Abstract:
A cutting tool for grooving and turning operations has a removably securable cutting insert. The cutting insert is clamped in an insert holder with a longitudinally extending insert receiving slot lower surface. The insert receiving slot lower surface has two spaced apart contact sections, including a first contact section at a rear end having a V-shaped slot clamping surface with a wedge angle α 1  in clamping contact with a first V-shaped insert clamping surface of the cutting insert lower surface also with a wedge angle α 1 , and a second contact section at a front end having a V-shaped slot clamping surface with a wedge angle α 2  making clamping contact with a second V-shaped insert clamping surface of the cutting insert lower surface also with a wedge angle α 2 , where α 1  and α 2  are different.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a cutting tool and a cutting insert for use in metal cutting processes in general, and for grooving and turning operations in particular. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cutting tools, cutting inserts, and insert holders in which they are retained for parting and grooving operations as disclosed in U.S. Pat. No. 4,801,224, are typically small in width and subjected to single direction cutting forces. These cutting forces, produced as a result of axial direction machine feed, are transmitted through the insert tip and the forward section of the insert holder lower surface. 
         [0003]    Support of the insert is provided by a lower V-shaped insert holder male surface (when viewed in cross-section) extending parallel to the axial machine feed direction with an obtuse internal angle between the two surface components, corresponding with an equivalent V-shaped surface on the insert with an obtuse external angle between the two surface components, where large forces can be absorbed whilst minimizing the risk of fracturing the insert. The upper surfaces of both the insert and insert holder also share these same features. 
         [0004]    U.S. Pat. No. 6,086,291 discloses a cutting tool for parting, grooving, and turning operations where each clamping surface includes a second V-shaped feature. A ridge style feature of narrower wedge angle is introduced along the length of the male V-shaped surface of the insert holder, and a flute style feature of narrower wedge angle is introduced along the length of the female V-shaped surface of the insert. 
         [0005]    The insert and insert holder are manufactured such that when assembled, a small gap exists between the ridge and flute side surfaces. Thus, during operation, the wider obtuse angled V-shaped surfaces generally support the central main forces, and the narrower angled ridge and flute V-shaped surfaces generally support the transverse forces. The presence of a small gap between the ridge and flute side surfaces may give rise to an initial transverse movement of the insert of magnitude equal to the gap size at commencement of a turning operation. 
         [0006]    U.S. Pat. No. 6,244,790 discloses a cutting tool for parting, grooving, and turning operations, introducing lower support surfaces with a series of intermeshing ridges and grooves of V-shaped profile, each with a common narrow wedge angle. This solution is aimed at providing increased stability of the insert within the insert holder against twisting, whilst, in theory, also reducing the risk of the insert lower surface splitting by providing a larger surface area for the clamping force to be distributed. 
         [0007]    Distribution of the clamping force over a large surface area requires successful mating of, and simultaneous contact between, the several ridge surfaces extending the entire longitudinal direction of the cutting insert, and the equal number of grooves extending along the entire longitudinal direction of the cutting insert pocket. 
       SUMMARY OF THE INVENTION 
       [0008]    In one aspect, the present invention is directed to a cutting insert comprising: 
         [0009]    upper and lower surfaces; 
         [0010]    a peripheral side surface extending between the upper and lower surfaces, the peripheral side surface comprising front and rear end surfaces with a longitudinal axis passing therebetween; 
         [0011]    peripheral edges formed at the intersection of the upper and lower surfaces with the peripheral side surface, wherein at least one portion of at least one of the peripheral edges comprises a cutting edge; and 
         [0012]    upper and lower clamping portions formed on the upper and lower surfaces respectively; 
         [0013]    wherein: 
         [0014]    at least a first of the upper and lower clamping portions has first and second insert clamping surfaces, each insert clamping surface having a generally V-shaped cross-section; 
         [0015]    surface components of the first insert clamping surface form a first wedge angle (α 1 ); 
         [0016]    surface components of the second insert clamping surface form a second wedge angle (α 2 ); 
         [0017]    wedge angles (α 1 ) and (α 2 ) are different from one another; and the first and second insert clamping surfaces have different longitudinal lengths. 
