Patent Publication Number: US-11396047-B2

Title: Method to machine a metal work piece by turning

Description:
RELATED APPLICATION DATA 
     The present application is a continuation of U.S. patent application Ser. No. 15/893,111, filed Feb. 9, 2018, which is a continuation of U.S. patent application Ser. No. 15/289,101, filed Oct. 7, 2016, which claims priority under 35 U.S.C. § 119 to EP Patent Application No. 15189176.9, filed on Oct. 9, 2015, which the entirety thereof is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the technical field of metal cutting. More specifically, the field of turning, which is performed by turning a metal work piece using a turning tool in a machine such as a CNC-machine. 
     The present disclosure refers to a method to form a surface on a metal work piece, the use of a turning insert in such method, a computer program having instructions which when executed by a computer numerical control lathe causes the computer numerical control lathe to perform such method, a computer readable medium having stored thereon such computer program, and a data stream which is representative of such computer program. 
     BACKGROUND 
     In turning of a metal work piece, the metal work piece rotates around a center axis. The metal work piece is clamped at one end by rotatable clamping means such as one or more chuck or jaws. The end of the work piece which is clamped can be called a clamping end or a driving end. For stable clamping, the clamping end or the driving end of the metal work piece may have a larger diameter than the opposite end of the metal work piece and/or has a larger diameter of a portion of the metal work piece located between the clamping end and the opposite end. Alternatively, the metal work piece may have a constant diameter before a machining, i.e. metal cutting, operation. 
     The turning insert is moved in relation to the metal work piece. This relative movement is called feed. The movement of the turning insert can be in a direction parallel to the center axis of the metal work piece, this is commonly called longitudinal feed or axial feed. The movement of turning insert can furthermore be in a direction perpendicular to the center axis of the metal work piece, this is commonly called radial feed or facing. Other angles of movement, or feed directions, are also possible, this is commonly known as copying or copy-turning. 
     In copying, the feed has both axial and radial components. During the relative movement of the turning insert, material from the metal work piece is removed in the form of chips. The chips are may be short and/or have a shape or direction of movement which prevents chip jamming and/or do not give a poor surface finish of the machined surface. 
     Common shapes of turning inserts which can be used for a wide range of feed direction include triangular turning inserts. Such inserts have in a top view, i.e. a rake face towards the viewer, the shape of a triangle where all three sides are of equal length and where the nose angle is 60°. The corners of the triangle are in the form of nose cutting edges, which typically has a radius of curvature in the range of 0.2-2.0 mm. Examples of such turning inserts are commonly designated TNMG and TCMT according to ISO standard, and are commonly made at least partly from coated or uncoated cemented carbide or cubic boron nitride (CBN) or ceramic or cermet. 
     Other common shapes of turning inserts have in a top view, i.e. a rake face towards the viewer, the shape of a rhombus where all four sides are of equal length and where the nose angle of an active nose portion is 80°. The active corners are in the form of nose cutting edges, which typically has a radius of curvature in the range of 0.2-2.0 mm. Examples of such turning inserts are commonly designated CNMG according to ISO standard, and are commonly made at least partly from coated or uncoated cemented carbide or cubic boron nitride (CBN) or ceramic or cermet. 
     Both the described triangular and rhombic turning inserts can be used for turning two walls forming an external 90° corner in a metal work piece, where one wall, at a greater distance from the rotational axis of a metal work piece, is perpendicular to the rotational axis and one cylindrical wall, at a smaller distance from the rotational axis, is parallel to the rotational axis, where the two walls are connected by a circular or curved segment. An external 90° corner in this context is a 90° corner formed on or at an external or outer surface of a metal work piece, such that the cylindrical wall or cylindrical surface is facing away from the rotational axis. This is in contrast to any corner which may be formed on or at an internal or inner surface inside a bore concentric with the rotational axis. 
     The circular or curved segment have a cross-section in a plane including the rotational axis in the shape of an arc, in the shape of a quarter of a circle or a quarter of a shape, which is substantially a circle, which has the same radius of curvature as the nose cutting edge of the turning insert. The circular or curved segment alternatively has a greater radius of curvature than the nose cutting edge of the turning insert. 
     In EP2572816B1, a turning tool is shown during machining of a work piece. The turning tool can be used for forming two walls forming an external 90° corner, without any reorientation of the turning tool. The tool includes a holder as well as a turning insert. In this case, the work piece is rotated at the same time as the tool is longitudinally fed parallel to the center axis of the. The setting angle, or entering angle, is the angle between the direction of the longitudinal feed and a main edge. The setting angle, or entering angle, is 95°. The turning insert has a rhombic basic shape and comprises two acute-angled corners having an angle of 80° and two obtuse-angled ones having an angle of 100°. A back clearance angle of 5° is obtained between the turning insert and the generated surface of the work piece. The generated surface of the work piece is substantially cylindrical. 
     Such a turning method as in EP2572816B1 gives an unsatisfactory tool life, or usage time, for the turning insert. 
     SUMMARY 
     To overcome the above disadvantages, the present disclosure is directed to a method to form a surface on a metal work piece including a first machining step of providing a turning insert including a first cutting edge, a second cutting edge and a convex nose cutting edge connecting the first and second cutting edges, and selecting a nose angle α formed between the first and second cutting edges to be less than or equal to 85°; providing a turning tool including the turning insert and a tool body, the tool body having a front end and a rear end, a main extension along a longitudinal axis extending from the front end to the rear end, and an insert seat formed in the front end in which the turning insert is mountable; arranging the orientation of the second cutting edge such that it forms a back clearance angle ψ of more than 90° in a feed direction; positioning all parts of the turning insert ahead of the nose cutting edge in the feed direction; rotating the metal work piece around a rotational axis A 3  in a first direction; moving the turning insert in a direction parallel to or at an angle less than 45° relative to the rotational axis such that the first cutting edge is active and ahead of the nose cutting edge in the feed direction and such that the surface at least partly is formed by the nose cutting edge; and setting the longitudinal axis of the tool body at an angle greater than zero but less than or equal to 90° relative to the rotational axis of the metal work piece. 
     According to the present method, the second cutting edge is not subject to wear during the first machining step, e.g. an axial turning step, and can be used in a subsequent second machining step, e.g. an out facing step i.e. fed perpendicular to and away from the rotational axis of the metal, or metallic, work piece, or in a subsequent turning operation in an substantially opposite or opposite direction relative to the first direction. 
     It is advantageous for the tool life of the turning insert that the wear of the cutting edges is distributed in an equal manner. According to the present method, it is possible to use the turning insert in a prior or subsequent second machining step, e.g. an out facing operation, without reorientation, preferably in such a way that insert wear is distributed over a longer cutting edge distance, with little or no overlap for the insert wear caused by the first machining step and the second machining step. 
     According to the present method, the chip control or chip evacuation is improved if the feed direction is away from a portion of the work piece which has a larger diameter than the diameter of the surface formed, such as for example a wall surface extending in a plane perpendicular to the rotational axis of the metal work piece. 
     According to the present method, the entering angle of the first cutting edge is reduced, resulting in relatively wider and thinner chips, which the inventors have found to give reduced wear of the first cutting edge. 
     The present method is thus related to axial or longitudinal or copy turning, which can be external or internal. The method can be an external turning method, i.e. a method where the surface which is formed is facing away from the rotational axis. The surface which is formed, or generated, is a rotational symmetrical surface, i.e. a surface which has an extension along the rotation axis of the metal work piece and where in a cross sections perpendicular to the rotational axis, each portion of the rotational symmetrical surface is located at a constant distance from the rotation axis of the metal work piece, where a constant distance is a distance which is within 0.10 mm, for example, within 0.05 mm. 
     The rotational symmetrical surface can be in the form of e.g. a cylindrical surface or a conical surface or a frustoconical surface or a tapered surface. The moving or feed direction of the turning insert is away from an imaginary plane perpendicular to the rotational axis. In other words, the moving of the turning insert is with a component of the movement in a direction parallel to the rotational axis of the metal work piece, e.g. the turning insert moves in a direction parallel to the rotational axis, or the turning insert moves in a direction at an angle, for example, an angle less than 15°, relative to the rotational axis. 
     In the first example, the rotational symmetrical surface is a cylindrical surface which is symmetrical around the rotational axis. In the second example, the rotational symmetrical surface is a conical surface, or a frustoconical surface, or a tapered surface, which is symmetrical around the rotational axis. The rational symmetrical surface generated or formed at least partly by the nose cutting edge has a wavy shape with small peaks and valleys, and the wavy shape is influenced at least partly by the curvature of the nose radius and the feed rate. The wave height is less than 0.10 mm, for example, less than 0.05 mm. 
     To form, or generate, a rotational symmetrical surface in this meaning is by metal cutting, where chips from the metal work piece are removed by at least one cutting edge. The final shape of the rotational symmetrical surface is formed solely or at least to the greatest extent or at least partly by the nose cutting edge. This is because the nose cutting edge is the part of the turning insert which is located at a shorter distance from the rotation axis of the metal work piece than all other parts of the turning insert. 
     More specifically, during the first machining step, one first point of the nose cutting edge is the part of the turning insert which is located closest to the rotational axis of the metal work piece. One second point, or trailing point, of the nose cutting edge, which is behind the first point in the feed direction, is the part of the turning insert which is located most rearward in the feed direction or in the direction of insert movement. This first point of the nose cutting edge is located on the same side of the bisector as the first cutting edge, where the bisector is a line which is between the first and second cutting edges at equal distance from the first and second cutting edges. 
     The second point of the nose cutting edge is located on the same side of the bisector as the second cutting edge. The first cutting edge and the second cutting edge are located on opposite sides of the convex nose cutting edge. The first, second and nose cutting edges are formed at borders of a top surface of the turning insert, which top surface comprises a rake face. 
