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

For Accurate Angles, Go to the Chalkboard

 In Chris Schwarz Blog, Woodworking Blogs

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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Showing 7 comments
  • 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
      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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