Interchangeable cutting head and rotary cutting tool having back-tapered conical external thread - Patents.com

Abstract

The rotary cutting tool 20 includes an interchangeable cutting head 22 and a tool holder 24. The interchangeable cutting head 22 includes a forward cutting portion 26 and a rearward mounting portion 28. The mounting portion 28 includes a male coupling member 38 including back-tapered conical external threads 42. The tool holder 24 includes a female coupling member 68 including internal threads 72. When the rotary cutting tool 20 is in the locked position (FIG. 7), the external threads 42 are threadingly engaged with the internal threads 72.

Description

[Technical field]

[0001] The subject matter of this application relates to rotary cutting tools of the type in which an interchangeable cutting head having a male coupling member is removably held to a female coupling member of a tool holder by a threaded coupling mechanism. [Background technology]

[0002] Rotary cutting tools may include a threaded coupling mechanism or "tool joint" for securely holding the interchangeable cutting head within the tool holder.

[0003] The interchangeable cutting head may include a male coupling member and the tool holder may include a female coupling member. The male coupling member may include male threads. The female coupling member may include female threads that correspond to the male threads on the male coupling member.

[0004] In some such rotary cutting tools, both the female and male threads are parallel threads. An example of such a rotary cutting tool is disclosed, for example, in U.S. Patent No. 6,485,220.

[0005] In other such rotary cutting tools, both the female and male threads are forward tapered conical threads. Examples of such rotary cutting tools are disclosed, for example, in U.S. Patent Nos. 7,611,311, 7,713,004, 9,643,262, and 9,643,264.

[0006] In yet another such rotary cutting tool, the external threads are forward tapered conical threads and the external threads are parallel threads. One such rotary cutting tool is disclosed in U.S. Pat. No. 10,105,771. Summary of the Invention

[0007] According to a first aspect of the present subject matter, there is provided an interchangeable cutting head having a head longitudinal axis extending from a forward direction to a rearward direction, the interchangeable cutting head comprising: a front portion forming the cutting portion; a rear portion forming a mounting portion, the mounting portion having male threads and including a male coupling member projecting rearwardly from the head base surface, the head base surface extending transversely to the head longitudinal axis and defining a boundary between the cutting portion and the mounting portion; The male thread has a male thread extending helically about a male thread axis and has a front exterior flank surface and a rear exterior flank surface, and an exterior upper surface extending between the front exterior flank surface and the rear exterior flank surface; the forward and aft exterior flanks face in generally opposite axial directions and bound a helical male thread groove having an exterior base surface; The male threads of the male coupling member are back-taper conical threads having at least one thread diameter that increases in a rearward direction.

[0008] In accordance with a second aspect of the present subject matter, there is provided a rotary cutting tool having a longitudinal axis and extending from a forward direction to a rearward direction, the rotary cutting tool comprising: It comprises a tool holder having a holder longitudinal axis and an interchangeable cutting head of the type described above threadedly engaged to the tool holder.

[0009] The above is a summary, and the features described below may be applicable to the subject matter of the present application in any combination, for example, any of the following features may be applicable to an interchangeable cutting head or a rotary cutting tool.

[0010] At least one of the external threads and the external grooves may extend around a respective cone having a cone angle.

[0011] Both external threads and grooves may extend around each of the cones, the outer cone and the inner cone, respectively.

[0012] The cone angle may be the same for the inner and outer cones.

[0013] The cone angle may be greater than or equal to 0.02° and less than or equal to 1.0°.

[0014] The cone angle may be just equal to 0.4°.

[0015] In a cross-sectional view taken in an axial plane containing the male thread axis, the external top surface is inclined relative to the male thread axis and defines a plurality of male thread crests that may be collinear with one another, and the external bottom surface is inclined relative to the male thread axis and defines a plurality of male thread roots that may be collinear with one another.

[0016] In a cross-sectional view taken at an axial plane containing the head longitudinal axis, the male thread defines an external thread form that may be trapezoidal.

[0017] The external threads may have a constant external thread pitch.

[0018] The tool holder may have a female coupling member having internal threads extending rearwardly from a holder front face, the holder front face extending transversely to the holder longitudinal axis, and the rotary cutting tool may be adjustable between a) an unlocked position in which the internal and external threads cannot be threadably engaged with one another, and b) a locked position in which the internal and external threads can be threadably engaged with one another such that the male coupling member can be releasably retained to the female coupling member.

