CN117206606A - Thread milling cutter - Google Patents

Abstract

The invention discloses a thread milling cutter, and belongs to the technical field of thread machining. The thread milling cutter comprises a cutting part and a cutting blade; wherein, at least two cutting planes are arranged on the cutting part at intervals along the axial direction of the cutting part; at least two cutting blades are arranged on each cutting plane at intervals, the tooth shapes of the cutting teeth of the cutting blades are different, and when the thread milling cutter rotates, a non-overlapping area exists between the cutting blades, so that the cutting blades can be spliced to form an overall tooth shape of a thread structure to be processed after the thread milling cutter rotates for a circle. The thread milling cutter disclosed by the invention is used for forming a complete thread structure through mutually matched machining of a plurality of cutting blades, the machining efficiency is higher, and the cutting force born by the thread milling cutter is smaller, so that the thread milling cutter can be protected, and the machining quality of the thread structure can be ensured.

Description

Thread milling cutter

Technical Field

The invention relates to the technical field of thread machining, in particular to a thread milling cutter.

Background

Currently, the commonly used thread milling cutter comprises three types of single teeth, three teeth and full teeth; the single-tooth and three-tooth thread milling cutters have smaller cutting amount on a workpiece during machining, so that the thread milling cutters bear smaller cutting force, but the machining efficiency of the single-tooth and three-tooth thread milling cutters is relatively lower; the full-tooth thread milling cutter can enable the whole cutting edge to be processed simultaneously during processing, so that the processing efficiency of the thread milling cutter is higher, but the cutting force born by the full-tooth thread milling cutter is larger, and when the cutting force is overlarge, the vibration phenomenon is easy to occur, and the vibration phenomenon not only can damage the thread milling cutter, but also can influence the quality of the processing surface of a workpiece.

In view of the above, there is a need for a thread milling cutter to solve the above problems.

Disclosure of Invention

The invention aims to provide a thread milling cutter, which has higher machining efficiency and smaller cutting force born by the thread milling cutter, so that the thread milling cutter can be protected, and the machining quality of a thread structure can be ensured.

To achieve the purpose, the invention adopts the following technical scheme:

a thread milling cutter comprising:

the cutting part is provided with at least two cutting planes at intervals along the axial direction of the cutting part;

and at least two cutting blades are arranged on each cutting plane at intervals, the tooth shapes of the cutting teeth of the cutting blades are different, and when the thread milling cutter rotates, a non-overlapping area exists between the cutting blades, so that the cutting blades can be spliced to form an overall tooth shape of a thread structure to be processed after the thread milling cutter rotates for a circle.

As an alternative, three cutting blades are arranged on the cutting plane, the three cutting blades are a first blade, a second blade and a third blade respectively, the cutting tooth profiles of the first blade and the second blade are trapezoidal, the setting positions of the cutting teeth of the first blade and the cutting tooth profile of the second blade are different, the cutting tooth profile of the third blade comprises a rectangular part and a trapezoidal part positioned above the rectangular part, and the cutting paths between the first blade, the second blade and the third blade are not completely overlapped.

Alternatively, the cutting tooth profile of the first and second blades overlap the rectangular portion of the third blade such that the overlapping profile of the first, second and third blades is trapezoidal in configuration.

Alternatively, the thread width of the thread structure is W, the height of the thread structure is H, the cutting tooth heights of the first blade and the second blade are H1,0.55H is less than or equal to 0.65H, the tooth tip widths of the first blade and the second blade are W2, w2=1/8W, and the cutting tooth width of the third blade is W1,0.5W is less than or equal to W1 is less than or equal to 0.6W.

Alternatively, in the adjacent two cutting planes, the cutting blades are arranged in a staggered manner in the circumferential direction of the cutting part, and the staggered angle between the adjacent two cutting blades is beta, and beta is more than or equal to 10 degrees and less than or equal to 60 degrees.

Alternatively, the cutting planes are uniformly distributed on the cutting part at intervals, and the interval L between two adjacent cutting planes is an integer multiple of the pitch of the thread structure.

As an alternative, the thread milling cutter further comprises a cutter handle, and the cutting part is arranged at one end of the cutter handle; the cutting insert is detachably disposed in the cutting plane.

As an alternative, the cutting insert is provided with a first threaded hole, the cutting part is provided with an insert groove, the insert groove is provided with a second threaded hole, and the bolt can be connected to the first threaded hole and the second threaded hole in a threaded manner.

