Ngk Spark Plug Company, Limited

Minoru Koide

Tatsuji Kinukawa

Naoki Andoh

Takashi Fujimoto

Inclined surfaces are formed on a rake face and a recessed groove is formed in the central portion between the inclined surfaces. A groove width of the recessed groove gradually increases from the position of the end cutting edge toward the rear, then gradually decreases such that the recessed groove has a narrowest portion at a position Pforward of the position Pof an upper end of a breaker wall and rearward of a positive rake angle rear end position Pand then gradually increases toward the rear up to the position Pof the upper end of the breaker wall. The dimensional relation WWWholds, where Wis the groove width at the end cutting edge, Wis the groove width at the narrowest portion, and Wis the groove width at the position Pof the upper end of the breaker wall.

Cutting insert

A cutting tool is provided which comprises a curved cutting edge at a nose, a pair of straight cutting edges between which the nose is located, and a chamfer extending along the curved cutting edge and the straight cutting edges so as to form a curved ridge at a junction of a portion of the chamfer extending along the curved cutting edge and a tool face. A portion of the chamfer increases in width from a junction of the curved cutting edge and each of the straight cutting edges to a midpoint of the curved cutting edge when observed in plan.

Cutting tool

A cutting tool and a holder-carrying tool which are capable of lowering the roughness of a surface to be finished (smoothing a surface), during a cutting process are disclosed. A cutting tool is provided on a side portion (on the side of a flank) thereof with a flat drag, which is adapted to remove the ridges and valleys of a surface to be finished, extending between: a terminal end section at which a curved surface of a nose portion terminates; and a flank. Namely, on the inner side of a tangent at the terminal end section of the curved surface of the nose portion, the flat drag is provided in the range of a flat drag angle of 0<&thgr;<5&deg;. A width (w) (viewed from the side of a rake face) of this flat drag is in the range of 0<w&lE;1.5 mm.

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Gifu, Japan

Minoru Koide