We all know the basic formulas using Pi:

Circumference of Circle = 2πr.

Area of circle = πr²

None of them, however, will help you find the center of an existing circle in a hurry. The formula for finding the centre is for math geniuses, but this simple device can be built to any size very quickly and will accurately locate the centre. (No math required)

Supplies

Materials

Thin absolutely straight material. I used 5/8” x 1,3/4” wide pieces ripped from MDF shelving with a manufactured straight edge.

White glue

Wood screws

Metal mending plate

Tools

Mitre saw

Drill with 1/16” bit

Metal shears

Screwdriver

Step 1: PREPARE THE PIECES

Cut two small pieces the same size with a 45 degree angle at each end

Cut a long piece with a 45 degree angle at one end

NOTE: Size of pieces are directly proportional to the size of the circles you are using.

Put the two small pieces together at the 45 degree angles. Cut the mending plate to fit at the joint. If necessary, drill holes in the mending plate for screws.

Step 2: ASSEMBLE

Glue the two small pieces together at the 45 degree angle.

Pre- drill then attach the mending plate on the underside with screws. Take care that the angle stays intact.

Turn the piece over and glue the long piece so it is exactly on one side of the angle. Drill and attach with screws.

Step 3: TO USE

Place the 45 degree angle at the circumference of any circle and draw a line along the inside edge of the long piece. Repeat this at several locations along the circumference. Where the lines intersect, that is your center.

(Great for cutting an actual pie in half too!)