Abstract:
An indexable cutting insert can be used for metal cutting processes in general and for radial and axial turning of a stepped square shoulder in particular. The cutting insert exhibits 180° rotational symmetry about three mutually perpendicular axes. The cutting insert has generally “S”-shaped cutting edges extending between raised and lowered corners. The cutting edges and side surfaces are concave in an end view of the cutting insert. The cutting insert enables radial and axial turning operations of a square shoulder with unlimited depth of cut.

Description:
RELATED APPLICATIONS 
       [0001]    This is a Continuation of U.S. patent application Ser. No. 11/422,454, filed Jun. 6, 2006, now U.S. Pat. No. ______ , which is a Continuation of U.S. patent application Ser. No. 10/375,112 filed Feb. 28, 2003, now U.S. Pat. No. 7,073,987. The contents of the aforementioned parent applications are incorporated by reference in their entirety. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a tangential indexable cutting insert for use in metal cutting processes in general and for radial and axial turning of a stepped square shoulder in particular. 
       BACKGROUND OF THE INVENTION 
       [0003]    Tangential cutting inserts, also known as on-edge, or lay down, cutting inserts, are oriented in an insert holder in such a manner that during a cutting operation on a workpiece the cutting forces are directed along a major (thicker) dimension of the cutting insert. An advantage of such an arrangement being that the cutting insert can withstand greater cutting forces than when oriented in such a manner that the cutting forces are directed along a minor (thinner) dimension of the cutting insert. Another advantage of such an arrangement is that with the minor dimension directed perpendicular to the cutting forces it is possible to maneuver the cutting insert between obstacles close to the workpiece. 
         [0004]    For turning a stepped square shoulder on a workpiece, a cutting tool assembly requires a cutting insert with an acute operative insert cutting corner, a tool back clearance angle along its inoperative cutting edge and an obtuse entering angle along its operative cutting edge. Such an entering angle enables an outwardly directed feed out movement to square out a shoulder, in particular, an outwardly directed radial feed out movement in the case of external axial turning operations and an outwardly directed axial feed out movement in the case of radial turning operations. 
         [0005]    In view of these restrictions, cutting inserts for turning stepped square shoulders are usually either rhomboidal or triangular; thereby having respectively, two or three indexable insert cutting corners for single-sided cutting inserts. Such cutting inserts are, for example, as illustrated and described in U.S. Pat. No. 4,632,608, each insert cutting corner being formed as a protruding nose portion at the junction between centrally depressed insert sides. The cutting inserts are preferably double sided so as to be respectively formed with four or six indexable insert cutting corners. 
         [0006]    With a view to increasing the number of cutting corners, a fully indexable non-tangential cutting insert is described in U.S. Pat. No. 6,074,137. The cutting insert comprises four substantially concave side edges extending between substantially square opposing upper and lower surfaces. Adjacent side edges meet at a cutting corner having an angle in the range of about 83°±5°. Although the cutting insert is substantially square and although it offers eight cutting corners, its depth of cut is limited. In fact, the maximal depth of cut is limited to less than the length of a side of an imaginary square, in which the insert is inscribed, in a top view of the insert. Furthermore, it is not a tangential cutting insert. 
         [0007]      FIGS. 1 and 2  show a cutting tool  20  with a tangentially seated cutting insert  22  for both axial and radial turning operations, also known as longitudinal and face turning operations. The cutting insert  22  is oriented with relief angles γ 1  and γ 2  for radial and axial turning operations, respectively. The cutting insert  22  has one operative cutting corner  24 , a first trailing non-operative cutting corner  26  during axial turning operations and a second trailing non-operative cutting corner  28  during radial turning operations. Major and minor cutting edges  30 ,  32  extend between the operative cutting corner  24  and non-operative cutting corners  28 ,  26 . 
