For Accurate Angles, Go to the Chalkboard - Popular Woodworking Magazine

## 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

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• Saville

How do we know the wooden protractors are accurately marked?

What about wood movement? From the grain orientation I would think the veryhigh and very low degree markings would change the most.

Perhaps the error inherent in these devices is small enough for fine woodworking work.

• pmac

I’m with jasalomon, I could easily see Crucible producing a version of this. With Crucible already producing bamboo french curves, a bamboo protractor isnt too far of a stretch. Accurate engraving might be tricky but I’m sure Rainy can figure it out. So Chris, is this a future Crucible tool?

• docwks

Not sure if this is a viable option as it’s not wood, but amazon has one, ETA hand2mind Protractor Tool for Dry Erase Board for \$14.70 it’s 18×11. It’s plastic.

• Tim0951

Chris, I’ve been going to garage sales and estate sales this summer. I picked up one of these large wooden protractors from an engineer recently. Maybe a spotty source but to all keep an eye out for the engineers because they have all the tools.

• jasalomon

Time to fire up the Crucible bamboo ply cutting and engraving operation? I’m picturing Chris hitting a big red button and Raney throwing on a lab coat and sliding down the firehouse pole, Ghostbusters style. Allowing for the possibility that may not be exactly how Crucible works though…

• David Lyell

Bahahaha, thank you for that image!

• LongLeaf

Had a saying in the military, Measure it with a micrometer, mark it with a grease pencil, cut it with an axe.

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