         [0018]    In specific embodiments of the cutting insert, one or more of the following features may be found: the second insert clamping surface may fully extend from the front end surface to the rear end surface; the second insert clamping surface may be a groove type V-shaped clamping surface; the second wedge angle (α 2 ) may be obtuse; the first wedge angle (α 1 ) may be less than the second wedge angle (α 2 ); the cutting insert may have mirror symmetry about a major plane passing through the upper and lower surfaces and containing the longitudinal axis; the cutting insert may have mirror symmetry about a minor plane perpendicular to the longitudinal axis; two portions of at least one of the peripheral edges comprise a cutting edge; and a second of the upper and lower clamping portions has a third insert clamping surface having surface components which form a third wedge angle (α 3 ) which is less than second wedge angle (α 2 ). 
         [0019]    In another aspect, the invention is directed to an insert holder comprising: 
         [0020]    a holder head with an insert receiving slot opening out to a forward end of the insert holder, wherein the insert receiving slot includes upper and lower receiving slot surfaces sharing a common longitudinal direction; and 
         [0021]    upper and lower clamping portions formed on the upper and lower receiving slot surfaces respectively, wherein the lower clamping portion has generally V-shaped first and second slot clamping surfaces positioned at respective first and second contact sections along the lower receiving slot surface; 
         [0022]    wherein: 
         [0023]    the first contact section is located adjacent a rear end of the lower receiving slot surface; 
         [0024]    the second contact section is located adjacent a front end of the lower receiving slot surface; 
         [0025]    surface components of the first slot clamping surface form a first wedge angle (α 1 ); 
         [0026]    surface components of the second slot clamping surface form an obtuse second wedge angle (α 2 ); and the first wedge angle (α 1 ) is smaller than the second wedge angle (α 2 ). 
         [0027]    In specific embodiments of the insert holder, one or more of the following features may be found: the first wedge angle (α 1 ) may be acute; the upper clamping portion may have a generally V-shaped slot clamping surface with surface components forming a third wedge angle (α 3 ); the third wedge angle (α 3 ) may be less than the second wedge angle (α 2 ); and the third wedge angle (α 3 ) may be equal to the first wedge angle (α 1 ). 
         [0028]    In still another aspect, the invention is directed to cutting tool comprising an insert holder and a cutting insert removably securable in the insert holder. 
         [0029]    In the inventive cutting tool, the cutting insert comprises:
       upper and lower surfaces;       
 
         [0031]    a peripheral side surface extending between the upper and lower surfaces, the peripheral side surface comprising front and rear end surfaces with a longitudinal axis passing therebetween; 
         [0032]    peripheral edges formed at the intersection of the upper and lower surfaces with the peripheral side surface, wherein at least one portion of at least one of the peripheral edges comprises a cutting edge; wherein: 
         [0033]    the lower surface has first and second insert clamping surfaces, each insert clamping surface having a generally V-shaped cross-section; 
         [0034]    surface components of the first insert clamping surface form a first wedge angle (α 1 ); surface components of the second insert clamping surface form an obtuse second wedge angle (α 2 ); and 
         [0035]    the first wedge angle (α 1 ) is smaller than the second wedge angle (α 2 ). 
         [0036]    Also, in the inventive cutting tool, the insert holder comprises:
       a holder head with an insert receiving slot opening out to a forward end of the insert holder, wherein the insert receiving slot includes upper and lower receiving slot surfaces sharing a common longitudinal direction;   upper and lower clamping portions formed on the upper and lower receiving slot surfaces respectively, wherein the lower clamping portion has generally V-shaped first and second slot clamping surfaces positioned at respective first and second contact sections along the lower receiving slot surface; wherein:   the first contact section is located adjacent a rear end of the lower receiving slot surface;   the second contact section is located adjacent a front end of the lower receiving slot surface;   surface components of the generally V-shaped slot clamping surface at the first contact section form a first wedge angle (α 1 );   surface components of the generally V-shaped slot clamping surface at the second contact section form an obtuse second wedge angle (α 2 ); and       
 
         [0043]    the first wedge angle (α 1 ) is smaller than the second wedge angle (α 2 ). 