         [0008]      FIG. 3  is an illustrative drawing showing the cutting tool  20  during either radial or axial turning operations of a workpiece  33 . Dashed lines  34  show an ideal square shoulder and the dash-dot line  35  is an imaginary extension of the worked face  36  of the workpiece  33 . As can be seen, for a radial turning operation, the second trailing non-operative cutting corner  28  and a portion of the major cutting edge  30  are oriented such that they “extend beyond” the imaginary extension  35  of the worked face  36  and would engage the workpiece  33  if an attempt were made to increase the depth of cut beyond a depth of cut, d, where the dashed line intersects the major cutting edge  30 . Thus, the depth of cut is limited during radial turning of a square shoulder. For axial turning in the configuration shown in  FIG. 3 , the depth of cut is also limited to d. Any increase in the depth of cut would lead to a non-square shoulder. Similarly, the insert could be configured with an orientation such that for an axial turning operation, the first trailing non-operative cutting corner  26  and a portion of the minor cutting edge  32  are disposed such that they have a limited depth of cut. Likewise, the insert could be configured with an orientation so that it has a limited depth of cut for both axial and radial turning operations due both to the first trailing non-operative cutting corner  26  and a portion of the minor cutting edge  32  and also to the second trailing non-operative cutting corner  28  and a portion of the major cutting edge  30 . 
       SUMMARY OF THE INVENTION 
       [0009]    In accordance with the present invention there is provided an indexable cutting insert, for use in a cutting tool for turning operations, comprising: 
         [0010]    two identical opposing end surfaces having 180° rotational symmetry about a first axis passing therethrough, 
         [0011]    a peripheral side surface extending between the two opposing end surfaces, and 
         [0012]    a peripheral edge formed at the intersection of each end surface and the peripheral side surface, at least two sections of each peripheral edge constituting cutting edges; 
         [0013]    the peripheral side surface comprising: 
         [0014]    two identical opposing major side surfaces having 180° rotational symmetry about a second axis passing therethrough, the second axis being perpendicular to the first axis; 
         [0015]    two identical opposing minor side surfaces having 180° rotational symmetry about a third axis passing therethrough, the third axis being perpendicular to the first axis and the second axis; 
         [0016]    a major plane defined by the first axis and the second axis; 
         [0017]    a minor plane defined by the first axis and the third axis; 
         [0018]    a median plane being defined by the second axis and the third axis; 
         [0019]    each end surface having four corners, two lowered corners and two raised corners, the lowered corners being closer to the median plane than the raised corners; 
         [0020]    in a side view of one of the minor side surfaces, all four corners are equidistant from the minor plane; 
         [0021]    in a side view of one of the major side surfaces, all four corners are equidistant from the major plane. 
         [0022]    In accordance with the present invention, the cutting insert has a maximum distance D 1  between the minor side surfaces that is greater than a maximum distance D 2  between the major side surfaces. 
         [0023]    In accordance with the present invention, in an end view of the cutting insert, each major side surface is recessed. 
         [0024]    In accordance with the preferred embodiment of the present invention, in an end view, the distance between the opposing major side surfaces varies from the maximum distance D 2  adjacent the corners of the cutting insert to a minimum distance d 2  at the intersection of the major side surfaces with the major plane. 
         [0025]    In accordance with a specific application of the present invention, the minimum distance d 2  is given by d 2 =D 2 −t, where the value t is given by 0.3 mm≦t≦0.4 mm. 
         [0026]    In accordance with the present invention, in an end view of the cutting insert, each minor side surface is recessed. 
         [0027]    In accordance with the preferred embodiment of the present invention, in an end view, the distance between the opposing minor side surfaces varies from the maximum distance D 1  adjacent the corners of the cutting insert to a minimum distance d 1  at the intersection of the minor side surfaces with the minor plane. 
         [0028]    In accordance with a specific application of the present invention, the minimum distance d 1  is given by d 1 =D 1 −s, where the value s is given by 0.05 mm≦s≦0.25 mm. 
         [0029]    In accordance with the present invention, each minor side surface merges with an adjacent major side surface at a corner side surface, wherein each corner side surface extends between a given raised corner of one of the two opposing end surfaces and a given lowered corner of the other of one of the two opposing end surfaces. 
         [0030]    In accordance with the preferred embodiment of the present invention, each cutting edge comprises a major edge, a minor edge and a corner edge, therebetween. 
         [0031]    In accordance with the present invention, each major edge, corner edge, and minor edge is formed at the intersection of adjacent major side surface, corner side surface, and minor side surface, respectively with an adjacent end surface. 
         [0032]    In accordance with the preferred embodiment of the present invention, the major edges are recessed in an end view. 
         [0033]    In accordance with the preferred embodiment of the present invention, the distance between the opposing major edges varies from the maximum distance D 2  adjacent the corner edges to the minimum distance d 2  at the intersection of the major edges with the major plane. 
         [0034]    In accordance with the preferred embodiment of the present invention, the minor edges are recessed in an end view. 