     The expression “positioning all parts of the turning insert ahead of the nose cutting edge in the feed direction” thus can alternatively be formulated as “positioning all parts of a top surface of the turning insert ahead of a trailing portion of the nose cutting edge in the feed direction.” 
     The nose angel of less than or equal to 85° gives a smililar advantage as that of a 90° corner, i.e. two wall surfaces being perpendicular to each other that can be machined with one nose portion of the turning insert, without any reorientation of the turning insert. Alternatively, a nose angle less than or equal to 85° is equal to a nose cutting edge having the shape of a circular arc of an angle of less than or equal to 85°. 
     The nose cutting edge may have a shape of a circular arc, or may have a shape that deviates slightly from a perfect circular arc. The nose cutting edge can have a radius of curvature of 0.2-2.0 mm. 
     The first and second cutting edges can be straight in a top view. Alternatively, the first and second cutting edges can be slightly convex or concave, with a radius of curvature that is more than two times greater, for example, more than ten times greater, than the radius of curvature of the convex nose cutting edge. 
     The moving of the turning insert is commonly known as feed. If the feed is parallel to the rotational axis of the metal work piece, it is called axial feed or longitudinal feed. The first cutting edge is ahead of the nose cutting edge in the feed direction. In other words, the first cutting edge forms, or is active at, an entering angle less than 90° and more than 1°, less than 45° and more than 3°, and less than 45° and more than 10°. In other words, the first cutting edge is a leading edge. The entering angle is the angle between the feed direction and the active cutting edge, which in this case is first cutting edge. 
     The second cutting edge forms a back clearance angle ψ of more than 90°, for example, more than 100°. In other words, the second cutting edge is a trailing edge. The angle between the feed direction, i.e. the direction of movement of the turning insert, and the second cutting edge is less than 90°, for example, less than 80°. In turning, at least in turning where a first cutting edge and a second cutting edge is located in a plane comprising the rotation axis, the entering angle plus the nose angle (the angle between the first and second cutting edges adjacent on opposite sides of the nose cutting edge) plus the back clearance angle ψ equals 180°. 
     In  FIG. 2  where the feed is parallel to the rotation axis, the back clearance angle is 90° plus κ 2 . Alternative formulations of the back clearance angle ψ includes end cutting edge angle, free cutting angle, and plan trail clearance angle. The rotating and moving are motions which are relative, which means that although it is preferred that the metal work piece rotates and that the turning insert moves in an axial direction, it is possible in e.g. bar peeling machines that the turning insert rotates around a non-rotating metal work piece, and that the metal work piece moves in an axial direction. 
     The turning insert can be mounted in a tool body. The tool body is turn mounted in a turning lathe or a CNC-machine. 
     The feed rate can be less than or equal to the radius of curvature of the nose cutting edge, if the nose cutting edge has a constant radius of curvature. This is to generate an acceptable surface finish. For example, for a turning insert having a nose cutting edge with a radius of curvature of 0.8 mm, the feed rate being less than or equal to 0.8 mm per revolution. For turning inserts having a nose cutting edge which deviates slightly from a circular arc, such as so called wiper radius or wiper insert, the feed rate can be slightly higher while still generating an acceptable surface finish. The formed or generated surface has an extension which corresponds to the feed direction. 
     According to an embodiment, the first machining step further includes the steps of clamping the metal work piece at a first end, setting the nose cutting edge a shorter distance to the first end than all other parts of the turning insert and moving the turning insert in a direction away from the first end. 
     According to the present method, chip jamming is further improved, because the moving of the turning insert, i.e. the feed direction, is towards an un-clamped or free end of the metal work piece. 
     The first end of the metal work piece is a clamping end or driving end. Thus, the clamping means, e.g. chuck or clamping jaws or tail stock, which holds the metal work piece, are controlled and driven by a motor hold the metal work piece in the first end. The headstock end of the machine is located at the first end of the metal work piece. The diameter of the first end of the metal work piece can be greater than the diameter of the surface. 
     According to an embodiment, the first machining step further includes the step of arranging the first cutting edge such that the first cutting edge cuts metal chips from the metal work piece at an entering angle κ 1  of 10-45°. 
     The first cutting edge is thus active at an entering angle κ 1  of 10-45°, for example, 20-40°. A lower entering angle gives too wide chips resulting in reduced chip control, and the risk of vibration would increase. A higher entering angle gives increased insert wear of the first cutting edge. Accordingly, the nose angle, i.e. the angle which the first and second cutting edges form relative to each other in a top view, is 25-50°. A top view is where a top surface, i.e. a rake face, of the turning insert is facing the viewer and is perpendicular to the view direction. The cutting depth can be 0.05-5.0 mm. 
     According to an embodiment, the first machining step further includes the step of providing that the turning insert comprises a third convex cutting edge adjacent to the first cutting edge and a fourth cutting edge adjacent to the third cutting edge, the method further including the step of arranging the forth cutting edge such that the fourth cutting edge cuts metal chips from the metal work piece at an entering angle κ 1  of 10-45°. 
     According to the present method, the tool life of the turning insert is further increased, i.e. the wear is further reduced, especially at relatively larger depths of cut, such as e.g. depth of cut greater than 1.0 mm. 
     The nose angel α, i.e. the angle between the first and second cutting edges, can be 70-85°. Thus, the wear of the nose cutting edge is further reduced. 
     According to an embodiment, the first machining step further includes the step of entering the turning insert into the metal work piece at an angle relative to the rotation axis A 3  which is less than 90°, and which angle is greater than the angle formed between the feed direction of the turning insert and the rotational axis A 3 . Accordingly, the wear, especially the wear at the nose cutting edge, of the turning insert  1  is further reduced. The turning insert is thus entering the metal work piece, i.e. going into the cut, gradually. 
     According to an embodiment, the first machining step further includes the step of entering the turning insert into the metal work piece such that the nose cutting edge moves along an arc of a circle. Thus, the wear, especially the wear at the nose cutting edge, of the turning insert is further reduced. When the turning insert enters the metal work piece, i.e goes into the cut, the nose cutting edge moves along an arc of a circle. 
     According to an embodiment, the first machining step further includes the step of entering the turning insert into the metal work piece such that the chip thickness during entry is constant or substantially constant. Accordingly, the insert wear is further reduced. 
     Chip thickness is defined as feed rate multiplied by sinus for the entering angle. Thus, by choosing and/or varying the feed rate and the movement and/or direction of the turning insert during entry, the chip thickness can be constant or substantially constant. The feed rate during entry can be less or equal than 0.50 mm/revolution. The chip thickness during entry can be less than or equal to the chip thickness during subsequent cutting or machining. 
     According to an embodiment, the surface is an external cylindrical surface, and in the moving of the turning insert is in a direction parallel to the rotational axis A 3 . 
     An external cylindrical surface is a surface having an extension along and at a constant or substantially constant distance from the rotational axis. The moving of the turning insert is the feed direction. 
     According to an embodiment, the turning insert has a top surface and an opposite bottom surface. A reference plane RP is located parallel to and between the top surface and the bottom surface. The present method further includes the step of arranging the first cutting edge such that the distance from the first cutting edge to the reference plane RP decreases as the distance from the nose cutting edge. In other words, this distance is decreasing as the distance from the nose cutting edge increases. 
     According to the present method, the chip breaking and/or chip control and/or tool life, i.e. insert wear, is improved, in axial turning away from the clamping end of the metal work piece. 
     The top surface can be a rake face. The bottom surface acts as a seating surface. The reference plane is parallel to a plane in which the nose cutting edges are located. The distance from different points of the first cutting edge to the reference plane varies in such a way that that this distance is decreasing at an increasing distance from the nose cutting edge. In other words, the distance from the first cutting edge to the reference plane is decreasing away from the nose cutting edge. 
     Alternatively formulated, a distance from the reference plane to a first portion of the first cutting edge is greater than a distance from the reference plane to a second portion of the first cutting edge, where the first portion of the first cutting edge is located between the nose cutting edge and the second portion of the first cutting edge. For example, a first point of the first cutting edge, adjacent to the nose cutting edge, is located a greater distance from the reference plane than a distance from a second point of the first cutting edge, located at a greater distance from the nose cutting edge than the first point of the first cutting edge, to the reference plane. The first cutting edge is sloping towards the bottom surface and the reference plane away from the nose cutting edge in a side view. 
     According to an embodiment the turning insert includes a top surface, an opposite bottom surface, and a reference plane RP is located parallel to and between the top surface and the bottom surface. The method further includes the step of arranging the fourth cutting edge such that the distance from the fourth cutting edge to the reference plane RP decreases at increasing distance from the nose cutting edge. By such a method the chip breaking and/or chip control and/or tool life, i.e. insert wear, is improved, in axial turning away from the clamping end of the metal work piece. 
     The top surface provides a rake face. The bottom surface provides a seating surface. The reference plane is parallel to a plane in which the nose cutting edges are located. The distance from the fourth cutting edge to the reference plane varies in such a way that that this distance is decreasing at increasing distance from the nose cutting edge. In other words, the distance from the fourth cutting edge to the reference plane is decreasing away from the nose cutting edge. Alternatively formulated, a distance from the reference plane to a first portion of the fourth cutting edge is greater than a distance from the reference plane to a second portion of the fourth cutting edge, where the first portion of the fourth cutting edge is located between the nose cutting edge and the second portion of the fourth cutting edge. For example, a first point of the fourth cutting edge, closer to the nose cutting edge, is located a greater distance from the reference plane than a distance from a second point of the fourth cutting edge, located at a greater distance from the nose cutting edge than the first point of the fourth cutting edge, to the reference plane. The fourth cutting edge slopes towards the bottom surface and the reference plane away from the nose cutting edge in a side view. 