         [0044]    Furthermore, in the inventive cutting tool, the clamping contact between the first insert clamping surface and the first slot clamping surface occurs only at the first contact section; clamping contact between the second insert clamping surface and the second slot clamping surface occurs only at the second contact section; and the holder head is formed of a first material and the cutting insert is formed of a second material which is harder than the first material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]    For a better understanding, the invention will now be described, by way of example only, with reference to the accompanying drawings in which chain-dash lines represent cut-off boundaries for partial views of a member and in which: 
           [0046]      FIG. 1  is of a perspective view of a cutting tool in accordance with a first embodiment of the present invention; 
           [0047]      FIG. 2  is a side view of the cutting tool shown in  FIG. 1 ; 
           [0048]      FIG. 3  is a top view of the cutting insert shown in  FIG. 1 ; 
           [0049]      FIG. 4  is a perspective top view of the cutting insert shown in  FIG. 1 ; 
           [0050]      FIG. 5  is a perspective bottom view of the cutting insert shown in  FIG. 1 ; 
           [0051]      FIG. 6  is a perspective top view of the insert holder shown in  FIG. 1 ; 
           [0052]      FIG. 7  is a perspective bottom view of the insert holder shown in  FIG. 1 ; 
           [0053]      FIG. 8  is a cross-sectional view of the cutting tool shown in  FIG. 2  taken along the line VIII-VIII; 
           [0054]      FIG. 9  is a cross-sectional view of the cutting tool shown in  FIG. 2  taken along the line IX-IX; 
           [0055]      FIG. 10  is a cross-sectional view of the cutting tool shown in  FIG. 2  taken along the line X-X; 
           [0056]      FIG. 11  is of a perspective view of a cutting tool in accordance with a second embodiment of the present invention; 
           [0057]      FIG. 12  is a side view of the cutting tool shown in  FIG. 11 ; 
           [0058]      FIG. 13  is a bottom view of the cutting insert shown in  FIG. 11 ; 
           [0059]      FIG. 14  is a perspective bottom view of the cutting insert shown in  FIG. 11 ; 
           [0060]      FIG. 15  is a perspective top view of the insert holder shown in  FIG. 11 ; 
           [0061]      FIG. 16  is a cross-sectional view of the cutting tool shown in  FIG. 12  taken along the line XVI-XVI; 
           [0062]      FIG. 17  is a cross-sectional view of the cutting tool shown in  FIG. 12  taken along the line XVII-XVII; 
           [0063]      FIG. 18  is a cross-sectional view of the cutting tool shown in  FIG. 12  taken along the line XVIII-XVIII; 
           [0064]      FIG. 19  is of a perspective view of a cutting tool in accordance with a third embodiment of the present invention; 
           [0065]      FIG. 20  is side view of the cutting tool shown in  FIG. 19 ; 
           [0066]      FIG. 21  is a top view of the cutting insert shown in  FIG. 19 ; 
           [0067]      FIG. 22  is a perspective bottom view of the cutting insert shown in  FIG. 19 ; 
           [0068]      FIG. 23  is a perspective top view of the insert holder shown in  FIG. 19 ; 
           [0069]      FIG. 24  is a cross-sectional view of the cutting tool shown in  FIG. 20  taken along the line XXIV-XXIV; 
           [0070]      FIG. 25  is a cross-sectional view of the cutting tool shown in  FIG. 20  taken along the line XXV-XXV; 
           [0071]      FIG. 26  is a cross-sectional view of the cutting tool shown in  FIG. 20  taken along the line XXVI-XXVI. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0072]    Attention is first drawn to  FIGS. 1 and 2 , showing a cutting tool  30  comprised of an insert holder  31  and a cutting insert  32 . The insert holder  31  is generally manufactured from steel, and the cutting insert  32  is generally manufactured by form pressing and sintering a cemented carbide, such as tungsten carbide, and can be coated or uncoated. 
         [0073]    The cuffing insert  32 , as shown in  FIGS. 3 to 5 , comprises upper and lower surfaces  33 ,  34  and a peripheral side surface  35  extending between the upper and lower surfaces  33 ,  34 . The peripheral side surface  35  comprises front and rear end surfaces  36 ,  37  with a longitudinal axis A 1  passing therebetween. Upper and lower clamping portions  38 ,  39  are formed on the upper and lower surfaces  33 ,  34  respectively. 
