Addison Pemberton, of Pemberton and Sons Aviation in Spokane, WA, sent this tip:

This is a way to make a really big holes in sheet metal with a hole sow or fly cutter and get a really round on size hole. This idea came from Nick Bishop at West Coast wings and it worked great on our Goose Center Section to add additional 4 3/4" inspection holes. The holes came out on size with in .015 and round and beautiful in .063 2024-T panels.

  1. Drill 1/4" pilot hole
  2. Open up pilot hole to 3/4 with a Unibit
  3. Install a 1/4 Bellcrank flange bearing with 2 ea #6 screws and nuts
  4. Let the pilot drill ride in the ID of the bell crank bearing
  5. Use a slow tuning drill motor and use WAD or oil lube unit you break through.

Thanks Nick for the great help this worked perfectly.

Addison Pemberton