Loose Tenon Joinery

LooseTenon 5F00 lead Loose Tenon Joinery

Loose
Tenon
Joinery

Rout 4 variations of
these super-strong
joints with a versatile
shop made jig.

By Bill Hylton

I've used a number of different
methods to create mortise and tenon
joints, but I keep coming back to loose
tenons, because they're easy, strong
and versatile. Instead of cutting a
tenon on one part and a mortise in
the other, I rout identical mortises in
both parts, and connect them with a
fitted strip of wood—a loose tenon.
Loose tenon joinery is perfect for casework,
tables and doors of all sizes.

The only tools you need to start
making loose tenon joints are a
plunge router equipped with an edge
guide, straight bits designed for
plunge cutting and a mortising
block—a shopmade jig I've designed
that you can make in a day.The mortising
block minimizes layout work
and allows routing both edge and end
mortises from the same router setup.

You can use off-the-shelf bits and
just about any plunge router, but a
precision edge guide is a must. I use
the Micro-Fence edge guide, which I
think is the best available (see Sources, below).

 

The mortising block

This jig holds the workpiece, supports
the router and controls its movement
(Fig. A, below).The jig consists of the
mortising block itself, a top extension,
an L-bracket and a clamp board for
bench mounting.

The face of the block has dadoes
and mounting-bolt holes for the two
work holders—horizontal for edge
mortising and vertical for end mortising.
The router sits on top of the block
and overhangs the workpiece.The
router's edge guide is housed in a
track formed by the L-bracket (Photo,
opposite). Adjustable stop blocks set
the mortise length.

 

How the jig works

• The jig's registration line locates the
workpiece.

• The jig's L-bracket tracks the router
and keeps the mortise aligned with
the edges of the workpiece.

• The mortise's width is determined
by the bit's diameter.To create mortises
wider than the bit, you reposition
the fence and make a second
pass.

• The mortise's depth is controlled by
the router's plunge mechanism.

• The mortise's length is governed by
the jig's adjustable stop blocks.

• The mortise's lateral (side-to-side)
positioning is controlled by the
router's edge guide.

 

Build the jig

1.Mill stock for the main parts and
cut the pieces to final dimensions (Fig.
B, below).The mortise block's body
and the horizontal work holder must
be exactly the same length, because
you reference from the ends to rout the
vertical keyways.

2. Rout 1/4" deep vertical keyways in
the mortising block and the horizontal
work holder.

3. Rout single 1/4" deep horizontal
keyways in the mortising block and the
vertical work holder.The block’s keyhole
is stopped.

4. Rout mounting-bolt slots in each
work holder, using a plunge router and
an edge guide.

5. Plane 1/2" thick stock to fit the
work holder keyways. Cut pieces to
length to create the keys. Attach them.

6. Clamp the horizontal work holder
to the mortising block.Tap a 1/2" brad
point drill at both ends of each slot to
transfer its location to the block.
Remove the work holder and scribe
vertical lines on the block through the
four points you marked. Clamp on the
vertical work holder, mark the slots and
scribe a pair of horizontal lines.

7.Drill holes for the work holder
mounting bolts at the four points
where the horizontal and vertical lines
intersect.To secure the 3/8" bolts, I cut
threads in the wood itself.To do this,
drill the four holes with a 5/16" bit and
use a 3/8"-16 tpi tap to cut the threads
(see Sources).No cutting fluid is needed;
just turn the tap into the hole, then
back it out. Alternatively, you can use Tnuts
or drive threaded inserts into the
body to secure the bolts.

8.Glue and clamp the top extension
to the mortising block. Clean off any
dried glue after removing the clamps.
Then joint the assembly to ensure that
its top surface is square to the face.

9. Attach a 3/8" thick wood fence to
your router's edge guide.Then size the
L-bracket parts to create a groove that
will house the fence.The fit should be
snug, so the fence slides without any
wobble.Glue the L-bracket parts together and install them.

10.Make both stop blocks from one
long piece of 5/8" by 2-3/4" stock. Rout
the 1/4" deep keyway and two mounting
bolt slots. Cut the stops to final
length.Make keys and attach them.

11. Rout matching keyways in the
top of the mortising block.

12. Set the stops in place on the
block and mark locations for mounting
bolt holes.Drill and tap the holes for
1/4"-20 tpi bolts.

13. Install toggle clamps on the
work holders (see Sources). I installed
longer threaded spindles on all the
clamps and used a 500-lb.size on the
vertical work holder. Be sure to mount
the clamps so they don't interfere with
the router.

14.Draw a registration line centered
on the face and top of the mortising
block.

15.Glue on the clamp block.

 

Create the basic loose tenon joint

1. Lay out an edge mortise (Photo
1). It doesn't have to be elaborate,
just lines marking the mortise ends
and centerline. Only one line is essential:
a centerline across the mortise.
This mark aligns with the jig's registration
line.

