The Window frames have a tooling hole that is at the center of radius for 2 opposing corners.
1) Tape window frame to desired location on inside of skin and transfer such the tooling holes to skin. Drill to #30.
2) Move Window frame to outside of skin.
3) Fabricate or buy small 1/8"ID x 3/16"OD x 3/16" long bushing and hold with Cleco to center window frame tooling hole onto 1/8" punched hole.
4) Locate frame rivet holes by extending lines from existing skin rivet holes nearby the windows. Locate 1/4" in from edge of frame. Drill #40 rivet holes in frame offline in drill press.
5) Reinstall with tooling hole and bushing and transfer drill to skin.
6) Drill Arc start and stop holes at tangent of arc using frame as template. Remove frame.
7) Use Dremel with Circle Cutting Guide and a RotoZip 1/8" bit. The pivot point on Circle cutter is 1/8" Set Pivot Point to radius and lock down. ( the pivot slide is a bit sloppy in the track so I used 0.032" shim to jam it tight so it would not move or twist. )
Use lubricate ( AlumTap or equivalent) the bit to avoid galling the bit which will cause ragged edges and uneven slot width.9) Tape bottom of Cutting guide to avoid scratches and Cut arcs in clockwise directions.
