The Spiral Point Drill—A New Concept in Drill Point Geometry

Abstract

Abstract The drilling process is one of the oldest and most widely used manufacturing operations. Billions of holes are drilled each year, and over 100 million drills are manufactured annually in the United States alone. However, in spite of its economic importance, the geometrical shape of the drill point (the so-called “chisel edge”) has remained virtually unchanged for over a hundred years, even though its disadvantages of lack of centering, and poor cutting action at the center, have long been recognized. This paper describes an investigation into the cause of these disadvantages and a search for other geometrical forms which might result in improved performance. In the course of this investigation a “three-dimensional spiral” point shape was devised with interesting technical and performance characteristics, together with a unique method of point generation. Photomicrographs are presented showing sections through the drill point and partly formed chips at various points along the cutting edge, both for the conventional chisel point and the spiral point shapes, showing characteristic differences in chip formation. The results of a series of investigations of cutting forces and other performance criteria such as roundness, hole size, and drill life, are presented for both of these shapes, together with a few case histories of results obtained with the new geometry under repetitive manufacturing conditions. A description is given of a method for producing this shape on any type of drill. A modified form of the basic spiral point geometry is shown, which has additional unique characteristics for the drilling of sheet metal, and which therefore may have important applications in the aircraft and other sheet-metal fabricating industries.