KR20080000544A - Rotary cutting tool - Google Patents

Abstract

A rotary cutting tool is provided to reduce excessive fraction applied to the contact surface between a tool sank and a central post by transmitting axial stress applied by a cutting head to an axial support surface of the tool sank and rotational torque to a perpendicular torque support surface. A rotary cutting tool comprises a cutting head(200) and a tool sank(100). The tool sank is integrated with a drill body having a chip flute. The cutting head is installed to a coupling structure formed at the top of the tool sank. The cutting head includes a central post(230) and a plurality of wings(210,220). The central post is coaxially installed to a rotary shaft of a drill body. The wings extend in a radial direction on the top of the central post. The combining structure of the tool sank includes a plurality of combining protrusions(110,120) and a central space(130). The combining protrusion extends from the edge of the tool sank in parallel to a rotary shaft. The central space is formed at the center of the combining protrusion and accommodates the central post of the cutting head. Each combining protrusion includes a torque support unit and a fraction holding unit. The torque support unit includes axial support surfaces(111a,121a) and recesses(111,121). The fraction holding unit is an inner wall of each combining protrusion. The inner wall of the combining protrusion contacts with the outer surface of the central post. The horizontal section of the fraction holding unit shapes into an arc. Each combining protrusion includes fastening elements interlocked with rotation guide elements of the central post.

Description

Rotary cutting tool

The present invention relates to a drilling tool, and more particularly to a rotary cutting tool capable of providing increased clamping force and durability through the surface contact of the cutting head and tool shank.

A drilling tool comprising a conventional replaceable cutting head is disclosed in WO2003 / 070408. 1 is a perspective view of a cutting head constituting the above-mentioned drilling tool, Figure 2 is a perspective view of the shank.

The cutting head 10 includes a tightening pin 13 and two wings 11 and 12 formed on the tightening pin 13. One side of the wing parts 11 and 12 is provided with the support surface 13a which contacts the support surface 22a of the shank 20 mentioned later.

The shank 20 includes two rims 21 and 22 arranged at angular intervals, and the chucking grooves 31 and 32 are formed by these rims 21 and 22. In addition, a space 30 is formed between the rims 21 and 22 to accommodate the fastening pin 13 of the cutting head 10.

Recesses 21c and 22c defined by the bottom surfaces 21b and 22b and the supporting surfaces 21a and 22a are formed on the upper side of the rim portions 21 and 22, so that the wing portions 11 and 22 of the cutting head 10 are formed. 12 is received in the recesses 21c and 22c, respectively.

In the state where the cutting head 10 and the shank 20 are fastened, the wings 11 and 12 of the cutting head 10 are located in the recesses 21c and 22c of the shank 20, respectively. The support surfaces 11a and 12a of the wing portions 11 and 12 contact the support surfaces 21a and 22a of the recesses 21c and 22c, and the bottom surface 21b of the recesses 21c and 22c. , 22b).

Meanwhile, in the state where the cutting head 10 and the shank 20 are fastened, the tightening pin 13 of the cutting head 10 is inserted into the space 30 of the shank 20, and the outer circumferential surface of the tightening pin 13 is It is in line contact with the inner peripheral surfaces of the rims 21 and 22 forming the space 30.

3 is a perspective view of the drilling tool, showing a state in which the cutting head 10 and the shank 20 shown in FIGS. 1 and 2 are engaged.

Hereinafter, the relationship between the tightening pin 13 of the cutting head 10 and the rims 21 and 22 of the shank 20 will be described with reference to FIGS. 1, 2, 4A, and 4B.

4A is a cross-sectional view showing the relationship between the rim portions 21 and 22 of the shank 20 and the tightening pins 13 of the cutting head 10 before the cutting head 10 is rotationally fixed in the shank 20. FIG. 4b is a cross-sectional view showing the relationship between the rim portions 21 and 22 of the shank 20 and the tightening pins 13 of the cutting head 10 in a state where the cutting head 20 is rotated in the shank 20. to be.