[0019] The female threads of the female coupling member may be straight threads.

[0020] The frictional engagement between the male and female threads may increase in a direction from the forward most turn of the male thread to the rearmost turn of the male thread.

[0021] The female thread may include an internal thread extending helically about the female thread axis and including leading and trailing inner flanks and an internal top surface extending between the leading and trailing internal flanks. The leading and trailing internal flanks may face in generally opposite axial directions and bound a helical female thread groove including an internal bottom surface. The leading and trailing external flanks may face in a forward direction. The trailing external flanks may face in a rearward direction. In the locked position, the rearward internal flank may abut the leading external flank.

[0022] In the locked position, the forward interior flank surface can be spaced a rearward flank distance from the rearward exterior flank surface, the interior top surface can be spaced an upward distance from the exterior bottom surface, and the interior bottom surface can be spaced a downward distance from the exterior top surface.

[0023] The aft flank distance, the upper distance and the lower distance may all decrease in the aft direction.

[0024] The female threads may have a constant female thread pitch that is the same as the male thread pitch.

[0025] For a better understanding of the present application, and to show how the same may be carried out in practice, reference will now be made to the accompanying drawings. [Brief description of the drawings]

[0026] [Figure 1] FIG. 2 is a perspective longitudinal sectional view of a rotary cutting tool. [Diagram 2] 2 is an exploded perspective vertical sectional view of the rotary cutting tool shown in FIG. 1. [Diagram 3] FIG. 3 is a side view of the replaceable cutting head shown in FIGS. 1 and 2. [Figure 4] A detail of FIG. [Diagram 5] FIG. 3 is a perspective view of the tool holder shown in FIGS. 1 and 2. [Figure 6] FIG. 6 is a longitudinal cross-sectional view of the female coupling member shown in FIG. 5. [Figure 7]2 is a detail of the longitudinal cross-sectional view of the rotary cutting tool shown in FIG. 1 when the rotary cutting tool is in a locked position. [Figure 8] FIG. 1 is a schematic diagram of a back-tapered conical external thread form and a parallel internal thread form superimposed on the external thread form when the rotary cutting tool is in a released position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] It will be understood that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some elements may be exaggerated relative to other elements for clarity or several physical components may be included in a single functional block or element. Where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

[0028] In the following description, various aspects of the subject matter of the present application are described. For purposes of explanation, specific configurations and details are described in sufficient detail to provide a thorough understanding of the subject matter of the present application. However, it will be apparent to one skilled in the art that the subject matter of the present application may be practiced without the specific configurations and details presented herein.

[0029] Attention is initially directed to Figures 1 and 2, which illustrate a rotary cutting tool 20 of a type used in milling operations, specifically end milling, in accordance with an embodiment of the present subject matter. The rotary cutting tool 20 has a longitudinal tool axis L about which the tool rotates in a rotational direction R.

[0030] The rotary cutting tool 20 includes an interchangeable cutting head 22 having a head longitudinal axis A that rotates in a rotational direction R about the head longitudinal axis A. The head longitudinal axis A is oriented in a forward direction D. F From rear direction D R The replaceable cutting head 22 may typically be formed from a cemented carbide material.

[0031] The rotary cutting tool 20 also includes a tool holder 24 having a holder longitudinal axis C. The tool holder 24 may typically be formed from steel. The interchangeable cutting head 22 may be removably held to the tool holder 24 by a threaded coupling mechanism. Such a threaded coupling mechanism may potentially be advantageous for other types of rotary cutting processes other than those mentioned above, such as, for example, reaming or drilling.

[0032] It should be understood that use of the terms "forward" and "rearward" throughout this description and claims refers to the relative position of the interchangeable cutting head 22 with respect to the tool holder 24 of the assembled rotary cutting tool 20, as seen in Figure 1. The terms "forward" and "rearward" may also be applied to the direction of the head longitudinal axis A toward the left and right in Figures 3 and 4, respectively, and to the direction of the holder longitudinal axis C toward the left and right in Figures 5 and 6, respectively. It is understood that the tool holder 24 also extends along its own forward to rearward direction along the holder longitudinal axis C.

