Redneck circle cutter attachment in DIY (Do It Yourself) Posted January 6, 2012 If you look at the 1st pic you can see the 3 6/32 bolts I have in the home made router base. These correspond with 10", 12" and 15" speaker cutouts. You drill a 1/8" hole and run the bolt for the selected size down thru the material. The bit is a 20mm straight bit. These have the cutters on the sides and they wrap around the top (bottom) of the bit. So you lower the router 1/4" at a time and cut the circle. Sure faster and easier than using a hand held jig saw. The major trick is stopping just shy of the completed hole on the last pass to avoid having the router dance across your work. Simply break the cut out and finish with a half round file. If you cut with a scrap piece underneath, you can screw down the center waste circle, clamp the outside of the baffle so it doesn't move and cut all the way through. This is done all the time cutting soundholes in acoustic guitars. Actually I use double stick tape to keep everythng place when I cut a sound hole through a guitar top but those parts a lot smaller and lighter.