Patent Publication Number: US-2023150036-A1

Title: Cutting head having four cutting portions and two convex clamping surfaces, and rotary cutting tool

Description:
FIELD OF THE INVENTION 
     The present invention relates to a rotary cutting tool and a cutting head having four cutting portions releasably secured to a tool shank associated therewith, for use in metal cutting processes in general, and for drilling operations in particular. 
     BACKGROUND OF THE INVENTION 
     Within the field of cutting tools used in drilling operations, there are some examples of cutting heads having more than two cutting portions releasably secured to a tool shank associated therewith. 
     U.S. Pat. No. 10,173,271 discloses a tool shank having a head receiving pocket at a forward end, and a plurality of chip flutes extending rearwardly therefrom along a longitudinal axis. The head receiving pocket has a support surface transverse to the longitudinal axis. A central recess is formed in the support surface and extends rearwardly therefrom. The central recess has a plurality of resiliently displaceable abutment portions circumferentially alternating with and spaced apart by a plurality of intermediate portions. Each abutment portion has a radially inward facing abutment surface, and each intermediate portion has an intermediate surface intersecting two circumferentially adjacent abutment surfaces. A rotary cutting tool includes the shank and a cutting head releasably mounted thereto. The cutting head has a mounting portion provided with a base surface and an engagement member protruding therefrom. In an assembled position, the engagement member is resiliently retained in the central recess against the plurality of abutment surfaces. 
     U.S. Pat. No. 11,110,521 discloses a cutting head rotatable about a first axis, having a cap portion and a rigid mounting protuberance joined thereto. The cap portion has a plurality of cutting portions circumferentially alternating with a plurality of head chip flutes, and a head base surface facing in an axial rearward direction. The mounting protuberance exhibits rotational symmetry about the first axis, extends axially rearwardly from the head base surface, and has a plurality of circumferentially spaced apart convex clamping surfaces. The plurality of cutting portions define a cutting diameter, the plurality of head chip flutes are inscribed by an imaginary first circle having a first diameter, and the plurality of clamping surfaces are circumscribed by an imaginary second circle having a second diameter. The first diameter is greater than the second diameter, and the second diameter is less than forty percent of the cutting diameter. 
     It is an object of the present invention to provide an improved cutting head having four cutting portions. 
     It is also an object of the present invention to provide an improved cutting head having good stability when releasably secured to a tool shank. 
     It is a further object of the present invention to provide an improved tool shank having an extended useful life. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a cutting head rotatable about a head axis in a first direction of rotation, the head axis establishing an axial forward direction and an axial rearward direction opposite the axial forward direction, the cutting head comprising: 
     a cap portion having exactly four cutting portions circumferentially alternating with four head flutes, and a head base surface facing in the axial rearward direction,
         each cutting portion having a front surface facing in the axial forward direction and intersecting a circumferentially adjacent and rotationally forward head flute with respect to the first direction of rotation to form a radially extending cutting edge, and       

     a rigid mounting protuberance extending axially rearwardly from the head base surface and having exactly two circumferentially spaced apart convex clamping surfaces, 
     wherein: 
     in a cross-section taken in a first horizontal plane perpendicular to the head axis and intersecting the mounting protuberance at the two clamping surfaces, only the two clamping surfaces are circumscribed by an imaginary first circle having a first diameter and a center coincident with the head axis. 
     Also, in accordance with the present invention, there is provided a rotary cutting tool comprising: 
     an elongated tool shank having a head receiving pocket at a forward end thereof and four shank flutes extending away from the forward end along a shank axis, and 
     a cutting head of the type described above releasably secured to the head receiving pocket. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG.  1    is a perspective view of a cutting head in accordance with some embodiments of the present invention; 
         FIG.  2    is a side view of the cutting head shown in  FIG.  1   ; 
         FIG.  3    is a top view of the cutting head shown in  FIG.  1   ; 
         FIG.  4    is a cross-sectional view of the cutting head shown in  FIG.  2   , taken along the line IV-IV; 
         FIG.  5    is a cross-sectional view of the cutting head shown in  FIG.  2   , taken along the line V-V; 
         FIG.  6    is a cross-sectional view of the cutting head shown in  FIG.  2   , taken along the line VI-VI; 
         FIG.  7    is a cross-sectional view of the cutting head shown in  FIG.  3   , taken along the line VII-VII; 
         FIG.  8    is an exploded perspective view of a rotary cutting tool in accordance with some embodiments of the present invention; 
         FIG.  9    is an end view of a tool shank in accordance with some embodiments of the present invention; 
         FIG.  10    is a side view of the tool shank shown in  FIG.  9   ; 
         FIG.  11    is a cross-sectional view of the tool shank shown in  FIG.  10   , taken along the line XI-XI; 
         FIG.  12    is a side view of the rotary cutting tool shown in  FIG.  8   , in a state of clamped assembly; 
         FIG.  13    is a cross-sectional view of the rotary cutting tool shown in  FIG.  12   , taken along the line XIII-XIII; 
         FIG.  14    is a side view of the rotary cutting tool shown in  FIG.  8   , in a state of unclamped assembly; and 
         FIG.  15    is a cross-sectional view of the rotary cutting tool shown in  FIG.  14   , taken along the line XV-XV. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first aspect of the present invention relates to a cutting head  20  rotatable about a head axis AH in a first direction of rotation R 1 , the head axis AH establishing an axial forward direction DF and an axial rearward direction DR opposite to the axial forward direction DF. 
