FIELD OF THE INVENTION

[0001] The present invention relates to a rotary cutting tool having a central coolant passage with a non-circular cross-sectional shape, for use in metal cutting processes in general, and for milling operations in particular.

BACKGROUND OF THE INVENTION

[0002] Within the field of rotary cutting tools used in milling operations, there are many examples in which the cutting tool has a central coolant passage, and some examples in which the central coolant passage has a non-circular cross-sectional shape.

[0003] US7,207,755 B2 discloses a cutting tool arrangement and a tool for chip removing machining, the cutting tool arrangement comprising a tool, fastening arrangement, and a shank. The tool is a one-piece unit having an axial channel. The axial channel is of non-circular crosssection to provide a key grip, and an end of the axial channel comprises material at least partly blocking the axial channel.

[0004] US2012/163931 Al discloses a tool which comprises a shank with a central, continuous internal channel and an insert which protrudes into the internal channel and is frictionally and/or mechanically positively connected with the shank, wherein the internal channel has one or more widenings which in work operation of the tool serve as cooling channels.

[0005] JP7057550 B1 (US2023/0063846 Al) discloses a rotary cutting tool configured to supply coolant fluid toward its cutting edges. The cutting tool includes a holding part and a cutting part, and a flow passage for guiding cooling fluid to an outlet port in the cutting part. The flow passage includes a plurality of first flow passages which at least partially extend parallel to the tool's rotation center axis, and a plurality of second flow passages extending from the first flow passages towards the cutting edges.

[0006] It is an object of the present invention to provide an improved rotary cutting tool having a central coolant passage with a non-circular cross-sectional shape. [0007] It is also an object of the present invention to provide an improved rotary cutting tool with coolant ducts extending transversely away from the central coolant passage such that flexibility of design is afforded with respect to the direction and extent of each coolant duct.

[0008] It is a further object of the present invention to provide an improved rotary cutting tool whereby uniform and axisymmetric flow of coolant fluid along each coolant duct is promoted.

SUMMARY OF THE INVENTION

[0009] In accordance with the present invention, there is provided a rotary cutting tool rotatable about a tool axis in a direction of rotation, the tool axis defining a forward-to-rearward direction, and comprising a tool body having a front cutting portion and a rear coupling portion, the front cutting portion having a front outer peripheral surface with a plurality of N circumferentially spaced apart cut-outs, where N is a specific integer number greater than one, each cut-out opening out at a front end of the front cutting portion and having an operative cutting edge associated therewith, wherein a central coolant passage extends along the tool axis from a rear end of the rear coupling portion to the front cutting portion, and a first plane perpendicular to the tool axis intersects the central coolant passage and the N operative cutting edges, wherein, in a cross-section taken in the first plane, the central coolant passage has a noncircular shape with N radially outer coolant regions, each radially outer coolant region having a first radially outermost coolant point, and the central coolant passage is circumscribed by an imaginary first circle having a first diameter and a center coincident with the tool axis, and wherein: at least one coolant duct extends transversely from each radially outer coolant region to intersect with and open out at one of the N cut-outs at a coolant exit port.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] 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: [0011] Fig. 1 is a first perspective view of a rotary cutting tool in accordance with some embodiments of the present invention;

[0012] Fig. 2 is an exploded second perspective view of the cutting tool shown in Fig. 1 ;

[0013] Fig. 3 is a side view of the cutting tool shown in Fig. 1 ;

[0014] Fig. 4 is an end view of the cutting tool shown in Fig. 1;

[0015] Fig. 5 is a cross-sectional view of the cutting tool shown in Fig. 3, taken along the line V-V;

[0016] Fig. 6 is a detailed view of the cutting tool shown in Fig. 5;

[0017] Fig. 7 is a cross-sectional view of the cutting tool shown in Fig. 5, taken along the line VII- VII;

[0018] Fig. 8 is a detailed view of the cutting tool shown in Fig. 7;

[0019] Fig. 9 is a cross-sectional view of the cutting tool shown in Fig. 8, taken along the line IX-IX;

[0020] Fig. 10 is a cross-sectional view of the cutting tool shown in Fig. 3, taken along the line X-X;

[0021] Fig. 11 is a detailed view of the cutting tool shown in Fig. 10; and

[0022] Fig. 12 is a cross-sectional view of the cutting tool shown in Fig. 3, taken along the line XII-XII.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Attention is first drawn to Figs. 1 to 4, showing a rotary cutting tool 20 according to the present invention.