         [0035]    In accordance with the preferred embodiment of the present invention, the distance between the opposing minor edges varies from the maximum distance D 1  adjacent the corner edges to the minimum distance d 1  at the intersection of the minor edges with the minor plane. 
         [0036]    In accordance with the preferred embodiment of the invention, each raised corner forms a corner cutting edge and adjacent major and minor edges form major and minor cutting edges, respectively. 
         [0037]    Generally, the major cutting edge has a length L 1  that is greater than half the distance D 1 . 
         [0038]    Generally, the minor cutting edge has a length L 2  that is approximately half the distance D 2 . 
         [0039]    In accordance with the preferred embodiment of the present invention, the cutting insert further comprises an insert through bore extending between the major side surfaces and having a bore axis coinciding with the second axis. 
         [0040]    In accordance with the present invention there is provided a cutting tool comprising: the cutting insert in accordance with the present invention, a shim, and an insert holder having an insert pocket in which the shim and the cutting insert are securely retained. 
         [0041]    In the cutting tool, the insert pocket comprises: a base surface, the base surface being abutted by a given major side surface of the cutting insert, a first side wall extending uprightly from the base surface, the first side wall being abutted by a given minor side surface of the cutting insert, and a second side wall extending uprightly from the base surface, the first side wall being adjacent the major side surface and transverse thereto; 
         [0042]    the shim comprises a top surface that is abutted by a non-operative end surface of the cutting insert, an opposing bottom surface that abuts the first side wall, and a perimeter surface extending therebetween; 
         [0043]    a shim screw, extending through the shim through bore and threadingly engaged with a threaded second bore of the second side wall, secures the shim to the insert pocket; and 
         [0044]    a securing screw, extending through the insert through bore, threadingly engaged with a threaded receiving bore of the base surface, secures the cutting insert to the insert pocket, the securing screw. 
         [0045]    If desired, each end surface of the cutting insert further comprises two frustums extending away from the median plane located on either side of the major plane, and the top surface of the shim, in accordance with the present invention, further comprises a raised area being a portion of the top surface of the shim protruding from the top surface of the shim; wherein 
         [0046]    the two frustums of the non-operative end surface abut the raised area of the top surface of the shim. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0047]    For a better understanding, the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0048]      FIG. 1  is of a side view of a typical prior art cutting tool; 
           [0049]      FIG. 2  is an end view of the cutting tool in  FIG. 1 ; 
           [0050]      FIG. 3  is a plan view of the cutting tool in  FIG. 1  in a turning operation. 
           [0051]      FIG. 4  is a perspective view of the cutting insert in accordance with the present invention; 
           [0052]      FIG. 5  is a first side view of the cutting insert in  FIG. 4 ; 
           [0053]      FIG. 6  is a second side view of the cutting insert shown in  FIG. 4 ; 
           [0054]      FIG. 7  is a cross-sectional view of the cutting insert shown in  FIG. 6  taken along C-C; 
           [0055]      FIG. 8  is an end view of the cutting insert shown in  FIG. 4 ; 
           [0056]      FIG. 9  is a side view of a cutting tool in accordance with the present invention; 
           [0057]      FIG. 10  is an end view of the cutting tool in  FIG. 9 ; 
           [0058]      FIG. 11  is a plan view of the cutting tool in accordance with the present invention in an axial turning operation; 
           [0059]      FIG. 12  is a detailed view of  FIG. 11 ; 
           [0060]      FIG. 13  is a plan view of the cutting tool in accordance with the present invention in a radial turning operation; 
           [0061]      FIG. 14  is a detailed view of  FIG. 13 ; 
           [0062]      FIG. 15  is a perspective exploded view of cutting tool in accordance with the present invention; and 
           [0063]      FIG. 16  is an end view of a cutting insert shown insert in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0064]    Attention is first drawn to  FIGS. 4 to 8 , showing a tangential indexable cutting insert  38  in accordance with present invention. The cutting insert  38  is generally manufactured by form pressing and sintering a cemented carbide, such as tungsten carbide, and can be coated or uncoated. The cutting insert  38  is generally rectangular in an end view and comprises two identical end surfaces  40 , and a peripheral side surface  42  extending between the end surfaces  40 . The cutting insert  38  and the end surfaces  40  have 180° rotational symmetry about a first axis R 1  that passes through the end surfaces  40 . Since the end surfaces  40  are identical, only one will be described, it being understood that the other end surface  40  has identical structure. 