     In some embodiments of the present invention, the cutting head  20  may preferably be manufactured by form pressing and sintering a cemented carbide, such as tungsten carbide, and may be coated or uncoated. 
     As shown in  FIGS.  1  to  3   , the cutting head  20  comprises a cap portion  22  and a rigid mounting protuberance  24  joined to the cap portion  22 . 
     It should be appreciated that the cutting head  20  may be of unitary one-piece construction, and the mounting protuberance  24  may have the same rigidity as the cap portion  22  and be devoid of resiliently displaceable elements. 
     As seen below, the cap portion  22  has a first plurality of cutting portions  26 , being exactly twice the number of a second plurality of convex clamping surfaces  38  provided on the mounting protuberance  24 . 
     As shown in  FIGS.  1  to  3   , the cap portion  22  has exactly four cutting portions  26  circumferentially alternating with four head flutes  28 , and a head base surface  30  facing in the axial rearward direction DR. 
     Also, as shown in  FIGS.  1  to  3   , each cutting portion  26  has a front surface  32  facing in the axial forward direction DF, and each front surface  32  intersects a circumferentially adjacent and rotationally forward head flute  28  with respect to the first direction of rotation R 1  to form a radially extending cutting edge  34 . 
     In some embodiments of the present invention, the four cutting edges  34  may be identical. 
     Also, in some embodiments of the present invention, the four cutting edges  34  may be circumferentially equi-spaced about the head axis AH. 
     Further, in some embodiments of the present invention, apart from a pair of key slots  36  formed in two diametrically opposed cutting portions  26 , the cap portion  22  may exhibit 4-fold rotational symmetry about the head axis AH. 
     As shown in  FIG.  3   , the four cutting edges  34  may define a cutting diameter DC corresponding to an imaginary cutting circle CC. 
     It should be appreciated throughout the description and claims, that the four radially outermost points of the four cutting edges  34  define the cutting diameter DC and lie on the imaginary cutting circle CC. 
     In some embodiments of the present invention, the cutting head  20  may be used for drilling operations. 
     As shown in  FIGS.  1  to  3   , the rigid mounting protuberance  24  extends axially rearwardly from the head base surface  30  and has exactly two circumferentially spaced apart convex clamping surfaces  38 . 
     In some embodiments of the present invention, a first vertical plane PV 1  containing the head axis AH may intersect the two clamping surfaces  38 , and the two clamping surfaces  38  may be described as a pair of diametrically opposed clamping surfaces  38 . 
     Also, in some embodiments of the present invention, the two clamping surfaces  38  may be partially cylindrically shaped, and in a cross-section taken in the first vertical plane PV 1 , as shown in  FIG.  4   , the two clamping surfaces  38  may extend parallel to the head axis AH. 
     In other embodiments of the present invention (not shown), the two clamping surfaces  38  may be partially conically shaped, and in a cross-section taken in a vertical plane containing the head axis AH and intersecting the two clamping surfaces  38 , the two clamping surfaces  38  may diverge away from the head axis AH in the axial rearward direction DR. In other words, in the rearward direction of the mounting protuberance  24 , there is an increase in diameter size of an imaginary circle circumscribing the two clamping surface  38 . 
     As shown in  FIGS.  1  and  2   , the mounting protuberance  24  may have at least two circumferentially spaced apart axial stopper portions  39  located axially rearward of the two clamping surfaces  38 . 
     In some embodiments of the present invention, the first vertical plane PV 1  may intersect two of the at least two circumferentially spaced apart axial stopper portions  39 , and in the cross-section taken in the first vertical plane PV 1 , as shown in  FIG.  4   , the said two axial stopper portions  39  may extend radially beyond the two clamping surfaces  38 . 