[0033] 3 and 4. The interchangeable cutting head 22 has a forward portion that forms a cutting portion 26 and a rearward portion that forms a mounting portion 28. According to certain embodiments of the present subject matter, the interchangeable cutting head 22 may be formed to have a unitary, integral, one-piece construction. This provides the advantage that the interchangeable cutting head 22 does not have a removable cutting insert (not shown).

[0034] 3, the cutting portion 26 includes at least one peripheral cutting edge 30. In this non-limiting example shown in the drawing, there may be just four peripheral cutting edges. Each peripheral cutting edge 30 is formed at the intersection of a peripheral flank face 32 and a peripheral rake face 34. The peripheral flank face 32 is arranged behind the peripheral cutting edge 30 in the direction of rotation R, and the peripheral rake face 34 is arranged ahead of the peripheral cutting edge 30 in the direction of rotation. The orientation of the peripheral cutting edges 30 allows for the execution of a metal cutting process.

[0035] According to certain embodiments of the present subject matter, the cutting portion 26 may include at least one flute 36 for evacuating chips (not shown) generated during the cutting process. One flute 36 is associated with each peripheral cutting edge 30. The replaceable cutting head 22 may include one or more end cutting edges 30b on an end face 37 of the cutting portion 26. In this non-limiting example shown in the drawings, the replaceable cutting head 22 may include just four end cutting edges 30b.

[0036] 3 and 4, the mounting portion 28 includes a male coupling member 38 that projects rearwardly from a head base surface 40. The head base surface 40 extends transversely to the head longitudinal axis A and defines the boundary between the cutting portion 26 and the mounting portion 28. That is, the cutting portion 26 is formed in front of the head base surface 40 and the mounting portion 28 is formed rearward of the head base surface 40. According to certain embodiments of the present subject matter, the male coupling member 38 may be rigid. The head base surface 40 may be perpendicular to the head longitudinal axis A. The head base surface 40 is intended to abut a corresponding surface 70 (described further below) on the tool holder 24 when the rotary cutting tool 20 is in a locked position, as described below.

[0037] The male coupling member 38 includes an external thread 42. With reference to FIGURE 3, the external thread 42 includes external threads 44 that extend helically about an external thread axis B. The external thread axis B is coincident with the head longitudinal axis A. Thus, the externally threaded portion 42 and the replaceable cutting head 22 are coaxial. With reference to FIGURE 4, the external threads 44 include a forward exterior flank surface 46 and a rearward exterior flank surface 48 and an exterior top surface 50 extending therebetween. The forward exterior flank surface 46 and the rearward exterior flank surface 48 are oriented in opposite axial directions D. F , D R , and the front outer flank surface 46 faces the forward direction D F , and the rear outer flank surface 48 faces in the rear direction D R. The leading exterior flank 46 and the trailing exterior flank 48 define an external thread groove 52. The external thread groove 52 extends helically about the external thread axis B and includes an external bottom surface 54. The external threads 42 have an external thread pitch PE. According to certain embodiments of the present subject matter, the external thread pitch PE can be constant.

[0038] As shown in FIG. 7 , in a cross-sectional view taken on an axial plane (i.e., a plane containing the male thread axis B), the external upper surface 50 forms a plurality of male thread crests 56 and the external bottom surface 54 forms a plurality of male thread roots 58.

[0039] In the same cross-sectional view, the forward external flank surface 46 and the rearward external flank surface 48 may be inclined at an external flank angle α with respect to a radial plane perpendicular to the male thread axis B. Preferably, the external flank angle α may be between 28° and 34°, more preferably 31°. The male thread 42 defines an external thread form 60, which may be trapezoidal. As used herein, "trapezoidal" refers to a geometric shape with four sides, two of which are parallel to one another, while "rectangle with no parallel sides" refers to a geometric shape with four sides, two of which are not parallel to one another. The external top surface 50 and the external bottom surface 54 may smoothly transition to the forward external flank surface 46 and the rearward external flank surface 48, respectively, which define a radius. Alternatively, the male thread form 60 may be triangular, with the external top surface 50 and the external bottom surface 54 forming an edge.

