Indexable, double-sided turning inserts for turning operations and and a turning tool are provided with cutting edges at alternating corners on opposite sides of the insert. Chipbreaker structures can be provided without interfering with providing large supporting surfaces. When the insert is used in a cutting operation, chips from one of the cutting edges in use are unlikely to damage cutting edges that are not in use but are on adjacent corners.

A cutting insert may include a first surface, a second surface, a third surface, and a land surface. The first surface may include a first corner and a first side. The land surface may be located between the first surface and the third surface. The land surface may include a first land surface connecting to the first corner, and a second land surface connecting to the first side. A width of the first land surface in a front view as viewed from a side of the first surface may be a first width, the first width at an end portion on a side of the second land surface may be larger than the width at a part connecting to a midportion of the first corner.

An insert based on an aspect includes a first surface having a corner portion, a second surface, a third surface, and a cutting edge located on at least part of a portion on which the first surface and the third surface intersect. The cutting edge is provided with a first cutting edge located on the corner portion and a second cutting edge adjacent to the first cutting edge, and the third surface is provided with a first portion located along the first cutting edge and a second portion located along the second cutting edge. Additionally, the second portion includes a first region having a first end portion and a second end portion, and a second region having a third end portion and a fourth end portion. An inclination angle 212 at the second end portion is greater than an inclination angle 211 at the first end portion, and an inclination angle 222 at the fourth end portion is smaller than an inclination angle 221 at the third end portion.

A peeling plate has upper and lower sides, lateral faces extending between the upper and lower sides, and primary and secondary cutting edges at the transition from the lateral faces to the upper side. The peeling plate in a plan view of the upper side has the shape of a substantially regular n-gon, n being five or six, and n lateral edges lying between the n lateral faces. A primary cutting edge and a secondary cutting edge are formed at the transition from at least one lateral face to the upper surface, wherein active primary cutting edges and active secondary cutting edges are spaced apart from a lateral edge. The lateral edge at the transition to the upper side forming an active cutting corner to the respective active primary cutting edge and active secondary cutting edge.

In an aspect of the disclosure, a cutting tool includes a base member and a coating layer located on a surface of the base member. The coating layer includes a lower layer, an upper layer, and an intermediate layer located between the lower layer and the upper layer. The intermediate layer includes a first layer, a second layer, and a third layer. The first layer contains TiC.sub.x1N.sub.y1O.sub.z1 (0x1<1, 0y1<1, 0<z1<1, and x1+1+z1=1). The second layer contains TiC.sub.x2N.sub.y2O.sub.z2 (0x2<1, 0y2<1, 0<z2<1, and x2+y2+z2=1). The third layer is located between the first layer and the second layer, and contains TiC.sub.x3N.sub.y3O.sub.z3 (0x3<1, 0y3<1, 0z3<1, and x3+y3+z3=1). Here, z1>z3 and z2>z3.

A cutting insert, a holder, and a cutting tool with which the cutting insert can be easily and stably mounted on the holder and a fabrication target object can be excellently fabricated are provided. A cutting tool 100 that is used to fabricate a fabrication target object W by cutting includes a holder 50 and a cutting insert 10 that is mounted on a distal end of the holder 50. The holder 50 includes an insert pocket 53 into which the cutting insert 10 is fitted and a stopper portion 61 that elastically locks the cutting insert 10 to be fitted into the insert pocket 53. The cutting insert 10 includes a cutting portion 11 including a cutting edge 13, a fitting portion 12 that is fitted into the insert pocket 53, and a lock portion 21 that is formed at the fitting portion 12 and is to be locked to the stopper portion 61 of the holder 50.

The present invention provides a fixing member that presses and fixes a cutting insert disposed on an insert mounting part of a tool body, the fixing member including: a fixing member body that has a pressing part for pressing the cutting insert; a fitting protrusion that is provided so as to protrude from a bottom part of the fixing member body, the fitting protrusion being fitted in a fitting hole formed in the tool body; and an engagement recess formed in a peripheral surface of the fitting protrusion, the engagement recess being engaged with a leading end of a fastening screw which is screwed into an internal thread that communicates with the fitting hole of the tool body, wherein the fitting protrusion is drawn into the fitting hole by the fastening screw that engages with the engagement recess, whereby the pressing part presses and fixes the cutting insert.

A cutting insert for a cutting tool includes a body having a cutting edge, a rake face, and micro channels provided on the rake face adjacent the cutting edge. The micro channels define a grid pattern of micro channels that intersect each other in a region of the rake face where contact between a chip and the rake face is assumed to occur during cutting with the cutting insert.

A cutting holder that includes: a columnar holder main body that has, at one end in a longitudinal-direction, an insert seating surface on which a cutting insert is capable of being mounted, and that is formed with a through-hole which is open, on one side, toward the insert seating surface and is open, on the other side, toward the other end; a clamp for insert having a clamping portion that presses the cutting insert against the insert seating surface, and a first engagement portion; and a screw having a second engagement portion that is engaged with the first engagement portion, in which the clamping portion of the clamp for insert is disposed on cutting edge side with respect to the screw disposed in the through-hole, the screw rotates, so that the clamp for insert moves along a rotation axis of the screw and the clamp for insert disposed on the cutting edge side is pulled by the screw disposed on the other end side, and the clamp for insert moves toward the other end side, so that the clamping portion presses the cutting insert against the insert seating surface.

To provide a cutting insert such that a tool body can sufficiently hold the cutting insert even if one of cutting parts is broken. The cutting insert includes two side surfaces opposed to each other, a fixing hole passing through the centers of the two side surfaces, and an outer circumferential surface that is disposed between the outer circumferential edges of the two side surfaces and are connected to the outer circumferential edges of the two side surfaces. The outer circumferential surface includes four cutting parts, a first outer circumferential surface part that is disposed between the first cutting part and the second cutting part, and a second outer circumferential surface part that is opposed to the first outer circumferential surface part and is disposed between the third cutting part and the fourth cutting part. In a side view of the side surfaces from the axial direction of the fixing hole, the first outer circumferential surface part and the second outer circumferential surface part each have the center recessed toward the fixing hole, and a virtual arc having the same diameter as the diameter of the circumcircle of the cutting insert is in contact with two points on each of the outer circumferential surface parts.