     In some embodiments of the present invention, each axial stopper portion  39  may have a stopper surface  41  facing in the axial forward direction DF. 
     Also, in some embodiments of the present invention, the mounting protuberance  24  may have four axial stopper portions  39  circumferentially equi-spaced about the head axis AH forming a bulge  43  at the distal end thereof. 
     As shown in  FIG.  5   , in a cross-section taken in a first horizontal plane PH 1  perpendicular to the head axis AH and intersecting the mounting protuberance  24  at the two clamping surfaces  38 , according to the first aspect of the present invention, only the two clamping surfaces  38  are circumscribed by an imaginary first circle C 1  having a first diameter D 1  and a center coincident with the head axis AH. 
     Reverting to  FIG.  4    and with reference to  FIG.  5   , each of the four axial stopper portions  39  extends radially outward of an axial projection of the first imaginary circle C 1 . In other words, an imaginary circle perpendicular to the head axis AH and having a center coincident therewith, and circumscribing the four axial stopper portions  39 , would have a diameter greater than the first diameter D 1 . 
     In some embodiments of the present invention, in the cross-section taken in the first horizontal plane PH 1 , no portion of the mounting protuberance  24  may be located outside the imaginary first circle C 1 , and it should be appreciated throughout the description and claims, that the imaginary first circle C 1  circumscribes the entire mounting protuberance  24  at only the two clamping surfaces  38 . 
     Also, in some embodiments of the present invention, in the cross-section taken in the first horizontal plane PH 1 , the two clamping surfaces  38  may form two clamping arcs  40  coincident with the imaginary first circle C 1 . 
     Further, in some embodiments of the present invention, the first vertical plane PV 1  may bisect the two clamping arcs  40  at midpoints thereof. 
     Yet further, in some embodiments of the present invention, the first vertical plane PV 1  may bisect the two clamping surfaces  38 . 
     As shown in  FIG.  5   , the first diameter D 1  may be less than forty percent of the cutting diameter DC, i.e., D 1 &lt;0.40*DC. 
     As shown in  FIG.  6   , in a cross-section taken in a second horizontal plane PH 2  perpendicular to the head axis AH and intersecting the cap portion  22 , the four head flutes  28  are inscribed by an imaginary second circle C 2  having a second diameter D 2  and a center coincident with the head axis AH, the imaginary second circle C 2  passing through four radially innermost head flute points NH, each head flute point NH associated with a corresponding one of the four head flutes  28 . 
     In some embodiments of the present invention, the second diameter D 2  may be greater than the first diameter D 1 , i.e., D 2 &gt;D 1 . 
     As shown in  FIGS.  1  to  3   , the rigid mounting protuberance  24  may have two circumferentially spaced apart convex guide surfaces  42 , and the two guide surfaces  42  may circumferentially alternate with the two clamping surfaces  38 . 
     As shown in  FIG.  5   , in the cross-section taken in the first horizontal plane PH 1 , the two guide surfaces  42  may be located inside the imaginary first circle C 1 . 
     Also as shown in  FIG.  5   , in the cross-section taken in the first horizontal plane PH 1 , the two guide surfaces  42  may be circumscribed by an imaginary third circle C 3  having a third diameter D 3  and a center coincident with the head axis AH, and the third diameter D 3  may be less than the first diameter D 1 , but greater than eighty-five percent of the first diameter D 1 , i.e., D 1 &gt;D 3 &gt;0.85*D 1 . 
     It should be appreciated throughout the description and claims, that although the imaginary third circle C 3  circumscribes the two guide surfaces  42  in the cross-section taken in the first horizontal plane PH 1 , the imaginary third circle C 3  does not circumscribe the entire mounting protuberance  24 , especially the two clamping surfaces  38 . 
     As shown in  FIG.  5   , in the cross-section taken in the first horizontal plane PH 1 , the two guide surfaces  42  may form two guide arcs  37  coincident with the imaginary third circle C 3 . 
     In some embodiments of the present invention, a second vertical plane PV 2  containing the head axis AH may intersect the two guide surfaces  42 , and the two guide surfaces  42  may be described as a pair of diametrically opposed guide surfaces  42 . 
     Also, in some embodiments of the present invention, the second vertical plane PV 2  may bisect the two guide arcs  37  at midpoints thereof. 
     Further, in some embodiments of the present invention, the second vertical plane PV 2  may bisect the two guide surfaces  42 . 
     As shown in  FIG.  5   , the first and second vertical planes PV 1 , PV 2  may be mutually perpendicular. 
