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Skill Builder: Dovetail Joints
Issue: October 2009
Posted Date: 8/17/2009
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by Sandor Nagyszalanczy
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Roll Over Images to Enlarge
Hand Cutting Dovetails
Although it's an involved process, few woodworking tasks will bring you
the sense of pride you'll get from hand cutting a dovetail joint. Like
most operations, there are lots of different ways to cut these joints.
Here, I'll share my own method for cutting through dovetails (which are
easier to cut than half- or full-blind dovetails) with a handsaw and a
chisel.
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| Photo 1 |
To prepare for cutting the joints, machine all stock square and flat
and consistent. To give you some leeway when fitting and trimming the
dovetails later, I recommend cutting your parts very slightly longer
than the full length of the desired assembly. For example, for a
dovetailed box that's 15 in. wide and 12 in. deep, cut the sides about
12 1/16 long and the front/back 15 1/16 in. long. This way, each of the
pins and tails are cut 1/32 in. long, making it easier to sand or plane
the joint surfaces flat after assembly, for a nice, clean final look.
(Photo 1)
To begin joint layout, label all your workpieces on the inside-facing
surfaces near the ends: T for tails (tails are the parts that look like
birds' tails) and P for pins (pins are wedge-shaped parts that fit
between the tails and interlock with them, giving the joint great
withdrawal strength, especially in one direction). On drawers, you
always cut the tails on the front-facing ends of the sides and pins on
the ends of the drawer front. The joint best resists coming apart this
way, even if the glue fails! Next, mark each pair of corners, to show
which will go together. The marks prevent you from accidentally cutting
the wrong joint on the wrong end, or orienting the pins incorrectly,
resulting in a project you can't assemble.
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Photo 2
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Set your marking gauge
exactly 1/32 in. wider than the thickness of your stock (in this
example, that's 25/32 in. for the 3/4 in. stock) and scribe a line
around the face and edges at the end of all the tail boards, but only
on the two faces of the pin pieces. (Photo 2)
Next, you'll lay out the dovetail joint on the pin boards. You must
decide on the angle and size/spacing of pins (and hence, the tails).
There are lots of opinions about the "best" angle for dovetails;
however, most through dovetails are cut at either 7 or 8 degrees. When
deciding the pin spacing, it's customary to start with a "half pin" at
both ends of the joint, and then evenly space full pins in between.
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| Photo 3 |
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| Photo 4 |
Sizewise, I think the wide end of full pins looks good when cut just a
little thinner than the thickness of the stock. When in doubt, try a
couple of different layouts and use your own eyes to judge which one
looks best to you.
Set a bevel gauge to your chosen dovetail angle and lock it in place.
Now mark the half pins on the end of the stock with a marking knife, (Photo 3) orienting the fat side of each pin towards the
inside surface of the board (the side marked with a "P"). Mark all the
full pins between the half pins, spaced as desired. Now, using a small
square, strike a line from the end of each bevel mark back to the
marking gauge line. (Photo 4)
To avoid cutting mistakes,
pencil mark the waste areas between the pins that you'll cut away.
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Photo 5
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| Photo 6 |
Repeat the process on all your pin boards.
Clamp the pin board in a tail vise vertically and cut down each pin
line with a dovetail saw (or a Japanese saw, or any other fine-toothed
saw). With the blade carefully positioned on the waste side of the
line, start your cut with the saw horizontal, (Photo 5)
then angle the saw and concentrate on cutting down only one marked
vertical line at a time (Photo 6).
Finish each cut with the
saw horizontal, cutting only as deep as the marking gauge line.
With the pins cut, clamp the board flat on the bench top, "P" side up.
Now use a sharp chisel to carefully remove the waste between the pins.