[0024] The rotary cutting tool 20 is rotatable about a tool axis AT in a direction of rotation RD, the tool axis AT defining a forward-to-rearward direction DF, DR, and comprises a tool body 22 having a front cutting portion 24 and a rear coupling portion 26, the rear coupling portion 26 located axially rearward of the front cutting portion 24.

[0025] As shown in Figs. 1 to 4, the front cutting portion 24 has a front outer peripheral surface 28 with a plurality of N circumferentially spaced apart cut-outs 30, where N is a specific integer number greater than one, i.e., N > 1. [0026] In some embodiments of the present invention, the front outer peripheral surface 28 may be cylindrical.

[0027] Also, in some embodiments of the present invention, N may preferably be eight or less than eight, i.e., 1 < N < 8.

[0028] Each cut-out 30 opens out at a front end 32 of the front cutting portion 24 and has an operative cutting edge 34' associated therewith.

[0029] In some embodiments of the present invention, as shown in Figs. 1 to 4, each cut-out 30 may have an insert receiving pocket 36 with a cutting insert 38 removably secured therein, and the operative cutting edge 34' may be formed on the cutting insert 38.

[0030] In other embodiments of the present invention (not shown), the N operative cutting edges 34' may be integrally formed on the tool body 22 such that the cutting tool 20 has a unitary one-piece (i.e., “monolithic”) construction.

[0031] As shown in Figs. 1 to 4, each cutting insert 38 may be indexable and have a plurality cutting edges 34, and each cutting insert 38 may be arranged in its associated insert receiving pocket 36 such that only one of the cutting insert's plurality of cutting edges 34 may be the operative cutting edge 34', i.e., positioned to engage a workpiece (not shown).

[0032] In some embodiments of the present invention, the cutting insert 38 may include a through bore 40, and the cutting insert 38 be removably secured to the tool body 22 by means of a clamping screw 42 occupying the through bore 40 and threadingly engaging a screw bore 44 in a seat surface 46 of the insert receiving pocket 36.

[0033] Also, in some embodiments of the present invention, the cutting insert 38 may be manufactured from a suitably hard material, for example, cemented carbide, and the tool body 22 may be manufactured from a less hard material, for example, tool steel.

[0034] Further, in some embodiments of the present invention, as shown in Figs. 1 to 4, the cutting insert 38 may be a 'radial' type cutting insert.

[0035] In other embodiments of the present invention (not shown), the cutting insert 38 may be a 'tangential' type cutting insert.

[0036] As shown in Figs. 5 and 7, a single central coolant passage 48 extends along the tool axis AT from a rear end 50 of the rear coupling portion 26 to the front cutting portion 24, and as shown in Figs. 3 and 7, a first plane Pl perpendicular to the tool axis AT intersects the central coolant passage 48 and the N operative cutting edges 34'. In embodiments in which each cut-out 30 has an insert receiving pocket 36, the first plane Pl may intersect each of the insert receiving pockets 36 and each of the associated seat surfaces 46.

[0037] As shown in Figs. 5 and 6, in a cross-section taken in the first plane Pl, the central coolant passage 48 has a non-circular shape with N radially outer coolant regions 52, each radially outer coolant region 52 having a first radially outermost coolant point NCO1, and the central coolant passage 48 is circumscribed by an imaginary first circle Cl having a first diameter DI and a center coincident with the tool axis AT.

[0038] In some embodiments of the present invention, as shown in Figs. 5 and 6, in the crosssection taken in the first plane Pl, each first radially outermost coolant point NCO1 may lie on the imaginary first circle Cl.