     According to an embodiment, the method further includes the step of setting the back clearance angle constant in relation to the feed direction during the formation of the surface. 
     In other words, in the case of a constant feed direction when forming the surface, the back clearance angle is constant when forming the surface. Thus, during the formation of the surface the turning insert do not rotate around any axis. 
     According to an embodiment, the method further includes the step of providing a turning tool having the turning insert and a tool body, wherein the method includes the further step of positioning all parts of the tool body ahead of the nose cutting edge in the feed direction. In other words, the turning tool is ahead of the nose cutting edge in the feed direction. By such a method, the possibility of out facing, or feeding in a direction perpendicular to and away from the rotational axis of the metal work piece, is further improved. 
     According to an embodiment, the method further includes the step of providing a turning tool including the turning insert and a tool body, the tool body having a front end and a rear end, a main extension along a longitudinal axis extending from the front end to the rear end, an insert seat formed in the front end in which the turning insert is mountable. The method further includes the step of setting the longitudinal axis of the tool body at an angle greater than zero but less than or equal to 90° relative to the rotational axis of the metal work pece. 
     According to the present method, the risk of vibrations is reduced, compared to if the longitudinal axis of the tool body were parallel to the rotational axis of the metal work piece, at least in the case where the feed direction is parallel to the the rotational axis of the metal work piece. According to the present method, the possibility to machine deep cavities or deep pockets are improved, because the risk of the tool body interfering the metal work piece is reduced. The setting of the longitudinal axis of the tool body is perpendicular, i.e. 90°, to the rotational axis of the metal work piece. The longitudinal axis of the tool body can be at a constant angle relative to the longitudinal axis of the tool body. 
     According to an embodiment, the method includes a second machining step of moving the turning insert in a direction away from the rotation axis A 3  such that the second cutting edge cuts chips from the metal work piece, and such that a surface perpendicular to the rotational axis A 3  of the metal work piece is formed. 
     According to the present method, two surfaces, which together form a corner, such as a 90° corner, can be formed with the same turning insert without reorientation of the turning insert, with reduced wear of the turning insert. More specifically, the insert wear is distributed in a more even manner, giving prolonged tool life. 
     The direction of the movement of the turning insert is away from the rotational axis of the metal work piece, i.e., in a direction perpendicular to the rotational axis, or at an angle which deviates up to 20° from a perpendicular direction to the rotational axis. The direction of rotation of the metal work piece around the rotational axis is the same direction for the first and second machining steps. The second machining step can be made either prior to or after the first machining step. The orientation of the turning insert can be constant during the first and second machining steps. Constant orientation means that the angles which parts of the turning insert, such as the first cutting edge, forms in relation to or relative to the rotational axis of the metal work piece is constant or has the same value at both the first and second machining steps 
     According to an embodiment, the method includes the step of in a sequence alternating the first and second machining steps, such that a corner having two surfaces is formed. According to the present method, the insert wear is further reduced. By such a method, the risk for chip jamming is further reduced, because the cutting time for each cut is reduced. 
     According to an embodiment, the method includes the step of in a sequence alternating the first and second machining steps, such that an external 90° corner having two wall surfaces is formed, wherein one wall surface is an outer cylindrical surface and in that one wall surface is perpendicular to the rotational axis A 3  of the metal work piece. 
     According to the present method, an external 90° corner can be formed with less risk of chip jamming, because the feed direction or the movement of the turning insert is not towards the wall surface which is perpendicular to the rotational axis of the metal work piece. According to the present, an external 90° corner can be formed with reduced insert wear. 
     The direction of movement of the turning insert during the first machining step is parallel to the rotational axis of the metal work piece. The direction of movement of the turning insert during the second machining step is perpendicular to and away from the rotational axis of the metal work piece. The direction of movement in this sense is during the major part of each machining step. 
     The entry or start or going into the cut part of each machining step is at least partly in a different direction than the major part. The entry or start or going into the cut part is thus a minor part of each machining step, in the sense that the volume of removed metal is less than 20% than the metal removed from the major part. The surface formed which is perpendicular to the rotational axis is a flat or substantially flat surface, i.e. the surface is located in a single plane. Substantially flat in this sense is a wavy surface, where the wave depth or wave height is less than 0.1 mm, for example, less than 0.05 mm. 
     The external 90° corner includes two wall surfaces, which are connected by a curved or arc-shaped surface. The radius of curvature of the curved or arc-shaped surface is equal to or greater than the radius of curvature of the nose cutting edge of the turning insert. The curved or arc-shaped surface has a surface area which can be less than 50%, for example, less than 10%, of the surface area of each of the wall surfaces. 
     According to an embodiment, the method includes a third machining step, including the steps of rotating the metal work piece around the rotation axis A 3  in a second direction, in that the second direction of rotation is opposite to the first direction of rotation, and moving the turning insert in a direction towards the rotation axis A 3  such that the second cutting edge cuts chips from the metal work piece. 
     Thus, during the third machining step, at least the second cutting edge of the turning insert is located on an opposite side or a substantially opposite side of the rotational axis, compared to the location of at least the first cutting edge of the turning insert during the first machining step. The third machining step can be performed prior to or after the first machining step. The third machining step can be performed prior to or after the second machining step. The third machining step can include a moving of the turning insert perpendicular to the rotational axis of the metal work piece. 
     According to an embodiment, the method includes the step of providing a turning tool comprising the turning insert and a tool body, the tool body having a front end and a rear end, a main extension along a longitudinal axis A 2  extending from the front end to the rear end, an insert seat formed in the front end in which the turning insert is mountable such that a bisector extending equidistantly from the first and second cutting edges forms an angle θ of 35-55° in relation to the longitudinal axis A 2  of the tool body. 
     According to an embodiment, the method includes the step of arranging the first cutting edge a shorter distance from the longitudinal axis A 2  of the tool body than the distance from the second cutting edge to the longitudinal axis A 2  of the tool body. 
     According to another aspect of the present disclosure, at least the above mentioned primary objective is achieved by means of the use of a turning insert in the method as initially defined. 
     According to a third aspect of the present disclosure, at least the above mentioned primary objective is achieved by means of a computer program having instructions, which when executed by a computer numerical control lathe, causes the computer numerical control lathe to perform the method as initially defined. 
     The method and methods described herein may be embodied by a computer program or a plurality of computer programs, which may exist in a variety of forms both active and inactive in a single computer system or across multiple computer systems. For example, they may exist as software program(s) of program instructions in source code, executable code or other formats for performing some of the steps. Any of the above may be embodied on a computer readable medium, which include storage devices and signals, in compressed or uncompressed form. The term computer numerical control (CNC) lathe refers to any machine which can be used for turning a metal work piece, and where the motion of the machine, such as tool path, depth of cut, feed rate, cutting speed and revolutions per time unit, is or can be controlled by a computer. 
     According to a fourth aspect of the present disclosure, at least the above mentioned primary objective is achieved by means of a computer readable medium having stored thereon a computer program having instructions which when executed by a computer numerical control lathe cause the computer numerical control lathe to perform the method as initially defined. 
     As used herein, a computer readable medium or storage medium can be any means that contain, store, communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example but not limited to, an electronic, magnetic, optic, electromagnetic, infrared, or semiconductor system, device, or propagation medium. More examples (a non-exhaustive list) of the computer readable medium can include the following: an electrical connection having one or more wires, a portable computer diskette, a random access memory (RAM), a read only memory (ROM), an erasable programmable read only memory (EPROM or Flash memory), an optical fiber, and a portable compact disc read only memory (CDROM). 
     According to a fifth aspect of the present disclosure, at least the above mentioned primary objective is achieved by means of a data stream which is representative of a computer program having instructions which when executed by a computer numerical control lathe cause the computer numerical control lathe to perform the method as initially defined. 
     The foregoing summary, as well as the following detailed description of the embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood that the embodiments depicted are not limited to the precise arrangements and instrumentalities shown. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing conventional turning of a cylindrical surface with a conventional turning insert. 
         FIG. 2  is a schematic view illustrating turning of a cylindrical surface by a first turning insert. 
         FIG. 2 a    is a schematic view showing turning of a cylindrical surface by a third turning insert. 
         FIG. 3  is a schematic view illustrating turning, including axial turning and out-facing, of a metal work piece with the first turning insert. 
         FIG. 3 a    is a schematic view showing turning, including axial turning and out-facing, of a metal work piece by a third turning insert. 
         FIG. 4  is a schematic view illustrating turning, including out-facing, of a metal work piece with the first turning insert. 
         FIG. 5  is a top view of a top surface of a nose portion of the first turning insert. 
         FIGS. 6-8  are detailed cross-sectional views taken along the lines VI-VI, VII-VII and VIII-VIII, respectively, in  FIG. 5 . 
         FIG. 9  is a side view of the nose portion in  FIG. 5 . 
         FIG. 10  is a schematic view showing a turning method according to an embodiment forming a surface using a conventional turning insert. 
         FIG. 11  is a schematic top view of a nose portion of a conventional turning insert, showing wear from conventional turning. 
         FIG. 12  is a schematic top view of a nose portion, showing wear from turning in  FIG. 13 . 
         FIG. 13  is a schematic view illustrating turning of a 90° corner by the first turning insert. 
         FIG. 14 a    is a perspective view showing a second turning insert. 
         FIG. 14 b    is a front view of the turning insert in  FIG. 14   a.    
         FIG. 14 c    is a side of the turning insert in  FIG. 14   a.    
         FIG. 14 d    is a top view of the turning insert in  FIG. 14   a.    
         FIG. 14 e    is a perspective view showing the turning insert in  FIG. 14 a    positioned in a partial tool body. 
         FIG. 14 f    is an exploded view showing the turning insert and tool body in  FIG. 14   e.    
         FIG. 15 a    is a perspective view showing a third turning insert. 