         [0065]    The peripheral side surface  42  comprises two opposed identical minor side surfaces  44 , two opposed identical major side surfaces  46 , and four opposed corner side surfaces  48 . Adjacent major and minor side surfaces  46 ,  44  merge at a common corner side surface  48 . The cutting insert  38  and the major side surface  46  have 180° rotational symmetry about a second axis R 2  perpendicular to the first axis of rotational symmetry R 1  and passing through the major side surfaces  46 . The cutting insert  38  and the minor side surface  44  also has 180° rotational symmetry about a third axis R 3  that passes through the minor side surfaces  44  and is perpendicular to both the first and second axis of 180° rotational symmetry R 1 , R 2 . 
         [0066]    The peripheral side surface  42  intersects each end surface  40  at a peripheral edge  50 . The peripheral edge  50  comprises two identical opposed major edges  52 , two identical opposed minor edges  54 , and four opposed corner edges  56 . Adjacent major and minor edges  52 ,  54  merge at a common corner edge  56 . The major edges  52  are formed at the intersection of the major side surfaces  46  with the end surfaces  40 , the minor edges  54  are formed at the intersection of the minor side surfaces  44  with the end surfaces  40 , and the corner edges  56  are formed at the intersection of the corner side surfaces  48  with the end surfaces  40 . 
         [0067]    For further description of the geometrical properties of the cutting insert  38 , a minor plane P 1 , to which the major edges  52  are generally parallel in an end view of the cutting insert  38 , is defined by the first and third axis of rotational symmetry R 1 , R 3 . A major plane P 2 , to which the minor edges  54  are generally parallel in an end view of the cutting insert  38 , is defined by the first and second axis of rotational symmetry R 1 , R 2 . A median plane M, which is perpendicular to both the minor and major plane P 1 , P 2 , is defined by the second and third axis of rotational symmetry R 2 , R 3 . A width dimension D 1  of the cutting insert  38  is defined as a maximum distance dimension between the minor side surfaces  44  measured parallel to the third axis R 3 . A length dimension D 2  of the cutting insert  38  is defined as a maximum distance dimension between the major side surfaces  46  measured parallel to the second axis R 2 . For the tangential cutting insert  38 , the width dimension D 1  is greater than the length dimension D 2 . 
         [0068]    Associated with each of the four corner edges  56  of a given end surface are four corners comprising two diametrically opposed raised corners  58  and two diametrically opposed lowered corners  60 . The lowered corners  60  are closer to the median plane M than are the raised corners  58 . In a side view of either of the minor side surfaces  44 , all four corners  58 ,  60  are equidistant from the minor plane P 1 . In a side view of either of the major side surfaces  46 , all four corners  58 ,  60  are equidistant from the major plane P 2 . Each corner side surfaces  48  extends between a given raised corner  58  of one end surface  40  and an adjacent lowered corner  60  on the opposing end surface  40 . Each corner side surface  48  has uniform radius of curvature along its length, and typically forms an arc angle of 95°±3°. The alternating raised and lowered corners  58 ,  60  enable the cutting insert  38  to have four same-handed raised corners  58  for indexing. 
         [0069]    Turning to  FIGS. 5 and 6 , and as discussed above, the insert body  57  has four side surfaces (two minor side surfaces and two major side surfaces) and identical first and second end surfaces. Without loss of generality, one of these end surfaces may be considered the top surface  40   a  while the other end surface may be considered the base surface  40   b,  in the orientation presented in  FIGS. 5 and 6 . The four side surfaces, together with the top surface  40   a  and the base surface  40   b,  define respective pairs of major  52  and minor  54  cutting edges at the top  40   a  and base  40   b  surfaces. Each side surface has two diagonally opposed lowered corners  60  spaced by equal first distances y from the median plane M of the insert body, and two diagonally opposed raised corners  58  spaced by equal second distances z from the median plane M, the second distances z being longer than the first distances y, and the distance  2   z  between raised corners  58  of the top surface  40   a  and the base surface  40   b  defining the height of the insert, in either a minor side view ( FIG. 5 ) or major side view ( FIG. 6 ) of the insert. 
