I made a flanging form from 3/4 inch MDF. I've seen some examples of rather elaborate forms and plugs and I wanted to keep it as simple as possible without the need of a lathe. I had an idea in my mind then saw someone else's idea that was similar to mine for flanging dies. I decided to copy John Rheney: http://home.mindspring.com/~rheney/html/flanging_dies.html
I made a copy of the master form but about 1/8 inch smaller (to allow the rib to sit on after fluting). The lightening holes were cut in this form the same size as the holes in the ribs. The hole edge was then routed with a 45 deg bit around each hole. The male dies were made using the flycutter and it left a 45 bevel just as the bit broke through. They were glued and tacked to 1/2 inch plywood block.
Note: When I later started using the dies I wanted to get a little more press/depth from the die so I added a ring that I cut from 1/8 inch fiber board that sliped around the male die flange.