         FIG. 15 b    is a front view of the turning insert in  FIG. 15   a.    
         FIG. 15 c    is a side of the turning insert in  FIG. 15   a.    
         FIG. 15 d    is a top view of the turning insert in  FIG. 15   a.    
         FIG. 15 e    is a top view of the turning insert in  FIG. 15 a    and a tool body. 
         FIG. 15 f    is a top view of the tool body in  FIG. 15   e.    
         FIG. 16 a    is a perspective view showing the first turning insert. 
         FIG. 16 b    is a front view of the turning insert in  FIG. 16   a.    
         FIG. 16 c    is a side view of the turning insert in  FIG. 16   a.    
         FIG. 16 d    is a top view of the turning insert in  FIG. 16   a.    
         FIG. 17 a    is a perspective view showing the turning insert In  FIG. 16 a    and a tool body. 
         FIG. 17 b    is a perspective view showing the bottom surface of the turning insert in  FIG. 16 a      
         FIG. 17 c    is a further perspective view showing the bottom surface of the turning insert in  FIG. 16 a      
         FIG. 17 d    is a perspective view showing the turning insert in  FIG. 15 a    seated in a tool body. 
         FIG. 17 e    is a perspective view showing the turning insert in  FIG. 15 a    and a tool body. 
         FIG. 17 f    is a top view showing the turning insert and the tool body in  FIG. 17   d.    
         FIG. 18 a    s a perspective view showing a fourth turning insert. 
         FIG. 18 b    is a top view of the turning insert in  FIG. 18   a.    
         FIG. 18 c    is a bottom view of the turning insert in  FIG. 18   a.    
         FIG. 18 d    is a side view of the turning insert in  FIG. 18   a.    
         FIG. 18 e    is a front top view of the turning insert in  FIG. 18   a.    
         FIG. 19 a    is a perspective view showing a fifth turning insert. 
         FIG. 19 b    is a top view of the turning insert in  FIG. 19   a.    
         FIG. 19 c    is a bottom view of the turning insert in  FIG. 19   a.    
         FIG. 19 d    is a side view of the turning insert in  FIG. 19   a.    
         FIG. 19 e    is a front top view of the turning insert in  FIG. 19   a.    
         FIG. 20 a    is a perspective view showing a sixth turning insert. 
         FIG. 20 b    is a top view of the turning insert in  FIG. 20   a.    
         FIG. 20 c    is a bottom view of the turning insert in  FIG. 20   a.    
         FIG. 20 d    is a side view of the turning insert in  FIG. 20   a.    
         FIG. 20 e    is a front top view of the turning insert in  FIG. 20   a.    
         FIG. 21 a    is a perspective view showing a seventh turning insert. 
         FIG. 21 b    is a top view of the turning insert in  FIG. 21   a.    
         FIG. 21 c    is a bottom view of the turning insert in  FIG. 21   a.    
         FIG. 21 d    is a side view of the turning insert in  FIG. 21   a.    
         FIG. 21 e    is a front top view of the turning insert in  FIG. 21   a.    
         FIG. 22 a    is a perspective view showing an eighth turning insert. 
         FIG. 22 b    is a top view of the turning insert in  FIG. 22   a.    
         FIG. 22 c    is a bottom view of the turning insert in  FIG. 22   a.    
         FIG. 22 d    is a side view of the turning insert in  FIG. 22   a.    
         FIG. 22 e    is a front top view of the turning insert in  FIG. 22   a.    
     
    
    
     All turning insert figures except  FIGS. 1 and 10  have been drawn to scale. 
     DETAILED DESCRIPTION 
     Reference is made to  FIG. 1 , which show a conventional metal cutting operation by turning using a conventional turning insert  1 . A metal work piece  50  is clamped by clamping jaws  52 , which are connected to a machine comprising a motor (not shown), such as a CNC-machine or a turning lathe. The clamping jaws press against an external surface at a first end  54 , or clamping end, of the metal work piece  50 . 
     An opposite second end  55  of the metal work piece  50  is a free end. The metal work piece  50  rotates around a rotational axis A 3 . The turning insert  1  is securely and removably clamped in an insert seat or a pocket in a tool body  2 . The tool body  2  has a longitudinal axis A 2 , extending from a rear end to a front end, in which the insert seat or pocket is located. The tool body  2  and the turning insert  1  together form a turning tool  3 . 
     The turning tool  3  is moved in relation to the metal work piece  50 , commonly designated feed. In  FIG. 1 , the feed is axial, also called longitudinal feed, i.e. the direction of the feed is parallel to the rotational axis A 3 . In this way, a cylindrical surface  53  is formed. 
     The turning insert  1  has an active nose with a nose angle α which is 80°, defined as the angle between the main cutting edge and the secondary cutting edge. As the turning insert  1  reaches closer to the wall surface which is perpendicular to the rotational axis A 3 , chip control is poor because there is not much space for the chips to get out from the cutting zone. There is also risk that chips hits or damages the machined surface. 
     The main cutting edge is behind the nose cutting edge. In other words, the entering angle for the main cutting edge is over 90°, in  FIG. 1  around 95°. The entering angle is defined as the angle between the cutting edge and the feed direction. In the turning method shown in  FIG. 1 , the back clearance angle is around 5°. The back clearance angle ψ is defined as the angle between the secondary cutting edge, which is a trailing edge, and a direction which is opposite, i.e. 180° in relation, to the feed direction. 
     Reference is made to  FIG. 2 , which show a turning operation, using a turning tool including a first turning insert. As in  FIG. 1 , a metal work piece is clamped by clamping jaws (not shown), which are pressed against an external surface at or adjacent to a first end  54  of the metal work piece. An opposite second end  55  of the metal work piece is a free end. The metal work piece rotates around a rotational axis A 3 . The turning insert, seen in top view, is securely and removably clamped in an insert seat or a pocket in tool body  2  by means of a screw  6 . The tool body  2  has a longitudinal axis A 2 , extending between a rear end and a front end  44 , in which the insert seat or pocket is located. 
     In  FIG. 2 , the feed is, to a greatest extent, axial, also called longitudinal feed, i.e. the direction of the feed is parallel to the rotational axis A 3 . In this way, an external cylindrical surface  53  is formed. At the entry of each cut, or immediately prior to the axial feed, the feed has a radial component, in such a way that the turning insert move along an arc of a circle. 
     The turning insert includes an active nose portion  15 , including an active nose cutting edge  10 . The active nose portion  15  further includes an active first cutting edge, which during axial turning parallel to the rotational axis A 3  has an entering angle κ 1  which is chosen to be in the range of 10-45°, for example, 20-40°. 
     The first cutting edge, which is the main cutting edge in the operation, is ahead of the nose cutting edge  10  in the axial feed direction. In other words, the first cutting edge is a leading edge. A second cutting edge, formed on or at the active nose portion  15 , is a secondary cutting edge or a trailing edge. If the feed direction would be radial, in such a way that the feed direction would be perpendicular to and away from the rotational axis A 3 , the second cutting edge would be active at an entering angle κ 2 . 
     A bisector  7  is defined by the first and second cutting edges. In other words, the bisector is formed between the first and second cutting edges. The first and second cutting edges converge at a point outside the turning insert. The bisector of the active nose portion  15  forms an angle θ of 40-50°, relative to the longitudinal axis A 2 . 
     The turning insert includes two inactive nose portions, comprising two inactive nose cutting edges  10 ′,  10 ″. In the axial turning operation, all parts of the turning insert are ahead of the active nose cutting edge  10  in the feed direction. In the axial turning operation, chips can be directed away from the metal work piece in a trouble-free manner. 
     In the machining step the turning insert  1  enters into the metal work piece  50  such that the nose cutting edge  10  moves along an arc of a circle. The turning insert  1  enters into the metal work piece  50 , or goes into cut, such that the chip thickness during entry is constant or substantially constant. At the entry, the depth of cut is increased from zero depth of cut. Such preferred entry reduces the insert wear, especially the wear at the nose cutting edge  10 . Chip thickness is defined as feed rate multiplied by entering angle. Thus, by choosing and/or varying the feed rate and the movement and/or direction of the turning insert during entry, the chip thickness can be constant or substantially constant. The feed rate during entry can be less than or equal than 0.50 mm/revolution. The chip thickness during entry can be less than or equal to the chip thickness during subsequent cutting or machining. 
     The cylindrical surface  53 , or rational symmetrical surface, generated or formed at least partly by the nose cutting edge in  FIGS. 1 and 2 , has a wavy shape with small peaks and valleys, and the wavy shape is influenced at least partly by the curvature of the nose radius and the feed rate. The wave height is less than 0.10 mm, for example, less than 0.05 mm. A thread profile is not a cylindrical surface  53  in this sense. 
     In  FIGS. 3 and 4 , the turning insert and tool body in  FIG. 2  can be seen in alternative machining operations, showing the versatile application area of the turning tool, especially with regard to feed direction.  FIG. 3  shows a machining sequence in six steps. Step 1 is a undercutting operation. Step 2 is axial turning away from the first end  54  or clamping end of the metal work piece. Step 3 is a profiling operation in the form of a feed which has both an axial and a radial component, generating a conical or frustoconical, i.e. tapered, surface. Step 4 is an operation similar to operation  2 . Step 5 is an out-facing operation generation a flat surface located in a plane perpendicular to the rotational axis A 3  of the metal work piece. Step 6 is an out-facing operation at the second end  55  or free end of the metal work piece. 
       FIG. 4  shows two machining steps, step 1 and step 2. In step 1, the radial feed is perpendicular to and towards the rotational axis A 3 . In 2, the radial feed is perpendicular to and away from the rotational axis A 3 , wherein a flat surface  56  perpendicular to the rotational axis A 3  is generated. In both cases, the second cutting edge is active at an entering angle κ 2  which is in the range of 10-45°, for example, 20-40°. The direction of rotational of the metal work piece around the rotational axis A 3  is in opposite directions for step 1 and 2. In step 2, the direction of rotation is the same as in  FIG. 1-3 . 
