Learned my lesson with a fly cutter years ago, they are just plain dangerous. Harbor freight sells several size punch kits that work well on aluminum and also SS firewalls. Cheap, 20-30 bucks.
RV6 completed 1991 sold.
RV7 #72018 N767T first flight 11/21/2017 150+ hrs.
IO-360M1B MT 3 blade, Dual AFS 5600.
1941 J3 Cub
2018 dues paid.