Center-free drill

Claim 1

An annular hole cutter having a shank, and an integral cylindrical body having a free end and an axial bore formed therethrough, characterized in that: (a) said cylindrical body is provided with a plurality of circumferentially spaced apart cutting teeth; (b) each of said cutting teeth is provided with an inner cutting edge having a radial face and an inner end and an outer end, and an outer cutting edge having a radial face and an inner end and an outer end; (c) the inner ends of the inner and outer cutting edges on each cutting tooth meet at a common leading cutter point; (d) the inner and outer cutting edges are positioned with the leading cutter point extending axially ahead of the cutting edges; (e) the plurality of cutting teeth are circumferentially spaced apart by an equal number of helical flutes which are formed around the periphery of the cylindrical body and which extend longitudinally thereof and have a side face; (f) the outer end of each of the inner and outer cutting edges is disposed circumferentially rearward of a radius line which intersects the leading cutter point; and, (g) the radial face of each outer cutting edge is formed as a continuation of the side face of one of the helical flutes, at the free end of the cylindrical body, and the radial face of each inner cutting edge is formed at the free end of the cylindrical body by a gullet formed through the body from the axial bore outwardly and communicating with one of the helical flutes, and the radial face angle of the inner cutting edge is different from the radial face angle of the outer cutting edge.