| 摘要 |
PROBLEM TO BE SOLVED: To prevent a lowering of performance such as the chattering vibration and chipping of a small-diameter throwaway tip for a drill. SOLUTION: This throwaway tip 1 is provided with a rear bearing surface 28 provided at a rear part; a pair of clamped bearing surfaces 1b, 1c adjoining the rear bearing surface 28 and respectively abutting on a pair of clamping pieces 21, 22 provided at a holder 2; and cutting edges 11, 12 provided at the front end. The ridgelines of the clamped bearing surfaces 1b, 1c and rear bearing surface 28 are chamfered (C-surfaces x, y). The throwaway tip 1 is provided with a side bearing surface 31 provided at a side part adjoining the clamped bearing surfaces 1b, 1c and rear bearing surface 28, and the ridgeline of the clamped bearing surface 1c and side bearing surface 31 is chamfered (C-surface z).
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