Expert Answers
Best uses for biscuit joinery
Does biscuit joinery improve
the strength of edge-to-
edge joints when gluing
up panels? If not, why bother
spreading glue in the slots or on
the biscuits? Just how strong are
biscuit joints, anyway? Are they
stronger than joining with dowels?Bob Whiteman
Highland Park, IllinoisThe fact that a well-prepared
and glued edge-to-edge joint will
break not at the glue line, but
adjacent to it confirms that such a joint
needs no reinforcement. The only reason
to use biscuits in an edge joint is for
alignment purposes; it’s a good approach
when dealing with bowed boards. Gluing
biscuits in their slots isn’t necessary.
Biscuits can be effectively used in
butt joints. But because of a biscuit’s
relatively shallow penetration into mating
workpieces, it won’t be as strong as a
proper mortise-and-tenon joint. When
it comes to reinforcing miter joints,
biscuits are very easy to install, and
typically plenty strong for the job.That’s
the application I mostly use them for.It’s hard to draw strength comparisons
between biscuits and dowels because
strength depends on the type of joint
and the size and number of biscuits
or dowels used. Because dowels can
more deeply penetrate the joining parts,
they typically offer better mechanical
strength. On the downside, dowel joints
are fussier to make and don’t offer
nearly as much long-grain to
long-grain glue surface
as biscuits. Thus,
they tend to pull
apart over time
in heavy use.
I’ve repaired
lots of ‘em
over the years. ■Paul Anthony
Senior Editor,
Woodcraft Magazine