Alternatively, the cutting insert is provided with chip flutes facing in a cutting rotation direction; chip grooves are formed between two adjacent cutting planes on the cutting part, and the chip grooves are communicated with the chip grooves.

As an alternative, the chip groove is of an annular structure, the width of the chip groove in the axial direction of the cutting part is smaller than L, L is the distance between two adjacent cutting planes, the depth of the chip groove is smaller than or equal to 0.15d, and d is twice the distance between the highest point of the cutting blade when the cutting blade rotates and the axial direction of the cutting part.

The beneficial effects of the invention are as follows:

at least two cutting planes are arranged on the cutting part at intervals along the axial direction of the cutting part, at least two cutting blades are arranged on each cutting plane at intervals, and the tooth shapes of the cutting teeth of the cutting blades are different and are incomplete tooth shapes; meanwhile, a non-overlapping area exists between the cutting blades, namely, the cutting blades are not fully overlapped, so that the cutting blades can be spliced to form a profile which is an integral tooth form of a thread structure to be processed after the thread milling cutter rotates for one circle; when the thread milling cutter performs rotary cutting, each component part of the thread structure can be cut through each cutting blade on the same cutting plane, so that the complete thread structure can be cut through the mutual cooperation of each cutting blade; compared with the full-thread milling cutter in the prior art, the method adopting the partial cutting thread structure reduces the cutting resistance of the thread milling cutter to the workpiece by each cutting blade on the same cutting plane, so that the cutting force born by the thread milling cutter is smaller, the vibration phenomenon which is easy to occur when the cutting force is overlarge can be avoided, the thread milling cutter can be well protected, and the processing quality of the thread structure can not be influenced; and, cutting is carried out simultaneously through the cutting insert on each cutting plane for the machining efficiency of thread milling cutter is higher.

Drawings

FIG. 1 is a schematic view of a thread milling cutter according to the present invention;

FIG. 2 is a front view of a thread milling cutter provided by the present invention;

FIG. 3 is a cross-sectional view taken along the A-A plane in FIG. 2;

FIG. 4 is a cross-sectional view of the B-B plane of FIG. 2;

FIG. 5 is a schematic view of the bottom structure of the thread milling cutter provided by the present invention;

FIG. 6 is a schematic view of the cutting tooth profile of the first, second and third blades provided by the present invention;

FIG. 7 is a front view of a first blade, a second blade, and a third blade provided by the present invention;

FIG. 8 is a bottom view of a cutting insert provided by the present invention;

fig. 9 is a schematic view of the structure of the thread milling cutter provided by the present invention when a cutting insert is not mounted.

Reference numerals illustrate:

10-cutting part; 20-a knife handle;

1-a cutting insert; 11-a first blade; 12-a second blade; 13-a third blade; 14-a first threaded hole; 15-chip flutes;

2-cutting a plane; 21-insert pocket; 211-a second threaded hole;

3-chip removal grooves; 4-overlap region.

Detailed Description

All of the features disclosed in this specification, or all of the steps in a method or process disclosed, may be combined in any combination, except for mutually exclusive features and/or steps.

Any feature disclosed in this specification may be replaced by alternative features serving the same or equivalent purpose, unless expressly stated otherwise. That is, each feature is one example only of a generic series of equivalent or similar features, unless expressly stated otherwise. Like reference numerals refer to like elements throughout the specification.

In order to make the technical problems solved, the technical scheme adopted and the technical effects achieved by the invention more clear, the technical scheme of the invention is further described below by a specific embodiment in combination with the attached drawings.

In this embodiment, a thread milling cutter is provided for cutting a complete thread structure on a workpiece, and the thread milling cutter has a small cutting force applied to the thread structure during the cutting and processing, and can ensure a high processing efficiency of the thread milling cutter. The thread structure may be an external thread or an internal thread, and the specific arrangement form of the thread structure and the specific structure of the workpiece are not limited herein.

