To avoid the dangers of fly-cutting, I searched and found an excellent adjustable hole cutter by Malco Model HC1. The range of hole it can cut is 2 to 12 inches and I purchased it from Wicks. The price is roughly four to five times the cost of a fly cutter, but the results are uniform and very, very controllable. The pivot point can slide along the bottom rail to set your radius. The cutter bit rides between two sets of ball bearings in the end of the frame. After placing the pivot point into an 11/32" hole in your sheet aluminum, you simply drill a hole and begin to swing the cutting head clockwise around the pivot, going at a steady unrushed pace around the entire circle. In the last 1/2", you are advised to slow down, but so far I've see no perilous conditions created by the tool at the point. It can work with any hand drill, with higher speeds working the best. I would highly recommend this tool, and look forward to using it on something lighter than the .40mm wing spar webs to see how quickly and efficiently it can work on thinner metal.