Hitachi Tool Engineering, Ltd.

Yoshihiro Kondoh

Takeshi Akamatsu

A small-diameter drill for deep hole drilling is provided which is capable of inhibiting the cutting chips from getting bitten and producing a straightness for a drilled hole, thus suitable for drilling a hole having a depth (L) which is 15 or more times the diameter (D) of a drilled hole. The small-diameter drillhas a diameterwhich is 1 mm or less and a drill sectionincluding cutting edge(s)and flute(s). The lengthof the fluteis at least 5 times and at most 10 times the drill diameter. The diameter of the drill section, after being reduced in diameter from the cutting edgetoward the rear of the drill section, is expanded in diameter so that the outer diameter at the end of the flutebecomes at least 0.9 times and at most 0.98 times the drill diameter. An expanded-diameter portionis provided between the drill sectionand a neck sectionconnected to a shankand is expended in diameter from the outer diameter at the endof the fluteup to 1 or less times the drill diameter. The diameter of the neck sectionis smaller than the drill diameter, and the lengthof the neck sectionis 10 or more times the drill diameter

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Shiga, Japan

Yoshihiro Kondoh