Specifically, as shown in fig. 1 to 9, the thread milling cutter includes a shank 20, a cutting portion 10, and a cutting insert 1; wherein the cutting part 10 is arranged at one end part of the left side of the tool shank 20, and at least two cutting planes 2 are arranged on the cutting part 10 at intervals along the axial direction of the cutting part; at least two cutting blades 1 are arranged on each cutting plane 2 at intervals, and the cutting teeth of each cutting blade 1 are different and are of incomplete tooth shapes; when the thread milling cutter rotates, a non-overlapping area exists between the cutting blades 1 on the same cutting plane 2, so that the cutting blades 1 can be spliced to form a profile which is an integral tooth form of a thread structure to be processed after the thread milling cutter rotates for one circle. In this embodiment, the cutting portion 10 and the shank 20 are integrally formed. In other embodiments, the cutting portion 10 and the shank 20 are in a split type connection. As shown in fig. 6, the area M of the overlapping region 4 of each cutting insert 1 in the same cutting plane 2 is larger than zero, and the area M of the overlapping region 4 is smaller than the area of the thread structure to be machined, that is, each cutting insert 1 in the same cutting plane 2 is not completely overlapped, that is, there is a non-overlapping region located above and an overlapping region 4 located below at the same time, and the axial direction of the cutting portion 10 is specifically a straight line as shown by Y in fig. 2.

It should be noted that, the shapes of the tooth form or the cutting tooth of the cutting insert 1, the area M of the overlapping region 4, the thread structure to be machined, and the like described in this embodiment refer to projections or cross sections of the corresponding structures and portions conventionally considered by those skilled in the art unless otherwise specified.

Compared with the prior art, the thread milling cutter in the embodiment converts an integral type blade structure for cutting and machining a thread structure into a plurality of cutting blades 1 which are mutually matched and machined together, namely a mode of cutting the thread structure in parts is adopted; by providing at least two cutting planes 2 on the cutting portion 10 at intervals in the axial direction thereof, at least two cutting inserts 1 are mounted on each cutting plane 2 at intervals, and the cutting teeth of the respective cutting inserts 1 are different; meanwhile, a non-overlapping area exists between the cutting blades 1, namely, the cutting blades 1 are not fully overlapped, so that the cutting blades 1 can project on the same plane to form a thread structure; when the thread milling cutter performs rotary cutting, each component part of the thread structure can be cut through each cutting blade 1 on the same cutting plane 2, so that the complete thread structure can be cut through the mutual matching of the cutting blades 1; compared with the full-tooth thread milling cutter which is completely overlapped in the prior art, the cutting resistance of the thread milling cutter to a workpiece is reduced by each cutting blade 1 on the same cutting plane 2, so that the cutting force born by the thread milling cutter is smaller, the vibration phenomenon which is easy to occur when the cutting force is overlarge can be avoided, the thread milling cutter can be well protected, and the processing quality of a thread structure is not influenced; in addition, the cutting inserts 1 on the respective cutting planes 2 simultaneously perform cutting processing, so that the processing efficiency of the thread milling cutter is high.

It should be noted that, since the thread milling cutter in the present embodiment receives a small cutting force during the cutting process, the cutting operation of the thread structure on the workpiece can be rapidly completed by increasing the rotation rate of the thread milling cutter and the feeding amount of the workpiece, so that the processing efficiency of the thread milling cutter can be further improved.

Further, in the present embodiment, as shown in fig. 4 to 7, three cutting blades 1 are disposed on each cutting plane 2, the three cutting blades 1 are disposed at intervals, and the three cutting blades 1 are a first blade 11, a second blade 12, and a third blade 13, respectively; the first blade 11 and the second blade 12 are respectively used for cutting two side parts of a thread structure, the third blade 13 is used for cutting a middle part of the thread structure, so that the first blade 11, the second blade 12 and the third blade 13 can be spliced to form an integral tooth-shaped profile of the thread structure after the thread milling cutter rotates for one circle, and a complete thread structure can be formed through mutual matching processing of the first blade 11, the second blade 12 and the third blade 13; that is, the cutting teeth of the first blade 11, the second blade 12 and the third blade 13 on each cutting plane 2 are designed specifically, are all incomplete tooth shapes, and when three cutting teeth rotate for one circle, the spliced profile is a complete tooth shape, so that a complete thread structure can be formed by machining.

Specifically, as shown in fig. 6, the cutting tooth profiles of the first blade 11 and the second blade 12 are each trapezoidal, and the setting positions of the cutting teeth of the first blade 11 and the second blade 12 are different; the cutting profile of the third blade 13 includes a rectangular portion and a trapezoidal portion located above the rectangular portion, and the cutting paths of the first, second and third blades 11, 12 and 13 do not entirely overlap each other.

