In preparation for making the cutouts in the baffles, I got to work making a circle jig for my router. I went to several hardware stores and none of them seemed to have what I was looking for, so I just got a cheap 1/4" piece of MDF (conveniently the same thickness as the base plate for my router) and had them cut it into strips that I could use for my own circle jig. First I marked the holes for the screws that held the stock base plate onto the router.
Next I took the project outdoors where I drilled holes large enough for the base plate screws to go through. I also drilled a big 1/2" hole in the center to let the router bit pass through.
After a couple minutes I had my holes and was ready to mount it to the router, or so I thought. I had forgotten that the screws were beveled, so I had to go back and countersink the screw holes so that they would sit flush with the bottom of the jig to keep it from scratching the baffle when I cut the circle.
As you can see from the following picture, I messed up one of the first holes when I tried to countersink it, and it ended up going all the way through. I just shifted the base plate, redrew the template and started over. It ended up working great. Now all I need to do to finish this off is measure from the far edge of the router bit to the point where I want to pivot and I'll be good to go to start making some perfect circles.