When I trimmed the flashing off my Van's canopy, I held the cutting disc in a horizontal position, and followed the line provided by the factory. This was a mistake. I should have held it vertically, and left as much material as possible. My cut drifted just a little, and when I carried it over to try it out on the frame, it was already too short. This was aggravated by the spreading action of the countersunk rivet head.

The plans call for an edge distance of 5/16". I don't see a reason to cut it so close, there is plenty of room for more. In the above picture, you can see that my edge distance is even less, and when I pulled the rivet, it cracked the canopy. If you look closely, even the stop drill did not stop the crack.

Since I have this situation for 18" or so along one side, there will be numerous rivets causing cracks. Considering the difficulty of replacing a canopy later, after all the fiberglass and painting is done, I have decided to buy a new canopy, this time from Todd's Canopies. I am going with the 1/4" model for extra protection from birds, and maybe it will be a little quieter. The 1/4" thickness weighs 6 pounds more than the stock 3/16".