     In some embodiments of the present invention, the mounting protuberance  24  may exhibit 2-fold rotational symmetry about the head axis AH. 
     As shown in  FIGS.  1 ,  2  and  5   , the rigid mounting protuberance  24  may have four transitional surfaces  45  circumferentially spaced apart by the two clamping surfaces  38  and the two guide surfaces  42 . 
     In some embodiments of the present invention, each transitional surface  45  may be planar. 
     Also, in some embodiments of the present invention, each transitional surface  45  may be parallel to the head axis AH. 
     As shown in  FIGS.  1  and  2   , a rake surface  44  is disposed on each head flute  28  adjacent its associated cutting edge  34 . 
     As shown in  FIG.  7   , in a cross-section taken in a third vertical plane PV 3  parallel to the head axis AH and transverse to one of the cutting edges  34  along at least a radially outer portion thereof, the rake surface  44  may be inclined at a positive rake angle α 1 . 
     It should be appreciated throughout the description and claims, that the term “positive rake angle” refers to an acute external angle formed between the rake surface  44  and an imaginary reference line parallel to the head axis AH and intersecting the associated cutting edge  34 . 
     In some embodiments of the present invention, the rake angle α 1  may be greater than seven degrees, i.e., α 1 &gt;7°. 
     As shown in  FIGS.  1  and  5   , the head base surface  30  includes a central base region  46  and four radially outer base regions  48 , and each head flute  28  intersects one of the four radially outer base regions  48  to form a radially outer base edge  50 . 
     As shown in  FIG.  5   , the central base region  46  may entirely surround the mounting protuberance  24 . 
     In some embodiments of the present invention, the four radially outer base regions  48  and the central base region  46  may be coplanar. 
     As shown in  FIG.  5   , the third vertical plane PV 3  intersects one of the radially outer base edges  50 . 
     In some embodiments of the present invention, as shown in  FIGS.  1  and  5   , a joining surface  52  may be disposed on each head flute  28  adjacent its associated radially outer base edge  50 . 
     As shown in  FIG.  7   , in the cross-section taken in the third vertical plane PV 3 , a straight tangent line LT tangential to the joining surface  52  may be inclined at a zero or positive joining angle β 1 . 
     It should be appreciated throughout the description and claims, that the term “zero joining angle” refers to a configuration in which the straight tangent line LT is parallel to the head axis AH, and the term “positive joining angle” refers to an acute internal angle formed between the straight tangent line LT and an imaginary reference line parallel to the head axis AH and intersecting the associated radially outer base edge  50 . 
     In some embodiments of the present invention, the joining angle β 1  may be less than the rake angle α 1 , i.e., β 1 &lt;α 1 . 
     For embodiments of the present invention in which the joining angle β 1  is less than the rake angle α 1 , it should be appreciated that in the cross-section taken in the third vertical plane PV 3 , as shown in  FIG.  7   , the joining surface  52  may be concave. 
     Also, for embodiments of the present invention in which the joining angle β 1  is less than the rake angle α 1 , it should be appreciated that the surface area of each of the four radially outer base regions  48  may be advantageously increased, whilst providing each of the four head flutes  28  with an optimally large flute volume. 
     For such embodiments, it should be appreciated that the increased surface area of each radially outer base region  48  contributes to providing a cutting tool with good stability when the cutting head  20  is releasably secured to a tool shank, and providing each head flute  28  with an optimally large flute volume is of greater importance when the cutting head  20  is configured with four circumferentially spaced apart head flutes  28 , compared to an alternative cutting head configuration (not shown), having, for example, only two or three circumferentially spaced apart head flutes. 
     As shown in  FIGS.  1  to  3   , each cutting portion  26  may have a torque transmission surface  54  facing opposite the first direction of rotation R 1 . 
     For embodiments of the present invention in which each cutting portion  26  has a torque transmission surface  54 , and the cap portion  22  substantially exhibits 4-fold rotational symmetry about the head axis AH, it should be appreciated that the cutting head  20  may be mounted on a tool shank in four index positions whereby each of the four torque transmission surfaces  54  makes contact with a different one of four shank drive surfaces, the four torque transmission surfaces  54  and four index positions being exactly twice the number of the second plurality of convex clamping surfaces  38  provided on the mounting protuberance  24 . 
     In some embodiments of the present invention, each torque transmission surface  54  may be located between its associated cutting portion&#39;s front surface  32  and one of the radially outer base regions  48 . 
     Also, in some embodiments of the present invention, each torque transmission surface  54  may be planar. 