When the cutting head 10 is positioned in the shank 20 to engage the cutting head 10 and the shank 20, the wings 11 and 12 of the cutting head 10 are recessed in the shank 20 ( Corresponding to the chucking grooves 31, 32 between the rims 21, 22 without being located in 21c, 22c, the curved outer circumferential surface 13a of the tightening pin 13 of the cutting head 10 also has a chucking groove ( 31, 32) (state of Fig. 4A).

Here, the outline of the curved outer circumferential surface 13a has an elliptic shape, and its long axis is located in the chucking groove to facilitate initial coupling.

Thereafter, when the cutting head 10 is rotated in the direction of the arrow of FIG. 4A, each of the vanes 11 and 12 of the cutting head 10 is positioned in the recesses 21c and 22c of the shank 20, respectively. The support surfaces 11a and 12a of the respective wing portions 11 and 12 are in contact with the support surfaces 21a and 22a of the recesses 21c and 22c, and the bottom thereof is the bottom surface of each recess 21c or 22c. It is located on (21b, 22b).

At the same time, the elliptical outer circumferential surface 13a of the tightening pin 13a of the cutting head 10 is in elastic contact with the inner circumferential surfaces of the rims 21 and 22 of the shank 20 (state of FIG. 4B). Therefore, the tightening pin 13 of the cutting head 10 is firmly coupled to the rims 21 and 22 of the shank 20, and the rotational force of the shank 20 is transmitted to the cutting head 10 by the coupling structure as described above. do.

However, the following problems occur in the bonding process of the cutting head 10 and the shank 20 as described above.

As shown in FIG. 4A, the outer circumferential surface of the tightening pin 13 of the cutting head 10 is composed of an elliptical outer circumferential surface 13a and a cutout portion 13b formed therebetween. Before rotation of the cutting head 10 is made, the boundary between the arc-shaped outer circumferential surface 13a of the tightening pin 13 and the cutout portion 13b is in contact with the inner circumferential surfaces of the rims 21 and 22.

In the process of inserting and rotating the tightening pin 13 of the cutting head 10, the sharp boundary between the rotating elliptical phase outer peripheral surface 13a and the cutout portion 13b is the rim 21, 22 of the shank 20. It will scratch the inner surface.

On the other hand, the cutting head 10 has undergone a drilling process, the cutting edge is worn, and thus replaced with a new cutting head. As the cutting head 10 is repeatedly mounted on the shank 20, the boundary formed on the tightening pin 13 of the cutting head 10 repeatedly contacts the scratch formed on the inner circumferential surfaces of the rims 21 and 22 of the shank 20. The depth and area of the scratches gradually increase. Such a scratch formed on the shank 20 lowers the bonding force between the cutting head 10 and the shank 20, and also shortens the life of the expensive shank 20.

As shown in FIGS. 4A and 4B, the tightening pin 13 of the cutting head 10 has an elliptical shape whose cross section is the long axis of the line connecting the central portions of the curved outer circumferential surfaces 13a. Thus, the arc-shaped outer circumferential surface 13a of the tightening pin 13 and the inner circumferential surfaces of the rims 21 and 22 of the shank 20 are in line contact in the longitudinal direction (contact section is shown as a point in FIG. 4B in cross section). . The contact between the tightening pin 13 of the cutting head 10 and the rims 21 and 22 of the shank 20 is also vulnerable to abrasion between the cutting head 10 and the shank 20 and causes a decrease in the bonding force.

In the structure of the cutting head 10 shown in FIG. 1, the axial pressure and the rotational torque of the shank 20 act on the inclined support surfaces 11a and 12a of the wings 11 and 12 so that the cutting head The fatigue load of the wing parts 11 and 12 of (10) increases. In addition, since there is no locking structure to fix in the axial direction, the axial fixation of the cutting head 10 is unstable.

