Patent Publication Number: US-2022234115-A1

Title: Turning insert for metal cutting

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention belongs to the technical field of metal cutting. More specifically the present invention belongs to the field of tools for turning comprising a round turning insert. 
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     The present invention refers to a turning insert according to the preamble of claim  1 . In other words, the present invention relates to a turning insert comprising a top surface, an opposite bottom surface, a reference plane between the top and bottom surfaces, a center axis intersecting the top and bottom surfaces, a side surface connecting the top surface and the bottom surface, a cutting edge adjacent to the top surface and the side surface, the cutting edge being circular and concentric in relation to the center axis, wherein the bottom surface comprises a set of radial grooves. 
     In turning of a metal work piece, the metal work piece rotates around a center axis. A turning tool is used to remove material from the metal work piece. The turning tool normally comprises a turning insert. A turning insert may have different shape, depending on factors such as the type of turning operation and component design. One common type of turning inserts are round turning inserts, i.e. turning inserts having a circular cutting edge. 
     U.S. Pat. No. 7,607,867B2 disclose a turning tool comprising a turning insert having a circular cutting edge. The bottom surface of the turning insert comprises a plurality of radial grooves. 
     The inventors have found that there is a need for an improved turning insert. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a turning insert having a circular cutting edge, which can be indexable in predetermined positions, which can give improved chip breaking both at low and high feed rates when used in more than one feed direction. 
     At least one of said objects is achieved by a turning insert comprising a top surface, an opposite bottom surface, a reference plane between the top and bottom surfaces, a center axis intersecting the top and bottom surfaces, a side surface connecting the top surface and the bottom surface, a cutting edge adjacent to the top surface and the side surface, the cutting edge being circular and concentric in relation to the center axis, wherein the top surface comprises a set of first protrusions, wherein a greatest distance from the reference plane to the first protrusions is greater than a distance from the reference plane to the cutting edge, wherein the bottom surface comprises a set of radial grooves, wherein the bottom surface comprises a set of flat surfaces, wherein the flat surfaces extend in a plane parallel to the reference plane, wherein in a top view each first protrusion is symmetrical in relation to a line extending between the center axis and a mid-point of the first protrusion, wherein the first protrusions are elongated in a direction parallel to the adjacent cutting edge. 
     By such a turning insert, chip breaking and/or chip control may be improved. The first protrusions bends the chip so it becomes more fragile. When turning using a round turning insert, the chip thickness varies. The thin part of the chip is controlled effeicietly solely by the elongated first protrusions. By such a turning insert, indexing positions can be predetermined. 
     The turning insert preferably comprises a wear resistant material such as cemented carbide, cubic boron nitride or ceramic. The top surface comprises a rake surface. The bottom surface comprises a seating surface. The reference plane is mid-way between the top and bottom surfaces. The center axis intersecting the top and bottom surfaces is perpendicular to the reference plane. Preferably, a through hole is concentric with the center axis. The side surface connecting the top surface and the bottom surface comprises a clearance surface. The side surface is preferably conical. In other words, an area of the top surface is preferably greater than an area of the bottom surface. A cutting edge is adjacent to, i.e. connects or borders to the top surface and the side surface. The cutting edge is 360° circular in a top view and is concentric in relation to or with the center axis. The cutting edge may be entirely located in a plane parallel to the reference plane. The top surface comprises a set, i.e. a number of spaced apart first protrusions. A protrusion is a portion of the top surface which protrudes upwards, i.e. in a direction away from the reference plane, in relation to surrounding or adjacent portions of the top surface. Said first protrusions are spaced apart from the cutting edge. A greatest distance from the reference plane to the first protrusions is greater than a distance from the reference plane to the cutting edge, where said distances are measured perpendicular to the reference plane. In other words, in a side view, the first protrusions are at least partly above the cutting edge, where the top surface is upwards and the bottom surface is downwards. The bottom surface comprises a set of radial grooves. In other words, said grooves extend towards the center axis. Said grooves preferably intersect the side surface. Said grooves preferably have a constant width and height along the length of the groove. Preferably, the set of radial grooves are evenly distributed around the center axis. Preferably, each of said radial grooves are uniform in cross-sections. Preferably, the number of radial grooves is even. Preferably, the number of radial grooves is 6-20, even more preferably 6-12, still even more preferably 6. The bottom surface comprises a set of flat surfaces. Preferably, the number of flat surfaces is equal to the number of grooves. Preferably, the flat surfaces are formed between adjacent pairs of grooves. Preferably, the flat surfaces intersect the side surface. Preferably, the flat surfaces are spaced apart from the center axis. In a top view, each first protrusion is symmetrical, i.e. mirror-symmetrical in relation to a line extending between the center axis and a mid-point of the first protrusion. The first protrusions are elongated in a direction parallel to the adjacent, i.e. closest or neighboring part of the cutting edge. In other words, each of the first protrusions are elongated in a direction perpendicular to a radius extending from the center axis to a midpoint of the respective first protrusion. Preferably, the first protrusions are evenly spaced around the center axis. Preferably, seen in a side view, the top surface slopes downwards from the cutting edge towards the first protrusions. Preferably, the number of first protrusions is 10-40, even more preferably 16-32. 
