As for my DIY circle jig.
All I did was remove the base plate from my dads plunge router. I then got a piece of 1/4" plexi the width of the base plate and about 15"long. You then mark the holes for the base plate onto the plexi and drill and countersink them so they dont scratch the surface of your project. You then take your bit that you will be using to cut the circles with and install it in the router. Attach the base plate. Then on a scrap piece of material cut though your new baseplate.
You now have a circle jig.
So say you need to cut an 8" hole. You take your tape measure and mark a spot 4" from the outside edge of the hole the bit cut through the plexi. Drill an 1/8" hole through the plexi at that point.
Go to your project mark your center and drill an 1/8 hole.
Leave the bit in the hole you drill and get your router. Put it in the 1/8 hole you drilled in the plate and your on your way. Its really easy.