The present invention is designed to solve the above problems of the rotary cutting tool, it is possible to maintain a tight coupling state of the tool shank and the cutting head and to prevent damage to the tool shank and the cutting head to increase the endurance life of the tool shank It is an object to provide a rotary cutting tool.

In the cutting tool according to the present invention, the cutting head is composed of a cylindrical center post concentric with the axis of rotation of the drill body and a plurality of wings extending radially in the upper end of the center post, each wing having an end face, an upper face, A lower surface, a front surface formed on the side of the drill rotation direction, and a rear surface formed on the opposite direction, wherein a chip flute is formed on the front surface and extends to the side wall of the center post, and the side wall of the center post forms a chip flute. It consists of a cutout portion and an outer circumferential surface of a circular arc positioned therebetween, a rotation guide element extending in the circumferential direction is formed on the outer circumferential surface of the center post.

The engaging structure has a plurality of engaging projections extending in a direction parallel to the axis of rotation from the edge of the tool shank to form a central space for accommodating the central post at its central portion, each engaging projection having friction between the upper torque support and the lower portion. Consists of a tightening portion, the torque support portion is provided with a recess defined by the axial support surface and the torque support surface to be seated on the side of the drill rotation direction, so that the inner wall of the friction tightening portion in surface contact with the outer peripheral surface of the center post The cross section forms an arc, the fastening element engaging the rotation guide element of the center post on the inner wall of the friction clamp.

In the surface contact, the inner wall of the friction tightening part is rotated in the reverse direction of the drill by forcibly inserting the center post until the rear surface of the wing is in contact with the torque supporting surface while the rotation guide element is engaged with the fastening element in the central space. It is made by elastically pressing the outer peripheral surface of the center post.

In the rotary cutting tool according to the invention, the rotation guide element is a rotation guide groove, and the fastening element is a protruding guide rib.

Further, the outer circumferential surface of the center post may be chamfered on the side of the drill reverse rotation direction, or the inner wall of the friction tightening portion may be chamfered on the side of the drill rotation direction.

Here, the torque support surface of the engaging projection is formed in parallel with the axial direction and the radial elastic displacement of the engaging projection is preferably larger toward the top.

The rotary cutting tool according to the present invention as described above has the following advantages.

In the drilling process, no excessive frictional force is applied to the contact surface between the tool shank and the center post since the axial stress applied through the cutting head is transmitted to the axial support surface of the tool shank and the rotational torque to the upright torque support surface, respectively.

The frictional area is increased by the surface contact between the outer circumferential surface on the arc of the center post and the inner wall surface of the engaging projection, so that wear of the central post and the engaging projection can be minimized and the total coupling force between both members can be increased.

The outer circumferential surface on the arc of the center post of the cutting head and the inner wall of the engaging projection of the tool shank can be contacted without generating a large resistance. Therefore, scratches and chippings do not occur on the inner wall of the engaging protrusion of the tool shank, and the life of the expensive tool shank can be extended.

Hereinafter, with reference to the accompanying drawings, a rotary cutting tool according to the present invention will be described in detail. In the following description, as an example of a rotary cutting tool according to the present invention, a drilling tool used in a drilling process will be described.

5 is a perspective view of a cutting head constituting a drilling tool according to the present invention, FIG. 6 is an exploded perspective view of a drilling tool according to the present invention having a cutting head and a tool shank, and FIG. 7 is a plan view of the tool shank shown in FIG. to be.

A drilling tool according to an embodiment of the present invention includes a cutting head 200 and a tool shank 100. The tool shank 100 is integrally formed with a long cylindrical drill body having a chip flute formed on its outer circumferential surface. In addition, the cutting head 200 is detachably mounted to the coupling structure formed at the upper end of the tool shank 100.