       FIG. 5  shows a top view of a nose portion  15  of the first turning insert, having a first  11  and a second  12  cutting edge connected by a convex nose cutting edge  10 . The first  11  and second  12  cutting edges on or at the same nose portion  15  form a nose angle α of 25-50° relative to each other, and the first  11  and second  12  cutting edges converge at a point (not shown) outside of the turning insert. A bisector  7  is located between, and at equal distances from, the first  11  and second  12  cutting edges. The bisector  7  intersects the nose cutting edge  10  at the center thereof. 
     A protrusion  30  is formed in the top surface of the turning insert, which protrusion has the major extension thereof along the bisector. The protrusion includes a first chip breaker wall  34  facing towards the first cutting edge, and a second chip breaker wall facing the second cutting edge. The distance, measured in a direction perpendicular to the first cutting edge  11 , and in a plane parallel to a reference plane RP, from the first cutting edge  11  to the first chip breaker wall  34  is increasing away from the nose cutting edge  10 . This gives improved chip control especially in a turning operation as in  FIG. 2 . The protrusion  30 , and thus the first chip breaker wall  34 , has a shorter extension than the first cutting edge  11 . 
       FIG. 9  shows a side view of the nose portion in  FIG. 5 . A bottom surface  9  is located opposite a top surface. The reference plane RP is located between and at equidistant length from the top and bottom  9  surfaces. Although the top and bottom surfaces are not flat, the reference plane RP can be positioned such that it is parallel to a plane intersecting the three nose cutting edges. A side surface  13  connects the top surface and the bottom surface  9 . The side surface  13  includes a first clearance surface  21  adjacent to the first cutting edge  11 , a third clearance surface  23  adjacent to the bottom surface  9 , and a second clearance surface  22  located between the first clearance surface  21  and the third clearance surface  23 . 
     The distance from the first cutting edge  11  to lower border line of the first clearance surface  21 , i.e. the border line of the first clearance surface  21  located closest to the bottom surface  9 , is decreasing away from the nose cutting edge. The height, in a direction perpendicular to the reference plane RP, of the first clearance surface  21  is less than the height of the second clearance surface  22 , in order to further increase the strength of the first cutting edge  11 . The height of the first clearance surface  21  is at least 0.3 mm in order to compensate for flank wear of the first cutting edge  11 . 
     The first cutting edge  11  slopes towards the bottom surface  9  and the reference plane RP slopes away from the nose cutting edge  10 . The distance from the first cutting edge  11  to the reference plane RP varies in such a way that that this distance is decreasing at an increasing distance from the nose cutting edge  10 , at least for a portion of the first cutting edge  11 . A distance from the reference plane RP to a first portion of the first cutting edge  11 , located adjacent to the nose cutting edge  10 , is greater than a distance from the reference plane RP to a second portion of the first cutting edge  11 , located further away from the nose cutting edge  10 . By such orientation of the first cutting edge  11 , the chip control is improved in axial turning away from the clamping end, as e.g. in an operation as seen in  FIG. 2 . A distance D 1  is measured in a direction perpendicular to the reference plane RP, representing the distance between the top surface of the protrusion  30  and the lowest point of the first cutting edge  11 . D 1  is 0.28-0.35 mm. By this, the chip breaking and/or chip control is further improved, in an operation as seen in  FIG. 2 . 
       FIGS. 6-8  show cross-sectional views taken along the lines VI-VI, VII-VII and VIII-VIII, respectively, in  FIG. 5 . The sections are perpendicular to the first cutting edge  11  in planes perpendicular to the reference plane RP. In  FIGS. 6-8 , the angles which the first, second and third clearance surfaces  21 ,  22 ,  23  form in relation to a plane parallel to the reference plane RP and intersecting the bottom surface  9  are designated γ, σ and ε, respectively. Angle σ is greater than angle ε. By this, out-facing can be made from a smaller work piece diameter with a reduced decrease in insert strength. Greater clearance angles are necessary at smaller diameters, but a great and constant clearance angle would give a reduced strength of the insert. 
     The second clearance surface  22  has the purpose of increasing the strength of the insert. The third clearance surface  23  is adjacent to the bottom surface. Angle γ is greater than angle ε. Angle σ is greater than γ. The third clearance surface  23  is convex or substantially convex, seen in cross section as in  FIGS. 6-8 , in order to further improve the lower diameter range, i.e. the minimum diameter where the turning insert can function in an out facing operation, while minimizing the reduction of insert strength. 
     The configuration of second cutting edge  12 , and the side surface  13  adjacent to the second cutting edge  12  are in accordance with the configuration of the first cutting edge  11 , and the side surface  13  adjacent to the first cutting edge  11 , which has been described in relation to  FIGS. 5-8  above. 
       FIG. 10  shows a method to form a surface  53  on a metal work piece comprising a first machining step. A known turning insert  1  is provided. The turning insert  1  includes an active nose portion  15 . The active nose portion  15  includes a first cutting edge  11 , a second cutting edge  12  and a convex nose cutting edge  10  connecting the first  11  and second  12  cutting edges. A nose angle α formed between the first  11  and second  12  cutting edges is less than or equal to 85°. The nose angle α is at least 25°. In  FIG. 10 , the nose angle α is 80°. The second cutting edge  12  forms a back clearance angle ψ of more than 90° in a feed direction  99 . If a subsequent or prior machining step is an out-facing operation, the back clearance angle ψ is at least 100°. For example, the back clearance angle ψ is less than 120°. The back clearance angle ψ is constant in relation to the feed direction  99  during the formation of the surface  53 . 
     All parts of the turning insert  1  are ahead of the active or surface generating nose cutting edge  10  in the feed direction  99 . Alternatively formulated, all parts of a top surface of the turning insert are ahead of a trailing portion of the nose cutting edge in the feed direction. 
     One first point of the nose cutting edge  10  is the part of the turning insert  1  that is located closest to the rotational axis of the metal work piece. One second point, or trailing point, of the nose cutting edge  10 , which is behind the first point in the feed direction  99 , is the part of the turning insert  1  that is located most rearward in the feed direction  99  or in the direction of insert movement. The first point of the nose cutting edge  10  is located on the same side of a bisector as the first cutting edge  11 , wherein the bisector is a line which is between the first and second cutting edges  11 ,  12  at equal distance from the first and second cutting edges  11 ,  12 . The second point of the nose cutting edge  10  is located on the same side of the bisector as the second cutting edge  12 . The first cutting edge  11  and the second cutting edge  12  are located on opposite sides of the convex nose cutting edge  10 . 
     The first, second and nose cutting edges  11 ,  12 ,  10  are formed at borders of a top surface of the turning insert  1 , which top surface includes a rake face. The expression “positioning all parts of the turning insert ahead of the nose cutting edge in the feed direction” thus can alternatively be formulated as “positioning all parts of a top surface of the turning insert ahead of a trailing portion of the nose cutting edge in the feed direction.” 
     All parts of the turning tool  3 , including the turning insert  1  and a tool body  2 , are ahead of the active or surface generating nose cutting edge  10  in the feed direction. Thus, all parts of the tool body  2  are ahead of the nose cutting edge  10  in the feed direction  99 . The turning tool  3  is clamped or connected to a turning lathe, such as a CNC-machine or CNC-lathe (not shown). A metal work piece, on which the surface  53  is formed, rotates around a rotational axis (not shown). 
     The tool body  2  includes a front end and a rear end, a main extension along a longitudinal axis A 2  extending from the front end to the rear end, and an insert seat formed in the front end in which the turning insert  1  is mounted. The longitudinal axis A 2  of the tool body  2  is perpendicular to the rotational axis of the metal work piece. 
     The turning insert  1  moves in a direction, defined by the feed direction  99 , which is parallel to or at an angle less than 45° relative to the rotational axis. In  FIG. 10 , the feed direction  99  is parallel to the rotational axis of the metal work piece. The first cutting edge  11  is active and ahead of the nose cutting edge  10  in the feed direction  99 . The first cutting edge is active, i.e. cuts metal, at an entering angle κ 1 , which is above 0°. The entering angle κ 1  can be at least 5°. For example, the entering angle κ 1  is in the range of 10-45°. In  FIG. 10 , the entering angle κ 1  is around 5°. A larger entering angle κ 1  shall be chosen if a larger depth of cut is needed. 
     The first cutting edge  11  is a leading edge. The second cutting edge  12  is a trailing edge. The surface  53  is at least partly formed by the nose cutting edge  10 . The surface  53 , which is formed is a rotational symmetrical surface, i.e. a surface  53 , which has an extension along the rotation axis of the metal work piece and where in cross sections perpendicular to the rotational axis, each portion of the rotational symmetrical surface  53  is located at a constant distance from the rotation axis of the metal work piece, where a constant distance is a distance which is within 0.10 mm, for example within 0.05 mm. 
     The rotational symmetrical surface  53  can be in the form of e.g. a cylindrical surface or a conical surface or a frustoconical surface or a tapered surface. The rational symmetrical surface  53  that is generated or formed at least partly by the nose cutting edge  10  has a wavy shape with small peaks and valleys, and the wavy shape is influenced at least partly by the curvature of the nose radius and the feed rate. The wave height can be less than 0.10 mm, for example, less than 0.05 mm. The active nose cutting edge  10  is the part of the turning insert  1  and the part of the turning tool  3  which is closest to the rotational axis of the metal work piece. 
