It was a little disconcerting making such a large cutout in a finished wing but it came out fine. I used a Dremel cutoff wheel to make the initial rough cutout. I was surprised at how much the aluminum plate sprung open after it was freed from the bend in the leading edge.
After making the rough cut out I used a sanding drum in the dremel to remove the last 1/16" all the way around the edge. I then deburred and polished the edge using a piece of fine sandpaper and a scotchbrite pad.
Left wing - duckworks cutout made with Dremel cutoff wheel