The cutting head 200 includes a cylindrical center post 230 that is concentric with the axis of rotation of the drill body and a plurality of wing portions 210 and 220 extending in the radial direction at the upper end of the center post 230.

Each wing portion 210, 220 has an end surface, an upper surface, a lower surface 211b, 221b, a front surface 221c formed on the side of the drill rotation direction, and a rear surface 211a, 221a formed on the opposite direction. do. A chip flute is formed on the front surface 221c and extends to the side wall of the center post 230.

The side wall of the center post 230 is composed of a cutout portion 232a constituting a chip flute and an outer circumferential surface 233a, 233b positioned therebetween, and a circumference on the outer circumferential surfaces 233a, 233b of the center post 230. Rotation guide elements 234a and 234b extending in the direction are formed. Here, the rotation guide elements 234a and 234b are grooves having a predetermined depth.

On the other hand, the chamfering part 235a, 235b is formed in the terminal part corresponding to back surface 211a, 221a among the circular arc outer peripheral surfaces 233a, 233b of the center post 230. As shown in FIG. The chamfered portions 235a and 235b may have various shapes. For example, as shown in FIGS. 5 and 8A, the end portions of the arcuate outer circumferential surfaces 233a and 233b of the posts 230 corresponding to the rear surfaces 211a and 221a are inclined downward toward the cutout portion 232a. It is possible to form chamfered portions 235a and 235b which are processed and subsequently have a small diameter partial arcuate face.

 The coupling structure formed on the tool shank 100 is formed at the center of the plurality of coupling protrusions 110 and 120 and the coupling protrusions 110 and 120 extending in a direction parallel to the rotation axis from the edge of the tool shank 100 and is cut. It consists of a central space 130 for receiving the center post 230 of the head 200.

Each engaging projection 110, 120 is composed of a torque support of the upper portion and the friction fasteners of the lower portion.

The torque support portion is formed on the side of the drill rotation direction, and is recessed to be defined by the axial support surfaces 111a and 121a and the torque support surfaces 111b and 121b so that the wings 210 and 220 of the cutting head 200 are seated. (111, 121).

The friction tightening portion is an inner wall of each engaging protrusion 110 and 120, and the inner wall of each engaging protrusion 110 and 120 has an arc-shaped cross section so as to be in surface contact with the outer circumferential surface of the center post 230. In addition, fastening elements 114 and 124 are formed on inner walls of the engaging projections 110 and 120 to engage the rotation guide elements 234a and 234b of the center post 230 of the cutting head 200.

The rotation guide elements 234a and 234b of the cutting head 200 are rotation guide grooves circumferentially extending to the arcuate outer circumferential surfaces 233a and 233b of the center post 230, and the fastening element of the tool shank 100 protrudes. Guide ribs 114 and 124 that are formed and can be received in the rotary guide grooves 234a and 234b.

The coupling process of the cutting head 200 and the tool shank 100 configured as described above will be described with reference to the drawings.

FIG. 8A is a cross-sectional view taken along the line AA of FIG. 6, wherein the center post 230 and the tool shank of the cutting head 200 before the cutting head 200 is rotated and fixed in the tool shank 100 (FIG. It is sectional drawing which shows the relationship of the engaging projection 110 and 120 of 100. FIG.

8B is a cross-sectional view taken along the line AA of FIG. 6, and the center post 230 of the cutting head 200 after the cutting head 200 is rotated and fixed in the tool shank 100. It is sectional drawing which shows the relationship of the engaging protrusion 110 and 120 of the tool shank 100. FIG.

First, the center post 230 of the cutting head 200 is positioned in the central space 130 of the tool shank 100. At this time, the outer circumferential surfaces 233a and 233b on the arc of the center post 230 are disposed to correspond to the spaces 140 and 150 between the engaging projections 110 and 120 of the tool shank 100, respectively (state of FIG. 8A). ).