       FIG. 11  shows the principle of conventional turning, where C 1  represents the feed direction in  FIG. 1 , and D 1  represents the wear on or at a nose portion from such operation. C 3  represents a conventional facing operation, i.e. feed perpendicular and towards the rotational axis A 3 , and D 3  represents the wear on or at a nose portion from such operation. The second cutting edge  12  is the main cutting edge in C 1  feed direction. The first cutting edge  11  is the main cutting edge in C 3  feed direction. A convex nose cutting edge  10  connects the first and second cutting edges  11 ,  12 . Transition points T 1 , T 2  represent the transition between the nose cutting edge  10  and the first  11  and second  12  cutting edge, respectively. The wear D 1 , D 3 , is dependent on both the depth of cut and the feed rate. However, it is clear that D 1  and D 3  overlap, resulting in high wear at the nose cutting edge  10 , or at least at a center portion of the nose cutting edge  10 . 
       FIG. 12  shows the principle of an alternative turning method. C 2  represents the main feed direction in  FIG. 2 , or the main feed direction in pass  2 ,  4 ,  6  and  8  in  FIG. 13 , i.e. an axial feed direction away from the clamping end of the metal work piece. D 2  represents the wear on or at a nose portion from such operation. C 4  represents an out-facing operation, i.e. feed perpendicular to and away from the rotational axis A 3 , as seen in the main feed directions in pass  1 ,  3 ,  5  and  7  in  FIG. 10 . D 4  represents the wear on or at a nose portion from such operation. The second cutting edge  12  is the main cutting edge in C 4  feed direction. The first cutting edge  11  is the main cutting edge in C 2  feed direction. A convex nose cutting edge  10  connects the first and second cutting edges  11 ,  12 . Transition points T 1 , T 2  represent the transition between the nose cutting edge  10  and the first  11  and second  12  cutting edge, respectively. 
     Each wear D 2 , D 4 , is dependent on both the depth of cut and the feed rate. However, it is clear that D 2  and D 4  do not overlap, or at least overlap to a lesser degree than in  FIG. 11 , resulting in reduced wear at the nose cutting edge  10 , or at least reduced wear at a center portion of the nose cutting edge  10 . The wear of the first and second cutting edges  11 ,  12  has a wider range, i.e. is distributed over a longer distance, compared to  FIG. 11 . However, because the smaller entering angles in feed C 2  and C 4  compared to the greater entering angles in C 1  and C 3 , the chip thickness in  FIG. 12  will be thinner and therefor give relatively small wear. At constant feed rate and depth of cut, the area of D 2  is equal to the area of D 3 , and the area of D 1  is equal to the area of D 4 . 
       FIG. 13  show an example of a machining sequence using the first turning insert. The left-hand side is the clamping end of the metal work piece. A 90° corner including a cylindrical surface  53  and a flat surface  56  is formed by turning. A sequence of steps 1-8 is shown. The entry for each step is shown as being perpendicular to the main feed direction of each step. The main feed direction in steps 1, 3, 5 and 7 is perpendicular to and away from the rotational axis A 3 . The main feed direction in steps 2, 4, 6 and 8 is parallel to the rotational axis A 3  and away from the clamping end. The entry for each cut is preferably as described in connection to  FIG. 2 . The wear of the turning insert  1  after the sequence of steps showed in  FIG. 13  is similar or identical to the wear shown in  FIG. 12 . 
       FIGS. 16 a -17 c    further describe the first turning insert, as well as a turning tool  3  which includes the turning insert  1  and a tool body  2 . The turning insert  1  includes a top surface  8 , which is or includes a rake face, and an opposite bottom surface  9 , functioning as a seating surface. A reference plane RP is located parallel to and between the top surface  8  and the bottom surface  9 . A center axis A 1  extends perpendicular to the reference plane RP and intersects the reference plane RP, the top surface  8  and the bottom surface  9 . A hole, for a screw, having openings in the top surface  8  and the bottom surface  9  is concentric with the center axis A 1 . The turning insert  1  includes side surfaces  13 ,  13 ′,  13 ″, functioning as clearance surfaces, connecting the top surface  8  and the bottom surface  9 . 
     Three nose portions  15 ,  15 ′,  15 ″ are formed symmetrically relative to or around the center axis A 1 . The nose portions  15 ,  15 ′,  15 ″ are identical. Each nose portion  15 ,  15 ′,  15 ″ includes a first cutting edge  11 , a second cutting edge  12  and a convex nose cutting edge  10  connecting the first  11  and second  12  cutting edges. The nose cutting edges  10 ,  10 ′,  10 ″ are located at a largest distance from the center axis A 1 , i.e. at a larger distance from the center axis A 1  than all other parts of the turning insert. In a top view, seen in  FIG. 16 d   , the first  11  and second  12  cutting edges on or at the same nose portion  15  forms a nose angle α of 25-50° relative to each other, in  FIG. 16 d    the nose angle α is 35°. 
     In a side view, such as in  FIG. 16 b   , at least a portion of the first and second cutting edges  11 ,  12  on or at each nose portion  15 ,  15 ′,  15 ″ slopes towards the bottom surface, such that in a side view, the first and second cutting edges  11 ,  12  have the highest points thereof bordering to the nose cutting edge  10  on or at the same nose portion  15 . In other words, the distance from the first cutting edge  11  and the second cutting edge  12  to the reference plane RP varies in such a way that that this distance is decreasing at an increasing distance from the nose cutting edge  10 . 
     The first and second cutting edges  11 ,  12  are linear or straight, or substantially linear or straight in a top view. Bisectors  7 ,  7 ′,  7 ″ extend equidistantly from each pair of first  11 ,  11 ′,  11 ″ and second  12 ,  12 ′,  12 ″ cutting edges. Each bisector  7 ,  7 ′,  7 ″ intersects the center axis A 1 . Indentations  17 ,  17 ′,  17 ″ are formed between each pair of nose cutting edges  10 ,  10 ′,  10 ″. 
     The bottom surface  9 , seen in  FIGS. 18 a  and 18 b   , includes rotation prevention means, with the purpose of reducing the tendency for the turning insert  1  to rotate around the center axis A 1  during cutting, in the form of three grooves  40 ,  40 ′,  40 ″, each groove  40 ,  40 ′,  40 ″ having a main extension in the same direction as the bisector  7 ,  7 ′,  7 ″ located adjacent the closest first  11  and second  12  cutting edges. Each groove  40 ,  40 ′,  40 ″ includes two seating surfaces, for example, at an obtuse angle, 100-160°, in relation to each other. 
     The turning insert  1  is intended to be securely clamped, by clamping means such as a screw or a top clamp, in an insert seat  4  located at a front end of a tool body  2 , as seen in  FIG. 17 a   . The contact between the insert seat  4  and the turning insert will now be described, see the shaded areas in  FIG. 17 c    and  FIG. 17 a   . The active nose cutting portion  15  is the part of the insert where groove  40  is located in  FIG. 17 c   . The two seating surfaces of groove  40  are in contact with two surfaces of a ridge  90  in the bottom of the insert seat  4 . One surface of each other groove  40 ′,  40 ″, the surfaces located at the largest distance from the active nose cutting edge  10 , are in contact with bottom surfaces  93 ,  94  in the bottom of the insert seat  4 . At least portions of the side surface  13  located at the greatest distance from the active nose cutting edge  10  may be in contact with rear seating surfaces  91 ,  92  formed at a rear end of the insert seat  4 . 
       FIGS. 14 a - f    show a second turning insert  1 , as well as, a turning tool  3 , which includes the turning insert  1  and a tool body  2 . The turning insert  1  includes a top surface  8 , which is or provides a rake face, and an opposite bottom surface  9 , functioning as a seating surface. The top  8  and bottom  9  surfaces are identical. This means that while in a first position, the top surface  8  functions as a rake surface, when the insert is turned upside down, the same surface is now functioning as a seating surface. 
     A reference plane RP is located parallel to and between the top surface  8  and the bottom surface  9 . A center axis A 1  extends perpendicular to the reference plane RP and intersects the reference plane RP, the top surface  8  and the bottom surface  9 . A hole for a screw, having openings in the top surface  8  and the bottom surface  9  is concentric with the center axis A 1 . 
     The turning insert  1  includes side surfaces  13 ,  13 ′,  13 ″, functioning as clearance surfaces, connecting the top surface  8  and the bottom surface  9 . Three nose portions  15 ,  15 ′,  15 ″ are formed symmetrically relative to or around the center axis A 1 . The nose portions  15 ,  15 ′,  15 ″ are identical. Each nose portion  15 ,  15 ′,  15 ″ includes a first cutting edge  11 , a second cutting edge  12  and a convex nose cutting edge  10  connecting the first  11  and second  12  cutting edges. The nose cutting edges  10 ,  10 ′,  10 ″ are located at a largest distance from the center axis A 1 , i.e. at a larger distance from the center axis A 1  than all other parts of the turning insert. 
     In a top view, seen in  FIG. 14 d   , the first  11  and second  12  cutting edges on or at the same nose portion  15  form a nose angle α of 25-50° relative to each other, in this case 45°. In a side view, seen in  FIG. 14 b   , at least a portion of the first and second cutting edges  11 ,  12  on or at each nose portion  15 ,  15 ′,  15 ″ slopes towards the bottom surface, such that in a side view, the first and second cutting edges  11 ,  12  have the highest points thereof adjacent to the nose cutting edge  10  on or at the same nose portion  15 . In other words, the distance from the first cutting edge  11  and the second cutting edge  12  to the reference plane RP varies in such a way that that this distance is decreasing as the distance from the nose cutting edge  10  increases. 
