Haunched Mortise & Tenon

Haunched Mortise & Tenon

13 steps for making a super-strong joint.

By Tom Caspar

Of all the variations on the mortise
and tenon joint, this is one of the
best. The haunch – that short little
stub tenon at the top of the joint – adds
strength and rigidity.A haunched joint can be used in many applications,
such as door frames, paneled rail-andstile
assemblies, and table legs and rails. Here,
we’re going to build a generic leg and rail joint,
using tools you’d find in a well-equipped small
shop.

There are lots of ways to machine a
haunched joint. I settled on this system because
it’s accurate, reliable and can be easily adapted
to joints of many sizes.

Lay out a mortise

A good rule of thumb: always begin by making
the mortises. It’s a lot easier to fine-tune a tenon to
fit a mortise than the other way around.

Mill stock for the legs and rails. Cut the legs to
exact length, but leave the rails extra-long.

Determine the depths of the mortises (Photo 1).
Draw a line from corner to corner on top of one
leg. Draw a partial tenon on the end of one rail, to
indicate its position and thickness. Continue these
lines across the leg to locate the mortises. Draw the
bottoms of the mortises, leaving some solid wood
between them.

Lay out the mortise (Photo 2). In most cases, the
haunch should be at least 1/2-in. down from the
top of the leg. Shortening this distance could weaken
the joint, depending on how easy the wood is to
split and the amount of stress on the joint. Use a
marking gauge for the most precise and foolproof
method to draw these layout lines.

Mark the lower end of the mortise on the leg.
Begin by marking the rail’s width. Start the mortise
1/8 in. or so above this line.

 

Make the mortises

Mortising is a two-step operation. First, you’ll use
a router table to create a shallow groove to accommodate
the tenon’s haunch (Photo 3). Later on,
you’ll deepen part of the groove using a mortising
machine.

Set up the router table with a straight bit that
matches the desired thickness of your tenons. Raise
the bit to the depth of the haunch. There are no
hard and fast rules here, but generally the haunch’s
depth is the same as its width. Clamp a stop block
to limit the length of the cut, which should extend
the full length of the mortise.

For the best results, always push the leg into the
bit from the right-hand side of the router table,
that is, from right to left. The bit’s rotation helps hold the leg tight against the fence, ensuring a
straight cut.

You’ll have to reposition the fence for half the
mortises. Begin by making one set of mortises.
Then, unplug the router, remove the stop and move
the fence out of the way. Turn one of the legs
around and place it over the bit. Move the fence up
to the leg and clamp it down. Then rout the remaining
mortises.

Move on to a mortising machine (Photo 4). Set
the chisel’s depth according to the layout on the
leg’s end. Mortising is a three-step operation. First,
cut the outer two holes, right on the gauge lines.
Second, make holes in between, spaced by about
half the chisel’s width. Third, center the chisel on
the waste areas between the holes and finish the
mortise.

Cut the cheeks

Now that you’ve established the mortise’s depth,
calculate the length of the tenon. A tenon should
not bottom out in a mortise, so there’s room for
glue to puddle; plan on a gap of 1/16 to 1/8 in.
between the end of the tenon and the bottom of
the mortise. Once you know the tenon’s length, cut
the rails to exact size. Draw a tenon all the way
around one rail.

There are many methods to cut tenons, but one
of the best begins by using a tenoning jig on your
tablesaw. It’s quick and accurate. You can make
your own tenoning jig,
or buy a commercial one for as little as $60.

One of the slickest ways to use a tenoning jig is to
cut both cheeks without re-adjusting the fence. The
key is a spacer whose thickness exactly equals the
width of the mortise plus the thickness of your sawblade’s
kerf. If your mortise is 3/8 in. wide, for
example, and your blade cuts a 1/8 in. kerf, make
the spacer 1/2 in. thick. You may have to adjust the
spacer’s thickness for a perfect fit, so it’s a good
idea to saw a tenon on a test piece first. Once
you’ve made the spacer, you can re-use it for future
projects to save setup time.

To begin, raise the blade to the correct height
(Photo 5). Place the spacer and rail in the jig, with
the rail’s outside face placed against the spacer.
Stand both pieces on the support board and tighten
the jig’s clamp. Remove the support board.

Adjust the jig right or left until the sawblade
aligns with the tenon’s layout line. Saw the rail
(Photo 6). Turn off the saw and unclamp the spacer and rail. Set aside the spacer. Stand the rail on the
support board again and clamp the rail to the jig.
Remove the support and saw the tenon’s other
cheek (Photo 7).

