US Patent 7041933 Complex hole shaping

A method for forming a complex hole through a wall of a structure. The complex hole has a smaller cross-sectional area within the wall and an outer portion with a larger cross-sectional area adjacent a first surface of the wall. The complex hole further has an inner portion extending between the smaller cross-sectional area and an inlet opening on a second surface of the wall. The method uses an EDM process to automatically first, form an entry hole in the wall extending from the first surface to a first location inside the wall, and second, form the outer portion of the complex hole in a direction moving from the first location inside the wall toward the first surface, and third, form the inner portion of the complex hole.