     Preferably, each radial groove is aligned with a mid-point of a first protrusion. In other words, a plane comprising and parallel to the center axis is aligned with a center of a radial groove and intersects a mid-point of a first protrusion. 
     Preferably, in a top view a distance from the mid-point of the first protrusion to the adjacent cutting edge is 0.3-1.0 mm, even more preferably 0.4-0.8 mm. By such a turning insert, chip breaking is further improved especially at low feed rates. 
     According to an embodiment, the number of first protrusions is a multiple of the number of radial grooves. 
     By such a turning insert, chip breaking is more even for each indexing position. 
     Preferably, the number of first protrusions is two to six times the number of radial grooves. 
     According to an embodiment, a distance between adjacent first protrusions is smaller than a length of a first protrusion. 
     By such a turning insert, the chip breaking and/or chip control is even further improved, especially at low cutting depths. 
     In other words, in a top view, adjacent first protrusions are spaced apart by a distance which is less than the maximum length of a first protrusion, i.e. the length measured in a direction perpendicular to a radius intersecting the center axis and a mid-point of the first protrusion. 
     According to an embodiment, each first protrusion is convex in a radial cross section and in a cross-section perpendicular to the radial cross section. 
     By such a turning insert, the chip breaking and/or chip control is even further improved. 
     In other words, a top of the first protrusion is non-flat. At least an upper portion of the first protrusion is convex. A lower portion may be concave, to provide a smooth transformation to a surrounding area of the top surface. 
     According to an embodiment, the first protrusions are evenly distributed around the center axis. 
     By such a turning insert, the chip breaking and/or chip control is even further improved. 
     In other words, in a top view, an angle between adjacent first protrusions is constant, where said angle is measured between radial lines intersecting the center axis and mid-points of adjacent first protrusions. 
     According to an embodiment, the top surface is mirror symmetrical in relation to a plane comprising and parallel to the center axis. 
     By such a turning insert, chip breaking is more even when used in longitudinal turning in opposite directions. 
     According to an embodiment, in a top view the first protrusions are oval shaped or substantially oval shaped. 
     By such a turning insert, the chip breaking and/or chip control is even further improved. 
     Said oval is in a top view elongated in a direction perpendicular to a radius intersecting a mid-point of the respective first protrusion, where said radius intersects the center axis. Preferably, each first protrusion is 2-5 times longer in a direction parallel to the cutting edge than in a radial direction. 
     According to an embodiment, the top surface comprises a set of second protrusions, wherein a greatest distance from the cutting edge to the first protrusions is smaller than a greatest distance from the cutting edge to the second protrusions. 
     By such a turning insert, the chip breaking and/or chip control is even further improved. The second protrusions bends or breaks the chip. The second protrusions are raised relative to the first protrusions to ensure chip forming takes place even if the first protrusions lift the chip. The thick part of the chip is partly controlled by the first protrusions, but mainly by the second protrusions. 
     The top surface comprises a set of preferably at least partly spaced apart second protrusions. The second protrusions protrude in a direction away from the reference plane in relation to at least some adjacent portions of the top surface. 
     According to an embodiment, a distance from the reference plane to the first protrusions is smaller than a distance from the reference plane to the second protrusions. 
     By such a turning insert, the chip breaking and/or chip control is even further improved. The second protrusions are raised relative to the first protrusions to ensure chip forming takes place even if the first protrusions lift the chip. 
