
Have modern glues and clamps
rendered
this ancient joinery
technique obsolete?
Absolutely not.

Drawboring is one of the simple
reasons that so much antique furniture survives today, some of
it as sound as the day it was made.
What is drawboring? It’s a
technique that greatly strengthens a mortise-and-tenon joint,
transforming it from a joint that relies on glue adhesion into a
joint that has a permanent and mechanical interlock. In essence,
you bore a hole through both walls of your mortise.
Then you
bore a separate hole through the tenon, but this hole is closer
to the shoulder of the tenon. Then you assemble the joint and
drive a stout peg through the offset holes. The peg draws the
joint tight. Drawboring offers several advantages compared to a
standard glued mortise and tenon:
-
The joint
will remain tight. A common problem with mortise-and-tenon
joints is that the joint can open up and develop an ugly gap
at the shoulder. Sometimes this is caused by the wood
shrinking as it reaches equilibrium with a new environment
(such as your living room with its forced-air heat).
Sometimes this gap is caused by simple seasonal expansion
and contraction, especially with woods that tend to move a
lot, such as fl at-sawn oak. The peg in a drawbored joint
keeps the tenon in tension against the mortise during almost
any shrinkage.
-
The joint can be assembled
without clamps. Drawboring is excellent for unusual clamping
situations. Driving the peg through the joint closes it and
clamps are generally not needed. Chairmakers use
drawboring to join odd-shaped pieces at odd angles. It’s
also an excellent technique when your clamps aren’t long
enough. Or when you don’t have enough clamps. Drawboring
also allows you to assemble a project one piece at a time if
need be.
-
The joint
can be assembled without glue. There is good evidence that
drawboring allowed early joiners to assemble their wares
without any glue. This is handy today when you’re joining
resinous woods (such as teak) that resist modern glues or
when you’re assembling joints that will be exposed to the
weather, which will allow water to get into them and destroy
the adhesive.
-
The joint doesn’t have to be
perfect. The mechanical interlock of drawboring means that
your tenon’s cheeks don’t have to have a piston fit with
your mortise’s walls. In fact, you might be surprised at how
sloppy the joint can be and still be tight after hundreds of
years.
Drawboring requires you to be careful only when
fitting the tenon’s shoulder against your mortised piece.
The other parts of the joint are not as important. And while
I never argue against doing a good job, drawboring ensures
that every joint (even the less-than-perfect ones) can be
tight for many lifetimes. For this reason, I think
drawboring is an excellent basic skill for beginning
woodworkers.
So why has drawboring become an
almost-lost art? It’s a good question, and one that I cannot
fully answer. I suspect that modern glues and machine-made
joinery made the technique less necessary, particularly for
manufactured furniture. Drawboring does require several extra
steps, and the benefits of it – particularly the long-term
durability of the joint – is not something that is apparent to a
customer.
Another reason the technique has
fallen out of favor, I suspect, is that manufacturers have
stopped making drawbore pins. These tapered steel tools allow
you to temporarily assemble the joint to check the fit and to
ease the path that the wooden peg will later follow. You can
drawbore without drawbore pins by relying on the peg (and luck)
alone. But once you use a proper set of drawbore pins, you will
wonder why they are not in every tool catalog.
Fortunately, you
can make your own set of drawbore pins inexpensively. The story
starting on page 3 shows you how.
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