require
some adjustability, but we know the end product will be the same size as
the dovetail bit itself! To reiterate then, if the way (socket) is only one
diameter wide then so should the tenon be. The depth of socket should be about
half of the way into thickness of the front; for 3/4" stock cut 3/8"
deep. The length of the tenon should nearly equal the depth of the socket.
An exact sectioned tenon will not fit into the socket when both are wet with
glue. Some experimentation will be necessary to achieve the desired "slip-no
rattle" fit.
CUTTING THE SOCKET
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| (7)
Make your templates from 1/2" MDF. Square both edges to the inside of the
cleat. |
A simple way to cut the socket is with
a right angle template (Fig 7), a 1" collar guide, a Jesada 10° 618-131 dovetail
bit (or equivalent), and a fixed base router, a DW 610 for example (Fig 8). Accuracy and consistency is critical
with dovetails and the template is key here. The template facilitates the set
up. Snug the cleat (under the template) up against the reference edge of the work
and clamp it down (Fig. 9).
The centerline of the cut will be the
distance from template to the reference point minus 1/2". For example,
if the template is 10-1/2" from the end of the work, (using the 1"
O.D. collar guide), the centerline of the routed dovetail pathway will be at
10". Besides the easy set up, the template picks the router up above the
work so surface tear out and chips will not "foul the footway" of
the passing router. Cutter visibility is improved so if you have to stop on
a scribe line you can see it and the template allows the collar guide to function.
An offset router subbase will add another measure of control and safety (Fig.
10).
With an offset subbase the router can
be pressed flat on the work, the transparency of the base allows inspection
of the work in progress and you can pull the collar against the template with
the subbase knob. If the collar should deviate from the working edge of the
template you will spoil the pathway. Subbases for
the DEWALT routers and their competitors are available from the author.
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| (8)
All but one production dovetail bit will fit through a 1" O.D. PC collar.
A fixed base with an offset sub-base of some sort, a collar guide, clamp
and the right angle template is a great ensemble for a safe and easy rout. |
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(9)
One measurement to the end of the work and a clamp-down completes the set
up. |
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(10)
Pull the collar snug against the template; any squiggle and you will spoil
the cut. A left to right (away from the operator) feed will aid in straight
line tracking of the router. |
THE CUT
With the template clamped down, let’s begin.
The pathway should be cleared with a straight bit first; we might break the dovetail
bit if we don’t. If you have a spare router also with a 1" collar and 1/4"
straight bit (solid carbide is best), you can use the same set up for the dovetail
cut. Now take 2 successive 3/16" deep cuts with the straight bit. Change
routers or cutters and rout the 3/8" deep dovetail way. You may get better
tracking if you feed the router from left to right against the template.
A dovetail dado (way) in the side of
a cabinet is done the same way with a template. Make your right angle template
such that the cutter is already on track along the template before the cutter
gets to the work. So allow an inch or so of template (minimum) length on both
sides of the work.
DOVETAIL SOCKETS FOR STILES AND LEGS
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| (11)
A stack of 1/4" MDF lifts will facilitate cutter depth changes. Remove one
for each cut. Mine are trapped on the 1/2" shoulder bolt. |
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| (12)
If you make no fence changes and feed the work as before the dovetail bit
will track right down the center of the pre-low. |
Open dovetail ways (mortises) at the end
of stick are more easily cut on the router table. Legs and rails are too skinny
to support a router and even if fixtured the process is cumbersome. The sockets
(mortises) should be preplowed just as before. To facilitate the depth changes,
make a set of 3/16" or 1/4" "lifts" to pick the work up off
the table. Remove a lift for each depth change. The work will proceed nicely
if you can fixture the lifts for easy positioning and removal. Mine are trapped
on a 1/2" shoulder bolt (Fig. 11). Before starting the cut, set up a stop
to limit the workpiece travel. Your work should be straight, flat, and square
and the fence should be too. If the work is misshapen and the fence out of squares,
the work will rock or squirm as you feed it. As the cutter engagement increases
so will the tendency to break or bend the cutter. No squiggles allowed!
Do your preplowing, removing a lift/pass,
feed the work straight to the stop and straight back out along the fence. The
preplow should be about 1/16" shallower than the dovetail. Dovetail bits
track better if they do some bottom cutting. Change to the dovetail bit and
make the single pass, single diameter cut (Fig. 12).
THE TENON
The dovetail tenons are all made the same
way; with the hand router, dovetail tenon-jig and edge guide. The shoulder width
is controlled by the adjustability of the edge guide, and the length of the tenon
by the depth mechanism of the router.
THE JIG
The
jig is simply two 3/4" thick equal area MDF rectangles (11" x 16-1/2")
joined in a dado with some hardware (Fig. 13A & 13B). The window is 3 -1/2"
x 9 1/4" and its near edge is 2-3/4" from the working edge of the top.
It needn't be parallel to anything; it’s just open cutter access to the work.
The work is indexed up against the router base and against the right angle fence
screwed to the vertical panel, (Fig. 14). A toggle clamp will help hold the work
but a c-clamp should also be employed for more security. To secure the jig, screw
it to your workbench (Fig. 15). Don’t make a "thing" out of this tool.
Braces and drywall screws will hold it together just fine. (For the reader who'd
rather use it than make
it, you can order
a jig from the author [Pat Warner].)
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(13A)
The two panels are joined in a dado and held fast with steel cross dowels
and 2" bolts. You needn't get this fancy. Twin threaded dry wall screws
will work. The dado must be referenced from the working edge of the top
platform panel.
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(13B)
The fence is the other critical element. It has to be 90° to the top, (shown
upside down). |
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(14)
Index the work up against the router sub-base. A toggle clamp is suggested
rather than a third hand. A cee-clamp should also be used for safety's sake
(again shown upside down). Work in this photo shown without sub-base/router
for clarity. |
THE CUTTING
| With the
work clamped to the jig, adjust the edge guide so the cutter will make an
arbitrary but shallow shoulder along the near edge of the work (Fig. 16).
Rotate the work 180° and take the same slice on the opposite face. Fit the
tenon. If the tenon is too long or short, raise or lower the cutter as necessary.
If the tenon is too wide (and it should be for your first approximation),
find out how much. Then divide the difference in the fit (also the difference
of the tenon width and dovetail bit diameter in this case) by two. Adjust
the edge guide by this amount. The Microfence edge guide is probably the
best tool for this. Recut, refit and recut until you achieve a slip-fit.
If there is socket interference
(Fig. 17), which is likely in square leg and rail assembly, one of the
tenons will have to be rabbetted slightly with the same dovetail bit.
Clamp the rail under the window horizontally for this cut. For the best
result test this on equivalent section stock first. It is nearly impossible
to notch the tenon the right amount without a few calibration cuts (Fig
18).
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| (15)
I bolted the jig to my bench. Too much junk in the way is always a hazard. |
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| (16)
With the work clamped, the jig bolted down, a good router, sub-base and
an adjustable edge guide, it's tough to screw this cut up. Cut only on the
near side of work. Don't trap the cutter on the far side. |
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(17)
Socket interference should be expected in a square leg. |
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(18)
Take a modest arbitrary cut on the tenon with the worked clamped under the
top. The end of the work has to be parallel to the working edge of the top.
Index it against the vertical panel. |
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