Classic Door Joinery

Classic Door Joinery

How to make strong
mortise and tenon joints
with a plunge router
and a tablesaw.

By Tom Caspar

Imagine turning the
clock back 500 years
and visiting a fellow woodworker
in any large European
town. You could instantly strike
up a conversation about the fine
points of building a door with mortise and tenon joints—
he’d know exactly what you’re talking about. Woodworkers
figured out this joinery a long time ago, and we use the
same design today.

Of course, we also have modern methods of building
doors, such as cope-and-stick joinery, but when it comes
to making a large door with a loose panel, the mortise and
tenon joint is still the way to go. Properly made, it will
never sag or come apart.

There are many ways to make a door with mortise and
tenon joints. I’d like to show you how to do it using very
basic power tools—a plunge router and a tablesaw. Just
about any plunge router will do, but I prefer using a small
one, equipped with an upcut spiral bit (see Sources, below). (A small router is easier to balance than a large one.)
You’ll need a dado set for your tablesaw.

When making mortise and tenon joints, it’s standard
practice to make the mortises first, then cut the tenons to
fit. Let’s begin by looking at a new style of mortising jig I’ve

Making the mortises

We’ll be using a new
type of router jig
that automatically
centers the mortises
in the grooves.

Making the tenons

We’ll be using a
dado set and a
dedicated sled to
get a precise fit.

How to build it

This jig is composed of two simple parts. First,
there’s a replacement sub-base for your router (the
Guided Sub-Base, Fig. B). It slides in the groove
that will receive the door panel. Second, there’s
a board that supports the router as you cut the
mortise (the Stop Support, Fig. A). Th is block has
stops that limit the router’s travel, controlling the
length of the mortise.

To make the Guided Sub-Base, start by cutting
a piece of 1/4" tempered hardboard or MDF (A)
about 1/2" wider and 1/2" longer than the base of
your router. Drill a 3/8" hole in the center of the
piece. Next, cut a 1/4" groove down the approximate
middle of the piece, using a dado set. Make
the groove 1/8" deep.

Make two guide strips (B), from one longer
piece, to fit snugly into the groove. Glue them in
place. Using the dado set, cut a 1/4" x 1/4" groove in
a scrap piece and test fi t the Sub-Base in the groove.
It should slide easily, but should not wiggle. You
may have to sand the sides of the guide strips to get
the right fit. Rub a little paraffi n wax on the Sub-
Base to keep it sliding smoothly. Clamp the Sub-
Base to your router (see photo, below).

Clamp or screw the Guided Sub-Base to your router. Using a ruler
as a straightedge, position the Sub-Base so the 1/4" wide guide
strips are exactly in line with a 1/4" bit.

To make the Stop Support, cut two pieces of
3/4" plywood or solid wood the exact same width
as your door stiles and about 20" long (C). Set one
piece aside, for use later. Drill two 3/4" dia. holes
near the ends of the other piece. Make a large stop
block with a pointed end (D), and fasten it to this
piece. Lastly, make two smaller stop blocks (E).
Drill pilot holes in the ends of these blocks, then
run in two small screws most of the way. Drill pilot
holes for fastening the blocks to the Stop Support–
you’ll attach them later.


Set up the jig’s stops

Begin by milling all your stiles and rails to fi nal width
and length. (Make a few extra pieces for testing the setup
operations ahead.) Mark the face sides of each piece. Using
a dado set, cut a 1/4" x 1/4" groove for the door panel along
the inside edges of all the stiles and rails, keeping their face
sides against the tablesaw’s fence. Th e groove doesn’t have to
be exactly centered; close is good enough. It can be off set, too.

Draw the width of your tenon on the end of one rail
(Photo 1). Clamp the rail in a vise and butt the Stop Support
against the rail. Make sure the large stop on the Support is tight
against the rail. Transfer the lines from the rail to the Support.

Turn the router upside down and place the Support on
the router (Photo 2). Draw a large X on the corner of the
Guided Sub-Base nearest the large stop. Align the bit with the
right-hand line on the Support (see Photo 2 inset). Clamp one of the
small stop blocks to the Support (Photo 3). Slide the Support
so the bit aligns with the left -hand pencil line and clamp the
second small stop block in place. Draw an X on top of this
stop. Remove the Support from the router, clamp the Support
in a vise and screw the stops to the Support.


Cut the mortises

To assemble the jig, place the test piece against the
Support. Butt the end of the piece up to the large stop
(Photo 4; see inset). Place the second Support Piece (it’s
just a plain board) against the test piece, making a threeboard
sandwich. Clamp all the pieces together, and clamp
the whole assembly down to the bench.

Place the router on top of the jig, with the X mark on
the Sub-Base near the X on the Support. Plunge the bit
about 1/4" into the wood, then move the router back and
forth between the stop blocks. Plunge the bit another 1/4"
and repeat the operation until you’ve reached the full depth
of the mortise.

Remove the router and make sure the mortise is in line
with the groove; if it isn’t, adjust the position of the Sub-
Base. Also, compare the length of the mortise with your
original layout lines. Adjust the screws in the stop blocks
as necessary. Be fussy about the end of the mortise farthest
away from the end of the stile—it has to be spot on. Once
the screws are set, rout both ends of all the stiles.


Saw the tenons

Set up a 3/4" wide dado set in your saw. Door tenons are
usually at least 1" long, so cutting them will require at
least two overlapping passes. Clamp a stop block to your
sled or miter gauge’s fence to ensure that all the tenons are
the same length (Photo 5).