In the state of FIG. 8A, when the cutting head 200 is rotated in the form of an interference fit in the direction opposite to the direction of drill rotation (the arrow direction in FIG. 8A), the rear surfaces of the wings 210 and 220 of the cutting head 200 ( 211a and 221a contact the torque supporting surfaces 111b and 121b constituting the recesses 111 and 121 of the engaging projections 110 and 120 of the tool shank 100, and the lower portions of the wings 210 and 220. The surfaces 211b and 221b contact the axial support surfaces 111a and 121a of the engaging projections 110 and 120.

Here, the inner diameter of the cylinder corresponding to the central space portion 130 before being pressed is formed to be slightly smaller than the diameter of the arcuate outer circumferential surface of the central post 230.

Therefore, the inner wall surfaces 112 and 122 of the engaging projections 110 and 120, which are friction fasteners, elastically pressurize the outer circumferential surface of the center post 230 of the cutting head 200, so that the cutting head 200 and the tool shank 100 Tightly coupled (state of FIG. 8B).

Hereinafter, the detailed functions of each part of the cutting head 200 and the tool shank 100 coupled through the above process will be described.

As shown in FIG. 6, the torque support surfaces 111b and 121b formed on the engaging projections 110 and 120 of the tool shank 100 are formed parallel to the axial direction of the drill body, and the axial support surfaces 111a and 121a) is preferably perpendicular to the axial direction.

By this structure, in the drilling process, the axial stress applied through the cutting head 200 is transmitted to the axial support surfaces 111a and 121a, and the rotational torque is transmitted to the torque support surfaces 111b and 121b, respectively. Excessive friction is not generated at the contact surface between the tool shank 100 and the cutting head 200.

As shown in FIG. 8A, the engaging protrusion 110 of the tool shank 100 and the virtual circle (shown in dashed lines) formed by the outer circumferential surfaces 233a and 233b on the arc of the center post 230 of the cutting head 200 are formed. The virtual source sources formed by the inner wall surfaces 112 and 122 of the 120 have almost the same radius of curvature.

In such a structure, the friction area is increased by the surface contact between the outer circumferential surfaces 233a and 233b of the center post 230 and the inner wall surfaces 112 and 122 of the engaging projections 110 and 120, thereby clamping against the same contact pressure. Can increase the power. Therefore, wear of the center post 230 and the engaging projections 110 and 120 can be minimized for the same design clamping force, and the durability of the tool shank 100 can be significantly increased.

On the other hand, when the cutting head 200 rotates in the tool shank 100 in the fixed state of FIG. 8B in the released state of FIG. 8A, at the initial stage of rotation, the cutting head 200 is positioned at the tip side of the outer peripheral surfaces 233a and 233b of the center post 230. The formed chamfered portions 235a, 235b correspond to the inner walls 121, 112 of the engaging projections 120, 110 of the tool shank 100. Therefore, the outer circumferential surfaces 233a and 233b of the center post 230 of the cutting head 200 and the inner walls 122 and 112 of the engaging protrusions 120 and 110 of the tool shank 100 have a large resistance between both members. Can be contacted smoothly without generating

In addition, even when the center post 230 is repeatedly rotated in the tool shank 100 to replace the cutting head 200, the engaging projection 120 of the tool shank 100 by the chamfered portions 233a and 233b as described above. , And scratches and chippings do not occur on the inner walls 121 and 112 of the 110, and thus the life of the expensive tool shank 100 can be extended.

The cutting head 200 with worn tips 201 and cutting edges 210a and 220a should be replaced with a new cutting head, for which the removal and mounting of the cutting head 200 to the tool shank 100 is repeated. Is done. Under these conditions, the present invention can reduce the damage of the tool shank, which is more expensive than the cutting head, and extend its life.

