| 摘要 |
PROBLEM TO BE SOLVED: To prevent chip biting to the outer circumferential side of a drill main body, and restrict generation of burrs at an outlet of a through hole by improving the form of an opening part at a tool tip part for an oil hole for internal lubrication in a drill. SOLUTION: The oil hole for internal lubrication in this drill is opened both in a tip surface and an outer circumferential surface of the drill main body, and length of the opening part directed to the outer circumferential surface in an axial line direction is set to be 0.05-0.7 times the drill diameter. Cutting oil of sufficient quantity and oil pressure can thus be supplied to the tip side and the outer circumferential side of the drill main body during machining. Chip biting on the outer circumferential side of the drill main body can be preliminarily prevented. Damage in the outer circumferential surface of the drill main body can be greatly reduced. Since sufficient cutting oil is supplied to outer circumferential parts of the drill till the instant when a through hole is formed, thereby burr at an outlet of the through hole can be greatly restricted. COPYRIGHT: (C)2004,JPO
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