Patent ID: 7473056

Claim:
A spade bit comprising: a shaft defining a longitudinal axis of the spade bit; a relatively thin, flat blade attached to the shaft, said blade having a relatively flat first face and a relatively flat second face opposite to said first face, said first face and said second face being joined by a first outer side edge and a second outer side edge; a tip formed along the longitudinal axis; a first cutting edge formed on the blade, said first cutting edge being straight and extending from the tip toward the first outer side edge and a second cutting edge formed on the blade, said second cutting edge being straight and extending from the tip toward the second outer side edge; and a first curved smooth flute formed in the first face adjacent to and extending along the first cutting edge and extending to a first end spaced axially from the first cutting edge and located in the first face and a second curved smooth flute formed in the second face adjacent to and extending along the second cutting edge and extending to a second end spaced axially from the second cutting edge and located in the second facet wherein the first flute and the second flute are each formed of a first curved surface and a second curved surface, the first curved surface extending from the first cutting edge to the first end and the second curved surface extending from the second cutting edge to the second end, and the first curved surface and the second curved surface having different radii of curvature where the first curved surface is tangential to said second curved surface.