     Further, in some embodiments of the present invention, as shown in  FIG.  2   , each torque transmission surface  54  may be inclined in the first direction of rotation R 1  as it extends in the axial rearward direction DR away from its associated cutting portion&#39;s front surface  32 . 
     As shown in  FIGS.  8  to  13   , a second aspect of the present invention relates to a rotary cutting tool  56  having the cutting head  20  secured to an elongated tool shank  58 . The tool shank  58  is provided with a head receiving pocket  60  at a forward end  62  thereof and four shank flutes  64  extending away from the forward end  62  along a shank axis AS, and the cutting head  20  is releasably secured to the head receiving pocket  60 . 
     In some embodiments the cutting head  20  may be releasably secured to the head receiving pocket  60  without the requirement of an additional fastening member, such as a clamping screw. 
     It should be appreciated throughout the description and claims, that when the cutting head  20  is releasably secured to the head receiving pocket  60 , and the rotary cutting tool  56  is in a state of assembly, the four shank flutes  64  extend away from the tool shank&#39;s forward end  62  in the axial rearward direction DR. 
     As shown in  FIGS.  8  to  10   , the four shank flutes  64  may be formed in a cylindrical shank peripheral surface  65  of the tool shank  58 . 
     In some embodiments of the present invention, the head axis AH may be coincident with the shank axis AS. 
     Also, in some embodiments of the present invention, the four shank flutes  64  may helically extend along the shank axis AS, and the four head flutes  28  may serve as corresponding extensions of the four shank flutes  64 . 
     Further, in some embodiments of the present invention, the tool shank  58  may preferably be manufactured from tool steel. 
     Yet further, in some embodiments of the present invention, the rotary cutting tool  56  may be used for drilling operations. 
     As shown in  FIGS.  8  and  9   , the head receiving pocket  60  has a shank support surface  66  transverse to the shank axis AS and a central recess  68  formed in the shank support surface  66 . 
     In some embodiments of the present invention, the central recess  68  may not intersect any of the four shank flutes  64 . 
     As shown in  FIG.  9   , the shank support surface  66  includes a central support region  70  and four radially outer support regions  72 . 
     In some embodiments of the present invention, the central recess  68  may be formed in the central support region  70 . 
     Also, in some embodiments of the present invention, each radially outer support region  72  may intersect the shank peripheral surface  65 . 
     Further, in some embodiments of the present invention, the four radially outer support regions  72  may be coplanar and located axially forward of the central support region  70 . 
     As shown in  FIGS.  9  and  11   , the central recess  68  has four circumferentially spaced apart resiliently displaceable abutment portions  74 , each abutment portion  74  having a radially inward facing abutment surface  76 . 
     In some embodiments of the present invention, the four abutment portions  74  may be identical, and the four abutment surfaces  76  may be arranged as two pairs of diametrically opposed abutment surfaces  76 . Thus, the tool shank  58  has a third plurality of abutment surfaces  76 , being the same in number as the first plurality of cutting portions  26  and exactly twice the number of the second plurality of convex clamping surfaces  38 . 
     In some embodiments of the present invention, the four abutment portions  74  may be independently resiliently displaceable, and for such embodiments it should be appreciated that radial displacement of one of the four abutment portions  74  does not cause radial displacement of any of the other three abutment portions  74 . 
     Also, in some embodiments of the present invention, the central recess  68  may include four intermediate portions  78  which circumferentially alternate with the four abutment portions  74 , and each intermediate portion  78  may have an intermediate surface  80  intersecting two circumferentially adjacent abutment surfaces  76 . 
     Further, in some embodiments of the present invention, each intermediate surface  80  may extend radially outwardly from the two circumferentially adjacent abutment surfaces  76 . 
     For embodiments of the present invention in which the four abutment surfaces  76  circumferentially alternate with the four intermediate surfaces  80 , the head receiving pocket  60  has a ‘circumferentially confined’ central recess  68 , which improves the resilience of the four abutment portions  74  and extends the useful life of the tool shank  58 . 
     As shown in  FIGS.  9  and  11   , prior to the cutting head  20  being releasably secured to the head receiving pocket  60 , the head receiving pocket  60  may exhibit 4-fold rotational symmetry about the shank axis AS. 
     Also, prior to the cutting head  20  being releasably secured to the head receiving pocket  60 , the tool shank  58  may exhibit 4-fold rotational symmetry about the shank axis AS. 
     According to the second aspect of the present invention, as shown in  FIGS.  12  and  13   , the mounting protuberance  24  is resiliently retained in the central recess  68  in any one of four index positions, and in each index position: 
     the head base surface  30  faces the shank support surface  66 , 
     the two clamping surfaces  38  make clamping contact with two operative abutment surfaces  76 ′ of the four abutment surfaces  76 , and 
     no clamping contact occurs between the rigid mounting protuberance  24  and two non-operative abutment surfaces  76 ″ of the four abutment surfaces  76 . 