[0040] The male thread 42 is a back-tapered conical thread. It will be understood that throughout this description and the claims, the term "back-tapered conical thread" refers to a thread in which at least one of the threads and grooves extends around a respective cone, the surface of which tapers radially outwardly toward the thread axis in the rearward direction, and at least one of the thread crests and thread roots thus increases in distance from the thread axis in the rearward direction. Thus, in a back-tapered conical thread, at least one thread diameter (thread diameter d1 of the male thread 44 or thread diameter d2 of the male thread groove 52, or both) increases in distance from the thread axis in the rearward direction D of the cutting head 22. FSuch a back-tapered conical thread may be formed by threading an external turning insert into the hollow front end of a cylindrical steel rod. As the steel rod rotates and moves axially to form the male thread, it also moves radially away from the "static" cutting insert, resulting in the thread having a conical shape. The cone and thread are coaxial. In this non-limiting example shown in FIG. 8, both the male thread and the female thread groove extend around their respective cones. Specifically, the thread groove extends around an inner end cone K1 defined by the point where the outer bottom surface 54 transitions to the forward outer flank surface 46. The male thread extends around an outer end cone K2 defined by the point where the outer top surface 50 transitions to the forward outer flank surface 46. Similarly, it should be understood that throughout this description and the claims, the term "forward tapered conical thread" refers to a thread in which the external threads extend around a cone, the surface of which tapers radially inwardly toward the thread axis in the rearward direction, and thus the thread crest decreases in distance from the thread axis in the rearward direction.

[0041] Each turn of the male thread form 60 is offset from the male thread axis B by a radial distance that is determined by the male thread 42 being a back-tapered conical thread such that the male thread 42 spirals backwards D about the thread axis. R Thus, the forward exterior flank surface 46 increases in the aft direction D R It spirals radially outward at

[0042] At least one of the external thread 44 and the external groove 52 may extend around a respective cone K1, K2 having a cone angle γ. The cone angle γ may be in the range 0.02°≦γ≦1.0°. Advantageously, the cone angle γ may be just equal to 0.4°. Both the external thread 44 and the external groove 52 may extend around a respective cone K1, K2. The cone angle γ may be the same for the inner end cone K1 and the outer end cone K2. It should be further understood that throughout this description, the use of the term "cone angle" refers to the angle formed by the tapered surfaces of the cones in a longitudinal section. It should be noted that the term "longitudinal section" refers to a section taken in a plane that includes the longitudinal axis. Such a longitudinal section results in an axial plane that includes the longitudinal axis.

[0043] The plurality of male thread crests 56 define the thread major diameter of the male thread 42, and the plurality of male thread roots 58 define the thread root diameter of the male thread 42. The male thread height H of the male thread 42 is calculated by subtracting the thread root diameter from the thread major diameter and dividing the result by two. E Male thread height H E is constant or varies in the rearward direction D depending on whether the male thread 44 and the male thread groove 52 extend around the respective cone. R In this non-limiting example shown in the drawing, the male thread height H E is constant in the rearward direction. According to certain embodiments of the present subject matter, the male threads 42 may have approximately 3 to 4 turns in the axial direction.

[0044] According to certain embodiments of the present subject matter, the external thread crests 56 may be inclined with respect to the external thread axis B and may be collinear with one another. Thus, the external top surface 50 may be on the outer end cone K2. The external thread roots 58 may be inclined with respect to the external thread axis B and may be collinear with one another. Thus, the external bottom surface 54 may be on the inner end cone K1.

[0045] 3 and 4, the male coupling member 38 includes a forward bearing portion 62. The forward bearing portion 50 is disposed on the forward side of the male threads 42. The forward bearing portion 62 is rotatable in the rearward direction D.R 2. The rotary cutting tool 20 includes a forward head abutment surface 64 that tapers radially inward toward the head longitudinal axis A at . That is, the forward head abutment surface 64 has a radially outwardly facing conical shape. It should be noted that the forward head abutment surface 64 is intended to abut a corresponding surface 94 (described further below) on the tool holder 24 when the rotary cutting tool 20 is in a locked position, as described below.

[0046] It should be understood that throughout this description and the claims, use of the terms "radially inward / inward" and "radially outward / outward" refer to relative positions in directions perpendicular to the head longitudinal axis A and / or holder longitudinal axis C in Figures 3, 4 and 6, toward and away from the respective axes.

