My eaa newsletter editor asked how to do this so here it is.
Flange a lightening hole.
First saw cut a 7/8" hardwood dowel. Set edge of hole in the slot and gently bend the flange a little bit on the first pass around. On the second pass around the slot stopped holding and slipped off the edge when it was bent enough. It really is all about feel and working a little at a time.
The flat plane was lost after flanging this hole so I set the flange on a taper of steel and gently hammered around the flange to tighten it down to the taper. That brought the flat plane back.