Abstract:
A cutting insert holder has a lower clamping jaw resiliently connected to an upper clamping jaw. The upper clamping jaw is provided with two elongated spaced apart parallel grooves. The cutting insert is retained in the cutting insert holder by means of a screw which passes through a through bore in the upper jaw of the insert holder, through a through bore in the cutting insert and is threadingly engaged into a threaded bore in the lower clamping jaw. The two elongated ridges in the upper surface of the cutting insert cooperate with the two elongated parallel grooves in the lower surface of the upper clamping jaw.

Description:
RELATED APPLICATIONS  
       [0001]    This is a Continuation of the National Stage Designation of PCT/IL00/00093, filed Feb. 20, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to a cutting tool and more particularly to a ball nose end mill, and an arrangement for retaining a replaceable cutting insert therein, especially an indexable cutting insert.  
         BACKGROUND OF THE INVENTION  
         [0003]    In conventional ball nose end mills cutting inserts are clamped in position by a retaining screw. A problem with this arrangement is that the accuracy of the initial location of the cutting edge of a cutting insert retained in the end mill is dependent on the accuracy with which the retaining screw is located in the end mill. Any play or clearance between the screw and the cutting insert results in a corresponding inaccuracy in the location of the cutting edge of the cutting insert.  
           [0004]    A solution to this problem is proposed in U.S. Pat. No. 4,883,391, in accordance with which a clamping screw is provided with a cylindrical portion which is held in engagement with a cylindrical bore portion in the end mill. However, this solution calls for both a very accurately manufactured cylindrical portion on the screw and a correspondingly very accurately manufactured cylindrical bore portion in the end mill. Both of these requirements increase the cost of manufacture of the end mill as a whole. Furthermore, any inaccuracies introduced into these two cylindrical elements during use of the end mill, will introduce a corresponding inaccuracy in the location of the cutting edge of the cutting insert.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with the present invention there is provided a cutting tool assembly comprising cutting insert holder and a cutting insert, the cutting insert holder comprising a clamping portion, at a front portion thereof, connected to a body portion;  
           [0006]    the clamping portion comprising:  
           [0007]    a lower clamping jaw having a lower peripheral surface and an upper surface;  
           [0008]    an upper clamping jaw resiliently connected to the lower clamping jaw, the upper clamping jaw having a lower surface and an upper peripheral surface, the lower surface being provided with two elongated spaced apart substantially parallel grooves;  
           [0009]    a through bore passing through the upper and lower clamping jaws, the through bore being internally threaded in one of the upper or lower clamping jaws; and  
           [0010]    an insert receiving slot defined between the upper and lower clamping jaws;  
           [0011]    the cutting insert comprising:  
           [0012]    an upper surface provided with two elongated spaced apart substantially parallel ridges;  
           [0013]    a lower surface;  
           [0014]    a peripheral side surface between the upper surface and the lower surface, the peripheral side surface being provided with at least one cutting edge;  
           [0015]    a rake surface associated with the at least one cutting edge; and  
           [0016]    a through bore passing through the cutting insert, from the upper surface to the lower surface;  
           [0017]    wherein the cutting insert is retained in the insert receiving slot in a retained position by means of a screw which passes through the through bore in the upper and lower jaws of the insert holder and through the through bore in the cutting insert, and wherein in the retained position at least a portion of the lower surface of the cutting insert abuts at least a portion of the upper surface of the lower clamping jaw and the two elongated ridges in the upper surface of the cutting insert cooperate with the two elongated parallel grooves in the lower surface of the upper clamping jaw.  
           [0018]    In accordance with a preferred embodiment of the present invention, the cutting insert is provided with at least one elongated recess in the lower surface of the cutting insert in a portion of the peripheral side surface, and the upper surface of the lower clamping jaw is provided with an insert location surface and at least a portion of a substantially upright surface of the at least one elongated recess in the lower surface of the cutting insert abuts the insert location surface in the upper surface of the lower clamping jaw.  
           [0019]    Also in accordance with the present invention there is provided a cutting insert comprising:  
           [0020]    an upper surface provided with two elongated spaced apart substantially parallel ridges;  
           [0021]    a lower surface;  
           [0022]    a side peripheral surface between the upper surface and the lower surface, the peripheral surface being provided with at least one cutting edge;  
           [0023]    a rake surface associated with the at least one cutting edge; and  
           [0024]    a through bore passing through the cutting insert, from the upper surface to the lower surface.  
           [0025]    Also in accordance with a preferred embodiment, the lower surface of the cutting insert is provided with at least one elongated recess in a portion of the peripheral side surface.  