[0047] 5 and 6, the tool holder 24 is rotated in a forward direction D F From rear direction D R Tool holder 24 has a holder longitudinal axis C extending rearwardly from a holder front face 70. Tool holder 24 includes a female coupling member 68 extending rearwardly from a holder front face 70. Holder front face 70 extends transversely to holder longitudinal axis C. According to certain embodiments of the present subject matter, holder front face 70 may be perpendicular to holder longitudinal axis C.

[0048] The female coupling member 68 includes an internal thread 72. As shown in a longitudinal cross-section of the female coupling member 68 encompassing the internal thread axis D (i.e., FIG. 6 ), the internal thread 72 includes internal threads 74 that extend helically about the internal thread axis D. The internal thread axis D is coincident with the holder longitudinal axis C. Thus, the internal thread 72 is coaxial with the tool holder 24. The internal threads 74 include a leading internal flank surface 76 and a trailing internal flank surface 78, and an internal top surface 80 extending therebetween. The leading internal flank surface 76 and the trailing internal flank surface 78 are oriented in opposite axial directions D. F , D R , and the front inner flank surface 76 faces the forward direction D F , and the rear inner flank surface 78 faces in the rear direction D R. The leading inside flank 76 and the trailing inside flank 78 define an internal thread groove 82. The internal thread 72 has an internal thread pitch PI. According to certain embodiments of the present subject matter, the internal thread pitch PI may be constant. The internal thread pitch PI may be the same as the external thread pitch PE.

[0049] The female thread groove 82 extends helically about the female thread axis D and includes an internal bottom surface 84. In a cross-sectional view taken in an axial plane (i.e., a plane containing the female thread axis D), the internal top surface 80 defines a number of female thread crests 88 and the internal bottom surface 84 defines a number of female thread roots 90. According to certain embodiments of the present subject matter, the multiple female thread crests 88 are parallel to the female thread axis D and may be collinear with one another. The multiple female thread roots 90 are parallel to the female thread axis D and may be collinear with one another.

[0050] In a cross-sectional view taken at an axial plane containing the female thread axis D (i.e., FIG. 6), the leading internal flank surface 76 and the trailing internal flank surface 78 may be inclined at an internal flank angle β relative to a radial plane perpendicular to the female thread axis D. Preferably, the internal flank angle β may be 31°. The female threads 72 define a female thread form 86 that may be trapezoidal. Referring now to FIG. 8, the sides of a rectangle without parallel sides may not be of equal length. The internal top surface 80 and the internal bottom surface 84 may smoothly transition to the leading internal flank surface 76 and the trailing internal flank surface 78, which respectively define radii. Alternatively, the female thread form 86 may be triangular with the internal top surface 80 and the internal bottom surface 84 forming an edge.

[0051] According to certain embodiments of the subject matter of the present application, the female threads 72 may be parallel threads. It should be understood that throughout this description and the claims, the term "parallel threads" refers to threads in which the threads and grooves extend around the respective cylinders, and therefore all thread crests 88 are equidistant from all thread roots 90. Specifically, the female threads 74 extend around an inner cylinder C1 defined by the points where the inner top surface 80 transitions into the leading inner flank surface and the trailing inner flank surface 78. The inner top surface 80 may be on the inner cylinder C1. The threads 82 extend around an outer cylinder C2 defined by the points where the inner bottom surface 84 transitions into the trailing inner flank surface 78. The inner bottom surface 84 may be on the outer cylinder C2.

[0052] The plurality of female thread crests 88 respectively define a thread root diameter of the female thread 72, and the plurality of female thread roots 90 respectively define an outer diameter of the female thread 72. The female thread height H of the female thread 72 is calculated by subtracting the thread root diameter from the outer diameter and dividing the result by two. I Thread height H is equal to I According to certain embodiments of the present subject matter, the female threads 72 may have approximately 3 to 4 turns in the axial direction.

[0053] 5 and 6, the female coupling member 68 includes a forward support portion 92. The forward support portion 92 is disposed on the forward side of the female threads 72. The forward support portion 92 is oriented in the rearward direction D. R 3. The holder includes a forward holder abutment surface 94 that tapers radially inwardly at a position toward the holder longitudinal axis C. That is, the forward holder abutment surface 94 has a radially inward facing conical shape. The forward holder abutment surface 94 is configured and dimensioned to complement the forward head abutment surface 64 discussed above.