To help keep your chisel plumb, you can clamp a square-edged scrap atop
the pin board. (Photo 7) Start each waste cut gradually,
creating a small notch just at the marking gauge line, then coming back
to chisel out a chip. (Photo 8) Repeat this process until
you've cut about halfway through, then flip the stock over and
carefully chisel out the rest. To assure that the tails seat fully,
undercut the middle section of each waste area slightly. (Photo 9). Use a chisel or a sharp knife to clean up the sawn edges of
the pins back to the marked lines, as necessary.
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Photo 10
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Photo 11
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Photo 12
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Photo 13
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When all the pin boards are done, it's time to transfer the pin pattern
of each board to its corresponding tail board. With the tail board "T"
side up on bench, carefully position the pin board directly over the
end of the tail board, with the narrow side of the pins showing. Use a
fine knife to transfer the profile of each pin (Photo 10).
Extend the ends of these marks to the edge of the tail board, using
your small square, then transfer the tails to the other side of the
board using your bevel square (still set to the same pin angle). Mark
the small waste area between tails with a pencil, and repeat the
transfer process on all your tail boards.
Saw down the tail lines with your saw, (Photo 11) then chisel
away the waste just as you did for the pin boards, undercutting the end
grain slightly to assure that the pins will slide into place smoothly
Use a sharp knife or the edge of a narrow chisel to clean out the sharp
corners at the base of each tail as necessary. (Photo 12).
To trial fit the joint, set the tail board "T" side up on the bench and
gently tap the corresponding pin board into place with a mallet. (Photo 13) Work slowly and don't force the joint together — it's
all too easy to damage the delicate edges of tails and pins at this
stage. If the joint doesn't slide together easily, tap the boards apart
and trim any shiny or burnished looking areas on the joint's
interlocking surfaces. Try the fit again and continue trimming until
the joint slides together snugly but smoothly.
Fixing Little Mistakes
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| Photo 14 |
A precisely fitting dovetail takes some practice to get right, so don't
expect a flawless joint the first few times you try. There are a couple
of good tricks you can try to get a better fit. If your saw blade
strayed or you've accidentally cut on the wrong side of the line,
leaving a gap between pin and tail, cut a very thin shim from your
joint stock and glue it into the gap. (Photo 14) When the
glue dries, sand or plane the surface down. Also, you can fill small
irregularities in the joint when you glue it up: After applying glue
and clamping the joint together, use a belt sander or random-orbit
sander to sand the protruding parts flat while the glue is still wet.
The sanding swarf tends to pack into any gaps left between pins and
tails, making for a cleaner finished look.
Routing Half-blind Dovetails:
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| Photo 15 |
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| Photo 16 |
Although they're time-consuming to cut by hand, half-blind dovetails
are relatively easy to cut using a template-style router jig and a
router fitted with a dovetail bit and a guide bushing. (Photo 15) While it does take quite a bit of fussing and adjustment to
get the joints fitting just right, both pins and tails are cut at the
same time in mating parts, (Photo 16) making this a very
fast process once the jig and router are set up and fine-tuned.
As for other dovetail joinery, it's paramount that the stock be milled
flat and to precise dimensions, with nice square ends on all parts.
You'll need to mill at least a couple of extra boards the same as the
stock for your project, to be used for jig setup. Label the parts as
described in hand-cut dovetails, above.
For this example, I'll cut half-blind dovetails in 1/2 in. thick drawer
sides using the Rockler dovetail jig; other jigs may require different
setup steps, so always refer to your jig's manual for precise
directions.
First, attach a 7/16 in. guide bushing to the sub-base of your router,
making sure that the guide's concentric with the collet. Install a 1/2
in. dia., 14 deg. dovetail bit in the router's chuck and set the bit's
cutting depth to 9/16 in. below the base of the router.
