Step 6: Preparing the Mint Tin
Using a Dremel with a cutting wheel and safety glasses, cut the rough outline of the tin window. Cut the corners in wide angles. Once the lid has the window removed, use a sanding attachment to round the edges, clean up burrs, and smooth everything out.
Drill the four screw holes out and an additional hole at the bottom center for the USB charger. Expand the charger hole with either small wire cutters or a "nibbler" tool. Hopefully yours will look better than mine.
Wash and dry the tin to get rid of the metal bits and dust.