| 摘要 |
PROBLEM TO BE SOLVED: To improve processability of chips near the tip center of a tool body, by forming a concave surface that projects to a face of a cutting blade on its tool's rotational direction side and directs to a tool's tip side, on the tool's inner peripheral side of a cross ridge line between a tip surface and a wall surface directing the rear side on the tool's rotational direction of a chip discharge groove. SOLUTION: In a tool body 1 of a throw away type drilling tool, a pair of chip discharge grooves 2, 2 that direct to the rear end of the tool's rotational direction T with twisting to its rear side are symmetric in relation to an axial line O are formed on the tool's outer periphery. A supply passage 3 of lubricating coolant which is opening to the tip surface 1A is formed in parallel with the axial line O in the tool body 1. Tip mounting seats 4, 4 to which tips 5 are respectively attached are formed at the tip of wall surfaces directing the tool's rotational direction T side of the discharge grooves 2, 2. By forming a concave surface 20 that directs to the tip of the tool with twisting to the tool's rotational direction T, on a cross ridge line between the tip surface 1A of the tool body 1 and the wall surface 2B of the discharge groove 2, discharge ability of the chip is improved.
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