     It should be appreciated throughout the description and claims, that clamping contact between the two clamping surfaces  38  and the two operative abutment surfaces  76 ′ results in radial outward displacement of the two associated abutment portions  74 . 
     It should also be appreciated throughout the description and claims, that no clamping contact occurs between the rigid mounting protuberance  24  and the two non-operative abutment surfaces  76 ″, and the mounting protuberance&#39;s two guide surfaces  42  may face the two non-operative abutment surfaces  76 ″ with minimal spacing therebetween. 
     In some embodiments of the present invention, in each index position, the head receiving pocket  60  may exhibit 2-fold rotational symmetry about the shank axis AS. 
     It should be appreciated that the rotary cutting tool&#39;s tool shank  58  has two operational configurations, namely, a first operational configuration in which the mounting protuberance  24  of a removably secured cutting head  20  is resiliently retained in the tool shank&#39;s central recess  68  in a first or second of the above said four index positions in which a same first pair of diametrically opposed abutment surfaces  76  are operative, and a second operational configuration in which the mounting protuberance  24  of a removably secured cutting head  20  is resiliently retained in the tool shank&#39;s central recess  68  in a third or fourth of the above said four index positions in which a same second pair of diametrically opposed abutment surfaces  76  are operative. 
     In the present rotary cutting tool  56 , the tool shank  58  has exactly twice as many radially inward facing abutment surfaces  76  in its central recess  68 , as the cutting head  20  has clamping surfaces  38  on its mounting protuberance  24 . Thus, in the fully assembled rotary cutting tool  56 , in the circumferential direction of the tool shank&#39;s central recess  68 , only alternate ones of the third plurality of abutment surfaces  76  are operative. More specifically, the second plurality of circumferentially spaced apart convex clamping surfaces  38  on the cutting head&#39;s mounting protuberance  24  are in abutment with alternate ones of the third plurality of circumferentially spaced apart and radially inward facing abutment surfaces  76  of the tool shank&#39;s central recess  68 . 
     It should also be appreciated that by having two operational configurations, the useful life of the rotary cutting tool&#39;s tool shank  58  may be advantageously extended. 
     It should further be appreciated that visual markings or indications (not shown) may be provided on the tool shank&#39;s forward end  62  to enable the first and second pairs of diametrically opposed abutment surfaces  76  to be distinguished from each other. 
     It should yet further be appreciated that the key slots  36  located on the cutting head&#39;s cap portion  22 , may provide a visual indication for the position of the two clamping surfaces  38  on the cutting head&#39;s mounting protuberance  24 , which may be relied upon when selecting the desired index position of the cutting head  20  in the tool shank&#39;s central recess  68 . 
     For embodiments of the present invention in which the four abutment portions  74  are independently resiliently displaceable, it should be appreciated that the useful life of the rotary cutting tool&#39;s tool shank  58  may be doubled. 
     It should further be appreciated that during the useful life of each of the tool shank&#39;s first and second operational configurations, several cutting heads  20  may be releasably secured to the tool shank&#39;s head receiving pocket  60  and used in drilling operations before being replaced after wear. 
     As shown in  FIGS.  12  and  13   , when the cutting head  20  is releasably secured to the head receiving pocket  60 , and the rotary cutting tool  56  is in a state of clamped assembly, the head base surface  30  may make contact with the shank support surface  66 , and apart from the two clamping surfaces  38  making clamping contact with the two operative abutment surfaces  76 ′, no other portion of the mounting protuberance  24  may make clamping contact with the central recess  68 . 
     In some embodiments of the present invention, at least three of the four radially outer base regions  48  may make contact with at least three of the four radially outer support regions  72 . 
     It should be appreciated that during drilling operations, axially rearward cutting forces will typically overcome any inaccuracies associated with the coplanarity of the four radially outer support regions  72 , resulting in contact between all four radially outer base regions  48  and all four radially outer support regions  72 . 
     Also, in some embodiments of the present invention, the central base region  46  may be spaced apart from the central support region  70 . 
     As shown in  FIG.  13   , in a cross-section taken in a third horizontal plane PH 3  perpendicular to the shank axis AS and passing through the central recess  68 , an imaginary fourth circle C 4  having a fourth diameter D 4  and a center coincident with the shank axis AS inscribes the two operative abutment surfaces  76 ′, while an imaginary fifth circle C 5  having a fifth diameter D 5  and a center coincident with the shank axis AS inscribes the two non-operative abutment surfaces  76 ″, and the fourth diameter D 4  is greater than the fifth diameter D 5 , i.e., D 4 &gt;D 5 . 
