Chain drilling is a manual roughing technique used to cut out a shape when a mill, bandsaw, or plasma cutter is unavailable or impractical. The fabricator drills multiple holes side-by-side along the desired contour, then knocks out the center piece and files down the remaining jagged edges. It is a slow, old-school method often used on thick plate.
Heard on the job
I can't fit this plate in the bandsaw, so I guess I have to chain drill the center out and file it square.