Custom Geometric Compass



Introduction: Custom Geometric Compass

About: Professional Educator for over 25 years. Avid DIYer! Why pay somebody to do what you can do yourself? Active in web design and development for over 20 years. After discovering have starte...

Have you ever had the problem where the tool you were working with just did not measure up?

For the first time ever, I found my tool just did not have enough reach. I needed just an extra 1/2 inch. Sure, I could go out and buy another tool with more reach, or I could Build It!

In this Instructable I will show how to Build a Tool. a custom geometric compass in order to draw a 10 diameter circle.

All you need is a piece of scrap wood or plastic that you have pulled from the trash, masking tape, and wood screw. Oh, and a few tools for building. Once complete, this will be another treasured tool for your making needs.

Step 1: Problem

Where did my tool fall short?

So I am just about to begin a project where I need to draw a 10 inch circle. But, I discover the tool I have will only give me 9 inches.

For those of you new to using a compass for circles this is how it works.

If you want to draw a 10 inch circle you open your compass so the distance between the compass needle and pencil tip is 5 inches. This is the radius of the circle. That distance of 5 inches doubled when drawing the circle will give you 10 inches.

My toolbox compass would only open up to 4.5 inches. Therefore, shorting me a 1/2 inch on the radius and 1 full inch on the circle diameter.

Now this Instructable is not how to draw a circle. If you want to see how a compass is used, see this short and simple YouTube video I found of how to use a compass


Step 2: Materials and Tools

Building your own compass is rather simple and should not take more than 30 minutes if you have the materials and tools available. Creating this instructable actually took me much longer than building the tool.


  • Piece of 1 x 8 x 1/2 inch wood ( or measurements similar)
  • 1 3/4 inch wood screw
  • Masking or Painters Tape


  • Drill Press
  • Pencil
  • Ruler
  • Calipers
  • 5/16 drill bit (diameter of the pencil to be used in compass)
  • 1/8 inch drill bit
  • Screwdriver

Step 3: Mark Your Radius Points

We need to measure and mark a 5 inch segment on the 1 inch strip of wood. This 5 inch segment will be the radius of the circle.

  1. Draw a square line the length of your wood. Preferably down the middle.
  2. Measure and mark points 5 inches between the points.

At these points you will eventually be drilling holes.

Step 4: Measure Pencil

Before we drill holes in our length of wood we need to know the diameter of the pencil. The diameter is the distance passing through the center of an object. In this case the pencil.

With the calipers measure from one side of the pencil to the other. Next transfer the calipers to the ruler. We have a diameter of 5/16 of an inch.

Note: A 5/16 inch drill bit was noted earlier. This drill bit will be used to bore a hole where we will insert the pencil later. Be sure to measure YOUR pencil as the size of bit may be different for you.

Step 5: Drill Holes in Wood

In an earlier step we marked the radius of 5 inches. We now need to drill holes at these marks.

I prefer to use a drill press for this step rather than a hand drill to ensure a true straight hole. One of the main reasons I have the drill press is specifically to drill straight perpendicular holes.

  1. Use the 1/8 inch bit to drill a pilot hole at one end of the radius.
  2. Use the 5/16 inch bit to drill a hole at the other end of the radius.

Step 6: Prepare Pencil

Upon fitting the pencil through the pencil hole I discovered it was not snug as needed. The pencil should not move easily through the hole as we want the wood to grab and hold the pencil. So I added one layer of painters tape around the pencil. The pencil now fits as snug as a bug in a rug.

Step 7: Drive Screw Through Wood

The 1 3/4 inch wood screw is going to be the "needle" or fixed point of the compass. Drive the screw through the wood. Be sure to drive it straight. Slow and easy!

Step 8: Insert Pencil

Insert pencil into the 5/16 inch hole.

Your tool is complete! Now go draw a circle.

Step 9: Draw Circle

Sorry, but you need two hands to use this tool, so just had to show you the outcome of the circle and not the actual usage. Bottom line is that it works. I got that extra 1/2 inch in radius and 1 more full inch in diameter to give me a 10 inch diameter circle.

Now I can move back to my original project now that I have a tool with more reach.

Be sure to follow me to see what project comes next where I will use this tool.

Overall a simple project that will save you the time and money needed to run to the store to get a larger compass. As long as your measurements are accurate, you should be able to build your own tool when needed. And, make any size circle you wish. Need more reach? Get a longer piece of wood and measure accordingly.

Votes appreciated!

Don't Buy It! Make It!

The Water Dog

Build a Tool Contest 2017

Participated in the
Build a Tool Contest 2017

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