[0054] The assembly of the rotary cutting tool 20 is known, for example, from U.S. Patent No. 6,485,220 B2, which is incorporated herein by reference in its entirety. It is noted that the rotary cutting tool 20 is adjustable between a released position and a locked (or assembled) position.

[0055] Attention is now directed to FIG. 8 , which shows a schematic diagram of the male thread form 60 of the back-tapered conical male thread 42. Superimposed thereon by dashed lines is the female thread form 86 of parallel female threads that are not threadingly engaged with one another (i.e., the rotating tool is in the released position). The cone angle γ of the male thread 42 forming the male thread form 60 has been exaggerated to clearly show the thread forms 60, 98 relative to one another, and therefore the distances do not represent true values. In accordance with certain embodiments of the present subject matter, the forward exterior flank surfaces 46 are spaced from their respective rearward interior flank surfaces 78 by a flank distance E. Moreover, the magnitude of the flank distance E is measured in the rearward direction D. R That is, the magnitude of the flank distance E decreases in the rearward direction D R decreases for successive turns of the screw.

[0056] To adjust the rotary cutting tool 20 to the locked position, the male threads 42 are threaded (i.e., turned) into the female threads 72. The flank distance E is reduced so that the forward exterior flank surface 46 initially abuts the rearward interior flank surface 78 at the rearmost thread turn. By continuing to thread the male threads 42 into the female threads 72, the forward exterior flank surface 46 is rotated in a forward direction D until the threaded connection is fully tightened and the rotary cutting tool 20 is in the locked position. F 2 and 3. Each successive turn of the thread gradually abuts the rear inner flank surface 78 at

[0057] In the locked position, the male coupling member 38 is removably retained in the female coupling member 68, and the male and female threads 42 and 72 are threadingly engaged with one another. Referring now to FIG. 7 , the forward head abutment surface 64 abuts the forward holder abutment surface 94. According to certain embodiments of the present subject matter, the rearwardly facing head base surface 40 may abut the forwardly facing holder front surface 70. The rearwardly facing inner flank surface 78 may abut the forwardly facing outer flank surface 46. The forwardly facing inner flank surface 76 may be spaced from the rearwardly facing outer flank surface 48 by a rearwardly facing distance D1. The inner top surface 80 may be spaced from the outer bottom surface 54 by an upward distance D2. The inner bottom surface 84 may be spaced from the outer top surface 50 by a downward distance D3. The magnitudes of the rearwardly facing distance D1, the upward distance D2, and the downward distance D3 are all measured in the rearwardly facing direction D1.R can be reduced to.

[0058] Configurations that provide decreasing flank distance E (as discussed above) provide that, when assembled (i.e., threadably engaged), the frictional engagement between the male threads 42 and female threads 72 (i.e., between the rearward inner flank surface 78 and the forward outer flank surface 46) increases in a direction from the forwardmost turn to the aftmost turn of the male threads 42. In particular, configurations where the cone angle γ is in the range of 0.02°≦γ≦1.0° provide that the male threads 42 are threadably engaged with the female threads 72 along their entire axial extent, providing sufficient frictional engagement at the forward end of the connection for secure installation.

[0059] Also, due to the configuration with reduced flank distance E, advantageously, when the rotary cutting tool 20 is assembled and operated, the contact force is reduced in the rearward direction D as compared to a conventional thread (e.g., parallel male threads threadingly engaged with parallel female threads). R Such thread engagement improves the stability of the rotary cutting tool 20 against lateral cutting forces.

[0060] Although the subject matter of the present application has been described in some detail, it should be understood that various changes and modifications can be made without departing from the spirit or scope of the invention, as hereinafter claimed.