On the other hand, the drill rotational direction of the inner walls 112 and 122 of the engaging projections 110 and 120, that is, corresponding to the chamfers 235a and 235b formed in the center post 230 at the beginning of rotation of the cutting head 200. The chamfers 112a and 122a may be formed in the region. The circumferential outer circumferential surfaces 233a and 233b of the center post 230 of the cutting head 200 and the tool shank by the chamfers 112a and 122a formed on the inner walls 112 and 122 of the engaging projections 110 and 120. Initial contact of the inner walls 121 and 112 of the coupling protrusions 120 and 110 of the 100 may be made more smoothly.

In the state of FIG. 8B, the inner wall 112, 122 of the engaging protrusion 110, 120 of the tool shank 100 is formed in the rotation guide grooves 234a, 234b formed in the center post 230 of the cutting head 200. As the guide ribs 114 and 124 formed are accommodated, the cutting head 200 is firmly engaged with the tool shank 100 without falling out in the axial direction of the drill body. In addition, the center post with respect to the tool shank 100 is rotated by the rotation guide grooves 234a and 234b and the guide ribs 114 and 124 accommodated therein during the rotation process from the released state of FIG. 8A to the fixed state of FIG. 8B. Rotation of 230 may be guided.

Here, the tool shank 100 may have rotation guide grooves formed on the inner walls 112 and 122 of the engaging projections 110 and 120, and guide ribs may be provided on the center posts 230 of the cutting head 200, respectively. It can also be configured.

However, the coupling protrusions 110 and 120 of the tool shank 100 are structurally more robust by the guide ribs 114 and 124 as described above, and because of this structure, the tool shank 100 of the present invention has a small diameter. Especially useful for drilling tools. In addition, the rotation guide grooves 234a and 234b can be easily formed in the center post 230 of the cutting head 200 having a small diameter.

On the other hand, the radial elastic displacement of the coupling protrusions 110 and 120 of the tool shank 100 is preferably increased upward. That is, as indicated by the dashed line in FIG. 9, in the state where the tool shank 100 and the cutting head 200 are not coupled, the inner walls 112 and 122 of the coupling protrusions 110 and 120 are formed. The diameter of the imaginary circle (ie, the gap between the inner walls 112 and 122 of the engaging projections 110 and 120) becomes smaller toward the top.

Due to the structure as described above, when the center post 230 of the cutting head 200 is inserted into the central space 130 of the tool shank 100, pressure is uniformly applied to the entire center post 230.

As shown in FIGS. 5 and 6, the cutting head 200 may further include a hinge pin 231 formed at the center of the bottom surface of the central post 230, and the tool shank 100 may further include a central space portion ( The center portion of the bottom surface 132 of the 130 may further include a hole 131 corresponding to the hinge pin 231 of the cutting head 200.

When the cutting head 200 and the tool shank 100 are coupled, the hinge pin 231 is inserted into the hole 131 to guide the rotational movement of the cutting head 200, so that both members can be accurately coupled.

9 is a cross-sectional view illustrating a state in which a tool shank and a cutting head are coupled to each other, and illustrates that cooling fluid flow paths 119 and 129 are formed in the tool shank 100. That is, cooling fluid flow paths 119 and 129 may be formed in the coupling protrusions 110 and 120 of the tool shank 100, and outlets thereof are disposed on the upper surfaces of the coupling protrusions 110 and 120.

The cooling fluid supplied from the outside flows through the cooling fluid flow paths 119 and 129 and is discharged to the cutting head 200 to cool the cutting head 200 and the workpiece being processed.

As a result of the comparative experiment, in the conventional rotary cutting tool, about 30 to 40 cutting heads can be interchangeably mounted for a single tool shank, but in the rotary cutting tool according to the present invention, about 70 tools for one tool shank are provided. The cutting head can be mounted interchangeably.

Preferred embodiments of the present invention described above are disclosed for purposes of illustration, and one of ordinary skill in the art will recognize that various modifications, changes, and additions can be made within the spirit and scope of the present invention. Modifications and additions should be considered to be within the scope of the following claims.

