US Patent 7887269 Spade bit with improved cutting geometry

A spade bit includes a shaft defining an axis, and a blade attached to the shaft and having a first blade portion and a second blade portion. The first blade portion defines a first leading face portion, and the second blade portion defines a second leading face portion. The first blade portion defines a first cutting edge portion, and the second blade portion defines a second cutting edge portion. The first cutting edge portion lies on a first border portion of the first leading face portion, and the second cutting edge portion lies on a second border portion of the second leading face portion. The first cutting edge portion and the second cutting edge portion both lie in a plane P1. An area A1 is bound by the plane P1 and the first leading face portion when the first blade portion is viewed in a first cross section taken along a plane P2 which is parallel to and spaced apart from the axis by a distance D1, and the area A1 increases as the distance D1 increases. The area A2 is bound by the plane P1 and the second leading face portion when the second blade portion is viewed in a second cross section taken along a plane P3 which is parallel to and spaced apart from the axis by a distance D2, and the area A2 increases as the distance D2 increases.