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Drill bit for marking hole centre for boring bit - has two radial cutting edges with perpendicular trailing edges lagging radii
Drill bit for marking hole centre for boring bit - has two radial cutting edges with perpendicular trailing edges lagging radii
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机译：钻头，用于标记镗孔的孔中心-具有两个径向切削刃，垂直后缘滞后半径
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摘要
The cylindrical drill bit (1) is used for marking the centres of holes in advance of drilling by a conventional helical drill bit. The marker bit (1) has two helicoidal grooves (2) with two radial cutting edges (4, 5) which lie in a common diametric plane (6). The cutting edges (4, 5) are formed by the intersection of the conical surface to the tip of the bit with one edge of the respective groove. The intersection of the trailing edges of the grooves with the tip surfaces may form arrisses (7, 8) which align perpendicular to the main cutting edges (4, 5). The arrisses (7, 8) however, are not truly radial, but lcoate nominally beyond a parallel line (9) which lies within the groove concerned. The cutting edges and the trailing arrisses of each groove may be joined by parallel inclined surfaces (10, 11). The two surfaces form a slender blade incorporating the point (13), and the angle of conicity of the bit may be 10 deg. less than that of the drill bit that follows.
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