     A distance from the cutting edge to top portions of the respective first protrusions is smaller than a distance from the cutting edge to top portions the respective second protrusions. In other words, in a side view at least portions of both the first protrusions and the second protrusions is above the cutting edge, where the top surface is upwards, and the bottom surface is downwards. Further, in the same view, at least portions of the second protrusions are above all portions of the first protrusions. 
     According to an embodiment, the first protrusion comprises a first surface facing the cutting edge, wherein the second protrusions comprises a second surface facing the cutting edge, wherein a greatest angle of the first surface in relation to the reference plane is smaller than a greatest angle of the second surface in relation to the reference plane. 
     By such a turning insert, chip breaking and/or chip control is further improved. At high feed and/or for the thick part of the chip, a steeper angle of the second surface of the higher second protrusion ensures a more aggressive bending of the chip. 
     Formulated differently, in radial cross sections, the maximum angle of the second protrusion is greater than the maximum angle of the first protrusion, where said angles are measured in relation to the reference plane. Said cross sections intersect respective mid-points of the respective first and second protrusions. Said angles are measured in respective radial planes intersecting mid-points of the first and second protrusion, respectively. Said first and second surfaces are chip forming- and/or chip breaking surfaces. 
     According to an embodiment, the number of first protrusions is equal to the number of second protrusions, wherein the first protrusions are identical or substantially identical, wherein the second protrusions are identical or substantially identical, wherein the first protrusions are smaller than the second protrusions when seen in a top view, wherein the first protrusions are at a constant distance or substantially constant distance from the center axis, wherein the second protrusions are at a constant distance or substantially constant distance from the center axis, wherein the second protrusions extend radially from a circular or substantially circular ring concentric with the center axis. 
     By such a turning insert, chip breaking and/or chip control is further improved. 
     The surface around the hole is preferably raised to the top of the second protrusions in order to increase resistance to wear of the second protrusions. In other words, said circular ring decreases the wear of the second protrusions. 
     The first protrusions are thus identical or substantially identical in shape. The second protrusions are thus identical or substantially identical in shape. The first and second protrusions, respectively, more precisely mid-points of respective first and second protrusions, are at a constant distance or substantially constant distance from the center axis. The second protrusions extend radially, towards the cutting edge, from a circular or substantially circular ring, i.e. a circumferential portion, concentric with the center axis. Said ring is preferably raised in relation to the cutting edge. Said ring is preferably raised in relation to the first protrusions. 
     According to an embodiment, the first and second protrusions radially overlap when seen in a top view, wherein the first and the second protrusions, respectively, are uniformly distributed around the center axis. 
     By such a turning insert, chip breaking and/or chip control is further improved. 
     The first and second protrusions thus partially overlap radially when seen in a top view. In other words, there exist radii which intersect a first protrusion and a second protrusion, seen in a top view, where said radii extend from the center axis to the cutting edge. The first and the second protrusions, respectively, are uniformly or evenly distributed around the center axis. In other words, adjacent pairs of first protrusions form a constant angle, 360° divided by the number of first protrusions, in relation to the center axis when seen in a top view. In a corresponding manner, adjacent pairs of second protrusions form a constant angle, 360° divided by the number of second protrusions, in relation to the center axis when seen in a top view. Said angles are equal. 
     In other words, radially overlap means that the sum of radial angles α 1 , α 2  for the first protrusions and the second protrusions exceeds 360°. 
     According to an embodiment, the radial grooves are aligned with mid-points of first or second protrusions. 
     By such a turning insert, chip breaking can be more even when machining in opposite directions longitudinally. 
     In other words, each radial groove is aligned with mid-points of first protrusions or mid-point of second protrusions. In other words, a plane comprising and parallel to the center axis is aligned with a center of a radial groove and intersects a mid-point of a first protrusion or a mid-point of a second protrusion. 
     According to an embodiment, a turning tool comprises a tool body and a turning insert according to one of the above described embodiments, wherein the turning tool comprises an insert seat, wherein the insert seat comprises a bottom surface and a rear surface, wherein the turning insert is mounted in the insert seat, wherein the bottom surface of the insert seat comprises a first ridge, wherein the side surface of the turning insert is in contact with the rear surface of the insert seat, wherein the first ridge is inside one of the radial grooves formed in the bottom surface of the turning insert. 
     By such a turning tool, rotation of the turning insert may be reduced. Such a turning tool can be manufactured in an economical manner. 