         [0070]    Each member of a first pair of side surfaces has a long diagonal S 1  extending between the pair of raised corners  58  and a short diagonal S 2  extending between the pair of lowered corners  60 . Similarly, each member of a second pair of side surfaces has a long diagonal T 1  extending between the pair of raised corners  58  and a short diagonal T 2  extending between the pair of lowered corners  60 . The long diagonal (S 1  or T 1 ) of a given side surface is non-parallel to the long diagonal of an opposite side surface of the insert. For instance, in the side view of the insert body seen  FIG. 6 , the long diagonal T 1  of one side surface crosses, and so is non-parallel to, the long diagonal T 1 ′ (shown in phantom) of the opposite side surface found on the other side of the insert body. 
         [0071]    Adjacent major and minor edges  52 ,  54  extend from the corner edge  56  of a given raised corner  58  with a variable slope to a respective lowered corner  60 . In a side view of the cutting insert  38 , adjacent each raised corner  58 , the slope of each major edge  52  (see  FIG. 6 ) is generally constant with the major edge  52  substantially parallel to the median plane M. Moving along the major edge  52  towards an adjacent lowered corner  60 , the slope gradually increases and finally decreases adjacent the lowered corner  60 . As can be seen in  FIG. 5  each minor edge  54  has a generally similar form to that of the major edges  52 . Thus in a respective side view, each major and minor edge  52 ,  54 , has a similar wavy elongated “S”-shape. 
         [0072]    In an end view of the cutting insert  38 , the major edges  52  are concave. In other words, the major edges  52  are recessed in an end view wherein, the distance between the opposed major edges  52  varies from approximately D 2  adjacent the corner edges  56  to a minimum distance d 2  at the intersection of the major edges  52  with the major plane P 2 . The minimum distance d 2  is defined by D 2 −t. In a non-binding example, t is greater than or equal to 0.3 mm and less than or equal 0.4 mm. In an end view of the cutting insert  38 , each major side surface  46  is also concave, being recessed in the same manner as its associated major edge  52 . It should be noted that the variation of the distance between the opposed major edges  52  (and likewise the opposed major side surfaces  46 ) need not decrease uniformly from the maximum value D 2  to the minimum value d 2 . 
         [0073]    In an end view of the cutting insert  38 , the minor edges  54  are also concave, in a similar manner to the major edges  52 . The distance between the opposed minor edges  54  in an end view, varies from approximately D 1  adjacent the corner edges  56  to a minimum distance d 1  at the intersection of the minor edges  54  with the minor plane P 1 . The minimum distance d 1  is defined by D 1 −s. In a non-binding example, s is greater than or equal to 0.05 mm and less than or equal 0.25 mm. Likewise, in an end view of the cutting insert  38 , each minor side surface  44  is concave, being recessed in the same manner as its associated minor edge  54 . The variation of the distance between the opposed minor edges  54  (and likewise the opposed minor side surfaces  44 ) need not decrease uniformly from the maximum value D 1  to the minimum value d 1 . 
         [0074]    It will be appreciated that whereas the whole of the peripheral edge  50  can function as a cutting edge, in practice, sections of the peripheral edge  50  adjacent the lowered corners  60  will not function as cutting edges. In accordance with a specific application of the present invention, each given peripheral edge  50  has an effective major cutting edge  66  that extends from an associated given raised corner  58  along the given corner edge  56  and the given major edge  52  for a given major cutting edge length L 1 , which is greater than one half of the width dimension D 1 . Additionally, in accordance with the specific application of the present invention, each peripheral edge  50  has an effective minor cutting edge  68  that extends from an associated given raised corner  58  along the given corner edge  56  and the given minor edge  54  for a given minor cutting edge length, L 2 , which is approximately one half of the length dimension D 2 , and more preferably is slightly greater than one half of D 2 . 
         [0075]    Attention is now drawn to  FIGS. 9 and 10 , showing side views of a cutting tool  70  in accordance with the present invention. The cutting insert  38  has relief angles y 1 , y 2  and presents an operative raised corner  58 ′ outward 1 y projecting from the cutting tool  70 . 
         [0076]    Attention is now drawn to  FIGS. 11 and 12 , showing the cutting insert  38  in an insert holder  72  in a plan view during an axial turning operation of a stepped square shoulder  74  of a workpiece  76  rotating about an axis A. Adjacent the stepped square shoulder  74  is a operative major edge  52 ′, an operative corner edge  56 ′ of an operative raised corner  58 ′ an operative minor edge  54 ′, and a trailing lowered corner edge  78 ′. It will be appreciated that an operative minor edge  54 ′ constitutes a secondary cutting edge or wiper and that only a small section of it adjacent the operative corner edge  56 ′ contacts the workpiece  76 . Due to the relief angles y 1 , y 2  and any other required orientation of the cutting insert  38 , an entering angle K is formed between the major edge  52  and the feed direction F 1 , and a back clearance angle Kn is formed between the operative minor edge  54 ′ and a cylindrical surface  80  of the workpiece  76 . As can be seen, the trailing lowered corner edge  78 ′ is completely relieved from the cylindrical surface  80  of the workpiece  76 , whereby the depth of cut for axial turning is unlimited. 
