when i cut mine i too went for the biggest i could cut and it worked out without a jig by letting the angle grinder guard rest along the rim while i was cutting. I would never do that again,. What I would do is go get a nice lid and use that for making your circle. I have had to make some makeshift lids because my holes are about 1/2 too much for a standard size lid. You'll appreciate a tight fitting lid when you are getting 12-13 gallons of water to strike temp.