It\’s not often I have to cut circles, and when I do, they don\’t normally have to be that precise, but I am making a bench top disc sander, and the backing board need to be 99% circular. I have seen many options for Circle Cutting Jigs, from the very professional, to the quick and simple. I just want something that will do the job, so went for quick and simple.
The other consideration, if you are going to make it with your router, is the size of your router. I have three, a big one, that for this job would be difficult to manage, a Dewalt medium sized router that is fixed in my router table wing on the table saw, and a Makita Trim router, which is very small, and will do the job on this occasion.
So, all I needed was a piece of scrap 1/2\” ply, longer than the diameter of the circle. You could just make one for the job in hand, but I decided I would make a re-usable jig, cutting up to 15\”, which would give me a 30\” circle, however on this occasion I only want a 12\” circle, so started mine at 6\”.