When I teach woodworking, most of my job is diagnosing defective dovetails. Tail walls that are not 90°. Floors of pin and tail boards that have lumps aplenty.
My diagnosis tools are my sensitive fingers, a small square and my eyes.
But in some situations, all of those tools fail. When cutting dovetails with skinny pins, it’s impossible to get a finger or a square into the joint to feel it up. The eye helps, but it usually needs some help.
When I was in Australia in March, almost every student owned one of the incredible Chris Vesper Double Squares. This square had a skinny blade that could reach into any joint and point out with great alacrity (thanks Megan) the problems inside the joint.
I don’t own one of the Vesper squares, though I wish I did. But when I returned home to the States, I remembered that I had an old Lufkin Diemaker’s Square with a similar blade. I’d bought it at a flea market in the 1990s for a ridiculous price ($5?).
Since then, it has become my go-to tool for evaluating the joints of my students. It’s not something I use myself, but if I were a beginning dovetailer, I’d probably want one to double-check my work.
I’ve devised in my head some ways of converting a combination square to hold a skinny blade to do this operation. And I’m sure that you are smart enough to come up with some way of checking your work. And that’s the bottom line: Pay attention. If you aren’t certain your walls are 90° and the floors are flat then you probably should check them.
— Christopher Schwarz