Place a test piece on the sled, face side down, and raise
the dado blade to cut about 1/32" lower than the panel
groove. Cut both passes, then compare the depth of the
cut to one of the door’s stiles (Photo 6). Raise the blade in
small increments, recutting the test piece, until the face of
the test rail is perfectly flush with the groove. Once you’re
set, cut tenons on the face sides of all the rails.

Turn over the test rail and repeat the same
procedure, starting with the blade 1/32" lower than the
groove (Photo 7). Check the fit of the tenon in a mortise
(Photo 8). At this point, the tenon should be too tight, or
not fit at all. Raise the blade in small increments, making
more test cuts, until the fit is correct.

How tight should the joint be? If you have to pound
or push hard on the rail to get it in the mortise, it’s too
tight. If there’s a gap between the tenon and mortise that’s
greater than the thickness of a piece of notebook paper,
it’s too loose.


Cut out the haunches

The last step in making the joint is to cut a notch just
above each tenon, leaving a small stub to fit into the
panel groove. Th is stub is called a “haunch,” making this
a “haunched mortise and tenon joint.” Th e best way to
lay out the haunch, which is identical on both ends of
each rail, is by directly marking from a stile. First, mark
the width of the tenon, so it’s exactly as wide as the
mortise (Photo 9). Second, mark the length of the haunch
(Photo 10).

You can saw the haunches by hand, but it’s faster to
use a bandsaw. Set up a rip fence to cut on the first line
you laid out. Clamp a stop to the fence to limit the length
of the cut. Use a miter gauge equipped with a fence and
stop block to make the second cut (Photo 11). Make this cut about 1/32" off the line, so the haunch doesn’t quite
bottom out in the panel groove (this guarantees that the
tenon’s shoulders will draw up tight).

Finally, round all the tenons with a file (Photo 12). A
10" double-cut flat *** gets the job done very quickly.
Place a mortise nearby for reference; you’ll be able to
copy the round shape, by eye, quite easily.


Why Use A Sled To Make Tenons?

To make tenons with a dado set, you must be able to
make a perfect right-angle cut on your tablesaw. Sad to
say, many stock miter gauges aren’t capable of this level
of precision because their bars have too much play in the
saw’s miter slots. If the head of the miter gauge wiggles
just a little bit as you make a cut, the shoulders of your
tenons won’t be straight or square or in the same plane,
front and back. And that leads to gaps or joints that are
out of square.

Here are a few solutions to the wiggle problem: First,
scrounge a second miter gauge and attach both gauges
to a long wooden fence. The fence will prevent both
gauges from wiggling. Second, use an aftermarket miter
gauge whose bar can be adjusted to custom-fit your
miter slots (see Sources, below). Third, build a sled with two
runners. Normally, a sled is just used for crosscutting with
a standard blade; if you use the same sled with a dado
blade, you’ll create a huge opening in its base and fence,
which is not ideal. It’s far better to build a dedicated sled
for making tenons—it will pay off many times over.

Click any image to view a larger version.

Fig. A: Stop Support

Fig. B: Guided Sub-Base

1. Draw layout lines on the mortising jig’s Stop Support directly
from one of the door’s rails. Cut 1/4" x 1/4" grooves in all the stiles
and rails first, then draw the width of the tenon on the end of one
of the rails.

2. Place the Stop Support on top of the
router. Line up the bit with the right-hand line on the Support.
Note the Xs on both parts of the jig—these marks will help you
orient the router the right way when you turn it over.

3. Clamp one of the stop blocks to the Support, so the adjusting
screw in the end of the block butts against the Guided Sub-Base.
Repeat this operation for the other stop block, then screw both
blocks to the Support.

4. Set up the jig and rout a mortise in a stile. The stile is clamped
between two support pieces to steady the router. Adjust the
screws in the stop blocks, if necessary, to fine-tune the mortise’s
length. Once you’re set, use the same setup to rout all the mortises.

5. Cut the tenons with a dado set, using a sled or a miter gauge.
Butt the rails against a stop, so all the cuts are equal in width.
First, cut only one face of a test piece.

6. Check the depth of the cut. Place the rail against a stile, face to
face; the rail’s face should be flush with the groove in the stile.
Adjust the height of the dado set, if necessary, then cut the face
sides of the tenons on all of the rails.

7. Cut the opposite sides of the tenons, starting with a test piece.
Lower the dado set a bit, so the tenon starts out a bit fat on the
first try. Then raise the blade little by little, making more cuts, until
the tenon is the right thickness.

8. Test the fit of the tenon in a rail. Once the dado set is at the
correct height, and the test tenon slides in nicely, cut the back
side of the tenons on all the rails.

9. Lay out the haunch—a notch above the tenon—directly from
a mortise. Clamp a stile in your vise, level with the face of the
tenon, to make this line easier to transfer.

10. Mark the length of the haunch directly from the same stile. This
time, clamp the stile so it’s even with the top edge of the rail.

11. Saw all of the haunches on the bandsaw. Set up a rip fence for
the first cuts; use a miter gauge for the second cuts.

12. Round the tenons with a file, to match the rounded ends of the


Note: Product availability and prices are subject to change.

Hartville Tool,, 800-345-2396, 1/4" Upcut Spiral Bit,
1/4" shank, #RRU2100.

Porter-Cable,, 888-848-5175, Model 450PK, Compact
Combination Fixed Base/Plunge Base router.

Woodhaven,, 800-344-6657, #4910 Deluxe Miter

This story originally appeared in American Woodworker April/May 2012, issue #159.