1 is a perspective view of a cutting head constituting a general drilling tool.

2 is a perspective view of the shank constituting a general drilling tool.

3 is a perspective view of a state in which the cutting head and the shank shown in FIGS. 1 and 2 are fastened.

4A is a cross-sectional view showing the relationship between the rim of the shank and the pin of the cutting head before the cutting head shown in FIG. 1 rotates in the shank shown in FIG.

4B is a cross-sectional view showing the relationship between the rim of the shank and the pin of the cutting head after the cutting head shown in FIG. 1 rotates in the shank shown in FIG.

5 is a perspective view of a cutting head constituting a drilling tool according to the present invention;

6 is an exploded perspective view of a drilling tool according to the invention with a cutting head and a tool shank;

7 is a plan view of the tool shank shown in FIG.

FIG. 8A is a cross-sectional view taken along the line A-A in FIG. 6, showing a relationship between the engaging projection of the tool shank and the center post of the cutting head before the cutting head rotates in the central space portion of the tool shank. FIG.

FIG. 8B is a cross-sectional view taken along the line A-A in FIG. 6, showing a relationship between the center post of the cutting head and the engaging projection of the tool shank after the cutting head rotates in the central space portion of the tool shank.

9 is a cross-sectional view showing a state in which a tool shank and a cutting head are coupled;

Claims (8)

In a rotary cutting tool having a long cylindrical drill body formed with a chip flute on the outer circumferential surface of the cutting head is detachably fixed to the coupling structure formed on the upper end of the tool shank, The cutting head is composed of a cylindrical center post concentric with the axis of rotation of the drill body and a plurality of wings extending radially in the upper end of the center post, each of which is end face, top face, bottom face, and drill rotation direction side. And a rear face formed in the opposite direction, wherein the front face has a chip flute formed to extend to the side wall of the center post, and the side wall of the center post has a cutout portion constituting the chip flute and its side face. An outer circumferential surface of an arc shape positioned between the outer circumferential surface of the center post, the rotation guide element extending in the circumferential direction; The engaging structure has a plurality of engaging projections extending in a direction parallel to the axis of rotation from the edge of the tool shank to form a central space for accommodating the central post at its central portion, wherein each engaging projection has an upper torque support and a lower portion. It consists of a friction fastener of the, the torque support is provided with a recess defined by the axial support surface and the torque support surface so that the wing portion is seated on the side of the drill rotation direction, the inner wall of the friction fastener is the center post The transverse cross-section of the cross section forms an arc so as to be in surface contact with the outer circumferential surface thereof, and a fastening element is formed on the inner wall of the friction clamping portion to engage the rotation guide element of the center post; The surface contact is the friction tightening portion by rotating the center post in the reverse direction of the drill with a force fitting until the rear surface of the wing portion in contact with the torque support surface in the state that the rotation guide element is engaged with the fastening element in the central space portion Rotating cutting tool, characterized in that the inner wall surface is made by elastically pressing the outer peripheral surface of the central post. 2. The rotary cutting tool according to claim 1, wherein the rotation guide element is a rotation guide groove, and the fastening element is a protruding guide rib. The rotary cutting tool according to claim 1, wherein the outer circumferential surface of the center post is chamfered on the reverse side direction of the drill. The rotary cutting tool according to claim 1, wherein the inner wall of the friction tightening portion is chamfered on the side of the drill rotation direction. The rotary cutting tool of claim 1, wherein a hinge pin is formed at a center of a bottom surface of the center post, and a hole corresponding to the hinge pin is formed at a center of a bottom surface of a central space. The rotary cutting tool according to claim 1, wherein the torque support surface of the engaging projection is formed parallel to the axial direction. The rotary cutting tool of claim 1, wherein a coolant outlet is formed on an upper surface of the coupling protrusion. 2. The rotary cutting tool according to claim 1, wherein the radially elastic displacement of the engaging projection is increased toward the upper portion.

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