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| Photo 17 |
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| Photo 18 |
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| Photo 19 |
After securing the dovetail jig in a bench vise, install the straight
finger template and set the template and the stop bar to the jig's 1/2
in. scale settings. (Photo 17) [Note: if your router's
sub-base isn't 5 3/4 in. dia., see the jig's manual for directions on
setting the stop bar correctly]
Place a board vertically into the left side of the jig and adjust the
side stops so that the stock is centered relative to the template
fingers (Photo 18). Make sure the board is square to the
jig, then tighten the screws that secure the stop. Repeat this on the
right side of the jig. Now slip boards into both horizontal and
vertical positions in the jig, with their sides flush against the
left-hand stops. Butt the stock ends against each other as shown (Photo 19). Set small scraps of the same thickness as your boards
at the other end of the jig,
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Photo 20
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| Photo 21 |
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| Photo 22 |
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| Photo 23 |
so that the jig's built-in clamps will
hold the stock securely.
Rout along the full length of each template finger, working in a
clockwise direction (Photo 20) while keeping the guide
bushing in firm contact with the template's edge. (Photo 21)
It's very important to never, ever lift the router until the bit is
clear of the template, lest you ruin it. Once all the dovetails are
routed, remove the test parts and trial fit them. (Photo 22)
If the fit is loose, set the bit to cut a smidgen deeper; if fit is
tight, make the depth of cut shallower. If the tails are proud of the
joint surface, reposition the jig's stop bar slightly farther from the
template; if the tails are sunken, move it closer. Repeat the test
cutting/fitting process with the test stock set against both left- and
right-hand stops until you're getting perfect joints.
When cutting your project parts, always rout boards marked as matching
pairs of joints at the same time, with the top edge of both parts set
against the stop, and with the part's inside faces pointing up and out.
(Photo 23)Hence, half of the joint board pairs will be cut using the left-hand stop, half using the right-hand stop.
Router Cutting Through Dovetails
You can use a template-style jig (as described above) for cutting
through dovetails, but the procedure requires switching templates when
cutting the tail portion of the joint.
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Photo 24
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Further, such jigs only produce
evenly spaced dovetails of fixed proportions. A more flexible type of
joinery jig, such as the Leigh D4, has adjustable template fingers that
let you set the size and spacing of dovetails to suit your needs and
tastes (Photo 24), and cut them in a simple two-step process. Instead of having a
single fixed template,
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| Photo 25 |
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| Photo 26 |
this style of jig has adjustable fingers that
work with a router guide bushing to control the bit's cut.
Here's a brief description of how to cut through dovetails with the
Leigh jig; see the jig's manual for complete details on the procedure.
The assembly that holds the template fingers slides onto a pair of
bars. (Photo 25) Scales on the assembly are positioned on
the bar to accommodate stock thickness. To set up the jig, first clamp
a pin board vertically into the jig, then arrange two outer guide
fingers to form half pins at the edges of the board. (Photo 26) Then, arrange the desired number of finger pairs in between,
to form the full pins.
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| Photo 27 |
To rout the pins, set up your router with a 7/16 in. guide bushing and
a 5/16 in. dia. straight bit. (Photo 27). As when routing
half-blind dovetails, carefully rout around each guide finger, working
the router from left to right, and never lift the router until you're
clear of the templates.
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| Photo 28 |
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| Photo 29 |
To prepare the jig for routing the tail portion of the joint, remove
the entire finger assembly, flip it over and remount it on the jig's
bars. (Photo 28) This puts the tail-cutting end of each
finger over the tail board, which also clamps vertically in the jig.
Tails are routed with an 8 degree dovetail bit using the same router
guide bushing (Photo 29) The bit's angle matches the angle
of the pins, and the fingers mirror the layout you set for cutting the
pins. As with any router-cut dovetails, it's best to cut sample joints
on scrap boards to check the fit of pins and tails. Readjusting the
position of the finger assembly on the jig's bars allows you to
fine-tune the final joint fit. |
Sandor Nagyszalanczy is a furniture designer/craftsman.
writer/photographer and regular contributor to Woodworker's Journal.
His
books are available at: http://sandorsworkshop.com/Books.html
©2009 Woodworker's Journal
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