Abstract: A combination drill bit for use in both hand held drills and stationary drill presses has a shanking end, a working end and a helical flute portion between the shanking and working ends. The helical portion has a helix length (L) of L = ( D × ? tan ? ? ? ) . The drill bit has a core that is tapered from the working end to the shanking end. A web thickness length at the working end is 10% to 35% of the diameter and the thickness length at the junction of the shanking end is 70% to 90% of the diameter. The drill bit is manufactured from a high speed steel including at least 5% by weight of cobalt.

Abstract: A cutting head for a drill bit has a body with an overall cruciform shape. One pair of opposing arms defines a main cutting edge. The other pair of opposing arms defines an auxiliary edge. The main cutting edge is defined by rake surfaces and relief surfaces. Each rake surface and relief surface is defined by a plurality of facets. The main cutting edge includes a chisel edge. A first pair of planar rake facets, one on each end of said chisel edge, and a first pair of planar relief facets, adjacent said chisel edge, defines a portion of the cutting edge. A remaining portion of the main cutting edge is defined at the apex of a plurality of curved rake facets and curved relief facets. The auxiliary edge is defined by a plurality of curved surfaces.

Abstract: A cutting head for a drill bit has a body with an overall cruciform shape. One pair of opposing arms defines a main cutting edge. The other pair of opposing arms defines an auxiliary edge. The main cutting edge is defined by rake surfaces and relief surfaces. Each rake surface and relief surface is defined by a plurality of facets. The main cutting edge includes a chisel edge. A first pair of planar rake facets, one on each end of said chisel edge, and a first pair of planar relief facets, adjacent said chisel edge, defines a portion of the cutting edge. A remaining portion of the main cutting edge is defined at the apex of a plurality of curved rake facets and curved relief facets. The auxiliary edge is defined by a plurality of curved surfaces.

Abstract: A combination drill bit for use in both hand held drills and stationary drill presses has a shanking end, a working end and a helical flute portion between the shanking and working ends. The helical portion has a helix length (L) of L = ( D × ? tan ? ? ? ) . The drill bit has a core that is tapered from the working end to the shanking end. A web thickness length at the working end is 10% to 35% of the diameter and the thickness length at the junction of the shanking end is 70% to 90% of the diameter. The drill bit is manufactured from a high speed steel including at least 5% by weight of cobalt.