     The first and second cutting edges  11 ,  12  are linear or straight, or substantially linear or straight in a top view. Bisectors  7 ,  7 ′,  7 ″ extend equidistantly from each pair of first  11 ,  11 ′,  11 ″ and second  12 ,  12 ′,  12 ″ cutting edges. Each bisector  7 ,  7 ′,  7 ″ intersects the center axis A 1 . Indentations  17 ,  17 ′,  17 ″ are formed between each pair of adjacent nose cutting edges  10 ,  10 ′,  10 ″. The turning insert  1  includes rotation prevention means in the form of a set of surfaces  41 ,  42 ,  43 ,  44 , where each surface  41 ,  42 ,  43 ,  44  extends in a plane which forms an angle of 5-60° in relation to the reference plane RP. The set of surfaces  41 ,  42 ,  43 ,  44  are formed at a central ring-shaped protrusion  30 , extending around the center axis A 1 . By such a configuration, the turning insert  1  can be made double-sided or reversible, giving an increased possible usage. 
     The first chip breaker wall  34  can be a part of the set of surfaces  41 ,  42 ,  43 ,  44 . An alternative solution (not shown) is to arrange the first chip breaking wall  34  as part of a further protrusion (not shown) at a greater distance from the center axis A 1 .  FIG. 14 e    show one possible clamping mode of the turning insert  1  by means of a clamp  95 , which presses the insert and keeps the insert in the insert seat  4  of the tool body  2 . 
       FIG. 14 f    shows the insert seat  4  in which the second turning insert  1  can be mounted by means of e.g. a top clamp  95 . The side surface  13  located at a greatest distance from the active nose cutting edge  10  includes two surfaces, which are pressed against rear surfaces  91 ,  92  of the insert seat  4 . The set of surfaces  41 ,  42 ,  43 ,  44  includes two front surfaces  41 ,  42 , which are in contact with surfaces of a front portion  90  of the bottom of the insert seat  4 . Front in this context is between the center axis A 1  and the active nose cutting edge  10 . The set of surfaces  41 ,  42 ,  43 ,  44  further includes two rear surfaces  43 ,  44 , which are pressed against rear bottom surfaces  93 ,  94  which are located in the bottom surface of the insert seat  4 , between the front portion  90  and the rear surfaces  91 ,  92  of the insert seat  4 . 
     Reference is made to  FIG. 2 a   , which shows turning using a third turning insert. As in  FIG. 1 , a metal work piece is clamped by clamping jaws (not shown), which are pressed against an external surface at a first end  54 , or clamping end, of the metal work piece. An opposite second end  55  of the metal work piece is a free end. The metal work piece rotates around a rotational axis A 3 . The turning insert, seen in top view, is securely and removably clamped in an insert seat or a pocket in tool body  2  by means of a screw. The tool body  2  has a longitudinal axis A 2 , extending from a rear end to a front end, in which the insert seat or pocket is located. In  FIG. 2 a   , the feed is, to a greatest extent, axial, also called longitudinal feed, i.e. the direction of the feed is parallel to the rotational axis A 3 . In this way, an external cylindrical surface  53  is formed. At the entry of each cut, or immidiately prior to the axial feed, the feed has a radial component, in such a way that the turning insert move along an arc of a circle. 
     The turning insert includes two opposite and identical nose portions  15 ,  15 ′ formed 180° relative each other around a center axis of the turning insert  1 . Each nose portion  15 ,  15 ′ includes a first cutting edge  11 , a second cutting edge  12  and a convex nose cutting edge  10  connecting the first  11  and second  12  cutting edges. One nose portion  15 , located closer to the rotational axis A 3  than the opposite inactive nose portion  15 ′, is active. Active means that the nose portion as placed such that it can be used for cutting chips from the metal work piece  50 . A bisector  7  extending equidistantly from the first  11  and second  12  cutting edges, intersecting the center of the nose cutting edge  10  and a center axis A 1  of the turning insert. The first and second cutting edges  11 ,  12  converge at a point (not shown) outside the turning insert. The bisector of the active nose portion  15  forms an angle θ, 40-50°, relative to the longitudinal axis A 2 . 
     In a top view the first  11  and second  12  cutting edges on the same nose portion  15  form a nose angle α of 70-85° relative to each other, which in  FIG. 2 a    is 80°. A third convex cutting edge  60  is formed adjacent to the first cutting edge  11 . A fourth cutting edge  61  is formed adjacent to the third cutting edge  60 , further away from the nose cutting edge  10 . A fifth convex cutting edge  62  is formed adjacent to the second cutting edge  12 . A sixth cutting edge  63  is formed adjacent to the fifth cutting edge  62 , further away from the nose cutting edge  10 . 
     In top view, as in  FIG. 2 a   , the first, second, fourth and sixth cutting edges  11 ,  12 ,  61 ,  63  are linear or straight, or substantially linear or straight. The main feed direction, towards the right in  FIG. 2 a   , is parallell to the rotational axis A 3  and away from the first end  54 , or clamping end, of the metal work piece  50 . In the feed direction, the fourth cutting edge  61  is active at an entering angle κ 1  of 10-45°, for example, 20-40°, which in  FIG. 2 a    is 30°. The fourth cutting edge  63  is the main cutting edge in the feed direction, i.e. the majority of the chips are cut by the fourth cutting edge  63 , at least at moderate to high depth of cut. To a lesser degree, third cutting edge  60 , the first cutting edge  11  and the nose cutting edge  10  are also active. The first cutting edge is ahead of the nose cutting edge  10  in the axial feed direction. All parts of the turning insert is ahead of the active nose cutting edge  10  in the feed direction. The second cutting edge  11 , formed on the active nose portion  15 , is inactive. 
     In the axial turning operation, chips can be directed away from the metal work piece in a trouble-free manner, especially compared to the machining shown in  FIG. 1  where the feed is towards the clamping end and towards a wall surface. In the machining step in  FIG. 2 a   , the turning insert  1  enters into the metal work piece  50  such that the nose cutting edge  10  moves along an arc of a circle. The turning insert  1  enters into the metal work piece  50 , or goes into cut, such that the chip thickness during entry is constant or substantially constant. At the entry, the depth of cut is increased from zero depth of cut. Such preferred entry reduces the insert wear, especially the wear at the nose cutting edge  10 . Chip thickness is defined as feed rate multiplied by entering angle. Thus, by choosing and/or varying the feed rate and the movement and/or direction of the turning insert during entry, the chip thickness can be constant or substantially constant. The feed rate during entry can be less or equal than 0.50 mm/revolution. The chip thickness during entry is less than or equal to the chip thickness during subsequent cutting or machining. 
     If the feed direction would be radial, in such a way that the feed direction would be perpendicular to and away from the rotational axis A 3 , the sixth cutting edge  63  would be active at an entering angle κ 2  of 10-45°, for example, 20-40°. 
     The cylindrical surface  53 , or rational symmetrical surface, generated or formed at least partly by the nose cutting edge in  FIGS. 1 and 2   a , has a wavy shape with small peaks and valleys, and the wavy shape is influenced at least partly by the curvature of the nose radius and the feed rate. The wave height is less than 0.10 mm, for example, less than 0.05 mm. A thread profile is not a cylindrical surface  53  in this sense. 
     In  FIG. 3 a   , the turning insert and tool body in  FIG. 2 a    can be seen in alternative machining operations, showing the versatile application area of the turning tool, especially with regard to feed direction. A machining sequence in six steps is shown. Step 1 is a undercutting operation. Step 2 is axial turning away from the first end  54 , or clamping end, of the metal work piece. Step 3 is a profiling operation in the form of a feed which has both an axial and a radial component, generating a conical or frustoconical surface. Step 4 is an operation similar to step 2. Step 5 is an out-facing operation generation a flat surface located in a plane perpendicular to the rotational axis A 3  of the metal work piece. Step 6 is an out-facing operation at the second end  55 , or free end, of the metal work piece. 
       FIGS. 15 a - f    and  FIGS. 17 d - f    further describe the third turning insert  1 , as well as a turning tool  3 , which includes the turning insert  1  and a tool body  2 . The turning insert  1  includes a top surface  8 , which is or includes a rake face  14 , and an opposite bottom surface  9 , functioning as a seating surface. A reference plane RP is located parallel to and between the top surface  8  and the bottom surface  9 . A center axis A 1  extends perpendicular to the reference plane RP and intersects the reference plane RP, the top surface  8  and the bottom surface  9 . A screw hole having openings in the top surface  8  and the bottom surface  9  is concentric with the center axis A 1 . 
     The third turning insert  1  includes side surfaces  13 , functioning as clearance surfaces, connecting the top surface  8  and the bottom surface  9 . Two opposite nose portions  15 ,  15 ′ are formed symmetrically relative to or around the center axis A 1 . The nose portions  15 ,  15 ′ are identical. Each nose portion  15 ,  15 ′ includes a first cutting edge  11 , a second cutting edge  12  and a convex nose cutting edge  10  connecting the first  11  and second  12  cutting edges. Each nose portion  15 ,  15 ′ further includes a third convex cutting edge  60 , formed adjacent to the first cutting edge  11 , and a fourth cutting edge  61  formed adjacent to the third cutting edge  60 , further away from the nose cutting edge  10 . Each nose portion  15 ,  15 ′ further includes a fifth convex cutting edge  62  formed adjacent to the second cutting edge  12 , and a sixth cutting edge  63  formed adjacent to the fifth cutting edge  62 , further away from the nose cutting edge  10 . In top view, as in  FIG. 15 d   , the first, second, fourth and sixth cutting edges  11 ,  12 ,  61 ,  63  are linear or straight, or substantially linear or straight. 
