I needed to cut some 8 inch plywood discs for an ongoing project. The discs didn't need to be permanent but needed to be fairly precise.
I didn't have a compass or string, it was late and I needed the plywood discs NOW.
So here's what I did with material I had laying around. Works great in a pinch!
Step 1: Materials
1.) Plywood (obviously)
2.) Corrugated Plastic (you can use anything that's fairly stiff like plastic, cardboard, wood, etc..)
3.) Box Cutter
5.) Wood Screw
6.) Sharpie (any pen, pencil, crayon, whatever would work fine)
Step 2: Measure Diameter You Need
Step 3: Cut Your Jig
Step 4: Attach Your Jig to the Boatd
Leave it a little loose so it will rotate freely around the screw.
Once attached, remeasure the jig from the Center of the screw and put a mark 1/2 the diameter down. So in my case I made a mark 4 inches from the center of the screw.
Use a drill bit that's a little larger than the tip of your sharpie and drill a hole directly on the mark.
Step 5: Draw Your Perfect Circle and Cut!
Once the circle or circles have been drawn, use your jigsaw to cut the discs.