Draw big circles with this shop-made beam compass



It’s surprising how often I seem to have the need to make a circle for a woodworking project and my regular drafting compass is too small. Usually, I will search around the shop and kitchen to find a bowl or a bucket that is close enough to the size I need. If I need a really big circle, I tie a string to a pencil and create an arc. This poses accuracy problems, and sometimes the string stretches.

A few weeks ago Jay Kopanski sent me a cool compass he made out of oak. I knew right away I had to make one!

You can make this compass any size you want. Mine is 22″ long, which will create nearly four-foot diameter circles. The beam runs in a track made by cutting a sliding dovetail. You can do this with a router bit, but I found that using a table saw was easier and gives you more size and angle options. If you start with a board about 4″ wide, you will have plenty of material to work with and won’t have to cut thin strips without support. Cut the sliding beam first, then cut the channel it rides in to get a good fit.


  1. Pretty cool.

    When I need a circle I draw it in a CAD program first, then create a cut file for the CNC…… 😉

    I do have a set of trammel points, but I don’t remember ever using them.

    • I don’t do facebook.

      CAD is “computer aided drawing”. SketchUp that Steve uses is a version, although it’s more properly described as a 3D modeling program. Either or both are certainly useful when designing and planning woodworking projects, but tend to have pretty steep learning curves. If you’re not pretty quick with computers in general it’s probably going to be more frustrating than helpful.

      CAD is essential to CNC because you have to have the drawing to start with before you can cut a part. Okay, that’s not necessarily true, you can program directly in the code the machine uses, but that would be like using longitude and latitude to give directions to the corner store instead of a map with street names.

    • Draft Sight has a very good free version. You can find it at:
      Cad can be used for everything from designing a skyscraper to helping with simple shop tasks.
      For example: I needed to cut a precise but odd angle. I used Draft site to draw a line, and then draw another line at the angle needed. I printed it on a piece of heavy paper and cut it out with a razor knife. I could then use it to set a table saw or miter saw at the exact angle needed. This is even helpful for calibrating tools with 22 ½, 45, and 90 degree angles. The cad program is exact.

  2. Hey Steve!

    Thank you for reminding us when we last saw this great tool! 🙂 🙂

    You did a very good job, as usual!

    As Columbo would say… One More Thing…

    If you made each end pointed, removed the pencil and nail, you would have ANOTHER great tool to measure Inside distances as well as check for Squareness…

    A perfect 3 in 1 tool!!

    Thank you very much!

  3. Steve! Always a pleasure watch your WWMM videos every Friday! Now, for the first time we’ve got captions in portuguese! Brazilian MeMo like me thank you for that…cheers mate!


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