Woodsmith #144 machine-cut-dovetails.pdf

W OODWORKING

T ECHNIQUE

M ACHINE - CUT

D OVETAILS

With a router and a dovetail jig you can

cut a perfect-fitting joint in seconds. The

trick is getting the jig set up properly.

still remember the first time I

used a dovetail jig. I don’t

know if it was the high-powered

scream of the router, the shower

of chips, or the rhythmic motion

of moving the router in and out

around the template, but I was

hooked. For the next few

months, I used dovetails on just

about ever y project I made.

Although that initial excite-

ment has subsided a little, I still

think a dovetail jig is a great

accessor y for any shop. I can’t

imagine building the chest-on-

chest featured in this issue with-

out one. For speed and accura-

cy, a dovetail jig is hard to beat.

But there’s more to cutting

dovetails than simply flipping

the switch on your router. The

jig and router requires a care-

ful setup. Plus, you’ll need a cou-

ple test pieces to “fine-tune” the

fit. Fortunately, this isn’t too dif-

ficult. All it takes is a little

patience and perseverance.

HALF-BLIND JIGS . There are sev-

eral kinds of dovetail jigs on the

market designed to cut a vari-

ety of dovetails. But one of the

more common types is that

which cuts half-blind dovetails,

see box below. (Half-blind dove-

tails are often used on drawers

where you don’t want the dove-

tails to be visible from the front.)

All half-blind dovetail jigs

work in the same fashion, see

series of photos at right. The

two workpieces are clamped in

the jig at a right angle. Then a

comb-like template is placed

over the workpieces. A bushing

on the router base (or some-

times a bearing on the router

bit) guides a dovetail-shaped bit

around the “fingers” of the tem-

plate, cutting both the pins and

the tails at the same time.

{ Clamp pieces in jig. After positioning both

workpieces underneath the jig template, tight-

en down the cams on the clamping bars to

hold the workpieces securely in place.

{ Rout dovetails. The template guides the

router in and out as the dovetails and pins

are routed simultaneously. This ensures a

perfectly-aligned joint every time.

HALF-BLIND DOVETAIL JIGS

While there are a number of half-blind

dovetail jigs on the market, they all

work in the same manner. The main

differences lie in the type of clamping

system (some use cams, others use

wing nuts), the material used for the

template (plastic or metal), and the

ease of adjusting the stops.

A bare-bones jig can be purchased

for as little as $60 while heavier-duty

versions sell for $300 to $350.

Editor’s Note : Although we used the

Woodsmith dovetail jig for this article,

the procedure is nearly identical for all

half-blind dovetail jigs of this type.

{ Test fit . With the pieces removed from the

jig, test the fit of the joint. The tails should

slide halfway into the sockets. A soft mallet

can then be used to drive the joint home.

Woodsmith

The template controls the spacing

of the dovetails. Most templates are

designed to cut 1 / 2 "-wide dovetails

spaced 7 / 8 " apart. So it’s best to plan

your projects so the width (height)

of the drawers is always a multiple of

7 / 8 ". This way, you’ll end up with a

joint that is symmetrical — a perfect

half-pin on both the top and the bot-

tom, see drawing in margin.

TEST CUTS . The template may control

the spacing of the dovetails, but there

are still a couple of adjustments that

you’ll have to make to control the fit

of the joint. And since you don’t want

to risk ruining your finished work-

pieces, you’ll need to practice on a

couple of test pieces that are the same

width and thickness as your drawer

pieces. Then once you get the set-

tings just right, you can rout the dove-

tails on your actual workpieces.

SETTING UP THE JIG . Essentially, there

are three different adjustments that

you’ll need to be concerned with

when setting up the jig.

First, a “stepped” stop on each

end of the jig is used to create an

offset between the two workpieces

and to position them from side-to-

side underneath the template. (On

some jigs, this offset is created by

using two separate stops.) This stop

ensures that the dovetails are cen-

tered on the width of the work-

pieces (leaving equal-sized half-pins

at the top and bottom).

When you’re making a drawer or

box, half the joints are cut on the left

side of the jig and half are cut on the

right side. (This way, the bottom of the

workpiece is always against a stop.)