     It should be appreciated throughout the description and claims, that in the cross-section taken in the third horizontal plane PH 3 , none of central recess&#39;s four abutment portions  74  and four intermediate portions  78  may traverse the imaginary fifth circle C 5 . 
     In some embodiments of the present invention, the first and third horizontal planes PH 1 , PH 3  may be coincident, and the first diameter D 1  may be greater than the fifth diameter D 5 , i.e., D 1 &gt;D 5 . 
     Also, for embodiments of the present invention in which the first and third horizontal planes PH 1 , PH 3  are coincident, the first diameter D 1  may be equal to the fourth diameter D 4 , i.e., D 1 =D 4 . Restated, the diameter of the outermost portions of the clamping surfaces  38  matches that of the operative abutment surfaces  76 ′. 
     Further, for embodiments of the present invention in which the first and third horizontal planes PH 1 , PH 3  are coincident, the third diameter D 3  may be less than the fifth diameter D 5 , i.e., D 3 &lt;D 5 . Restated, the diameter of the outermost portions of the guide surfaces  42  is less than that of the non-operative abutment surfaces  76 ″. 
     For embodiments of the present invention in which the four circumferentially spaced apart resiliently displaceable abutment portions  74  are identical, it should be appreciated that prior to the cutting head  20  being releasably secured to the head receiving pocket  60 , as shown in  FIG.  11   , in the cross-section taken in the third horizontal plane PH 3 , the imaginary fifth circle C 5  inscribes all of the four abutment surfaces  76 . 
     Also, for embodiments of the present invention in which the four circumferentially spaced apart resiliently displaceable abutment portions  74  are identical, it should be appreciated that prior to the cutting head  20  being releasably secured to the head receiving pocket  60 , as shown in  FIG.  11   , in the cross-section taken in the third horizontal plane PH 3 , the four shank flutes  64  are inscribed by an imaginary sixth circle C 6  having a sixth diameter D 6  and a center coincident with the shank axis AS at four first flute points N F   1 . 
     In some embodiments of the present invention, a radial flute axis AF perpendicular to the shank axis AS and containing one of the four first flute points N F   1  may intersect one of the four abutment surfaces  76 , and each first flute point N F   1  may be located a minimum first wall thickness T 1  from its adjacent abutment surface  76  along its associated radial flute axis AF. 
     Also, in some embodiments of the present invention, the sixth diameter D 6  may be between ninety percent and one hundred and ten percent of the second diameter D 2 , i.e. D 2 *0.90&lt;D 6 &lt;D 2 *1.10. 
     As shown in  FIG.  11   , in the cross-section taken in the third horizontal plane PH 3 , prior to the cutting head  20  being releasably secured to the head receiving pocket  60 , each shank flute  64  has a second flute point N F   2  spaced apart from the first flute point N F   1  and located a minimum second wall thickness T 2  from its adjacent intermediate surface  80 . 
     In some embodiments of the present invention, the minimum second wall thickness T 2  may be equal to or less than the minimum first wall thickness T 1 , i.e. T 2 &lt;T 1 . 
     For embodiments of the present invention in which the minimum second wall thickness T 2  is equal to or less than the minimum first wall thickness T 1 , it should be appreciated that the close proximity of each shank flute  64  to its adjacent intermediate surface  80  is a main parameter for regulating the resilience of the associated abutment portion  74 . 
     As shown in  FIGS.  8  to  10   , the tool shank&#39;s forward end  62  may have four drive protuberances  82  protruding from the shank support surface  66 , and each drive protuberance  82  may have a drive surface  84  adjacent one of the radially outer support regions  72  facing in the first direction of rotation R 1 . 
     In some embodiments of the present invention, each drive surface  84  may intersect the shank peripheral surface  65 . 
     When the cutting head  20  is releasably secured to the head receiving pocket  60 , and the rotary cutting tool  56  is in a state of clamped assembly, as shown in  FIG.  12   , at least two of the four drive surfaces  84  may make contact with at least two of the four torque transmission surfaces  54 . 
