Patent ID: 7740426
Filing Date: 2010-06-22
Classification: B23B,Y10T

Abstract:
1. A drill which comprises a cylindrical main body and a shank contiguous to each other, and which is to be rotated about an axis of said cylindrical main body in a predetermined rotating direction, for drilling a hole in a workpiece, wherein said cylindrical main body has: at least one flute each of which is formed in said cylindrical main body and extends from an axially distal end of said cylindrical main body to an axially proximal end of said cylindrical main body, so as to provide a cutting edge at said axially distal end of said cylindrical main body; at least one land each of which is provided by a peripheral portion of said cylindrical main body not cut away by said at least one flute; and a web provided by a central portion of said cylindrical main body which extends in an axial direction of said cylindrical main body; wherein said web includes a back-tapered portion which is provided by at least an axially distal end portion of said web, such that a thickness of said web in said back-tapered portion is continuously reduced as viewed in a direction away from said axially distal end of said cylindrical main body toward said shank, wherein said web further includes a constant-thickness portion which is contiguous to said back-tapered portion and which is provided by at least an axially proximal end portion of said web, such that the thickness of said web in said constant-thickness portion is constant, wherein said cylindrical main body has a large diameter portion provided by an axially distal end portion thereof, and a small diameter portion contiguous to said large diameter portion and having a diameter that is smaller than a diameter of said large diameter portion, such that a step is provided between said large and small diameter portions, and wherein said large diameter portion provided by said axially distal end portion of said cylindrical main body has an axial length which is larger than an axial length of said back tapered portion of said web provided by said axially distal end portion of said web, such that a boundary between said back-tapered portion and said constant-thickness portion of said web is located in said large diameter portion of said cylindrical main body.