     The grooves and the ridge are arranged such that a small rotation, i.e. between 0° and 1°, even more preferably between 0° and 0.5°, of the turning insert around the center axis thereof is possible. The grooves and the ridge are arranged such that a rotation above 1°, preferably above 0.5°, is prevented. There is a vertical gap between the first ridge and the turning insert, where vertical means in a direction parallel to the center axis of the turning insert. 
     According to an embodiment, the bottom surface of the insert seat comprises one or more support surfaces, wherein the support surfaces extends in a common plane, wherein the flat surfaces of the turning insert is in contact with the support surfaces. 
     According to an embodiment, a method to machine a metal work piece comprises the steps of providing a metal work piece, providing the above described turning tool, rotating the metal work piece around a rotational axis thereof, arranging the turning tool such that the first ridge is oriented perpendicular to the rotational axis of the metal work piece, cutting the metal work piece by moving the turning tool in a first direction parallel to the rotational axis of the metal work piece, and cutting the metal work piece by moving the turning tool in a second direction parallel to the rotational axis of the metal work piece, where the second direction is opposite to the first direction. 
     The metal work piece rotates in the same direction around the rotational axis thereof during the machining in the first and second directions. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The present invention will now be explained in more detail by a description of embodiments of the invention and by reference to the accompanying drawings. 
         FIG. 1  is a perspective view of a turning insert 
         FIG. 2  is a front view of the turning insert in  FIG. 1   
         FIG. 3  is a top view of the turning insert in  FIG. 1   
         FIG. 4  is a magnified view of a section of  FIG. 3   
         FIG. 5  is a is a cross-sectional view taken along line  5 - 5  of  FIG. 3   
         FIG. 6  is a is a cross-sectional view taken along line  6 - 6  of  FIG. 3   
         FIG. 7  is a perspective view of the turning insert in  FIG. 1  where the bottom surface is shown 
         FIG. 8  is a bottom view of the turning insert in  FIG. 1   
         FIG. 9  is a schematic cross-sectional view of a turning insert mounted in an insert seat 
         FIG. 10  is a magnified view of a section of  FIG. 9   
         FIG. 11  is a bottom view of the turning insert in  FIG. 1  and portions of a bottom surface of an insert seat 
         FIG. 12  is a side view of  FIG. 11   
         FIG. 13  is a perspective view of an insert seat for the turning insert in  FIG. 1   
         FIG. 14  is a top view of  FIG. 13   
         FIG. 15  is a side view of  FIG. 13   
         FIG. 16  is a front view of  FIG. 13   
         FIG. 17  is a perspective view of the insert seat in  FIG. 13  and the turning insert in  FIG. 1   
         FIG. 18  is a top view of  FIG. 17   
         FIG. 19  is a side view of  FIG. 17   
         FIG. 20  is a front view of  FIG. 17   
         FIG. 21  is a perspective view of a tool body comprising the insert seat in  FIG. 13   
         FIG. 22  is a front view of  FIG. 21   
         FIG. 23  is a side view of  FIG. 21   
         FIG. 24  is a top view of  FIG. 21   
         FIG. 25  is a perspective view of a turning tool comprising the tool body in  FIG. 21  and the turning insert in  FIG. 1   
         FIG. 26  is a front view of  FIG. 25   
         FIG. 27  is a side view of  FIG. 25   
         FIG. 28  is a top view of  FIG. 25   
         FIG. 29  is a perspective view of a tool body 
         FIG. 30  is a front view of  FIG. 29   
         FIG. 31  is a side view of  FIG. 29   
         FIG. 32  is a top view of  FIG. 29   
         FIG. 33  is a perspective view of a turning tool comprising the tool body in  FIG. 29 , the turning insert in  FIG. 1  and the shim in  FIG. 43   
         FIG. 34  is a front view of  FIG. 33   
         FIG. 35  is a side view of  FIG. 33   
         FIG. 36  is a top view of  FIG. 33   
         FIG. 37  is a perspective view of the tool body in  FIG. 29  and the shim in  FIG. 43   
         FIG. 38  is a front view of  FIG. 37   
         FIG. 39  is a side view of  FIG. 37   
         FIG. 40  is a top view of  FIG. 37   
         FIG. 41  is a schematic view of turning using the turning tool in  FIG. 25   
         FIG. 42  is a schematic view of turning using the turning tool in  FIG. 25   
         FIG. 43  is a perspective view of a shim 
         FIG. 44  is a top view of the shim in  FIG. 43   
         FIG. 45  is a front view of the shim in  FIG. 43   
         FIG. 46  is a transparent side view of the shim in  FIG. 43   
     
    
    
     All turning insert figures have been drawn to scale. 
