Make this affordable circle cutting jig in under 15 minutes!

Step 1: Tools & Materials

Tools

Jigsaw
Plunge Router
1/4" straight or spiral upcut bit
Flush trim bit
Drill
Tape Measure

Materials

32" x 8" x 1/2" piece of plywood - I used 1/4" plywood but it wasn't quite thick enough to properly countersink the screws.
1 Screw

Step 2: Attaching Your Router

First flip your plunge router base over and remove the screws. Take the plastic bottom over to your plywood and transfer the hole locations. Make sure you put it at the end of your plywood piece. Drill and countersink the transferred holes so the jig lays flat while cutting. Then connect your plunge router base with the screws from earlier and plunge into the jig using your preferred bit.

Step 3: Pivot Point

Take the radius of the circle you want to cut and measure that distance away from the hole left by your plunge router.

In this case I wanted my circle to have a 3' diameter so I measured 18" away from the edge of the hole and marked a point. I then drilled a hole there.

Step 4: Optional: Shape the Jig

I rounded the corners of my jig and tapered its sides. This is completely optional and purely for aesthetics.

Step 5: Time to Cut a Circle!

Find the center of the board you want to cut your circle out of and screw the jig down. If you're making something that will be visible, such as a table top, make sure to put the jig on the underside. Turn your router on and rotate the jig clockwise, lowering the bit with each pass. Be aware of the surface below your board so you don't cut into it. If your lumber is thinner you can simply raise it up and complete the cutting. However, if it is thicker, you will need to use a jig saw and flush trim bit to finish cutting the circle. I simply cut as deep as my bit would reach, used a jig saw to cut between the void left, and a flush trim bit to clean up the remaining wood.