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Drawboring Resurrected

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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?  Itís 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. Itís also an excellent technique when your clamps arenít long enough. Or when you donít 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 youíre joining resinous woods (such as teak) that resist modern glues or when youíre assembling joints that will be exposed to the weather, which will allow water to get into them and destroy the adhesive.

  • The joint doesnít have to be perfect. The mechanical interlock of drawboring means that your tenonís cheeks donít have to have a piston fit with your mortiseís 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 tenonís 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? Itís 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 Ė particularly the long-term durability of the joint Ė 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.


 
Learn how. Discover why. Build better.
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