         [0074]    According to a first embodiment of the present invention, the lower clamping portion  39  is comprised of two V-shaped insert clamping surfaces  40 ,  41 . The first is a ridge type V-shaped insert clamping surface  40 , as shown in  FIG. 10 , with two surface components  42 ,  43  forming an internal wedge angle α 1 , and the second is a groove type V-shaped insert clamping surface  41 , as shown in  FIG. 8 , with two surface components  44 ,  45  forming an obtuse external wedge angle α 2 , where α 1  is less than α 2 . The groove type V-shaped insert clamping surface  41  fully extends from the front end surface  36  to the rear end surface  37 , whereas the ridge type V-shaped insert clamping surface  40  may extend longitudinally from a point rearward of the front end surface  36  to a point forward of the rear end surface  37 . That is, the groove type V-shaped clamping surface  41  and the ridge type V-shaped insert clamping surface  40  may have different longitudinal lengths (i.e., lengths taken along the longitudinal axis A 1 ), with the latter being shorter than the former. On the other hand, the groove type V-shaped insert clamping surface  41  and the ridge type V-shaped insert clamping surface  40  may have the same longitudinal lengths. The upper clamping portion  38  is comprised of a single ridge type V-shaped insert clamping surface  46 , as shown in  FIG. 9 , with two surface components  47 ,  48  forming an internal wedge angle α 3 , where α 3  is less than α 2 . 
         [0075]    Upper and lower peripheral edges  49 ,  50  are formed at the intersection of the upper and lower surfaces  33 ,  34  with the peripheral side surface  35 , where two cutting edges  51  are formed on the upper peripheral edge  49 . 
         [0076]    Also according to the first embodiment, the cutting insert  32  may have mirror symmetry about a major plane P 1 , passing through the upper and lower surfaces  33 ,  34  and the longitudinal axis A 1 , and in addition mirror symmetry about a minor plane P 2 , which is perpendicular to P 1 . 
         [0077]    It should be appreciated that throughout the detailed description and claims, the surface components of the V-shaped clamping surfaces are substantially planar, and use of the term; V-shaped clamping surface, is not restricted to a clamping surface with two surface planar components forming a ‘V’ shape and intersecting at a vertex point (when viewed in cross-section), but also accounts for a clamping surface with a curve or radius joining the two planar surface components, or a clamping surface with a secondary groove or ridge feature between the two planar surface components. 
         [0078]    It should also be appreciated that throughout the detailed description and claims, an “internal angle” refers to an angle between two surface components of a member surface as measured internal to the member, whereas an “external angle” refers to an angle between two surface components of a member surface as measured external to the member. 
         [0079]    As shown in  FIGS. 6 and 7 , the insert holder  31  comprises a holder head  52  having an insert receiving slot  53  opening out to a forward end  54  of the insert holder  31 , with upper and lower receiving slot surfaces  55 ,  56  sharing a common longitudinal direction from a front end  57  to a rear end  58  of the lower receiving slot surface  56 . Extending rearwards from the insert receiving slot  53  is a narrow spring slot  59  which divides the holder head  52  into an upper clamping jaw  60  and a lower base jaw  61 . 
         [0080]    According to the first embodiment of the present invention, a lower clamping portion  62  formed on the lower receiving slot surface  56  is comprised of two V-shaped slot clamping surfaces  63 ,  64 , the first a groove type V-shaped slot clamping surface  63  and the second a ridge type V-shaped slot clamping surface  64 . The two V-shaped slot clamping surfaces  63 ,  64  are positioned at separate contact sections  65 ,  66  along the longitudinal direction of the lower receiving slot surface  56 . A first contact section  65  is positioned adjacent the rear end  58 , where two surface components  67 ,  68  of the groove type V-shaped slot clamping surface  63 , as shown in  FIG. 10 , form an external wedge angle α 1 , and a second contact section  66  is positioned adjacent the front end  57 , where two surface components  69 ,  70  of the ridge type V-shaped slot clamping surface  64 , as shown in  FIG. 8 , form an obtuse internal wedge angle α 2 , where α 1  is less than α 2 . 
         [0081]    As shown in  FIG. 6 , a rear step  71  transverse to the longitudinal direction of the lower receiving slot surface  56  defines the physical boundary of the first contact section  65 , and a front step  72  transverse to the longitudinal direction of the lower receiving slot surface  56  defines the physical boundary of the second contact section  66 . 
         [0082]    A groove type guiding surface  73  forward of the rear step  71  and a ridge type guiding surface  74  rearward of the front step  72  on the lower receiving slot surface  56 , are not features of the lower clamping portion  62  of the insert holder  31 , and do not provide a means of clamping contact with the lower clamping portion  39  of the cutting insert  32 . 
         [0083]    An upper clamping portion  75  formed on the upper receiving slot surface  55  is comprised of a single groove type V-shaped slot clamping surface  76 , with two surface components  77 ,  78 , as shown in  FIG. 9 , forming an external wedge angle α 3 , where α 3  is less than α 2 . 
