How to Make Your Own Geometric Compass

Compasses are used extensively in math and drafting courses.

The geometric compass, also called a drafting or drawing compass, is used to make perfect circles and arcs. Commercial compasses have two long pieces, one with a needle at the end and the other with a pencil. The needle marks the center and the pencil leg rotates around the needled leg. Making a geometric compass at home takes only a few supplies and can be done in an afternoon.

Things You'll Need

• 8- to 12-inch pieces of 1-by-2-inch pieces of wood
• 2- to 3-inch piece of 1-by-2-inch wood
• Ruler
• Pencil
• Drill
• Sandpaper
• Needle
• Wood glue
• Wing nut screw
• Screw
• Wing nut

Instructions

1. Measure 1 inch down from one end of each of the two long 1-by-2 inch pieces of wood and make a mark with a pencil.

2. Find the center of the piece of wood and make a mark indicating the center at the 1-inch mark created in Step 1 on each piece of wood.

3. Drill a 1/4-inch hole through the marking for each wooden piece.

4. Mark the center of the bottom of one of the pieces, opposite from the drilled hole, with a ruler.

5. Drill a 1/4-inch hole into the bottom of the piece of wood.

6. Find the center of the top edge of the short piece of wood with a ruler.

7. Drill a 1/2-inch hole through the short piece of wood through the center hole.

8. Measure up 1 inch from the bottom of the short piece of wood and find the center at the 1-inch mark with a ruler.

9. Drill a 1/4-inch hole through the short piece of wood. You may drill all the way through the wood or stop once you reach the already drilled hole coming from the opposite direction.

10. Sand all pieces of wood to remove rough edges.

11. Place the needle into the bottom drilled hole on the long piece of wood. Secure with wood glue to hold the needle in place.

12. Nail or glue the short piece of wood onto the other long piece of wood. If nailing, avoid nailing into the center-drilled holes.

13. Place a pencil into the center drill hole on the short piece of wood.

14. Insert a wing nut screw into the hole at the bottom of the piece of wood to hold the pencil in place. The wing nut allows the pencil to be removed to be sharpened and adjust the height of the pencil in the compass.

15. Connect the long pieces of wood with a screw through the hole. Place a washer on the screw and tighten with a wing nut. This will allow the compass to be adjusted in size, as needed.

References

• Institute and Museum of the History of Science: How to Make Galileo's Compass