For Accurate Angles, Go to the Chalkboard

Laying out accurate angles on your work is critical. So it’s funny to me that we spend $100 on a Starrett square for 90°, then spend $1.59 on a plastic school protractor for every angle that isn’t 90°.

Lucky for us, we don’t have to spend $100 to get a protractor that is accurate enough for woodwork. (Yes, I have used a machinist dial protractor and find they make you chase errors that aren’t there.)

The answer is a chalkboard protractor – the large protractors that geometry teachers would use to lay out constructions on the chalkboard. These are still made today for teachers who use chalkboards or large dry-erase boards. These large protractors are also common on the secondary market.

My mom bought me an old Acme protractor years ago that is my favorite. It’s 15-3/4” wide and has a wooden handle that helps me hold it in place on the work. The best part about the tool is that the individual degree marks are 1/8” away from each other. This allows me to dial in to a fraction of a degree with ease.

On a typical plastic protractor that is 6” wide, the degree marks are about 1/32” apart. That’s a huge difference – especially for my 50-year-old eyes.

So what if you can’t find a vintage one like mine?

Amazon carries a large plastic one by ETA that is less than $15. Here’s the link.

There are wooden ones still made, but I haven’t been able to find any that feature 1° increments. Most seem to have 5° increments. If anyone finds a reliable source for wooden ones with 1° increments, please post a comment.

One last note: I know there are lots of ways to set angles accurately. Heck, I used to do it with a framing square. And I’ve tried a lot of gizmos through the years. For some reason my brain is most compatible with the 180° half-circle protractor. If you have a favorite method, that’s cool. Don’t poop on me, and I won’t return the poo.

— Christopher Schwarz