     The nose cutting edges  10 ,  10 ′ are located at a largest distance from the center axis A 1 , i.e. at a larger distance from the center axis A 1  than all other parts of the turning insert. In a top view, seen in  FIG. 15 d   , the first  11  and second  12  cutting edges on the same nose portion  15  forms a nose angle α of 75-85° relative to each other, in  FIG. 15 d    the nose angle α is 80°. In a side view, such as in  FIG. 15 c   , at least a portion of the fourth and sixth cutting edges  61 ,  63  on each nose portion  15 ,  15 ′,  15 ″ slopes towards the bottom surface  9 , such that in a side view, the fourth and sixth cutting edges  61 ,  63  has the highest points thereof closer to the nose cutting edge  10  on the same nose portion  15 . In other words, the distance from the fourth cutting edge  61  and the sixth cutting edge  63  to the reference plane RP varies in such a way that that this distance is decreasing at increasing distance from the nose cutting edge  10 . Further, the first, second third and fifth cutting edges  11 ,  12 ,  60 ,  62  are sloping towards the bottom surface  9  in a corresponding manner, such that in relation to the bottom surface  9 , the nose cutting edge  10  is further away than the first and second cutting edges  11 ,  12 , which in turn are further away than the third and fifth cutting edges  60 ,  62 , which in turn are further away than the fourth and sixth cutting edges  61 ,  63 . 
     Bisectors  7 ,  7 ′ extend equidistantly from each pair of first  11 ,  11 ′ and second  12 ,  12 ′ cutting edges. Each bisector  7 ,  7 ′ intersects the center axis A 1 , and the bisectors  7 ,  7 ′ extend in a common direction. The bottom surface  9  is identical to the top surface  8 . In a top view, as in  FIG. 15 d   , the fourth cutting edge  61  forms an angle β of 0-34° relative to the bisector  7 , which in  FIG. 15 d    is 10-20°. 
     The top surface  8  includes protrusions  30  having a first chip breaker wall  34  facing the fourth cutting edge  61 . The distance from the fourth cutting edge  61  to the first chip breaker wall  34  is increasing away from the nose cutting edge  10 . The protrusions  30  are intended to function as seating surfaces, and the top surface of each protrusion is flat and parallel to the reference plane RP. The protrusions  30  are the part of the turning insert  1  which are located at the greatest distance from the reference plane RP. The protrusion includes a second chip breaker wall facing the sixth cutting edge. The distance, from the fourth cutting edge  61  to the first chip breaker wall  34 , is measured in a direction perpendicular to the fourth cutting edge  61 , and in a plane parallel to the reference plane RP, to the first chip breaker wall  34 . The protrusion  30 , and thus the first chip breaker wall  34 , does not necessarily have to extend along the whole length of the fourth cutting edge  61 . Still, the distance from the fourth cutting edge  61  to the first chip breaker wall  34  is increasing at the portion of the fourth cutting edge  61  where perpendicular to this fourth cutting edge  61 , the first chip breaker wall  34  extends. 
     A distance D 1  measured in a plane perpendicular to the reference plane RP between the top surface of the protrusion  30  and the lowest point of the fourth cutting edge  61  is 0.28-0.35 mm. Bumps  80 , or protrusions, are formed in the top surface  8 . The bumps  80  are located at a distance, greater than 0.3 mm and less than 3.0 mm, from the fourth cutting edge  61 . The bumps  80  are located between the fourth cutting edge  61  and the first chip breaker wall  34 . The bumps  80  have a non-circular shape in top view, such that a major extension, which is 0.8-3.0 mm, of the bumps is in a direction substantially perpendicular to or perpendicular to the fourth cutting edge  61 . The minor extension of the bumps perpendicular to the major extension is 0.5-2.0 mm. The bumps  80 , or protrusions, are portions of the top surface  8  which extends away from the reference plane in relation to the surrounding area. 
     In a top view as in  FIG. 15 d   , the bumps  80  can have an elliptic or oval or substantially elliptic or oval shape. The bumps  80  are separated from each other. The bumps  80  can be located at a constant distance from each other. The bumps  80  also can be located at a constant distance from the fourth cutting edge  61 . In the first embodiment, there are 5 bumps adjacent to the fourth cutting edge. It is possible to have 2-10 bumps adjacent to the fourth cutting edge. 
     There is at least one further bump  80 , for the third turning insert there are 2-3 bumps  80 , located perpendicular to and having an major extension in a direction perpendicular to the third cutting edge  60 , and at least one further bump  80 , in the first embodiment 1-2 bumps  80 , located perpendicular to and having an major extension in a direction perpendicular to the first cutting edge  11 . 
     The third turning insert  1  is symmetrical, or mirror images, on opposite sides of the bisectors  7 ,  7 ′. Therefore, bumps  80  are formed in a corresponding manner at a distance from the second, fifth and sixth cutting edges  12 ,  62 ,  63 . 
     By such a turning insert  1 , chip breaking and/or chip control is further improved, especially at lower depth of cut, i.e. when the depths of cut is such that the first cutting edge  11  is active and that the fourth cutting edge  61  is inactive. At such low depth of cut, the chip is very thin, due to the low entering angle by the first cutting edge  11 , and the bump or bumps  80 , closest to the first cutting edge  11 , function as chip breakers. The major extension of the bumps  80  gives the effect that the time, until the wear of the bumps  80  reduces the effect of the bumps  80  on the chips, is increased. 
     Reference is now made to  FIGS. 18-22   a - e , which shows a fourth, fifth, sixth, seventh and eighth type of turning insert, respectively, suitable for the method according to the invention. These inserts differ from the third insert only with regards to the bottom surface and the side surfaces. 
     Thus, the fourth, fifth, sixth, seventh and eighth turning inserts  1 , shown in  FIGS. 18-22   a - e  respectively, have the same or identical shape, form, dimension, value and interrelations between features and elements as the third turning insert with regards to the top surface  8 , reference plane RP, screw hole, first cutting edge  11 , nose cutting edge  10 , second cutting edge  12 , third cutting edge  60 , fourth cutting edge  61 , fifth cutting edge  62 , sixth cutting edge  63 , nose angle α, bisector  7 , angle β, rake face  14 , protrusion  30 , first chip breaker wall  34 , second chip breaker wall, distance D 1  and bumps  80 . 
     The fourth, fifth, sixth and seventh turning inserts  1 , shown in  FIGS. 18-21   a - e , are formed such that a first side surface  13  includes a first clearance surface  21  adjacent to the first cutting edge  11 , a third clearance surface  23 , and a second clearance surface  22  located between the first clearance surface  21  and the third clearance surface  23 . 
     The angle which the second clearance surface  22  forms in relation to the bottom surface  9 , measured in a plane perpendicular to the first cutting edge  11 , is greater than the angle which the third clearance surface  23  forms in relation to the bottom surface measured in a plane perpendicular to the first cutting edge  11 . 
     The angle which the second clearance surface  22  forms in relation to the bottom surface  9 , measured in a plane perpendicular to the first cutting edge  11 , is greater than the angle which the first clearance surface  21  forms in relation to the bottom surface measured in a plane perpendicular to the first cutting edge  11 . 
     The side surfaces  13 ,  13 ′ of each nose portion  15 ,  15 ′ are configured symmetrically in relation to a plane perpendicular to the reference plane RP and comprising the bisector  7 . The clearance surface adjacent to the second cutting edge  12  is formed or arranged in a corresponding manner. The advantages from the clearance surface arrangements are that out-facing can be performed at small metal work piece diameters, and that larger depth of cut is possible in out-facing. 
     Reference is now made to  FIGS. 18 a - e   , which shows the fourth turning insert  1 . The bottom surface  9  includes rotation prevention means  40 , in order to reduce movement of the turning insert  1  relative to the insert seat  4  during machining. The rotation prevention means  40  are in the form of two grooves  40 ,  40 ′ having a common major extension, which major extension is corresponding to the extension of the bisectors  7 ,  7 ′. 
     Reference is now made to  FIGS. 19 a - e   , which shows the fifth turning insert  1 . The bottom surface  9  includes rotation prevention means  40 , in order to reduce movement of the turning insert  1  relative to the insert seat  4  during machining. The rotation prevention means  40  are in the form of two grooves  40 ,  40 ′ having a common major extension, which major extension is corresponding to the extension of the bisectors  7 ,  7 ′. Each groove  40 ,  40 ′ includes two surfaces which are form an obtuse angle, in the range of 100-160°, in relation to each other. 
     Reference is now made to  FIGS. 20 a - e   , which show a sixth turning insert  1 . The bottom surface  9  includes rotation prevention means  40 , in order to reduce movement of the turning insert  1  relative to the insert seat  4  during machining. The rotation prevention means  40  are in the form of two ridges  40 ,  40 ′ having a common major extension, which major extension is corresponding to the extension of the bisectors  7 ,  7 ′. 
     Reference is now made to  FIGS. 21 a - e   , which show a seventh turning insert. The bottom surface  9  includes a flat surface  9 , which is parallel to the reference plane RP. 
     Reference is now made to  FIGS. 22 a - e   , which show an eighth turning insert  1 . The bottom surface  9  includes a flat surface  9 , which is parallel to the reference plane RP. The flat surface  9  is ring-shaped around the center axis of the turning insert. A first side surface  13  includes a first clearance surface  21  adjacent to the first cutting edge  11  and a third clearance surface  23 . The third clearance surface  23  borders to the bottom surface  9 . 
     The angle, which the first clearance surface  21  forms in relation to the bottom surface  9 , measured in a plane perpendicular to the first cutting edge  11 , is greater than the angle which the third clearance surface  23  forms in relation to the bottom surface measured in a plane perpendicular to the first cutting edge  11 . The clearance surface adjacent to the second cutting edge  12  is formed or arranged in a corresponding manner. The advantages from the clearance surface arrangements are that out-facing can be performed at small metal work piece diameters, and that larger depth of cut is possible in out-facing. 
     The protrusion  30  includes grooves formed in the top surface of the protrusion  30 . The grooves have a major extension perpendicular to the bisector  7 . 
     Although the present embodiment(s) has been described in relation to particular aspects thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred therefore, that the present embodiment(s) be limited not by the specific disclosure herein, but only by the appended claims.