A cutting insert of a substantially horizontal cylindrical segment shape and having top and bottom surfaces with a circular segment shape. The cutting insert has a convex side and a flat side, a top cutting edge which is formed where the convex side and the top surface meet, and a bottom cutting edge which is formed where the convex side and the bottom surface meet. The cutting insert includes a hole extending from the convex side towards the flat side. The hole is positioned at a center of a surface of the flat side.

A tool head has a longitudinal axis, forward and rearward ends, and top, bottom and peripheral surfaces. The peripheral surface has first and second side walls provided with respective first and second serrated portions, each of the first and second side walls being divided into spaced apart top and bottom side wall portions. The peripheral surface also has a stopper wall which faces in the rearward direction, extends transversely to the second side wall and is provided with a stopper serrated portion. A rear wall formed at the rearward end and connects the first and second side walls. The tool head also includes an insert retaining portion proximate the forward end, and a coupling portion which extends in the direction of the rearward end and includes vertically spaced apart top and bottom coupling arms separated by a coupling recess opening out to the rear wall.

A tool head has a longitudinal axis, forward and rearward ends, and top, bottom and peripheral surfaces. The peripheral surface has first and second side walls provided with respective first and second serrated portions, each of the first and second side walls being divided into spaced apart top and bottom side wall portions. The peripheral surface also has a stopper wall which faces in the rearward direction, extends transversely to the second side wall and is provided with a stopper serrated portion. A rear wall formed at the rearward end and connects the first and second side walls. The tool head also includes an insert retaining portion proximate the forward end, and a coupling portion which extends in the direction of the rearward end and includes vertically spaced apart top and bottom coupling arms separated by a coupling recess opening out to the rear wall.

A cutting insert according to one aspect has a flat plate shape including a first main surface having a polygonal shape, a second main surface located opposite to the first main surface, and an outer peripheral surface located between the first main surface and the second main surface. The cutting insert includes a cutting portion located in regions including at least a corner portion of the first main surface, and a main body portion located in a region other than the corner portion. A thickness of the main body portion is larger than a thickness of the cutting portions, and the main body portion includes a recessed portion or a protruding portion located in the outer peripheral surface thereof.

A cutting insert according to one aspect has a flat plate shape including a first main surface having a polygonal shape, a second main surface located opposite to the first main surface, and an outer peripheral surface located between the first main surface and the second main surface. The cutting insert includes a cutting portion located in regions including at least a corner portion of the first main surface, and a main body portion located in a region other than the corner portion. A thickness of the main body portion is larger than a thickness of the cutting portions, and the main body portion includes a recessed portion or a protruding portion located in the outer peripheral surface thereof.

A cutting insert according to an aspect includes a base portion and a cutting portion. The cutting portion includes a front end surface, an top surface, a first lateral surface, a second lateral surface, a front cutting edge, and a lateral cutting edge. The front cutting edge includes a first cutting edge and a second cutting edge, and a radius of curvature of the first cutting edge is greater than a radius of curvature of the second cutting edge.

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. The Y axis holder has a shape in which an end portion thereof in the X axis direction is projected from the cutting edge of the cutting insert, and a positioning portion to determine the projection amount of the cutting insert from the tool rest is disposed on the end portion.

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. The Y axis holder has a shape in which an end portion thereof in the X axis direction is projected from the cutting edge of the cutting insert, and a positioning portion to determine the projection amount of the cutting insert from the tool rest is disposed on the end portion.

A cutting insert may include a base and a cutting part. The cutting part may include an upper surface, a first cutting edge and a second cutting edge. The first cutting edge may be located on a first ridgeline. The second cutting edge may be located on a second ridgeline. The upper surface may include a first inclined surface, protrusions and a first upheaved part. The first inclined surface may be located along the first ridgeline. The protrusions may be located side by side in a direction along the first ridgeline on the first inclined surface. The first upheaved part may be located at a side further away from the first ridgeline than the pair of protrusions. The second cutting edge may be inclined downward. An upper end of the first upheaved part may be located above the second cutting edge.

A cutter insert tool holder effects bidirectional linear cuts on a work surface. The tool holder includes two elongated slots sized to accommodate first and second cutting insert holders. The tool holder includes an actuator arm that is placed in a first pivoting position by contacting the work surface while the tool holder is displaced along the work surface in a first direction, the pivoting actuator arm causes an actuator cam to contact and engage the second cutting insert holder so that it is withdrawn while the first cutting insert forms a cut in the work surface. When the tool holder is displaced along the work surface in a second direction opposite the first direction, the pivoting actuator arm causes the actuator cam to contact and engage the first cutting insert holder so that it is withdrawn while the second cutting insert forms a cut in the work surface.