[0039] Also, in some embodiments of the present invention, as shown in Figs. 5 and 6, in the cross-section taken in the first plane Pl, each first radially outermost coolant point NCO1 may define one of N apex points of an N-sided first regular polygon RP1.

[0040] For embodiments of the present invention in which the N radially outer coolant regions 52 of the central coolant passage 48 define an N-sided first regular polygon RP1, in the crosssection taken in the first plane Pl, it should be appreciated that N is a specific integer number greater than two, i.e., N > 2.

[0041] Figs. 1 to 6 show an embodiment of the present invention in which N is equal to three, i.e., N = 3, and the N-sided first regular polygon RP1 is an equilateral triangle.

[0042] As shown in Figs. 1 and 4, the front cutting portion's front end 32 may have a forwardfacing first end surface 54.

[0043] In some embodiments of the present invention, the central coolant passage 48 may terminate axially rearward of the first end surface 54. For such embodiments of the present invention, it should be appreciated that the tool axis AT may intersect the first end surface 54.

[0044] As shown in Figs. 5 and 6, in the cross-section taken in the first plane Pl, the central coolant passage 48 may include N radially recessed coolant regions 56 circumferentially alternating with the N radially outer coolant regions 52. [0045] In some embodiments of the present invention, each radially recessed coolant region 56 may have a first radially innermost coolant point NCI1 located inside the first regular polygon RP1.

[0046] For such embodiments of the present invention, it should be appreciated that the N radially recessed coolant regions 56 contribute to preserving the core strength of the tool body 22. [0047] According to the present invention, as shown in Figs. 5 to 8, at least one coolant duct 58 extends transversely from each radially outer coolant region 52 to intersect with and open out at one of the N cut-outs 30 at one or more coolant exit ports 60.

[0048] By configuring each coolant duct 58 to extend from one of the radially outer coolant regions 52 of the non-circular central coolant passage 48 to one of the N cut-outs 30, as shown in Figs. 5 and 7, it should be appreciated that greater flexibility of design is afforded with respect to the direction and extent of each coolant duct 58.

[0049] In some embodiments of the present invention, as shown in Figs. 7 and 8, each coolant duct 58 may merge with the associated radially outer coolant region 52 via convexly curved joining surfaces 61, such that smooth and undisturbed flow of coolant fluid from the central coolant passage 48 to each coolant duct 58 is promoted. For such embodiments of the present invention, it should be appreciated that the cutting tool body 22 may be produced by means of additive manufacturing, resulting in an additively manufactured tool body. One skilled in the art can determine whether a given tool body has been made by an additive manufacturing process by inspecting the microscopic structure of the material constituting the tool body.

[0050] Also, in some embodiments of the present invention, each cut-out 30 may intersect the first end surface 54, and each coolant exit port 60 may be located axially rearward of the first end surface 54.

[0051] Further, in some embodiments of the present invention, as shown in Figs. 5 and 7, each coolant duct 58 may direct coolant fluid towards the operative cutting edge 34' of the associated cut-out 30.

[0052] It should be appreciated that directing coolant fluid towards the operative cutting edge 34' significantly reduces wear and extends the useful life thereof.

[0053] As shown in Figs. 5 and 6, in the cross-section taken in the first plane Pl, each first radially outermost coolant point NCO1 may be located on a concavely curved first inner wall 62 of the associated radially outer coolant region 52, and the first inner wall 62 may have a first radius

Rl.

[0054] In some embodiments of the present invention, as shown in Fig. 6, each coolant duct 58 may extend away from the first inner wall 62 of the associated radially outer coolant region 52. [0055] For embodiments of the present invention in which N is equal to two, i.e., N = 2 (not shown), and the central coolant passage 48 has two radially outer coolant regions 52 with two concavely curved first inner walls 62, it should be appreciated that in a cross-section of the central coolant passage 48 taken perpendicular to the tool axis AT, the central coolant passage 48 may have a figure '8' shape.

