Abstract: Provided is a cutting insert easy to be gripped by an operator or a robot hand. First and second end surfaces (10, 20) are formed in substantially polygonal shapes having second and fourth corners (B, H) formed at obtuse angles and first and third corners (A, G) formed at acute angles. A peripheral side surface (30) includes a first curved portion (41) connecting the first and third corners (A, G), a second curved portion (42) connecting the second and fourth corners (B, H), and a first side surface (31) interposed between the first and second curved portions (41, 42). The first side surface (31) is inclined with respect to a center axis (O). The second curved portion (42) is provided with a grip portion (50), and the grip portion (50) includes at least one of a shape of each of plane surfaces (51, 53) chamfered parallel to the center axis (O) and a shape of a recessed portion (52) formed to be spaced apart from the first and second end surfaces (10, 20) and recessed toward the center axis (O).

Abstract: A shank for a tool bit employing an offset arrangement is provided, the shank being able to respond to various types of machining through replacement of heads and having a structure to save time and steps necessary for such replacement of the heads. A cutting tool having such shank is also provided. A shank 53 of a head-replaceable cutting tool has at least one head attaching part 53A, 53B that is arranged off-center relative to an axis 53X of the shank 53. The axis 53X of the shank 53 corresponds to an axis extending in a longitudinal direction of the shank 53, and the head attaching part 53A, 53B may be arranged so as to be off-center in a direction perpendicular to the axis 53X.

Abstract: Provided is a holder of a cutting insert that performs turning on a work by feeding a cutting edge in a Y axis direction which is different from a longitudinal direction (X axis) of a tool holder installed in a tool rest, and that can easily adjust the projection amount without contacting a part of the holder to the tool rest. A Y axis holder holds the cutting insert including a cutting edge to perform turning on a work that moves along the Z axis, and is installed in a state where relative movement in the X axis direction with respect to the tool rest is possible, such that a projection amount of the cutting insert along the X axis is changeable. The Y axis holder performs turning on the work using the cutting insert when the holder moves in the Y axis direction which is different from the X axis direction.