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Reference is made to  FIGS. 1-3, 7 and 8  which show a turning insert  1 . The turning insert  1  comprises a top surface  2  comprising a rake surface and an opposite bottom surface  3  functioning as a seating surface. A reference plane RP extends mid-way between the top and bottom surfaces  2 ,  3 . A center axis A 1  intersects the top and bottom surfaces  2 ,  3 . A side surface  4  connects the top surface  2  and the bottom surface  3 . A cutting edge  5  is adjacent to the top surface  2  and the side surface  4 . The cutting edge  5  is circular and concentric in relation to a center axis A 1 . A through hole  36  for a screw extends between the top and bottom surfaces  2 ,  3 . The top surface  2  comprises a set of first protrusions  6 . 
     As can be seen in  FIGS. 5 and 6 , a greatest distance from the reference plane RP to the first protrusions  6  is greater than a distance from the reference plane RP to the cutting edge  5 . 
     As can best be seen in e.g.  FIG. 8 , the bottom surface  3  comprises a set of radial grooves  10  and a set of flat surfaces  19 . The flat surfaces  19 , arranged to function as support surfaces or contact surfaces, extend in a plane parallel to the reference plane RP. 
     In a top view as in  FIG. 3 , each first protrusion  6  is symmetrical in relation to a line extending between the center axis A 1  and a midpoint  45  of the first protrusion  6 . The first protrusions  6  are elongated in a direction parallel to or substantially parallel to the adjacent cutting edge  5 . 
     The number of first protrusions  6  is a multiple of the number of radial grooves  10 . 
     As can be seen in  FIG. 4 , a distance  41  between adjacent first protrusions  6  is smaller than a length  42  of a first protrusion  6 . 
     As seen in  FIG. 5 , each first protrusion  6  is convex in a radial cross section. 
     The first protrusions  6  are evenly distributed around the center axis A 1 , and are located at constant distance from the center axis A 1 . 
     As can be seen in  FIG. 3 , a radial angle α 1  for a first protrusion  6  is greater than a radial angle α 2  of a second protrusion  7 , where said angles are measured between radial lines intersecting end points of the respective protrusion  6 ,  7 . The first and second protrusions  6 ,  7  radially overlap when seen in a top view. The sum of radial angles α 1 , α 2  for the first protrusions  6  and the second protrusions  7  exceeds 360°. 
     The first and the second protrusions  6 ,  7 , respectively, are uniformly distributed around the center axis A 1 . 
     As can be seen in e.g.  FIG. 3  the top surface  2  of the turning insert  1  is mirror symmetrical in relation to a plane comprising the center axis A 1 . The number of first protrusions  6  is equal to the number of second protrusions  7 . The first protrusions  6  are identical. The second protrusions  7  are identical. 
     In a top view the first protrusions  6  are oval shaped or substantially oval shaped. Said oval is in a top view elongated in a direction perpendicular to a radius intersecting a mid-point of the respective first protrusion, where said radius intersects the center axis. In other words, a length  42  of a first protrusion  6  is greater than a width  43  of a first protrusion  6 , where said width  43  is measured radially in a top view and where said length is measured perpendicular to said width  43 , as seen in  FIG. 4 . 
     The top surface  2  comprises a set of second protrusions  7 . As can be seen in e.g.  FIG. 3 , a greatest distance from the cutting edge  5  to the first protrusions  6  is smaller than a greatest distance from the cutting edge  5  to the second protrusions  7 . In other words, the first protrusions  6  are closer to the cutting edge  5 , while the second protrusions  7  are closer to the center axis A 1 . As can be seen in  FIGS. 5 and 6 , the top surface  2  slopes downwards from the cutting edge  5 . 
