Stacks of sheets to be bound are fed into a drilling apparatus which forms a series of smooth openings into which binding elements are subsequently inserted. The stack of sheets is temporarily covered at the drilling station with a protective layer of drill lubricating material held in place by a wooden drill block which prevents development of burrs at the drill openings. The formation of the holes in the stack may be by means of a special design spiral drill or by means of a special design hollow drill.