Panic, the way he cuts the radius is with a homemade tool. It's an old drill motor with a two flute milling bit in the chuck attached to an adjustable arm with a bearing at the other end. He drills a center hole in the sheet aluminum, attaches the bearing with a bolt through the center hole, drills a hole on the edge of the radius for the milling bit to fit through, adjusts the arm to the correct length, then simply zips the thing around and voila...a perfect circle. He can cut up to 24" holes with his gadget.
Here are some pix of the installed shroud.
He is going to make a few adjustments to the prototype. He thinks he can make ten out of a sheet of aluminum. He's probably going to make ten and get them powder-coated satin black to see if there is a market for them. If he does, I'll post his contact info in the swap meet just in case anyone is interested.
