This instructable will show how to make an accurate and easy to use jig for cutting perfect circles with a router. There are many pre-made circle cutting jigs on the market, but they are fairly expensive, and many of them don't have a very large maximum radius. Several of them also rely on a series of holes to control the size, which can be a problem if you need a very precisely sized circle that happens to be in between the sizes of two of the holes.
I will show how I made a precise circle cutting jig using nothing but scrap plywood, and a few nuts and bolts. This basic plan can be modified to make accurate circles of almost any size.
Please practice shop safety, especially when working with power tools. Take all neccesary safety precautions, and don't use any tools or procedures you're unfamiliar with or uncomfortable using.