     As seen in  FIGS. 5 and 6 , a distance from the reference plane to the first protrusions  6  is smaller than a distance from the reference plane to the second protrusions  7 . As seen in e.g.  FIG. 5 , the first protrusion  6  comprises a first surface  8  facing the cutting edge  5 . As seen in e.g.  FIG. 6 , the second protrusions  7  comprises a second surface  9  facing the cutting edge  5 . A greatest angle θ 1  of the first surface  8  in relation to the reference plane RP is smaller than a greatest angle θ 2  of the second surface  9  in relation to the reference plane RP. 
     The first protrusions  6  are smaller in width, i.e. radially, than the width of the second protrusions  7  when seen in a top view. The first protrusions  6  are at a constant distance or substantially constant distance from the center axis A 1 . 
     The second protrusions  7  are at a constant distance or substantially constant distance from the center axis A 1 . 
     The second protrusions  7  extend radially from a circular or substantially circular ring  11 , i.e. a ring-shaped protrusion, concentric with the center axis A 1 . The first protrusions  6  are spaced apart from said circular ring  11 . 
     The radial grooves  10  are aligned with mid-points of first or second protrusions  6 ,  7 . 
       FIGS. 25-28  show a turning tool  13  comprising a tool body  14  and the above described turning insert  1 . The tool body  14  is shown in detail in  FIGS. 21-24 . The turning tool  13  comprises an insert seat  15 . The insert seat  15  comprises a bottom surface  16  and a rear surface  17 . The turning insert  1  is mounted in the insert seat  15 . The bottom surface  16  of the insert seat  15  comprises a first ridge  18 . 
     The side surface  4  of the turning insert  1  is in contact with the rear surface  17  of the insert seat  15 , 
     The first ridge  18  is inside one of the radial grooves  10  formed in the bottom surface  3  of the turning insert  1 . 
     The grooves and the ridge are arranged such that a small rotation, i.e. between 0° and 1°, even more preferably between 0° and 0.5°, of the turning insert around the center axis thereof is possible. The grooves and the ridge are arranged such that a rotation above 1°, preferably above 0.5°, is prevented. 
     The bottom surface  16  of the insert seat  15  comprises support surfaces  21 ,  32  extending in a common plane. The flat surfaces  19  of the turning insert  1  is in contact with the support surfaces  21 ,  32 . 
     The turning insert  1  is mounted in the insert seat  15  by means of a screw (not shown). 
     As seen in  FIGS. 9 and 10 , the first ridge  18  is smaller than one of the radial grooves  10  when seen in a cross-section perpendicular to the main extension of said one of the radial grooves  10 . Said first ridge  18  is inside or contained within said one of the radial grooves  10 . 
     A hole  36  for the screw is connecting the top and bottom surfaces  2 ,  3  of the turning insert  1 . A threaded hole  22  for said screw intersects the bottom surface  16  of the insert seat  15 . 
     The screw preferably comprises a screw head and an external thread. A through hole  36  for the screw is connecting the top and bottom surfaces  2 ,  3  of the turning insert  1 . The bottom surface  16  of the insert seat  15  comprises a threaded hole  22  for the screw. The screw is at least partly located inside said hole  36  formed in the insert and at least partly inside said threaded hole  22 . 
     The radial grooves  10  intersect the hole  36  formed in the turning insert  1 . The radial grooves  10  extend radially between the hole  36  and the side surface  4 . 
     The bottom surface  16  of the insert seat  15  comprises seat grooves  23 . The first ridge  18  is formed between the seat grooves  23 . The first ridge  18  and the seat grooves  23  are at least partially located on opposite sides in relation to a plane comprising the support surfaces  21 ,  32 . 
     The bottom surface  16  of the insert seat  15  comprises a second ridge  24 . The first ridge  18  and the second ridge  24  are aligned in a top view as seen in e.g.  FIG. 14 . The first and second ridges  18 ,  24  are spaced apart and separated by the hole  22  formed in the bottom surface  16  of the insert seat  15 . The first ridge  18  is longer than the second ridge  24  when seen in a top view. The first ridge  18  and the second ridge  24  are separated by 180° in a top view. The The first ridge  18  and the second ridge  24  are aligned with the longitudinal axis A 2  of the turning tool  13 , or aligned with a line parallel to said longitudinal axis A 2 , when seen in a top view. 
     The tool body  14  comprises a rear end coupling portion  25  suitable to be connected to a machine interface (not shown) of a CNC-lathe (not shown). The coupling portion  25  extends along a longitudinal axis A 2  of the turning tool  13 . The first and second ridges  18 ,  24  extends primarily along or parallel to the longitudinal axis A 2  of the turning tool  13 . 
