The best defense against these stresses is a well-designed, tight-
fitting mortise-and-tenon joint that locks apron to leg. The mortise
and tenon is not only a good joint for tables, but it’s also widely
used in the construction of all types of furniture, including cabinet
doors and chairs.Make tenons as thick and as long as possible
When deciding on the sizes of joinery components, the key is
to attain a workable balance. Too large a mortise, and you risk
weakening the leg; too skimpy a tenon, and you lose glue and
mechanical strength. Ideally, you want the tenon to be as big as
possible, with the joint located to maximize the mechanical con-
nection. That means the shoulders on both sides of the tenon
(which butt against the leg) must be substantial enough to resist
bending and twisting forces.
When laying out the size and placement of tenons, a full-scale,
top-view drawing will help you understand the orientation and
relationship of all the parts and will help as you cut the joints.
Thicker tenons are better—You want the tenon to be as thick
as possible. A good rule of thumb is to size the tenon thickness
a little more than one-third the thickness of the apron. While them a k i n g a h a u n c h e d m o r t i s e
Chisel the sloped
section of the
mortise by hand.
This area, called the
haunch, helps prevent
twisting. When chisel-
ing, leave the table
legs long to keep
them from splitting
near the top.Check the results using a small shopmade template. The template, cut
to the angle of the haunch, makes it easy to check your progress as you
chisel the top of the mortise.Use a plunge router with a fence. The plunge router will allow you
to creep up on the full depth of the mortise by taking light passes. The
fence will ensure accurate alignment of the mortise with each pass. For
efficiency, size the mortise to a straight bit in your collection.1
one-third rule is a good general guide to follow, sometimes it’s
better to make exceptions. If I’m building a table out of a soft-
wood, such as butternut, with aprons only^3 ⁄ 4 in. thick, I make
the tenons at least^5 ⁄ 16 in., maybe even^3 ⁄ 8 in. thick. Any smaller,
and a sharp bump to the leg might snap the tenon right off. Be-
cause you rarely see the thickness of an apron, one good design
strategy is to make it thicker—^7 ⁄ 8 in. or 1 in. will provide larger,
stronger shoulders.
Long tenons provide more glue surface—When it comes to
tenon length, you want to create as much strong long-grain glue
surface as you can. Naturally, a longer tenon has more glue surface
along its cheeks (the wide faces of the tenon) and provides more
mechanical strength to the joint. As a general rule, the longer the
tenon, the better, assuming the leg it mates with can accommodate
it without risk of damage. A tenon that’s three to four times longer
than its thickness is quite adequate.
Shoulders resist bending forces—When designing a mortise-
and-tenon joint, look to create shoulders that are as large as pos-
sible and to have a shoulder on each side of the tenon (rather
than one side only). Such a design is better suited to resisting
bending stresses from either direction. The shoulders have the2
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