When cutting precision joinery by hand, sometimes a joint that’s off by a fraction of a degree is the difference between it seating or splitting apart. When diagnosing joinery problems of students, I use a vintage diemakers square (I wrote about this in 2013 here). It allows me to sneak into places no normal square can go and is more accurate than my eyeball.
Diemakers squares can be expensive, so I was thrilled to see that Chris Kuehn of Sterling Tool Works has produced a Dovetailing Ruler that can fit into a standard 6” combination square, converting it into a superb diagnosis tool.
The $25 ruler is the exact same thickness as the standard blade for a 6” square, .075”. Its major width, .329”, allows the blade to sneak under the square’s clamping screw to lock it down. The small leg of the ruler is .091” wide, allowing you to get into the smallest joints.
The Dovetailing Ruler is a fantastic idea and is much less expensive than a diemakers square. Even though I don’t need it for the dovetails I personally cut, I will definitely be using it for double-checking some hand-cut finger joints in my next project where dead-on perfect is the only way to go. Also, these little blades are great for checking the depths of small holes and a hundred other uses at the bench.
If you’re a machinist, you can make one for yourself. But the rest of us without milling machines should click here and order one. Highly recommended.
— Christopher Schwarz
P.S. The Dovetailing Ruler is .010” too thick to work in a 4” combination square, but making the Dovetailing Ruler thinner would not have been a good idea in my opinion.