         [0077]    Attention is now drawn to  FIGS. 13 and 14 , showing the cutting insert  38  in an insert holder  72  in a plan view during an radial turning operation of a cylindrical surface  80  of a workpiece  76  rotating about an axis A. Adjacent the cylindrical surface  80  is an operative major edge  52 ′, an operative corner edge  56 ′ of the operative corner edge  58 ′ an operative minor edge  54 ′, and a trailing lowered corner edge  78 ″. It will be appreciated that an operative major edge  52 ′ constitutes a secondary cutting edge or wiper and that only a small section of it adjacent the operative corner edge  56 ′ contacts the workpiece  76 . Due to the relief angles y 1 , y 2  and any other required orientation of the cutting insert  38 , an entering angle K is formed between the operative minor edge  54 ′ and the feed direction F 2 , and a back clearance angle Kn is formed between the operative major edge  52 ′ and a stepped square shoulder  74  of the workpiece  76 . As can be seen, the trailing lowered corner edge  78 ″ is completely relieved from the stepped square shoulder  74  of the workpiece  76 , whereby the depth of cut for radial turning is unlimited. 
         [0078]    The seating and securing of the cutting insert  38  will now be described with reference to  FIG. 15 , showing various elements not mentioned above. These elements include two frustums  82  on each end surface  40 , an insert pocket  84  of the insert holder  72 , an insert through bore  86 , a securing screw  88 , a shim  90 , and a shim screw  92 . 
         [0079]    The insert pocket  84  comprises first and second side walls  94 ,  96  uprightly extending from a base surface  98  of the insert pocket  84 . The shim  90  comprises a top surface  100 , a flat opposing bottom surface  102 , and a perimeter surface  104  extending therebetween. The top surface  100  of the shim  90  comprises a raised area  106  extending away from the bottom surface  102  of the shim  90 . A shim through bore  108  extends between the top surface  100  and the bottom surface  102 . The two frustums  82  of each end surface  40  extend away from the median plane M and are located on either side of the major plane P 2 . The frustums  82  are likely to impede chip flow, thereby limiting the lengths L 1 , L 2  of the major and minor cutting edges  66 ,  68 . 
         [0080]    The shim  90  is secured in the insert pocket  84  with its bottom surface  102  abutting the second side wall  96 . The shim screw  92 , extends through the shim through bore  108  and threadingly engages with a threaded second bore  110  passing through the second side wall  96 , securing the shim  90  to the insert pocket  84 . The cutting insert  38  is secured in the insert pocket  84  with a non-operative end surface  40  adjacent the top surface  100  of the shim  90 . The first side wall  94  abuts the minor side surface  44  of the cutting insert  38 , and the base surface  98  abuts the major side surface  46 . The two frustums  82  of a non-operative end surface  40  abut the raised area  106  of the top surface  100  of the shim  90 . The securing screw  88  extends through the insert through bore  86  and threadingly engages a threaded receiving bore  112  in the base surface  98  of the insert pocket  84 . 
         [0081]    It will be appreciated that the particular form of the end surfaces  40  will depend on the design factors that take into account various working conditions. For example, in order to increase the effective cutting wedge angle, a land  114  is provided adjacent the peripheral edge  50  (see  FIG. 7 ). A rake surface  116  slopes downwardly and inwardly from the land  114 . If desired the rake surface can be provided with suitable chip control elements. 
         [0082]    It is advantageous to have recessed side surfaces and side edges to take into consideration manufacturing tolerances so that the sides will not become convex or partially convex, when viewed in an end view, and interfere with the workpiece. It is possible to use straight side edges, i.e., the major side surface  46  and the major edges  52  could be straight, as in  FIG. 16 , either by tight manufacturing tolerances during pressing and sintering or by additional steps of grinding. 
         [0083]    Although the present invention has been described to a certain degree of particularity, it should be understood that various alterations and modifications could be made without departing from the spirit or scope of the invention as hereinafter claimed.