Claims

1. It has a longitudinal axis (L) and a forward direction (D Ｆ ) to the rear (D Ｒ ), a tool holder (24) having a holder longitudinal axis (C) and an interchangeable cutting head (22) threadedly engaged with the tool holder (24); The replaceable cutting head (22) is Ｆ ) from the rear direction (D Ｒ ), and the replaceable cutting head (22) has a head longitudinal axis (A) extending along the a front portion forming a cutting portion (26); a rear portion forming a mounting portion (28), the mounting portion (28) comprising a male coupling member (38) having external threads (42) and projecting rearwardly from a head base surface (40), the head base surface (40) extending transversely to the head longitudinal axis (A) and defining a boundary between the cutting portion (26) and the mounting portion (28); the male thread (42) comprises an external thread (44) extending helically around a male thread axis (B) and comprises a forward external flank surface (46) and a rearward external flank surface (48), and an external upper surface (50) extending between the forward external flank surface (46) and the rearward external flank surface (48); The front external flank surface (46) and the rear external flank surface (48) are oriented in opposite axial directions (D Ｆ , D Ｒ ) and defining an external helical thread groove (52) having an external bottom surface (54); The male thread (42) of the male coupling member (38) is Ｒ At least one thread diameter (d １ , d ２ ) is a back taper conical thread, The tool holder (24) has a female coupling member (68) having internal threads (72) extending rearwardly from a holder front face (70), the holder front face (70) extending transversely to the holder longitudinal axis (C); The rotary cutting tool (20) comprises: a release position in which the female thread (72) and the male thread (42) are not threadedly engaged with each other; a locked position in which the male coupling member (38) is releasably retained to the female coupling member (68) by the female threads (72) and the male threads (42) being threadedly engaged with one another; The female threads (72) of the female coupling member (68) are straight threads; In a cross-sectional view taken on an axial plane including the male screw axis (B), The outer upper surface (50) forms a plurality of male thread crests (56) which are inclined with respect to the male thread axis (B) and are in line with one another; The rotary cutting tool (20), wherein the exterior bottom surface (54) defines a plurality of external thread roots (58) that are inclined relative to the external thread axis (B) and collinear with one another.

2. 2. The rotary cutting tool (20) of claim 1, wherein at least one of the external thread (44) and the external thread groove (52) extends around a respective cone (K1, K2) having a cone angle (γ).

3. 3. The rotary cutting tool (20) of claim 2, wherein the external thread (44) and the external thread groove (52) extend around an outer end cone (K2) and an inner end cone (K1), respectively.

4. The rotary cutting tool (20) of claim 3, wherein the cone angle (γ) is the same for the inner cone (K1) and the outer cone (K2).

5. The rotary cutting tool (20) of claim 2, wherein the cone angle (γ) is in the range of 0.02°≦γ≦1.0°.

6. The rotary cutting tool (20) of claim 5, wherein the cone angle (γ) is exactly equal to 0.4°.

7. 2. The rotary cutting tool (20) of claim 1, wherein, in a cross-sectional view taken on an axial plane containing the head longitudinal axis (A), the external threads (42) define an external thread form (60) that is trapezoidal.

8. The rotary cutting tool (20) of claim 1, wherein the external threads (42) have a constant external thread pitch (PE).

9. 2. The rotary cutting tool (20) of claim 1, wherein frictional engagement between the male threads (42) and the female threads (72) increases in a direction from a forward-most turn of the male threads (42) toward a rear-most turn of the male threads (42).

10. the female thread (72) comprises a female thread (74) extending helically around a female thread axis (D) and comprises a leading internal flank surface (76) and a trailing internal flank surface (78), and an internal upper surface (80) extending between the leading internal flank surface (76) and the trailing internal flank surface (78); The front internal flank surface (76) and the rear internal flank surface (78) are oriented in opposite axial directions (D Ｆ , D Ｒ ) and defining an internal helical thread groove (82) having an internal bottom surface (84); The front external flank surface (46) and the front internal flank surface (76) are in the forward direction (D Ｆ ) facing The rearward outer flank surface (48) and the rearward inner flank surface (78) are in the rearward direction (D Ｒ ) facing The rotary cutting tool (20) of claim 1, wherein in the locked position, the rearward interior flank (78) abuts the forward exterior flank (46).

11. In the locked position, the leading inside flank surface (76) is spaced from the trailing outside flank surface (48) by a trailing flank distance (D1); The inner top surface (80) is spaced an upward distance (D2) from the outer bottom surface (54); The rotary cutting tool (20) of claim 10, wherein the inner bottom surface (84) is spaced a downward distance (D3) from the outer top surface (50).

12. The rear flank distance (D1), the upper distance (D2) and the lower distance (D3) are all in the rearward direction (D Ｒ 12. The rotary cutting tool (20) of claim 11, wherein the cutting edge is reduced to

13. 9. The rotary cutting tool (20) of claim 8, wherein the female threads (72) have the same constant female thread pitch (PI) as the male thread pitch (PE).

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