| 摘要 |
PROBLEM TO BE SOLVED: To provide a twist drill with excellent durability by adopting an tool profile of a sharper edge when drilling a comparatively ductile material to be cut such as stainless steel and preventing welding and press adhesion of an outer periphery in a high speed cutting of 25 m or more. SOLUTION: This coated cemented carbide twist drill is constituted by making a helix angle as a high helix angle of 35 deg. to 45 deg., forming a tip cutting edge into a protrusion shape in a tip view of the drill, providing the tip cutting edge on a 1 to 10% rotating direction rear side of an edge diameter for a virtual line for joining an uppermost protrusion part of the protrusion shape part to a thinning edge, forming a cutting face into a protrusion shape in cross section perpendicular to the axis within an effective edge length of the twist drill and forming a chamfering surface in a connecting part of the cutting face and an outer periphery.
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