2.Position a test piece on the jig, using
the horizontal work holder (Photo 2).

3.Adjust the work holder so the edge
of the workpiece is flush with the jig's
top. Line up the workpiece centerline
with the block's registration line (Photo
3).Adjust the toggle clamps to hold the
work securely.

4. Install a bit designed for mortising in
the router.Up-spiral bits are popular these
plunge cuts, but they're not essential.

5. Install the router on the jig and
test-slide the edge guide's wood fence
in the L-bracket groove. Apply wax, if
necessary.

6. Bottom the bit onto the workpiece.
Then move the router to center
the bit on the mortise centerline
(Photo 4). Lock down the edge guide
and set the plunge depth.

7. Install the stop blocks to establish the length of the mortise (Photo 5).

8. Rout the mortise (Photo 6).
That's all it takes. As long as the faces
of the workpieces are oriented the
same way on the jig, all the edge
mortises routed with this setup will
be the same, regardless of where they
fall on the workpiece. Just scribe a
centerline across each mortise, and
align it with the registration line on
the block (Photo 7). If all of the mortises
are located in the same place on
each workpiece, you don’t even have
to mark them. Instead, just fasten a
stop on the jig against the end of
your test piece and use it to register
the workpieces.

9.The only change you have to
make to rout the matching end mortises
is to switch work holders (Photos 8
and 9).

10.Mill loose tenon stock to complete
the joint. First, plane a length of
stock to fit the mortises. It should slip
in without wiggling or binding. Rip the
blank to width, slightly less than the
mortises’ length.Next, round the
blank’s edges to match the mortises.
Then cut individual loose tenons from
the blank.

 

Reinforce a cope and stick joint

Routed cope and stick joints look
great, but their stub tenon construction
may not be suitable for large cabinet
doors. Adding loose tenons
strengthens these joints.

Rout the mortises before you rout
the cope and stick profiles, so you don't
have to work around stub tenons on the
ends of the rails. (The mortises won't
interfere when you rout the profiles.)
Center the mortises across the thickness
of the workpiece.They probably won’t
align with the stub tenons produced by
the cope cuts, but that doesn’t matter,
because everything will be hidden in
the assembled joint.

Start with the end mortises.Offset
them away from the rails' inner edges,
so the panel groove won't cut into the
mortises (Photos 12, 13 and 14).
Locate the edge mortises in the stiles according to the rails' offset end
mortises.

Be mindful of the rails' offset
mortises when you rout the profile
and panel grooves. It's all too easy
to rout the wrong edge.

 

Twin mortise joints

In post-and-rail constructions
made using thick stock, you can
make stronger joints by doubling
the loose tenons.The inside mortises
on the posts of these corner
joints will intersect, so they must
be shorter; their tenons are
mitered.The outside post mortises
are deeper, so their tenons can be
longer.The rail mortises can all be
the same depth.

Orient the workpieces with their
outside faces against the mortising
block. Set up and rout the outside
mortises.You'll have to change
work holders when you switch
from routing edge to end mortises.
Reposition the bit and rout the
inside mortises (Photo 15). Reduce
the final plunge depth when you
rout these mortises in the posts.

 

Loose tenon table joint

In this construction, the apron usually
is inset from the leg faces.My
approach is to set up for the mortises
in the legs (Photos 16 and 17).To
rout the aprons, I use double-faced
tape to install a shim equal in thickness
to the inset between the apron
and the block (Photo 18).Be sure to
install the aprons outside-face-in
before routing their mortises.

Sources

(Note: Product availability and costs are subject to change since original publication date.)

Micro Fence, microfence.com, 800-480-6427, Micro Fence
Edge Guide.

Buy Destaco, buydestaco.com, 800-560-9292, De-Sta-Co Horizontal
Toggle Clamps, #215U;
#225U (500 lb. cap.).

Tap and Die sets are available at
hardware stores and home centers.

Fig. A: Loose Tenon Mortising Jig

LooseTenon 5F00 fig a Loose Tenon Joinery

Despite their name, loose tenon joints
fit as precisely as traditional mortise
and tenon joints, and are just as strong.

Fig. B: Dimensions

Mortising Block

LooseTenon 5F00 fig b mort block Loose Tenon Joinery

Stop Block

LooseTenon 5F00 fig b stop block Loose Tenon Joinery

Horizontal Work Holder

LooseTenon 5F00 fig b hor work holder Loose Tenon Joinery

Vertical Work Holder

LooseTenon 5F00 fig b vert work holder Loose Tenon Joinery

This story originally appeared in American Woodworker April/May 2009, issue #141.

AW141cover Loose Tenon Joinery

April/May 2009, issue #141

Purchase this back issue.