         [0084]    Also according to the first embodiment, a fastening screw  79  positioned within the through bore  80  of the upper clamping jaw  60  and rotatable in a threaded bore  81  of the lower base jaw  61 , maybe used to control the distance between the upper and lower receiving slot surfaces  55 ,  56 , in order to clamp or release the cuffing insert  32 . 
         [0085]    Assembly of the cutting insert  32  within the insert holder  31  of the first embodiment can be described in the following four stages:— 
         [0086]    The first stage requires confirmation that the distance between the upper and lower receiving slot surfaces  55 ,  56  is sufficient to accept the cutting insert  32 . This may require an operator to rotate the fastening screw  79  in an anti-clockwise direction to allow the spring effect of the spring slot  59  to release the upper clamping jaw  60 . 
         [0087]    The second stage of assembly requires the operator to interface the groove type V-shaped insert clamping surface  41  of the cutting insert  32  lower surface  34  with the ridge type V-shaped slot clamping surface  64  of the insert holder  31  lower receiving slot surface  56 . 
         [0088]    The third assembly stage requires the operator to slide the cutting insert  32  along the longitudinal direction of the lower receiving slot surface  56 , until an end abutment surface  82  of the cutting insert  32 , generally parallel to minor plane P 2 , abuts against a vertical abutment wall  83  of the insert holder  31 . 
         [0089]    The fourth assembly stage requires the operator to rotate the fastening screw  79  in a clockwise direction to overcome the spring effect of the spring slot  59 , and close the distance between the upper and lower receiving slot surfaces  55 ,  56  until the cutting insert  32  is firmly secured in the insert holder  31 . 
         [0090]    With the cutting insert  32  firmly secured in the insert holder  31 , clamping contact occurs between the cutting insert  32  and insert holder  31  as described below. 
         [0091]    The groove type V-shaped insert clamping surface  41  of the cutting insert  32  lower surface  34  is in clamping contact with the ridge type V-shaped slot clamping surface  64  at the second contact section  66  of the insert holder  31  lower receiving slot surface  56 , where as shown in  FIG. 8 , the surface components  44 ,  45  of the groove type V-shaped insert clamping surface  41  of the cutting insert  32  lower surface  34  are in respective abutment with the surface components  69 ,  70  of the ridge type V-shaped slot clamping surface  64  of the insert holder  31  lower receiving slot surface  56 , and the surface components  44 ,  45  and  69 ,  70  share a common obtuse wedge angle α 2 . Wedge angle α 2  has a typical range of 120°-150°. 
         [0092]    The ridge type V-shaped insert clamping surface  40  of the cutting insert  32  lower surface  34  is in clamping contact with the groove type V-shaped slot clamping surface  63  at the first contact section  65  of the insert holder  31  lower receiving slot surface  56 , where as shown in  FIG. 10 , the surface components  42 ,  43  of the ridge type V-shaped insert clamping surface  40  of the cutting insert  32  lower surface  34  are in respective abutment with the surface components  67 ,  68  of the groove type V-shaped slot clamping surface  63  of the insert holder  31  lower receiving slot surface  56 , and the surface components  42 ,  43  and  67 ,  68  share a common wedge angle α 1 , where α 1  is less than α 2 . Wedge angle α 1  has a typical range of 60°-120°. 
         [0093]    Clamping contact between the V-shaped clamping surface components  44 ,  45  and  69 ,  70  at the second contact section  66  of the insert holder  31  lower receiving slot surface  56  occurs at a greater distance from major plane P 1  of the cutting insert  32  than clamping contact between the V-shaped clamping surface components  42 ,  43  and  67 ,  68  at the first contact section  65  of the insert holder  31  lower receiving slot surface  56 . 
         [0094]    No clamping contact is made between the cutting insert  32  and insert holder  31 , as shown in  FIG. 9 , along the longitudinal direction of the insert holder  31  lower receiving slot surface  56 , between the rear step  71  of the first contact section  65  and the front step  72  of the second contact section  66 . 
         [0095]    The ridge type V-shaped insert clamping surface  46  of the cutting insert  32  upper surface  33  is in clamping contact with the groove type V-shaped slot clamping surface  76  of the insert holder  31  upper receiving slot surface  55 , where as shown in  FIG. 9 , the surface components  47 ,  48  of the ridge type V-shaped insert clamping surface  46  of the cutting insert  32  upper surface  33  are in respective abutment with the surface components  77 ,  78  of the groove type V-shaped slot clamping surface  76  of the insert holder  31  upper receiving slot surface  55 , and the surface components  47 ,  48  and  77 ,  78  share a common wedge angle α 3 , where α 3  is less than α 2 . Wedge angle α 3  has a typical range of 60°-120°. 
