Another tool & die tip: To quickly and easily locate a hole a given but imprecise distance from edges of multiple parts I would use a transfer punch and a die [like the ones from an ironworker] A die [or a washer]of for instance 2" outside diameter held flush with the edge or edges and a transfer punch locates You about 1" edge to center quickly and easily. I generally used masking tape to bush up to an odd size. Enco, MSC, Travers, and other industrial suppliers sell transfer punches, sets to 17/32" are pretty inexpensive, but often "cheap" in the bad way. The transfer screws mentioned above come in 2 varieties, one looks like a setscrew with a point, the other like a short bolt with a hex head, these stamp a circle concentric with the point, makes it easy to tell if You stayed on target when deepening the punch mark.