More specifically, as shown in fig. 6, the cutting tooth profiles of the first blade 11 and the second blade 12 overlap with the rectangular portion of the third blade 13 such that the overlapping profiles of the first blade 11, the second blade 12 and the third blade 13 have a trapezoid structure, which may be identical or similar to the profile of the thread structure to be processed, to ensure the processing accuracy of the thread milling cutter. Wherein, the trapezoid cutting tooth profiles of the first blade 11 and the second blade 12 may be isosceles trapezoids, and the upper bottom surfaces of the trapezoid cutting tooth profiles of the first blade 11 and the second blade 12 may overlap with the boundary between the trapezoid portion and the rectangular portion of the third blade 13.

Of course, in other embodiments, the cutting tooth profiles of the first blade 11 and the second blade 12 may be other shapes, for example, the first blade 11 and the second blade 12 may be right trapezoid or triangle, etc. Meanwhile, the upper bottom surfaces of both the first blade 11 and the second blade 12 may be lower than the boundary between the trapezoidal portion and the rectangular portion of the third blade 13, or may be higher than the boundary of the third blade 13.

In other embodiments, two or more cutting inserts 1 may be disposed on each cutting plane 2, and the specific number of the cutting inserts 1 is not limited, so long as the cutting inserts 1 on the cutting plane 2 can be matched with each other to form a complete thread structure.

Specifically, as shown in fig. 6 and 7, the thread width of the thread structure to be formed by working is W, the height of the thread structure is H, the cutting tooth heights of the first blade 11 and the second blade 12 are H1,0.55 h.ltoreq.h1.ltoreq.0.65H, the tooth tip widths of the first blade 11 and the second blade 12 are W2, w2=1/8W, and the cutting tooth widths of the third blade 13 are W1,0.5 w.ltoreq.w1.ltoreq.0.6W. Fig. 7 (a) is a front view of the first blade 11, fig. 7 (b) is a front view of the second blade 12, and fig. 7 (c) is a front view of the third blade 13.

Through the setting of the cutting tooth parameters of the first blade 11, the second blade 12 and the third blade 13, the first blade 11, the second blade 12 and the third blade 13 can have an overlapping area 4, and a complete thread structure can be formed through the mutual matching processing of the first blade 11, the second blade 12 and the third blade 13, so that the reliability of the thread structure processing is higher.

Further, as shown in FIG. 8, the rake angle of the cutting insert 1 on the same cutting plane 2 is α, -5-25 to facilitate machining of the cutting insert 1 while ensuring the cutting amount; the rake angles of the first blade 11, the second blade 12 and the third blade 13 may be the same or different, and the rake angles of the respective blades may be adjusted according to a specific cutting amount, so that the cutting process of the screw structure may be more facilitated. Here, the specific setting angle of the rake angle of each blade is not limited.

Specifically, as shown in fig. 5, each of the cutting inserts 1 in the adjacent two cutting planes 2 is arranged offset in the circumferential direction of the cutting portion 10, so that each of the cutting inserts 1 in one of the cutting planes 2 does not cut the workpiece when cutting the workpiece, thereby preventing the plurality of cutting inserts 1 in the two cutting planes 2 from simultaneously contacting the workpiece and cutting the workpiece, and further reducing the cutting force borne by the entire thread milling cutter.

Specifically, as shown in fig. 5, in the adjacent two cutting planes 2, the offset angle between the adjacent two cutting inserts 1 is β, 10+.β+.60°, to better ensure that the cutting inserts 1 on the two cutting planes 2 can be offset for cutting.

Further, as shown in fig. 9, each cutting plane 2 is uniformly distributed on the cutting portion 10 at intervals, and the distance L between two adjacent cutting planes 2 is an integer multiple of the pitch of the thread structure, so that the whole thread milling cutter can be processed to form a complete thread structure after being rotated for an integer multiple of the number of turns. For example, when the pitch of the thread structure is 3mm, the distance L between two adjacent cutting planes 2 may be taken to be 12mm, so that L is equal to four times the pitch, thereby enabling the entire thread milling cutter to form a complete thread structure after four rotations.

