Patent ID: 7887269

Claim:
A spade bit, comprising: a shaft defining an axis about which the spade bit is configured to be rotated; a blade attached to said shaft and having a first blade portion and a second blade portion, wherein (i) said first blade portion defines a first concave leading face portion and a first convex trailing face portion, and (ii) said second blade portion defines a second concave leading face portion and a second convex trailing face portion, wherein (i) said first blade portion includes a first shoulder that defines a first cutting edge portion, and (ii) said second blade portion includes a second shoulder that defines a second cutting edge portion, wherein (i) said first cutting edge portion lies on a first border portion of said first concave leading face portion, and (ii) said second cutting edge portion lies on a second border portion of said second concave leading face portion, wherein said first cutting edge portion and said second cutting edge portion both lie in a plane P 1 , wherein (i) an area A 1 is defined between said plane P 1 and said first concave leading face portion when said first blade portion is viewed in a first cross section taken along a plane P 2 which is parallel to and spaced apart from said axis by a distance D 1 , and (ii) said area A 1 increases as said distance D 1 increases, and wherein (i) an area A 2 is defined between said plane P 1 and said second concave leading face portion when said second blade portion is viewed in a second cross section taken along a plane P 3 which is parallel to and spaced apart from said axis by a distance D 2 , and (ii) said area A 2 increases as said distance D 2 increases.