[0056] In some embodiments of the present invention, the first radius Rl may be greater than ten percent of the first diameter DI, i.e., Rl > 0.10*Dl.

[0057] Also, in some embodiments of the present invention, each first inner wall 62 may have a first angular extent EA1 of greater than ninety degrees, i.e., EA1 > 90°. In some embodiments, the first angular extent EA1 may even be greater than 180°.

[0058] For embodiments of the present invention in which the concavely curved first inner wall 62 has a relatively large first radius Rl, i.e., Rl > 0.10*Dl, and/or a relatively large first angular extent EA1, i.e., EA1 > 90°, it should be appreciated that smooth and undisturbed flow of coolant fluid from the central coolant passage 48 to each coolant duct 58 is promoted.

[0059] As shown in Fig. 6, in the cross-section taken in the first plane Pl, each first radially innermost coolant point NCI1 may be located on a convexly curved second inner wall 64 of the associated radially recessed coolant region 56.

[0060] In some embodiments of the present invention, each convexly curved second inner wall 64 may tangentially merge with a circumferentially adjacent concavely curved first inner wall 62. [0061] For embodiments of the present invention in which the convexly curved second inner wall 64 tangentially merges with a circumferentially adjacent concavely curved first inner wall 62, it should be appreciated that smooth and undisturbed flow of coolant fluid from the central coolant passage 48 to each coolant duct 58 is promoted. For such embodiments of the present invention, it should be appreciated that the cutting tool body 22 may be produced by means of additive manufacturing. [0062] As shown in Fig. 6, in the cross-section taken in the first plane Pl, the plurality of N cut-outs 30 may be inscribed by an imaginary second circle C2 at N first radially innermost cutout points NGI1.

[0063] In some embodiments of the present invention, at least N coolant ducts 58 may traverse the imaginary second circle C2, or an axial projection thereof.

[0064] Also, in some embodiments of the present invention, each of the at least N coolant ducts 58 may traverse the imaginary second circle C2, or an axial projection thereof, rotationally ahead of the associated first radially innermost cut-out point NGI1. For such embodiments of the present invention, it should be appreciated that the associated first radially innermost cut-out point NGI1 of each of the at least N coolant ducts 58 is the first radially innermost cut-out point NGI1 of the cut-out 30 to which the coolant duct 58 extends and intersects.

[0065] As shown in Fig. 6, the imaginary second circle C2 has a second diameter D2 and a center coincident with the tool axis AT.

[0066] In some embodiments of the present invention, the first diameter DI may be greater than fifty percent of the second diameter D2, i.e., DI > 0.50*D2.

[0067] For embodiments of the present invention in which the first diameter DI is relatively large, i.e., DI > 0.50*D2, it should be appreciated that configuring the central coolant passage 48 to have the N radially recessed coolant regions 56 may have even greater significance in preserving the core strength of the tool body 22.

[0068] As shown in Figs. 1 to 4, each operative cutting edge 34' has an axially forwardmost cutting point NFC and an operative primary cutting edge portion 66' extending radially outwardly and axially rearwardly from the axially forwardmost cutting point NFC.

[0069] In some embodiments of the present invention, the first plane Pl may intersect the N operative primary cutting edge portions 66'.

[0070] As shown in Figs. 3 and 4, each operative cutting edge 34' may have an operative secondary cutting edge portion 70' extending radially inwardly from the associated axially forwardmost point NFC.

[0071] In some embodiments of the present invention, each operative secondary cutting edge portion 70' may be described as a wiper edge. [0072] As shown in Fig. 4, the N axially forwardmost points NFC may define an imaginary third circle C3 having a third diameter D3 and a center coincident with the tool axis AT.

[0073] In some embodiments of the present invention, the third diameter D3 may be greater than the second diameter D2, i.e., D3 > D2.

[0074] As shown in Fig. 3, the N axially forwardmost points NFC may be contained in a second plane P2 perpendicular to the tool axis AT, and no portion of the cutting tool 20 may be located axially forward of the second plane P2.