         [0096]    The second embodiment of the cutting tool  130 , as shown in  FIGS. 11 and 12 , comprises a cutting insert  132  and insert holder  131 . 
         [0097]    The cutting insert  132 , as shown in  FIGS. 13 and 14 , comprises upper and lower surfaces  133 ,  134 , and a peripheral side surface  135  extending between the upper and lower surfaces  133 ,  134 . The peripheral side surface  135  comprises front and rear end surfaces  136 ,  137  with a longitudinal axis A 1 ′ passing therebetween. Upper and lower clamping portions  138 ,  139  are formed on the upper and lower surfaces  133 ,  134  respectively. 
         [0098]    The lower clamping portion  139  is comprised of two groove type V-shaped insert clamping surfaces  140 ,  141 . The first groove type V-shaped insert clamping surface  140 , as shown in  FIG. 18 , has two surface components  142 ,  143  forming an external wedge angle α 1 , and the second groove type V-shaped insert clamping surface  141 , as shown in  FIG. 16 , has two surface components  144 ,  145  forming an obtuse external wedge angle α 2 , where α 1  is less than α 2 . A groove type guiding surface  184  adjacent the front end surface  136 , is not a feature of the lower clamping portion  139  of the cutting insert  132 , and does not provide a means of clamping contact with a lower clamping portion  162  of the insert holder  131 . 
         [0099]    The upper clamping portion  138  is comprised of a single groove type V-shaped insert clamping surface  146 , as shown in  FIG. 17 , with two surface components  147 ,  148  forming an external wedge angle α 3 , where α 3  is less than α 2 . 
         [0100]    Also according to the second embodiment, the cutting insert  132  may have mirror symmetry about a major plane P 1 ′, passing through the upper and lower surfaces  133 ,  134  and the longitudinal axis A 1 ′, and in addition rotational symmetry about a minor axis A 2 ′, which is perpendicular to the longitudinal axis A 1 ′ and passes through the peripheral side surface  135 . Upper and lower peripheral edges  149 ,  150  are formed at the intersection of the upper and lower surfaces  133 ,  134  with the peripheral side surface  135 , where a cutting edge  151  is formed on a portion of each of the upper and lower peripheral edges  149 ,  150 . 
         [0101]    As shown in  FIG. 15 , the insert holder  131  of the second embodiment, comprises a holder head  152  having an insert receiving slot  153  opening out to a forward end  154  of the insert holder  131 , with upper and lower receiving slot surfaces  155 ,  156  sharing a common longitudinal direction from a front end  157  to a rear end  158  of the lower receiving slot surface  156 . 
         [0102]    A lower clamping portion  162  is formed at a first and second contact section  165 ,  166  adjacent the rear and front ends  158 ,  157  of the lower receiving slot surface  156 , respectively. Each of the first and second contact sections  165 ,  166  is comprised of two ridge type V-shaped slot clamping surfaces  163 ,  164 . The first V-shaped slot clamping surface  163 , as shown in  FIG. 18 , has two surface components  167 ,  168  forming an internal wedge angle α 1 , and the second V-shaped slot clamping surface  164 , as shown in  FIG. 16 , has two surface components  169 ,  170  forming an obtuse internal wedge angle α 2 , where α 1  is less than α 2 . 
         [0103]    An upper clamping portion  175  formed on the upper receiving slot surface  155  is comprised of a single ridge type V-shaped slot clamping surface  176 , as shown in  FIG. 17 , with two surface components  177 ,  178  forming an internal wedge angle α 3 , where α 3  is equal to α 1 . 
         [0104]    With the cutting insert  132  firmly secured in the insert holder  131 , clamping contact occurs between the cutting insert  132  and insert holder  131  as described below. 
         [0105]    The second groove type V-shaped insert clamping surface  141  of the cutting insert  132  lower surface  134 , is in clamping contact with the second ridge type V-shaped slot clamping surface  164  at the second contact section  166  of the insert holder  131  lower receiving slot surface  156 , where as shown in  FIG. 16 , the surface components  144 ,  145  of the second groove type V-shaped insert clamping surface  141  of the cutting insert  132  lower surface  134  are in respective abutment with the surface components  169 ,  170  of the second ridge type V-shaped slot clamping surface  164  of the insert holder  131  lower receiving slot surface  156 , and the surface components  144 ,  145  and  169 ,  170  share a common obtuse wedge angle α 2 . 