     By virtue of clamping contact occurring between the two clamping surfaces  38  and the two operative abutment surfaces  76 ′ and no clamping contact between the rigid mounting protuberance  24  and the two non-operative abutment surfaces  76 ″, it should be appreciated that the tool shank&#39;s forward end  62  may undergo very slight torsional twisting, which may result in only two diametrically opposed drive surfaces  84  of the four drive surfaces  84  making contact with two diametrically opposed torque transmission surfaces  54  of the four torque transmission surfaces  54 , although during drilling operations, rotational cutting forces will typically overcome the said slight torsional twisting, resulting in contact between all four drive surfaces  84  and all four torque transmission surfaces  54 . 
     In some embodiments of the present invention, the four drive surfaces  84  and the four torque transmission surfaces  54  may be correspondingly inclined with respect to the first direction of rotation R 1 . 
     By configuring each drive surface  84  to be slanted away from the first direction of rotation R 1  as it extends away from its associated radially outer support region  72 , as shown in  FIG.  12   , it should be appreciated that a component of the rotational cutting forces is directed axially rearwardly and the robustness of the four drive protuberances  82  is increased. 
     The present invention further relates to a method of assembling the rotary cutting tool  56 , comprising the steps of:
         a) orienting the head base surface  30  to face the shank support surface  66 ;   b) aligning the head axis AH with the shank axis AS;   c) rotationally aligning the two clamping surfaces  38  with two of the four intermediate portions  78 ;   d) inserting the mounting protuberance  24  into the central recess  68 , until the head base surface  30  makes contact with the shank support surface  66 , as shown in  FIG.  14   ; and   e) rotating the cutting head  20  about its head axis AH opposite the first direction of rotation R 1 , until the two clamping surfaces  38  are resiliently retained against two operative abutment surfaces  76 ′ of the four abutment surfaces  76 , as shown in  FIG.  12   .       

     In some embodiments of the present invention, in step d), the rotary cutting tool  56  is in a state of unclamped assembly whereby none of the four abutment portions  74  are being resiliently displaced, and in the cross-section taken in the third horizontal plane PH 3 , as shown in  FIG.  15   , an imaginary seventh circle C 7  having a seventh diameter D 7  and a center coincident with the shank axis AS may inscribe all of the four abutment surfaces  76 . 
     For embodiments of the present invention in which the first and third horizontal planes PH 1 , PH 3  are coincident, the first diameter D 1  may be greater than the seventh diameter D 7 , i.e., D 1 &gt;D 7 , although due to the two clamping surfaces  38  being rotationally aligned with two of the four intermediate portions  78 , no radially outward forces FR are being applied to any of the four abutment portions  74  and the head receiving pocket  60  has a configuration identical to that prior to the cutting head  20  being releasably secured thereto. 
     Also, in some embodiments of the present invention, in step d), the head receiving pocket  60  may exhibit 4-fold rotational symmetry about the shank axis AS. 
     It should be appreciated that step e) is typically performed by using an assembly tool (not shown) which engages the cutting head&#39;s key slots  36 . 
     In some embodiments of the present invention, in step e), the cutting head  20  may be rotated by approximately 45 degrees about its head axis AH relative to the tool shank&#39;s central recess  68 , until the rotary cutting tool  56  achieves a state of clamped assembly. 
     It should also be appreciated that step e) is typically performed until at least two of the four drive surfaces  84  make contact with at least two of the four torque transmission surfaces  54 . 
     Also, in some embodiments of the present invention, in step e), the two abutment portions  74  associated with the two operative abutment surfaces  76 ′ are being resiliently displaced, and in the cross-section taken in the third horizontal plane PH 3 , as shown in  FIG.  13   , the imaginary fourth circle C 4  inscribes the two operative abutment surfaces  76 ′ and the fourth diameter D 4  is greater than the seventh diameter D 7 , i.e., D 4 &gt;D 7 . 
     It should further be appreciated in step e), that radially outward forces FR are being applied to the said two abutment portions  74  associated with the two operative abutment surfaces  76 ′ by the two clamping surfaces  38 . 
     Further, in some embodiments of the present invention, in step e), the two abutment portions  74  associated with the two non-operative abutment surfaces  76 ″ are not being resiliently displaced, and in the cross-section taken in the third horizontal plane PH 3 , as shown in  FIG.  13   , the imaginary fifth circle C 5  inscribes the two non-operative abutment surfaces  76 ″ and the fifth diameter D 5  is equal to the seventh diameter D 7 , i.e., D 5 =D 7 . 
     It should yet further be appreciated in step e), that no radially outward forces FR are being applied to the said two abutment portions  74  associated with the two non-operative abutment surfaces  76 ″. 
     Yet further, in some embodiments of the present invention, in step e), the head receiving pocket  60  may exhibit 2-fold rotational symmetry about the shank axis AS. 
     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 scope of the invention as hereinafter claimed.