           [0026]    In accordance with a preferred embodiment of the present invention, the two elongated grooves in the lower surface of the upper clamping jaw are located adjacent to and on either side of the through bore in the upper clamping jaw.  
           [0027]    Further in accordance with a preferred embodiment of the present invention, the two elongated ridges in the upper surface of the cutting insert are located adjacent to and on either side of the through bore in the cutting insert  
           [0028]    Still further in accordance with a preferred embodiment of the present invention, each of the two elongated ridges in the upper surface of the cutting insert have an indentation in a portion thereof.  
           [0029]    Yet still further in accordance with a preferred embodiment of the present invention, the indentation is in a region adjacent the through bore in the cutting insert.  
           [0030]    In accordance with one specific application, the cutting insert is generally oval in shape in a top view and is provided with two diametrically opposite sets of cutting edges. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]    For a better understanding the invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
         [0032]    [0032]FIG. 1 is a perspective view of a cutting tool assembly according to the present invention;  
         [0033]    [0033]FIG. 2 is a perspective view of the front portion of the cutting tool assembly of FIG. 1;  
         [0034]    [0034]FIG. 3 is an exploded view of the cutting tool assembly of FIG. 2;  
         [0035]    [0035]FIG. 4 is a perspective view of the cutting insert holder according to the present invention;  
         [0036]    [0036]FIG. 5 is a bottom perspective view of the cutting insert holder of FIG. 4 with the lower clamping jaw removed for clarification purposes;  
         [0037]    [0037]FIG. 6 is a top perspective view of the cutting insert holder of FIG. 4 with the upper clamping jaw removed for clarification purposes;  
         [0038]    [0038]FIG. 7 is a top perspective view of the cutting insert according to the present invention;  
         [0039]    [0039]FIG. 8 is a bottom perspective view of the cutting insert according to the present invention;  
         [0040]    [0040]FIG. 9 is a top view of the cutting insert according to the present invention;  
         [0041]    [0041]FIG. 10 is a bottom view of the cutting insert according to the present invention;  
         [0042]    [0042]FIG. 11 is a side view of the cutting tool assembly of FIG. 2;  
         [0043]    [0043]FIG. 12 is a view of the cutting tool assembly of FIG. 2 in a direction along a line parallel to and passing between the grooves in the upper clamping jaw;  
         [0044]    [0044]FIG. 13 is an enlarged cross sectional view of the cutting tool assembly of FIG. 2 taken in a plane passing through and perpendicular to the ridges in the upper surface of the cutting insert, showing the relative position between the cutting insert and the clamping portion prior to tightening the screw, which is not shown for the sake of clarification;  
         [0045]    [0045]FIG. 14 is a cross sectional view of the cutting tool assembly as in FIG. 13 but showing the situation in the first stage of tightening the screw;  
         [0046]    [0046]FIG. 15 is an enlarged detail of the circled portion in FIG. 14; and  
         [0047]    [0047]FIG. 16 is a cross sectional view of the cutting tool assembly as in FIG. 13 but showing the situation in the final stage of tightening the screw. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0048]    Attention is first drawn to FIGS.  1  to  6 . As shown, a cutting tool assembly  10  having an axis of rotation A comprises a cutting insert holder  12  and a cutting insert  14  mounted therein and secured by a screw  15 . The cutting insert holder  12  comprises an elongated cylindrical body portion  16  and a clamping portion  18  in a front portion  20  thereof. The clamping portion  18  consists of an upper clamping jaw  22  separated from a lower clamping jaw  24  by an insert receiving slot  26 . The upper clamping jaw  22  has an upper peripheral surface  27 , having a chip evacuation recess  21  in a front portion thereof, a lower surface  23  and a substantially radially directed through bore  28 . The lower clamping jaw  24  has a lower peripheral surface  29 , having a chip evacuation recess  25  in a front portion thereof, an upper surface  30  and a substantially radially directed threaded bore  31  which is aligned with the through bore  28  in the upper clamping jaw. The upper surface  30  has a base abutment surface  32  constituting a clamping region and a rear abutment surface  34 , constituting an insert location surface, that is slanted with respect to the longitudinal axis A and directed substantially perpendicular to the base abutment surface  32 . Shown in the figure is a channel  35  that separates the rear abutment surface  34  from the base abutment surface  32 . It should be noted that the channel  35  is created during the manufacturing process and is not an essential feature of the lower clamping jaw  24 . At the rear of the insert receiving slot  26  is a flexibilizing bore  36  which is transversely directed to the longitudinal axis A and merges with the upper clamping jaw  22  and the lower clamping jaw  24  creating a resilient connection between the two jaws.  