[0075] In some embodiments of the present invention, the cutting tool 20 may be used in milling operations, during which the operative primary cutting edge portion 66' of each operative cutting edge 34' may be subjected to a major portion of the cutting forces associated therewith, and the operative secondary cutting edge portion 70' may be subjected to a minor portion of the cutting forces associated therewith.

[0076] Also, in some embodiments of the present invention, each coolant duct 58 may direct coolant fluid towards the operative primary cutting edge portion 66' of the associated operative cutting edge 34'.

[0077] It should be appreciated that directing coolant fluid towards the operative primary cutting edge portion 66' of the associated operative cutting edge 34' significantly reduces wear and extends the useful life thereof.

[0078] As shown in Figs. 5 to 8, each coolant duct 58 may have a circumferentially closed inner duct surface 68, and each coolant duct 58 may extend along a duct axis AD from the central coolant passage 34 to the associated coolant exit port 60.

[0079] In some embodiments of the present invention, each duct axis AD may be rectilinear, and each coolant duct 58 may extend from the central coolant passage 48 to the associated coolant exit port 60 without its duct axis AD intersecting the associated inner duct surface 68.

[0080] For such embodiments of the present invention, as shown in Figs. 5 to 8, each coolant duct 58 may linearly extend along its duct axis AD from the central coolant passage 48 to the associated coolant exit port 60.

[0081] For other embodiments of the present invention (not shown), each coolant duct 58 may have a certain degree of longitudinal curvature, although each coolant duct 58 may still extend from the central coolant passage 48 to the associated coolant exit port 60 without its rectilinear duct axis AD intersecting the associated inner duct surface 68.

[0082] For embodiments of the present invention in which each coolant duct 58 linearly extends along its duct axis AD, it should be appreciated that uniform and axisymmetric flow of coolant fluid along each coolant duct 58 is promoted.

[0083] Also, for embodiments of the present invention in which each coolant duct 58 is advantageously constrained to linearly extend along its associated duct axis AD, it should be appreciated that configuring each coolant duct 58 to extend from one of the radially outer coolant regions 52 of the non-circular central coolant passage 48 to one of the N cut-outs 30 has even greater significance in affording flexibility of design with respect to the direction and extent of each coolant duct 58.

[0084] As shown in Fig. 8, each coolant duct 58 has a duct length DL measured along its rectilinear duct axis AD.

[0085] In some embodiments of the present invention, the duct length DL may be more than forty percent of the second diameter D2, i.e., DL > 0.40*D2.

[0086] Also, in some embodiments of the present invention, as shown in Fig. 8, each coolant duct 58 may extend in the forward direction DF as it extends away from the central coolant passage 48 to one of the N cut-outs 30.

[0087] As shown in Fig. 6, in the cross-section taken in the first plane Pl, each coolant duct 58 has an axially projected duct length DLP.

[0088] For embodiments of the present invention in which each coolant duct 58 extends in the forward direction DF as it extends away from the central coolant passage 48 to one of the N cutouts 30, it should be appreciated that the axially projected duct length DLP is less than the duct length DL, i.e., DLP < DL.

[0089] In some embodiments of the present invention, the axially projected duct length DLP may be greater than half the difference between the first diameter DI and the second diameter D2, i.e., DLP > 0.5*(D2 - DI).

[0090] Configuring the central coolant passage 48 to be non-circular and have N radially outer coolant regions 52 advantageously enables each coolant duct 58 to have a sufficiently long axially projected duct length DLP and duct length DL, such that it may linearly extend along its duct axis AD and direct a uniform and axisymmetric flow of coolant fluid towards the operative cutting edge 34'.

[0091] In some embodiments of the present invention, each coolant duct 58 may have a noncircular cross-section shape.

[0092] Also, in some embodiments of the present invention, each coolant duct 58 may have a cross-sectional area which varies along its length from the central coolant passage 48 to the associated coolant exit port 60.

