While there have been too many words written about dovetails, there has been far too little written about using wood compression in the joint.
The only time I hear it discussed is on the woodworking show circuit, when a demonstrator is dovetailing a purpleheart board to accept a white pine one. The demonstrator has a wide margin of error when he assembles the joint because of what Glen D. Huey calls “the mash factor.” You can compress pine – a lot – when it is dovetailed into a stout wood.
In my shop, I use wood compression when cutting dovetails to keep things tight without splitting. Here’s how.
After I cut the first half of the joint I show it to the other half and use a knife to mark the shape of what I want to remove. Then I saw out the joint, but I stand off a tiny wee little itsy bit from the knife line.
How far I stand off depends on the wood. With soft woods, such as white pine, it might be 10 thou or so – I’m just guessing at the measurement. With hard woods, such as cherry or walnut, it’s less. With oak or teak or maple it’s almost nothing. I leave the knife line and the tiniest sliver possible. But I still leave something. Everything compresses.
— Christopher Schwarz