         [0049]    The lower surface  23  of the upper clamping jaw  22  has a semi cylindrical groove  40 , which, when viewed from the top of the cutting insert holder  12 , is directed preferably perpendicular to the rear abutment surface  34 , and an open sided groove  42  which is parallel to the groove  40 . The upper surface  43  of the groove  42  constitutes a top front abutment surface.  
         [0050]    Attention is now drawn to FIGS.  7  to  11 . The cutting insert  14  has a flat disc like body with an axis of rotational symmetry B, an upper surface  46 , a lower surface  48  and a peripheral side surface  50  connecting between the upper surface  46  and the lower surface  48 . A through bore  51  aligned with the axis B passes through the cutting insert  14 .  
         [0051]    The peripheral side surface  50  has two identical sets of cutting edges. Each set of cutting edges consists of an upper cutting edge  52  and a lower cutting edge  54 . The upper cutting edge  52  meets with the lower cutting edge  54  at apex  56 . The upper cutting edge  52  has a rake surface  58  and a relief surface  60 . The lower cutting edge  54  has a rake surface  62  and a relief surface  64 . In the region between the two apexes  56 , on diametrically opposite sides of the peripheral side surfaces  50 , the relief surface  60  of each set of cutting edges merges with the relief surface  64  of the other set of cutting edges at merging regions  65  (see FIG. 11).  
         [0052]    The lower surface  48  of the cutting insert has a bottom abutment surface  66  and two identical symmetrically disposed rear abutment surfaces  68  directed substantially perpendicular to the bottom abutment surface  66 . On each side of the lower surface  48  of the cutting insert, the rake surface  62  together with rear abutment surface  68  form an elongated recess in a portion of the peripheral side surface.  
         [0053]    The upper surface  46  of the cutting insert has two identical elongated parallelly extending ridges  70  and  72 . The ridges  70  and  72  are directed substantially perpendicular to the rear abutment surfaces  68  when viewing the cutting insert  14  from the top. The ridge  70  is identical to the ridge  72  and therefore only one ridge will be described. The ridge  70  extends between the two relief surfaces  64  and has a flat top surface  74 . The ridge  70  has an indentation  76  substantially in the middle thereof. The ridge  70  also has an inner side surface  78  and outer side surface  80 , both of which are curved.  
         [0054]    The assembly of the cutting tool assembly  10  will now be described, primarily with reference to FIGS.  13  to  16 . The cutting insert  14  is inserted into the insert receiving slot  26  such that the upper surface  46  of the cutting insert  14  is facing towards the lower surface  23  of the upper clamping jaw  22 , the ridge  70  is introduced into and parallel to the groove  40 , and the ridge  72  is introduced into and parallel to the groove  42 . In this position the cutting insert  14  is slid into the insert receiving slot  26  till a rear abutment surface  68  of the cutting insert abuts against the rear abutment surface  34  of the upper surface  30  of the lower clamping jaw  24 . Now, the screw  15  (not shown in FIGS.  13  to  16 ) is inserted into the through bore  28  of the upper clamping jaw  22 , through the through bore  51  of the cutting insert  14 , and threadingly engaged into the threaded bore  31  of the lower clamping jaw  24 .  
         [0055]    The tightening of the screw  15  can conveniently be considered as a two stage process in the clamping of the insert. FIG. 13 shows the relative position between the cutting insert  14  and the clamping portion  18  prior to tightening of the screw  15 . In the first stage of tightening, as shown in FIG. 14, the upper clamping jaw  22  and the lower clamping jaw  24  approach each other. At this stage the ridge  70  abuts the inner surface of the groove  40 . Due to the difference in the cross sectional shape between the ridge  70  and the groove  40  a clearance  82  is formed between the upper region  84  of the groove  40  and the top surface  74  of the ridge  70 . Due to this clearance the ridge  70  abuts the groove  40  along front abutment region  86  and rear abutment region  88 . The front abutment region  86  coincides generally with a line along the inner side surface  78  and the rear abutment region  88  coincides generally with a line along the outer side surface  80 . Because of the indentation  76  in the ridge  70  the front and rear abutment regions are both divided into two portions. In the second and final stage of the tightening of the screw (as shown in FIG. 16) the upper surface  43  of the groove  42  abuts the flat top surface  74  of the ridge  72 .  
         [0056]    As a result, the cutting insert  14  is retained in a firm and precise manner in the insert holder with the ridge  70  wedged into the groove  40 , the ridge  72  clamped by the upper surface  43  of the groove  42  and the rear abutment surface  68  of the insert abutting against the rear abutment surface  34  of the upper surface  30  of the lower clamping jaw  24 .  
         [0057]    Although the present invention has been described to a certain degree of particularity, it should be understood that various alterations and modifications can be made without departing from the spirit or scope of the invention as hereinafter claimed.