Through making L be the integer multiple of screw pitch of screw structure to can adjust screw milling cutter's rotation number of turns through setting up the concrete numerical value of L, that is, screw milling cutter just can accomplish complete screw structure's processing as long as the stroke of rotatory integer multiple screw pitch, thereby can reduce screw milling cutter's rotation number of turns, in order to improve screw milling cutter's machining efficiency better. Here, L is specifically not limited to a few integer multiples of the pitch, and is determined according to the working conditions and the working requirements of the thread milling cutter.

Specifically, as shown in fig. 9, four cutting planes 2 are provided in the axial direction of the cutting portion 10 in the present embodiment, so that the cutting inserts 1 on the four cutting planes 2 can simultaneously cut the workpiece, and the cutting efficiency of the screw structure on the workpiece is ensured to be high. Here, the specific number of the cutting planes 2 to be provided is determined according to the thread length of the thread structure so that the simultaneous processing through the respective cutting planes 2 can form the thread structure of a desired thread length.

Specifically, the cutting insert 1 is detachably disposed on the cutting plane 2; on the one hand, it is possible to facilitate the installation and replacement of the entire cutting insert 1; on the other hand, after one of the cutting edges on the cutting insert 1 is worn, the other cutting edges on the cutting insert 1 can be directly installed at the cutting position in an indexing mode, so that the indexing function of the cutting insert 1 can be realized, and the use cost of the thread milling cutter can be reduced. In the present embodiment, the first blade 11, the second blade 12, and the third blade 13 each have three cutting edges.

Further, as shown in fig. 7 and 9, a first screw hole 14 is provided on the cutting insert 1, an insert pocket 21 is provided on the cutting portion 10, and a second screw hole 211 is provided in the insert pocket 21, and a bolt can be screwed into the first screw hole 14 and the second screw hole 211, so that the cutting insert 1 can be lockingly mounted on the insert pocket 21 by the bolt; when the cutting blade 1 needs to be replaced or indexed, the replacement and the indexing of the cutting blade 1 can be realized by unscrewing the bolt, and the operation is simple and convenient, and the time and the labor are saved. In other embodiments, a snap-fit or other connection may be used to achieve a detachable connection between the cutting insert 1 and the insert pocket 21, which is not particularly limited herein.

Specifically, as shown in fig. 2, 3 and 9, chip pockets 15 are provided on the cutting insert 1 toward the cutting rotation direction; and be provided with chip groove 3 between two adjacent cutting planes 2 on cutting portion 10, chip groove 3 is linked together with chip groove 15 for the piece that cutting insert 1 cut down from the work piece is arranged to chip groove 3 through chip groove 15, and outside the whole thread milling cutter is discharged from chip groove 3 again, more is favorable to the discharge of piece, prevents that the piece from piling up and causes the damage to thread milling cutter, in order to guarantee the normal cutting work of screw milling cutter to the work piece.

Further, as shown in fig. 9, the chip groove 3 is of an annular structure, the width of the chip groove 3 in the axial direction of the cutting portion 10 is smaller than L, L is the distance between two adjacent cutting planes 2, the depth of the chip groove 3 is smaller than or equal to 0.15d, d is twice the distance between the highest point of the cutting blade 1 during rotation and the axial direction of the cutting portion 10, so that the width and depth of the chip groove 3 are ensured to be proper, the chip removal effect of the chip groove 3 is ensured, the strength and hardness of the whole cutting portion 10 are not affected by the chip groove 3, and the stability of the cutting portion 10 in the cutting process is ensured to be good.

The specific working procedure of the thread milling cutter in this embodiment is as follows:

first, the first blade 11, the second blade 12 and the third blade 13 are respectively mounted on the same cutting plane 2 at intervals of bolts; turning the whole thread milling cutter so that the cutting blades 1 on the respective cutting planes 2 simultaneously cut the workpiece, so that the cutting teeth of the first blade 11 and the cutting teeth of the second blade 12 respectively cut both side portions of the thread structure, and the cutting teeth of the third blade 13 cut the middle portion of the thread structure; after the whole thread milling cutter rotates for one circle, the profiles cut by the first blade 11, the second blade 12 and the third blade 13 can be spliced to form a complete tooth profile, and after the whole thread milling cutter rotates for four circles, a complete thread structure is obtained by machining. In which the cut chips are discharged to the outside of the entire thread milling cutter through the chip flute 15 of the cutting insert 1 and the chip groove 3 of the cutting part 10.