         [0106]    The first groove type V-shaped insert clamping surface  140  of the cutting insert  132  lower surface  134 , is in clamping contact with the first ridge type V-shaped slot clamping surface  163  at the first contact section  165  of the insert holder  131  lower receiving slot surface  156 , where as shown in  FIG. 18 , the surface components  142 ,  143  of the first groove type V-shaped insert clamping surface  140  of the cutting insert  132  lower surface  134  are in respective abutment with the surface components  167 ,  168  of the first ridge type V-shaped slot clamping surface  163  of the insert holder  131  lower receiving slot surface  156 , and the surface components  142 ,  143  and  167 ,  168  share a common wedge angle α 1 , where α 1  is less than α 2 . 
         [0107]    Clamping contact between the V-shaped clamping surface components  144 ,  145  and  169 ,  170  at the second contact section  166  of the insert holder  131  lower receiving slot surface  156  occurs at a greater distance from major plane P 1 ′ of the cutting insert  132  than clamping contact between the V-shaped clamping surface components  142 ,  143  and  167 ,  168  at the first contact section  165  of the insert holder  131  lower receiving slot surface  156 . 
         [0108]    No clamping contact is made between the cutting insert  132  and insert holder  131 , as shown in  FIG. 17 , along the longitudinal direction of the insert holder  131  lower receiving slot surface  156  between the first and second contact section  165 ,  166 . 
         [0109]    The groove type V-shaped insert clamping surface  146  of the cutting insert  132  upper surface  133  is in clamping contact with the ridge type V-shaped slot clamping surface  176  of the insert holder  131  upper receiving slot surface  155 , where as shown in  FIG. 17 , the surface components  147 ,  148  of the groove type V-shaped insert clamping surface  146  of the cutting insert  132  upper surface  133  are in respective abutment with the surface components  177 ,  178  of the ridge type V-shaped slot clamping surface  176  of the insert holder  131  upper receiving slot surface  155 , and the surface components  147 ,  148  and  177 ,  178  share a common wedge angle α 3 , where α 3  is less than α 2 . 
         [0110]    The third embodiment of the cutting tool  230 , as shown in  FIGS. 19 and 20 , comprises a cutting insert  232  and insert holder  231 . 
         [0111]    The cutting insert  232 , as shown in  FIGS. 21 and 22 , comprises upper and lower surfaces  233 ,  234 , and a peripheral side surface  235  extending between the upper and lower surfaces  233 ,  234 . The peripheral side surface  235  comprises front and rear end surfaces  236 ,  237  with a longitudinal axis A 1 ″ passing therebetween. Upper and lower clamping portions  238 ,  239  are formed on the upper and lower surfaces  233 ,  234 , respectively. 
         [0112]    The lower clamping portion  239  is comprised of two groove type V-shaped insert clamping surfaces  240 ,  241 . The first groove type V-shaped insert clamping surface  240 , as shown in  FIG. 26 , has two surface components  242 ,  243  forming an external wedge angle α 1 , and the second groove type V-shaped insert clamping surface  241 , as shown in  FIG. 24 , has two surface components  244 ,  245  forming an external wedge angle α 2 , where α 1  is less than α 2 . An upper clamping portion  238  formed on the upper surface  233 , is comprised of a single groove type V-shaped insert clamping surface  246 , as shown in  FIG. 25 , with two surface components  247 ,  248  forming an external wedge angle α 3 , where α 3  is less than α 2 . 
         [0113]    Also according to the third embodiment, the cutting insert  232  may have mirror symmetry about a major plane P 1 ″, passing through the upper and lower surfaces  233 ,  234  and the longitudinal axis A 1 ″. Upper and lower peripheral edges  249 ,  250  are formed at the intersection of the upper and lower surfaces  233 ,  234 , respectively, with the peripheral side surface  235 , and a cutting edge  251  is formed along a portion of the upper peripheral edge  249 . 
         [0114]    As shown in  FIG. 23 , the insert holder  231  of the third embodiment comprises a holder head  252  having an insert receiving slot  253  opening out to a forward end  254  of the insert holder  231 , with upper and lower receiving slot surfaces  255 ,  256  sharing a common longitudinal direction from a front end  257  to a rear end  258  of the lower receiving slot surface  256 . 