[0093] As shown in Fig. 9, in a cross-section taken in a third plane P3 perpendicular to one of the duct axes AD and intersecting the associated coolant duct 58, the coolant duct 58 may have an elliptical shape.

[0094] Also, as shown in Fig. 9, in the cross-section taken in the third plane P3, an imaginary fourth circle C4 having a fourth diameter D4 and a center coincident with the duct axis AD circumscribes the associated coolant duct 58.

[0095] In some embodiments of the present invention, the fourth diameter D4 may be less than thirty percent of the first diameter DI, i.e., D4 < 0.30*Dl.

[0096] As shown in Fig. 6, in the cross-section taken in the first plane Pl, a fourth plane P4 contains the tool axis AT and the first radially outermost coolant point NCO1 of one of the radially outer coolant regions 52. The duct axis AD associated with said radially outer coolant region 52, forms a first angle al with the fourth plane P4.

[0097] In some embodiments of the present invention, the first angle al may be greater than sixty degrees and less than one hundred and twenty degrees, i.e., 60° < al < 120°.

[0098] As shown in Fig. 6, in the cross-section taken in the first plane Pl, each duct axis AD, intersects the fourth plane P4 of the associated radially outer coolant region 52 at an intersection point NI.

[0099] In some embodiments of the present invention, the intersection point NI may be located closer to the associated first radially outermost coolant point NCO1 than the tool axis AT.

[0100] As shown in Fig. 6, in the cross-section taken in the first plane Pl, an imaginary fifth circle C5 inscribes the first regular polygon RP1.

[0101] In some embodiments of the present invention, an axial projection of each duct axis AD may traverse the first regular polygon RP1 outside the imaginary fifth circle C5. [0102] As shown in Fig. 5, in the cross-section taken in the first plane Pl, the first radially outermost coolant point NCO1 of each radially outer coolant region 52 is located a minimum first distance DSIMIN from the coolant exit port 60 of one of the associated coolant ducts 58, and the first radially outermost coolant point NCO1 of each radially outer coolant region 52 is located a minimum second distance DS2MIN from the coolant exit port 60 of one of the non-associated coolant ducts 58.

[0103] In some embodiments of the present invention, the minimum first distance DSIMIN may be greater than the minimum second distance DS2MIN, i.e., DSIMIN > DS2MIN.

[0104] Also, in some embodiments of the present invention, the coolant exit port 60 of said non-associated coolant duct 58 may be rotationally adjacent and ahead of the coolant exit port 60 of said associated coolant duct 58.

[0105] As shown in Figs. 5 and 6, the first plane Pl may intersect at least N coolant ducts 58. [0106] In some embodiments of the present invention, the first plane Pl may intersect exactly N coolant ducts 58 along the entire lengths thereof. For such embodiments of the present invention, as shown in Figs. 5 and 6, in the cross-section taken in the first plane Pl, communication between the central coolant passage 48 and the plurality of N cut-outs 30 via the said exactly N coolant ducts 58 is clearly visible.

[0107] As shown in Figs. 5 and 6, in the cross-section taken in the first plane Pl, the tool body 22 may exhibit N-fold rotational symmetry about the tool axis AT.

[0108] As shown in Figs. 7 and 8, two coolant ducts 58 may extend transversely from each radially outer coolant region 52 to intersect with and open out at the same cut-out 30.

[0109] In some embodiments of the present invention, the two duct axes AD associated with the said two coolant ducts 58 may be parallel.

[0110] As shown in Fig. 3, each operative major cutting edge 34' has an axially rearwardmost cutting point NRC, and a fifth plane P5 perpendicular to the tool axis AT and intersecting the central coolant passage 48 axially rearward of the first plane Pl may contain the plurality of N axially rearwardmost cutting points NRC.

[0111] In some embodiments of the present invention, each operative primary cutting edge portion 66' may extend between the axially forwardmost cutting point NFC and the axially rearwardmost cutting point NRC of the associated operative major cutting edge 34'. [0112] As shown in Figs. 10 and 11, in a cross-section taken in the fifth plane P5, the central coolant passage 48 may have a non-circular shape defined by the N radially outer coolant regions 52, which are circumscribed by an imaginary sixth circle C6 having a sixth diameter D6 and a center coincident with the tool axis AT.