So you’ll have to set the stop at each

” offset

between the two workpieces and to

position them from side-to-side

&/ 1 6

beneath the template. You’ll need

to adjust each end of the jig inde-

pendently, since half the joints are

cut on the left and half on the right.

end independently, see Step 1.

The second adjustment to make is

to the template. Two stop nuts on the

threaded rods control the front-to-

back positioning of the template,

which affects the depth of the sock-

ets. (The sockets are the spaces into

which the dovetails fit.)

And finally, raising or lowering the

height of the dovetail bit in the router

controls the fit of the dovetails.

Later, you’ll fine-tune each of these

adjustments. But for now, you just

want to get them “in the ballpark” so

you can make your first test cut, see

Steps 2 through 4.

adjust the stop so the edge of

the front test piece is centered in the

first notch or opening of the template.

or out so fingers of template are

centered over the “joint line” between

the two test pieces.

4 Mount &/ 1 6” guide bushing onto

router. Then to start with, raise

” from router base. It may have

to be adjusted slightly later on.

!/2

Woodsmith

1 The stops on the ends of the jig

are used to create a

2 With the test pieces in the jig,

3 Stop nuts should be adjusted in

bit

Rout Test Pieces

{ To get a perfect-

fitting joint,

you’ll need to

rout a few test

pieces first.

Once you have the initial

settings in place, you’re ready

to start making your

test cuts and “tweak-

ing” the adjustments. To

do this, place a test drawer

side under the clamping bar

on the front of the jig and a test

drawer front under the clamping

bar on top of the jig.

Make sure that both pieces are

tight against the stops and the end

of the drawer side piece is flush with

the top face of the drawer front piece.

(This is also important when it

comes to routing the dovetails in

your actual workpieces.)

ADD TEMPLATE . Next mount the tem-

plate on the jig. Hold it down flat on

the workpieces while you tighten

the wing nuts. Check to make sure

the template is resting flat and isn’t

flexed by the workpieces (especially

if your template is plastic).

ROUT THE TEST PIECES . Now the pieces

can be routed. To prevent chipout,

start by making a light scoring pass

from right to left, see Step. 5. Safety

Note: It’s normally not a good idea

to rout in this direction (backrout-

ing). But it’s okay in this case since

you are taking just a light pass.

After the initial scoring cut, start

gently moving the router in and out

of the fingers, beginning on the left-

hand side of the jig, see Step 6. You

should be able to feel the guide bush-

ing stop at the back of each notch.

Let the bushing and the template

guide the router. You want to keep

the bushing in contact with the edge

of the template, but you don’t need

side, start by making a light pass

from right to left. This skim cut estab-

lishes a clean shoulder line.

to right in and out of the notches.

Push the router into each notch until

the bushing hits the back of the notch.

to force it. Shop Tip: To help the

router glide smoothly over the tem-

plate, tr y applying a little paste wax to

the router base and the template.

One other thing. When you’re rout-

ing the dovetails, be careful to keep

the router base flat on the template at

all times. If you accidentally tip the

router or lift it up, the bit will take a

chunk out of your dovetails, your tem-

plate, or both. (This is not good.)

REMOVE TEMPLATE . When you’ve fin-

ished routing the dovetails in the

test pieces, turn off the router and

remove the template to examine the

dovetails. It’s a good idea to leave

the pieces in the jig until after you’ve

checked to make sure that you’ve

routed ever y pin and socket clean-

ly, see Step 7. This way, if you miss

a spot you can simply place the tem-

plate back on the workpieces and

clean up the area you missed.

TEST FIT . Now you can remove the

test pieces from the jig and see how

they fit. Before fitting the pieces

together, though, take a second to

blow out any chips in the sockets

and lightly sand off any wood fibers

remaining on the pieces, see Step 8.

Slide the pieces together to see how

they fit, see Step 9. Ideally, you should

be able to slide the dovetails about

halfway into the sockets by hand.

Then a light tap or two with a mallet

should fully seat the tails.

Don’t worr y if the fit isn’t perfect

on the first tr y. Chances are you’ll

have to make some adjustments to

the jig or the router bit (or both),

see box on opposite page.

The important thing is to avoid tr y-

ing to adjust ever ything in one fell

swoop. Instead, focus on one thing at

a time and keep making test cuts until

you get it right. Shop Note: You can

re-use your test pieces by simply trim-

ming the dovetails off the ends.

Once you’re satisfied with the fit, tr y

cutting a test joint on the right side of

the jig as well to make sure the stop

on this end is positioned correctly.

(You shouldn’t have to change the bit

setting or the stop nuts for the tem-

plate.) Now you’re ready to rout the

dovetails on your actual pieces.

not the workpieces) and check to

make sure that all of the dovetails

and sockets are uniform.

blow out any remaining wood

chips and sand off any “whiskers” that

are still attached to the pieces.

the sockets about half way. A

couple of taps with a mallet should

drive them in the rest of the way.

Woodsmith

5 To prevent chipout on the drawer

6 Next, move the router from left

7 Finally, remove the template (but

8 Before testing the fit of the joint,

9 The dovetails should easily fit into

Rout Drawer Pieces

The procedure for routing the dove-

tails on the final workpieces is the

same one that you used for routing

your test pieces. But this is where

all your patience in adjusting the

jig pays off. Now it’s just a matter

of clamping each piece in the jig

and routing the dovetails. The only

trick is keeping all the drawer

pieces organized as you go along.

LAY OUT JOINTS . To help keep things

straight, I like to start by laying out all

four drawer pieces on top of my

bench, with the inside faces up, see

detail ‘a.’ Then I number the match-

ing corners (starting at the left, front

corner) and label each piece (front,

back or side). Finally, label or mark

the bottom edge of each piece.

When you’ve got all the pieces

labeled, you’re ready to start routing

the first corner. There are two main

things to remember when placing the

pieces in the jig. First, the pieces are

always inserted so the inside faces

out. And second, the bottom edges

should always be against the stops.

This means that you have to cut half

the joints on the left side of the jig

and half on the right side. Shop Tip:

To help myself keep straight which

corner goes where, I also label the

ends of the jig, see drawing above.

ROUT FIRST CORNER . To rout the first

corner, place the drawer side in the

front of the jig and the drawer front

on the top of the jig, just like you did

with the test pieces. Make sure the

pieces are against the stops and the

clamps are tightened securely. Then

rout the dovetails.

At this point, you’ve routed the joint

at the left front corner of the drawer

(No. 1). Next, rout the right rear cor-

ner joint (No. 3) using the same pro-

cedure. (Place the drawer back piece

on the top of the jig.)

The other two joints (Nos. 2

and 4) are routed with the pieces

tight against the stop block on

the right side of the jig.

When routing on the right side of

the jig, follow the same procedure.

Make a scoring pass from right to left

and then move the router in and out

of the notches from left to right.

Now it’s just a matter of repeating

this process to cut the dovetails on

the remainder of the drawers. W

TESTING THE FIT

Setting up to

rout machine-cut

dovetails is

always a trial and

error effort.

There’s usually

lots of fiddling

around with test

pieces and adjusting of the

jig to get a perfect fit.

TOO LOOSE . If the joint is so loose that the

pieces wiggle around when they’re put

together, the depth of cut is too shallow, see

first photo. Increase the depth of cut about

1 / 32 " and tr y again.

TOO TIGHT . If a trial cut is so tight that

the pieces can’t be tapped together, the

router bit is extended out too far from the

router base. Decrease the depth of cut

about 1 / 32 " and tr y again.

TOO DEEP . If the pins on the drawer sides

go too far into the sockets on the draw-

er front, the sockets are too deep, see

middle photo below. To correct this,

move the template for ward (toward you)

by turning the stop nuts on the studs

counterclockwise. (Be sure to adjust the

nuts on both ends of the jig.)

TOO SHALLOW . If the pins don’t go far

enough into the sockets, move the

template back (away from you) by

turning the stop nuts clockwise.

OFFSET . If the top edges of the two pieces

aren’t flush when you assemble the joint,

the problem is either with the offset of the

stop blocks (it should be 7 / 16 ") or the fact

that the pieces weren’t tight against the

stops, see third photo.

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