         [0115]    A lower clamping portion  262  formed on the lower receiving slot surface  256 , is comprised of two ridge type V-shaped slot clamping surfaces  263 ,  264  positioned at separate contact sections  265 ,  266  along the longitudinal direction of the lower receiving slot surface  256 . A first contact section  265  is positioned adjacent the rear end  258 , where two surface components  267 ,  268  of the first ridge type V-shaped slot clamping surface  263 , as shown in  FIG. 26 , form an internal wedge angle α 1 , and a second contact section  266  is positioned adjacent the front end  257 , where two surface components  269 ,  270  of the second ridge type V-shaped slot clamping surface  264 , as shown in  FIG. 24 , form an obtuse internal wedge angle α 2 , where al is less than α 2 . 
         [0116]    An upper clamping portion  275  formed on the upper receiving slot surface  255  is comprised of a single ridge type V-shaped slot clamping surface  276 , with two surface components  277 ,  278 , as shown in  FIG. 25 , forming an internal wedge angle α 3 , where α 3  is less than α 2 . 
         [0117]    With the cutting insert  232  firmly secured in the insert holder  231 , clamping contact occurs between the cutting insert  232  and insert holder  231  as described below. 
         [0118]    The second groove type V-shaped insert clamping surface  241  of the cutting insert  232  lower surface  234  is in clamping contact with the second ridge type V-shaped slot clamping surface  264  at the second contact section  266  of the insert holder  231  lower receiving slot surface  256 , where as shown in  FIG. 24 , the surface components  244 ,  245  of the second groove type V-shaped insert clamping surface  241  of the cutting insert  232  lower surface  234  are in respective abutment with the surface components  269 ,  270  of the second ridge type V-shaped slot clamping surface  264  of the insert holder  231  lower receiving slot surface  256 , and the surface components  244 ,  245  and  269 ,  270  share a common obtuse wedge angle α 2 . 
         [0119]    The first groove type V-shaped insert clamping surface  240  of the cutting insert  232  lower surface  234  is in clamping contact with the first ridge type V-shaped slot clamping surface  263  at the first contact section  265  of the insert holder  231  lower receiving slot surface  256 , where as shown in  FIG. 26 , the surface components  242 ,  243  of the first groove type V-shaped insert clamping surface  240  of the cutting insert  232  lower surface  234  are in respective abutment with the surface components  267 ,  268  of the first ridge type V-shaped slot clamping surface  263  of the insert holder  231  lower receiving slot surface  256 , and the surface components  242 ,  243  and  267 ,  268  share a common wedge angle α 1 , where α 1  is less than α 2 . 
         [0120]    The groove type V-shaped insert clamping surface  246  of the cutting insert  232  upper surface  233  is in clamping contact with the ridge type V-shaped slot clamping surface  276  of the insert holder  231  upper receiving slot surface  255 , where as shown in  FIG. 25 , the surface components  247 ,  248  of the groove type V-shaped insert clamping surface  246  of the cutting insert  232  upper surface  233  are in respective abutment with the surface components  277 ,  278  of the ridge type V-shaped slot clamping surface  276  of the insert holder  231  upper receiving slot surface  255 , and the surface components  247 ,  248  and  277 ,  278  share a common wedge angle α 3 , where α 3  is less than α 2 . 
         [0121]    In accordance with some embodiments, the three wedge angles α 1 , α 2 , and α 3  formed between the surface components  42 ,  43 ,  142 ,  143 ,  242 ,  243 ;  44 ,  45 ,  144 ,  145 ,  244 ,  245 ;  47 ,  48 ,  147 ,  148 ,  247 ,  248  of the V-shaped clamping surfaces  40 ,  140 ,  240 ;  41 ,  141 ,  241 ;  46 ,  146 ,  246  of the cutting inserts  32 ,  132 ,  232  have values higher or lower than the matching wedge angle on the insert holder  31 ,  131 ,  231  by approximately 1°, in order to control the location of resultant clamping contact regions between the cutting insert  32 ,  132 ,  232  and the insert holder  31 ,  131 ,  231  following assembly, and therefore reduce the risk of excessive stress concentrations during operation, and use of the expression “common wedge angle” means wedge angles common to within the approximate 1°. 
         [0122]    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.