Cut off the waste pieces on the bandsaw and test the
tenon’s fit. It should slide into the mortise without
much resistance. If it’s too tight, plane or joint the
spacer to make it thinner. If the mortise is looser than
the thickness of a piece of paper, add masking tape or
paper to the spacer to make it thicker. Cut another
test piece before sawing your project’s pieces.

Cut the shoulders and haunch

Saw the tenon’s shoulders (Photo 8). Depending
on whether your tenon is centered or not, you may
have to adjust the blade’s height for each side.

Use the bandsaw to cut out the haunch and the
tenon’s bottom edge. Transfer the leg’s gauge lines
to the tenon (Photo 9). Set up the bandsaw’s fence
and a stop block to make these two rip cuts (Photo
10). Use a miter gauge and stop block to crosscut the
haunch (Photo 11). A single setup will work for both
ends of the rail for all three cuts.

At the bottom of the tenon, you’re left with only a
small sliver to crosscut. It’s difficult to bandsaw this
piece precisely flush with the tenon’s shoulders, so
it’s best to make the cut slightly proud. After you’re
done sawing, clamp the rail in your bench and pare
this shoulder with a chisel (Photo 12). At the same
time, bevel the ends of the tenon to make it easier to
insert into the mortise during glue-up.

It’s best to take the glue-up in stages, first gluing
opposite pairs of legs and rails. When these assemblies
are dry, clamp them in your bench and even up
the tops of the rails with the legs (Photo 13). Plane in
from each end, so you don’t chip off part of the leg.

 

This story originally appeared in American Woodworker November 2007, issue #132.

 

Click any image to view a larger version.

A haunch strengthens a
standard mortise and tenon
joint in two ways: it helps
prevent the rail from twisting
and increases the joint’s glue
surface area.

1. Begin by
laying out
the mortises.

Draw a diagonal
line across
the leg’s end to
determine each
mortise’s maximum
depth.
The joint will
be stronger if
the mortises
don’t meet.

2. Lay out the
mortise’s
haunch
and
lower end. It’s a
good practice to
position the
lower end above
the rail’s bottom
edge. This way,
the rail will fully
hide the mortise.

3. Rout a shallow
groove

to begin making
the mortise.
Use a stop
block to control
the groove’s
length and a
rounded board,
clamped to the
table, to hold
the leg tight
against the
fence.

4. Chop the
mortise

using a mortising
machine.
The groove
helps to guide
the chisel. Use
stops or the
layout lines
you made
above to position
the chisel
at the mortise’s
ends.

5. Make the
tenon
using
a tenoning jig,
which holds
the rail vertically.
Stand the
rail on a support
board,
which you’ll
remove before
sawing. Raise
the blade 1/16-
in. below the
tenon’s shoulder.

6. Clamp a
spacer
board
between
the rail and the
jig. Remove the
support board,
so the rail and
spacer sit
above the saw
table. This prevents
them
from dragging
and tipping as
you cut. Saw
the outside
cheek.

7. Remove the
spacer
to
cut the tenon’s
other cheek.
The spacer
method frees
you from fiddling
with the
jig to fine-tune
the tenon’s
thickness. Keep
the spacer for
making more
joints this size
in future projects.

8. Saw the
tenon’s
shoulders

using a miter
gauge and a
stop block. The
cutoff pieces
are a potential
kickback hazard.
Remove
most of the
waste first,
using the
bandsaw.

9. Lay out the
haunch and
bottom
of the
tenon. Stand
one rail on a
mortise and
transfer the
layout lines. To
aid in leveling
the joint later
on, position
the rail 1/32 in.
above the leg’s
end.

10. Make two
rip cuts

using the bandsaw
and a
fence. With a
sharp blade, the
cut surfaces will
be sufficiently
straight and
smooth for a
good joint. Use
a stop block to
avoid cutting
too far.

11. Crosscut
the
haunch
using a
miter gauge.
The haunch
should be 1/32
in. or so shorter
than the
depth of the
mortise’s
groove. This
ensures that
the rails’ shoulders
butt
against the leg.

12. Pare the
small
shoulder

below the
tenon. One
advantage of a
haunched joint
is that you
don’t have to
pare end grain
above the
tenon, too.
Bevel the
tenon to make
glue-up easier.

13. The rails
should
be proud after
gluing. Plane
them flush. This
safety margin
avoids having
to level the
tough end
grain on the
ends of the
legs, should
the rails have
ended up too
low.