| 摘要 |
A twist drill (21) includes a cutting head (25) including a drill tip (27). The drill tip (27) includes a chisel edge (41) defining the forwardmost area of the cutting head, and two main cutting edges (43a, 43b), each main cutting edge (43a, 43b) extending between the chisel edge (41) and an outer end (45a, 45b) of the main cutting edge. The chisel edge (41) forms an acute angle (¸) with a line (L) extending between the top outer ends (45a, 45b) of the main cutting edges (43a, 43b). The drill tip (27) further includes two concave recesses (47a, 47b), one concave recess (47a, 47b) of the two concave recesses (47a, 47b) being disposed on each side of the chisel edge (41), the line (L) intersecting the two concave recesses (47a, 47b).
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