Click any image to view a larger version.

LooseTenon 5F00 intro Loose Tenon Joinery

Adapt your router to the jig by installing a fence on the edge guide that fits the slot
formed by the jig's L-bracket.This keeps the bit aligned as the router slides back and forth.
To move the bit laterally, you simply adjust the edge guide.

The Basic Loose Tenon Joint

LooseTenon 5F00 basic loose tenon joint Loose Tenon Joinery

LooseTenon 5F00 1 Loose Tenon Joinery

1. Lay out one edge mortise on a test piece
to set up the router and jig.The mortise
centerline is used for positioning the workpiece
on the mortising block—it's the only
layout mark required for every mortise.

LooseTenon 5F00 2 Loose Tenon Joinery

2. Set up the jig to rout the edge mortises.
Install the horizontal work holder and position
the test workpiece so its edge is flush
with the top of the jig.Then tighten the
bolts.

LooseTenon 5F00 3 Loose Tenon Joinery

3. Align the work's mortise centerline with
the jig's registration line.Then lock the test
piece in position.

LooseTenon 5F00 4 Loose Tenon Joinery

4. Install the router and adjust the edge
guide to center the bit on the work.Then
adjust the router's plunge-depth stop to the
desired mortise depth.

LooseTenon 5F00 5 Loose Tenon Joinery

5. Install the stop blocks. Move the router to
one end of the mortise and align the bit's
edge with the layout mark. Slide the stop
against the router and tighten the bolt. Set
the second stop the same way.

LooseTenon 5F00 6 Loose Tenon Joinery

6. Rout the mortise with a series of shallow
cuts. Plunge the bit about 1/8", feed quickly
to the far stop, retract the bit, return to the
starting position and go again.

LooseTenon 5F00 7 Loose Tenon Joinery

7. Mark your stocks' outside faces and
always orient the same face against the
mortising block when you rout. Once all the
edge mortises are routed, switch to the vertical
work holder to rout the end mortises.

LooseTenon 5F00 8 Loose Tenon Joinery

8. To mount the vertical holder, clamp a
workpiece with its mortise centerline
aligned with the jig's registration line. Slide
the holder against the workpiece and tighten
the bolts.

LooseTenon 5F00 9 Loose Tenon Joinery

9. Install the router and rout the end mortise.
The length, width, depth and placement of
the mortise don't change when you switch
work holders.

LooseTenon 5F00 10 Loose Tenon Joinery

10. Size a loose tenon blank. Plane a length of
stock to fit the mortises. It should slip in
without wiggling or binding. Rip the blank
to width, slightly less than the mortises'
length.

LooseTenon 5F00 11 Loose Tenon Joinery

11. Round the tenon blank's edges to match
the mortises.Then use a crosscut sled to cut
individual loose tenons from the blank.

Reinforce a Cope and Stick Joint

LooseTenon 5F00 reinforce a cope and stick joint Loose Tenon Joinery

LooseTenon 5F00 12 Loose Tenon Joinery

12. This variation requires offsetting the rail
mortises, so they don't interfere with the
panel groove. Lay out the offset mortise on
a pre-routed rail.Then use this rail to position
the vertical work holder.

LooseTenon 5F00 13 Loose Tenon Joinery

13. Rout the mortises before you rout the cope
and stick profiles.Your initial set-up positions
the mortise in only one end of each
rail, because both ends of the rail must be
routed with the same face against the block.

LooseTenon 5F00 14 Loose Tenon Joinery

14. To position the mortise in the other end,
install a shim equal to the panel groove's
depth between the work stop and the rail.

Twin Mortise Joints

LooseTenon 5F00 twin mortise joints Loose Tenon Joinery

LooseTenon 5F00 15 Loose Tenon Joinery

15. Rout twin mortises in two steps. Lay out
and rout the first mortises in both the
edges and ends. Reposition the bit for the
second mortises and go again. Always orient
the same face against the fence.

Table Joint

LooseTenon 5F00 table joint Loose Tenon Joinery

 

LooseTenon 5F00 16 Loose Tenon Joinery

16. With table joints, the aprons are usually inset
from the legs.Start by mortising the legs.
Clamp the leg with its outside faces against
the block and the work-holder.Position the
bit, set the stops and rout the mortise.

LooseTenon 5F00 17 Loose Tenon Joinery

17. Flip and rotate the leg to rout the second
mortise. It doesn't matter that the leg now
extends in the opposite direction, because
the mortises are centered on the jig's registration
line.

LooseTenon 5F00 18 Loose Tenon Joinery

18. To inset the aprons from the legs, you offset
their mortises by the amount of the
inset. Attaching a shim of the desired thickness
to the jig automatically offsets the
mortise correctly.

 Loose Tenon Joinery

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