Created 72 x 72 access hole for trim tab actuator and rod.
Used hole saw to create large round opening Created 1/4" radius in each corner by step drilling down to 1/2" diameter Rough cut sides by tin snipping corner to corner Filed sides straight and tangential to corner radii Finished up corners by hand-sanding with 1/2" spindle sanding cylinder Deburred entire perimeter
Fabricated 110 x 110 cover plate from 0.025" Beveled edges for tight fit to skin