| 摘要 |
PURPOSE:To make rapid feed drilling performable without using a bush as well as to prevent chips from being bitten in space between a drill body circumference and a drilling hole wall by installing a land part of the same diameter as a cutting edge tip, in the drill body circumference. CONSTITUTION:A cutting edge tip 33 consists of cemented carbide, while its axial length is set to be 1-6 times over the edge diameter, two chip discharge grooves 37 are formed, a cutting edge 39 is formed in the tip of a surface to be turned to a direction of rotation of each chip discharge groove and a margin part 41 in the edge, respectively, and furthermore a guide pad part 43 is formed in an edge contacting with a surface to be turned to the opposite direction against the direction of rotation. And, an oil hole 45 is installed in the inner part of the cutting edge tip, opened to the tip end, and it is formed as pierced through up to the rear end. A shank base metal 35 is fixed by means of brazing, and it is composed of high-speed tool steel, and in the first half part 47, there are provided with a chip discharge groove 51, a land part 53 in succession to each rear end of the margin part 41 and the guide pad part 43 and another oil hole to be interconnected to the oil hole 45.
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