초록 ▼

A self-centering twist drill bit 20 is formed with a “fishtail”cutting section 32 having major cutting lips 72 and 74 on a working end 26 thereof at a point angle of 190°. Tip relief surfaces 76 and 78 trail cutting lips 72 and 74. A pilot tip 38 on the working end 26 extends axially from the “fisht

A self-centering twist drill bit 20 is formed with a “fishtail”cutting section 32 having major cutting lips 72 and 74 on a working end 26 thereof at a point angle of 190°. Tip relief surfaces 76 and 78 trail cutting lips 72 and 74. A pilot tip 38 on the working end 26 extends axially from the “fishtail”cutting section 32 and is formed with a split point having leading cutting edges 40 and 42 and minor cutting lips 46 and 48. Outer surfaces 58 and 60 of pilot tip 38 are each formed with a radial relief and a back taper and joins with cutting section 32 along fillets 92 and 100 which are also radially relieved.

대표청구항 ▼

A self-centering drill bit, which comprises: an elongated drill body having a shank end and a working end; flutes formed in the drill body and extending to a free end of the drill body at the working end; the working end of the drill body being formed with a major cutting section of a prescribed maj

A self-centering drill bit, which comprises: an elongated drill body having a shank end and a working end; flutes formed in the drill body and extending to a free end of the drill body at the working end; the working end of the drill body being formed with a major cutting section of a prescribed major drill diameter and including major cutting lips for cutting a primary hole in a workpiece; a pilot tip formed on the working end of the drill body and extending from the major cutting section in a direction away from the shank end of the drill body; the pilot tip of the drill body being formed with minor cutting lips of a minor drill diameter smaller than the major drill diameter for cutting a secondary hole in the workpiece; the pilot tip being formed with at least one outer surface which extends from the major cutting section generally in an axial direction of the drill body; the outer surface of the pilot tip having a forward edge contiguous with one flute and a trailing edge contiguous with another flute and wherein the outer surface is continuous and uninterrupted between the forward and trailing edges thereof; the outer surface of the pilot tip raking radially inwardly from the forward edge to the trailing edge to form a radial relief clearance on the outer surface, and the outer surface of the pilot tip being formed with an inward back tape extending toward the major cutting section in an axial direction to form an axial relief clearance on the outer surface.