[0113] Also, as shown in Figs. 10 and 11, in the cross-section taken in the fifth plane P5, each radially outer coolant region 52 has a second radially outermost coolant point NCO2, and each second radially outermost coolant point NCO2 lies on the imaginary sixth circle C6.

[0114] In some embodiments of the present invention, as shown in Figs. 10 and 11, in the cross-section taken in the fifth plane P5, each second radially outermost coolant point NCO2 may define one of N apex points of an N-sided second regular polygon RP2.

[0115] For embodiments of the present invention in which the N radially outer coolant regions 52 of the central coolant passage 48 define an N-sided second regular polygon RP2, in the crosssection taken in the fifth plane P5, it should be appreciated that N is a specific integer number greater than two, i.e., N > 2.

[0116] In some embodiments of the present invention, the N-sided second regular polygon RP2 may be rotationally coincident with the N-sided first regular polygon RP1. In this context, two axially spaced apart triangles are said to be “rotationally coincident”, if they share the same center and same angular orientation, when projected onto a common plane. Thus, the central coolant passage 48 does not “twist” as it extends in the axial direction between the fifth plane P5 and the first plane Pl. In other embodiments (not shown), the central coolant passage 48 may experience such a “twist”, in which case the N-sided second regular polygon RP2 may be rotationally offset with the N-sided first regular polygon RP1.

[0117] Also, in some embodiments of the present invention, in any cross-section taken in a plane perpendicular to the tool axis AT and located between the first and fifth planes Pl, P5, the radially outermost coolant points of the central coolant passage 48 may define an N-sided regular polygon rotationally coincident with the first and second regular polygons RP1, RP2.

[0118] It should be appreciated that the abovementioned term "any cross-section" may also be interpreted as "every cross-section". [0119] In some embodiments of the present invention, the sixth diameter D6 may be equal to or greater than the first diameter DI and less than one hundred and twenty percent of the first diameter DI, i.e., DI < D6 < DI* 1.20.

[0120] As shown in Fig. 11, in a cross-section taken in the fifth plane P5, the plurality of N cut-outs 30 may be inscribed by an imaginary seventh circle C7 at N second radially innermost cut-out points NGI2, and the imaginary seventh circle C7 may have a seventh diameter D7 and a center coincident with the tool axis AT.

[0121] In some embodiments of the present invention, the seventh diameter D7 may be greater than ninety percent and less than one hundred and ten percent of the second diameter D2, i.e., D2*0.90 < D7 < D2*1.10.

[0122] Also, in some embodiments of the present invention, the rear coupling portion's rear end 50 may have a rearward-facing second end surface 72, and the central coolant passage 48 may intersect and open out at the second end surface 72.

[0123] As shown in Fig. 12, in a cross-section taken in a sixth plane P6 perpendicular to the tool axis AT and intersecting the rear coupling portion 26 and the central coolant passage 48, the central coolant passage 48 may have a circular shape with an eighth diameter D8.

[0124] In some embodiments of the present invention, the eighth diameter D8 may be greater than the first diameter DI, i.e., D8 > DI.

[0125] Also, in some embodiments of the present invention, the eighth diameter D8 may be greater than the sixth diameter D6, i.e., D8 > D6.

[0126] As shown in Fig. 2, the rear coupling portion 26 may have an annular shaped shoulder surface 74 facing in the rearward direction DR.

[0127] In some embodiments of the present invention, the shoulder surface 74 may intersect the front outer peripheral surface 28.

[0128] As shown in Figs. 1 to 3, the rear coupling portion 26 may have an external threaded portion 76 helically extending along the tool axis AT.

[0129] In some embodiments of the present invention, the external threaded portion 76 may be located axially rearward of the shoulder surface 74.

[0130] 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.