In the thread milling cutter in the embodiment, three special cutting teeth are arranged on the same cutting plane 2 and are of incomplete tooth shapes, so that the profile formed by splicing the three cutting teeth after rotating for one circle is of complete tooth shapes, and the cutting resistance of the thread milling cutter can be reduced while the thread structure is processed; meanwhile, each cutting blade 1 on two adjacent cutting planes 2 is arranged in a staggered mode, so that the cutting resistance of the thread milling cutter can be reduced better; also, the cutting inserts 1 on the respective cutting planes 2 can be simultaneously machined, so that the machining efficiency of the screw structure is high.

The foregoing is merely exemplary of the present invention, and those skilled in the art should not be considered as limiting the invention, since modifications may be made in the specific embodiments and application scope of the invention in light of the teachings of the present invention.

Claims (10)

1. A thread milling cutter, characterized by comprising:

a cutting part (10), wherein at least two cutting planes (2) are arranged on the cutting part (10) at intervals along the axial direction of the cutting part;

the thread milling cutter comprises cutting blades (1), wherein at least two cutting blades (1) are arranged on each cutting plane (2) at intervals, the tooth shapes of the cutting teeth of the cutting blades (1) are different, and when the thread milling cutter rotates, a non-overlapping area exists between the cutting blades (1), so that the cutting blades (1) can be spliced to form an overall tooth shape of a thread structure to be processed after the thread milling cutter rotates for a circle.

2. The thread milling cutter according to claim 1, wherein three cutting blades (1) are provided on the cutting plane (2), the three cutting blades (1) are a first blade (11), a second blade (12) and a third blade (13), the cutting tooth profiles of the first blade (11) and the second blade (12) are trapezoidal, the setting positions of the cutting teeth of the first blade (11) and the second blade (12) are different, the cutting gear profile of the third blade (13) comprises a rectangular portion and a trapezoid portion located above the rectangular portion, and the cutting paths between the first blade (11), the second blade (12) and the third blade (13) do not completely overlap.

3. The thread milling cutter according to claim 2, wherein the cutting tooth profile of the first (11) and the second (12) blade overlaps the rectangular portion of the third blade (13) such that the overlapping profile of the first (11), the second (12) and the third blade (13) is in a trapezoidal configuration.

4. The thread milling cutter according to claim 2, wherein the thread width of the thread structure is W, the height of the thread structure is H, the cutting tooth heights of the first blade (11) and the second blade (12) are H1,0.55 h+.1+.0.65H, the cutting tooth tip widths of the first blade (11) and the second blade (12) are W2, w2=1/8W, and the cutting tooth widths of the third blade (13) are W1,0.5 w+.w1+.0.6W.

5. The thread milling cutter according to any one of claims 1 to 4, wherein in adjacent two of the cutting planes (2), the cutting inserts (1) are arranged offset in the circumferential direction of the cutting portion (10), and the offset angle between adjacent two of the cutting inserts (1) is β,10 ° β being 60 °.

6. The thread milling cutter according to any one of claims 1 to 4, wherein each cutting plane (2) is uniformly spaced on the cutting portion (10), and a spacing L between adjacent two cutting planes (2) is an integer multiple of a pitch of the thread structure.

7. The thread milling cutter according to any one of claims 1 to 4, further comprising a shank (20), the cutting portion (10) being provided at one end of the shank (20); the cutting insert (1) is detachably arranged in the cutting plane (2).

8. The thread milling cutter according to claim 7, wherein the cutting insert (1) is provided with a first threaded hole (14), the cutting portion (10) is provided with an insert pocket (21), a second threaded hole (211) is provided in the insert pocket (21), and a bolt is threadably connected to the first threaded hole (14) and the second threaded hole (211).

9. The thread milling cutter according to any one of claims 1 to 4, wherein the cutting insert (1) is provided with chip flutes (15) directed in the cutting rotation direction; chip grooves (3) are formed between two adjacent cutting planes (2) on the cutting part (10), and the chip grooves (3) are communicated with the chip grooves (15).

10. The thread milling cutter according to claim 9, wherein the chip groove (3) has a ring-like structure, a width of the chip groove (3) in an axial direction of the cutting portion (10) < L, L being a distance between adjacent two of the cutting planes (2), a depth of the chip groove (3) being equal to or less than 0.15d, d being twice a distance between a highest point of the rotation of the cutting insert (1) and an axis of the cutting portion (10).