I hate cutting circles in wood mainly because it's difficult to get the perfect diameter (or close enough) that I need.
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
Here's what I used:
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
I needed a disc to fit inside a cardboard tube. Because of normal variation, I measured the tube across numerous areas to get an average.
Step 3: Cut Your Jig
Once you have the measurement, 8 inches in this case, over measure your plastic (or whatever material you have) by 2 inches and then cut a strip that's about 2 inches wide.
Step 4: Attach Your Jig to the Boatd
Once you've cut the jig, use a wood screw to attach it to the CENTER of your circle to be cut.
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!
Place the sharpie in the drilled hole and draw your circle using the jig as a guide. The best way is to press straight down and give a little lateral traction while drawing. Make the circle with one motion, it will minimize error.
Once the circle or circles have been drawn, use your jigsaw to cut the discs.