Patent ID: 6929434

Claim:
A rotary twist drill configured to drill a hole in an object to be drilled, said twist drill comprising: a shaft portion configured to retain said drill for drilling; a cutting portion disposed adjacent said shaft portion; said shaft portion and said cutting portion defining a central longitudinal axis disposed through said shaft portion and said cutting portion; said cutting portion comprising a tip portion and a fluted portion; said tip portion being configured to cut a hole in an object; said tip portion comprising at least one chisel edge; said fluted portion being disposed between said tip portion and said shaft portion and having at least one helical chip flute disposed to curve helically about said central longitudinal axis; said fluted portion comprising at least one helical land surface adjacent a corresponding helical chip flute; said at least one helical land surface and its corresponding helical chip flute forming an edge, a portion of which is a cutting edge; said cutting edge portion of said fluted portion being configured and disposed to further cut and enlarge the diameter of a hole cut by said tip portion, and to form a smoother finish on the interior surface of the hole than the finish formed by said tip portion; said cutting edge portion of said fluted portion being configured and disposed to bulge outwardly in a radial direction away from said central longitudinal axis to form a bulge on said fluted portion which extends radially beyond said tip portion; said cutting edge portion of said fluted portion comprising a first edge area, a second edge area, and a third edge area; said first edge area being disposed at a first longitudinal distance measured along said central longitudinal axis from said tip portion; said second edge area being disposed at a second longitudinal distance, greater than said first longitudinal distance, measured along said central longitudinal axis from said tip portion; said third edge area being disposed at a third longitudinal distance, greater than said second longitudinal distance, measured along said central longitudinal axis from said tip portion; said second edge area being disposed further away, measured radially from said central longitudinal axis, than all of: said first edge area, said third edge area, and said tip portion; and at least one of said first edge area and said second edge area comprising a curved portion having a curvature in addition to said helical curvature.