| 摘要 |
PROBLEM TO BE SOLVED: To provide a tool for promoting guiding performance of a drill and obtaining excellent stability by remarkably lengthening the drill service life without inducing chipping of an edge and breaking of a drill body in a cemented carbide drill when becoming intermittent cutting like the parting surface side of through hole work. SOLUTION: This twist drill composed of cemented carbide or TiCN cermet, is characterized in that another pair of margin parts are arranged on the heel part side for connecting a land part and a cutting discharge groove in a cross- sectional view perpendicular to the axis of the twist drill, and a position of the margin parts is formed in a position of 60 deg. to 105 deg. toward the heel side from the cutting edge corner relative to a straight line joining both cutting edge corners together by passing through the drill center.
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