A cutting insert includes an upper surface and upper edge. The upper surface includes a second side part, a first corner part, and a second corner part. The upper surface further includes a first surface and a second surface. The upper edge includes a first edge located at the first corner part, a second edge located at the second side part, and a third edge located at the second corner part. The second surface includes a first region extending toward the first corner part, and a second region extending toward the second corner part. A distance between the first region and the upper edge is smaller at a side of the second edge than at a side of the first edge. A distance between the second region and the upper edge is smaller at a side of the second edge than at a side of the third edge.

A cutting insert includes an upper surface and a cutting edge. The upper surface includes a first surface and a second surface which is located further inward than the first surface. The cutting edge includes a first cutting edge and a second cutting edge. The first surface includes a first region along the first cutting edge, a second region adjacent to the first region, and a third region which is adjacent to the second region and along the second cutting edge. The second surface includes a fourth region, a fifth region and a sixth region. A width of the second region is smaller than each of a width of the first region and a width of the third region. An inclination angle of the fifth region is smaller than each of an inclination angle of the fourth region and an inclination angle of the sixth region.

A cutting part (1) for a tool head (2) for a lathe (3) for machining a workpiece (4), having a cutting edge (5) for removing material from the workpiece (4) and having a rake face (6) for guiding away the removed material or cuttings. The problem of providing a cutting part (1) which can be realized in a simple manner and with which lead-free materials can also be machined is solved in that a flat structure (7) is formed in the rake face (6) of the cutting part (1) adjoining the cutting edge (5) for breaking the cuttings. A lathe (3) for machining a workpiece (4), having a tool head (2) is provided with at least one such cutting part (1).

A cutting part (1) for a tool head (2) for a lathe (3) for machining a workpiece (4), having a cutting edge (5) for removing material from the workpiece (4) and having a rake face (6) for guiding away the removed material or cuttings. The problem of providing a cutting part (1) which can be realized in a simple manner and with which lead-free materials can also be machined is solved in that a flat structure (7) is formed in the rake face (6) of the cutting part (1) adjoining the cutting edge (5) for breaking the cuttings. A lathe (3) for machining a workpiece (4), having a tool head (2) is provided with at least one such cutting part (1).

To perform machining on a workpiece under wider variety of machining conditions. A first rising surface is adjacent to a cutting portion across a first surface, the first rising surface being inclined upward away from the first surface in a direction along a center axis and being away from the center axis toward a rear end of a main body. A second rising surface extends from a second surface toward the rear end of the main body, and is inclined upward away from the second surface in the direction along the center axis. In the direction along the center axis, a rear end of the first rising surface is closer to the rear end of the main body than a front end of the second rising surface.

The edge portion includes an upper surface, a side surface, and a land surface. The side surface has a front side surface and a pair of lateral side surfaces. An intersection between the land surface and the front side surface forms a front cutting edge. An intersection between the land surface and each of the pair of lateral side surfaces form a corresponding one of a pair of lateral cutting edges. The edge portion contains 80 vol % or more of diamond. A chip breaker recess is provided between the upper surface and the land surface. The surfaces forming the chip breaker recess include a rake face and a breaker wall surface. The upper surface has a front edge portion opposite to the front cutting edge from the chip breaker recess. A pair of protruding portions are provided to extend from the front edge portion toward the front cutting edge.

The edge portion includes an upper surface, a side surface, and a land surface. The side surface has a front side surface and a pair of lateral side surfaces. An intersection between the land surface and the front side surface forms a front cutting edge. An intersection between the land surface and each of the pair of lateral side surfaces form a corresponding one of a pair of lateral cutting edges. The edge portion contains 80 vol % or more of diamond. A chip breaker recess is provided between the upper surface and the land surface. The surfaces forming the chip breaker recess include a rake face and a breaker wall surface. The upper surface has a front edge portion opposite to the front cutting edge from the chip breaker recess. A pair of protruding portions are provided to extend from the front edge portion toward the front cutting edge.

There is provided a throw-away tip which includes a blade containing diamond and is excellent in chip processability. The throw-away tip comprises a body and a blade provided to the body and having a cutting edge, the blade containing 80% by volume or more of diamond, the blade having a land surface extending along the cutting edge, and a chip breaker having a recess located opposite to the cutting edge with the land surface therebetween, the recess having a side surface having an inclined surface that recedes continuously as a distance thereof from the land surface increases in magnitude and that has a shape identical to that of a portion of a side surface of a shape of a body of revolution.

There is provided a throw-away tip which includes a blade containing diamond and is excellent in chip processability. The throw-away tip comprises a body and a blade provided to the body and having a cutting edge, the blade containing 80% by volume or more of diamond, the blade having a land surface extending along the cutting edge, and a chip breaker having a recess located opposite to the cutting edge with the land surface therebetween, the recess having a side surface having an inclined surface that recedes continuously as a distance thereof from the land surface increases in magnitude and that has a shape identical to that of a portion of a side surface of a shape of a body of revolution.

A cutting insert including a surface involved in cutting, for which a cutting tool material of a hard sintered body is used. A radius of a nose R portion is 0.4 mm or greater and 2.4 mm or less, an apex angle of the nose R portion is 50 or greater and 95 or less, a rake angle at a position of a bisecting plane of the apex angle of the nose R portion is 1 or greater and 10 or less, a chamfer provided in a cutting edge portion is a negative land with unequal width, and at least on one side of the negative land with respect to a boundary which is an apex of a nose R portion cutting edge, a width of the negative land gradually decreases from the apex of the nose R portion cutting edge to a position at which the nose R portion cutting edge is connected to a linear cutting edge. Let W1 be the width of the negative land at the apex of the nose R portion cutting edge, and W2 be the width of the negative land at both ends of the nose R portion cutting edge, then the W1 is 0.04 mm or greater and 0.2 mm or less, and a ratio of the W1 to the W2 is 1.5 or greater.