     The first ridge  18  has a main extension thereof along or parallel to the longitudinal axis A 2  of the turning tool  13  when seen in a top view. 
     The center axis A 1  of the turning insert  1  is perpendicular or substantially perpendicular to the longitudinal axis A 2  of the turning tool  13 . 
     The first ridge  18 , the second ridge  24  and the radial grooves  10  formed in the bottom surface  3  of the turning insert  1  have corresponding or substantially corresponding shapes in cross sections, as seen in  FIGS. 9 and 10 . 
     The number of ridges  18 ,  24  formed in the bottom surface  16  of the insert seat  15  is smaller than the number of radial grooves  10  formed in the bottom surface  3  of the turning insert  1 . 
     As seen in  FIGS. 9 and 10 , the first ridge  18  comprises planar ridge side surfaces  26 ,  27  connected by a ridge crest  28 . The ridge side surfaces  26 ,  27  form an angle of 70-110° in relation to each other. Each radial groove  10  comprises radial groove side surfaces  29 ,  30  connected by a radial groove root  31 . The radial groove side surfaces  29 ,  30  form an angle of 70-110° in relation to each other. Each radial groove  10  is uniform or substantially uniform in cross sections along the length of the radial groove, where the length is in a radial direction. In a corresponding manner, the first and second ridges  18 ,  24  are uniform or substantially uniform. 
     A gap is formed at least between one of the pair of adjacent ridge side- and radial groove side surfaces  26 ,  29 ,  27 ,  30 . In  FIG. 10 , a gap is formed between both of said adjacent pairs of side surfaces  26 ,  29 ,  27 ,  30 . A gap is always formed between the ridge crest  28  and the radial groove root  31 . 
     The bottom surface  16  of the insert seat  15  comprises two support surfaces  21 ,  32  located in a common plane. In a top view as seen in e.g.  FIG. 14 , an area of the support surfaces  21 ,  32  are greater than an area of the ridge or ridges  18 ,  24 . 
     As seen in e.g.  16 , the rear surface  17  of the insert seat  15  comprises two spaced apart rear contact surfaces  33 ,  34 . The rear contact surfaces  33 ,  34  are separated by a recess  35 . 
     The tool body  14  may comprise the insert seat  15  as seen in  FIGS. 21-24 . In such a case, the bottom surface  3  and the side surface  4  of the turning insert  1  is partly in contact with the tool body  14 , as seen in  FIGS. 25-28 . Alternatively, the turning tool  13  may comprise a shim  37 , such as the shim  37  shown in  FIGS. 43-46 . In such case, as seen in  FIGS. 33-36 , the bottom surface  3  of the turning insert  1  is in contact with the shim  37 , while the side surface  4  of the turning insert  1  is in contact with the tool body  14 . 
       FIGS. 41 and 42  schematically show a method to machine a metal work piece  38  by means of any of the above described turning tools  13 . The metal work piece  38  rotates in one direction around a rotational axis A 3  thereof. The first ridge is oriented perpendicular to the rotational axis A 3  of the metal work piece  38 . Cutting the metal work piece  38  is made by first moving the turning tool  13  in a first direction  39  parallel to the rotational axis A 3  of the metal work piece  38 , and thereafter cutting the metal work piece  38  by moving the turning tool  13  in a second direction  40  parallel to the rotational axis A 3  of the metal work piece  38 , where the second direction  40  is opposite to the first direction  39 . 
     In  FIG. 41 , one ridge surface  27  as seen in  FIG. 10  is in contact with one radial groove side surface  30 , while in  FIG. 42 , one other ridge surface  26  is in contact with one other radial groove side surface  29 . Thus, the turning insert have made a rotational movement of a predetermined angle around the center axis thereof when comparing the end of the pass shown in  FIG. 41  and the end of the pass shown in  FIG. 42 . In other words, in  FIG. 41 , there is at least a partial gap between the other ridge surface  26  and the one other radial groove side surface  29 . In a corresponding manner, in  FIG. 42  there is at least a partial gap between said one ridge surface  27  and said one radial groove side surface  30 . In other words, the ridge crest  28  seen in  FIG. 10  forms an angle in a top view in relation to the radial groove root  31 . This can be understood from  FIG. 11 .