Your boxes look great Goat, but a trick we use at my job is to go a little under the line on whatever you're cutting, and sand down to it (allows you to clean up the rough edges and make your circle perfectly round) trust me I do aviation work and they nitpick about every little thousandth of an inch you're off //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif
Either that or find yourself a 12" hole saw //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif