JP4666282B2 - Drill - Google Patents

Description

  The present invention relates to a drill used for drilling a workpiece, and more particularly to a drill having a hard sintered body on a cutting edge provided at the tip of a drill body.

  Conventionally, a drill used for drilling a workpiece includes a hard sintered body such as a diamond sintered body or a CBN (cubic boron nitride) sintered body on a cutting edge provided at the tip of the drill body. (For example, refer to Patent Document 1). In this type of drill, for example, a pair of chip discharge grooves are formed on the outer periphery of a drill body having a substantially cylindrical shape that rotates around an axis, for example, on opposite sides of the axis. Also, a substantially straight line extending from the center of the tip around the axis toward the outer peripheral side of the drill body at the intersection ridge line part of the wall surface facing the front side in the drill rotation direction of the chip discharge groove and the tip flank, that is, the tip edge of the wall surface Each of the shaped cutting blades is formed. And the recessed part which is dented one step from this wall surface and opened to the tip flank and the outer peripheral surface is formed in the portion of the wall surface facing the front side in the drill rotation direction of the chip discharging groove, and the substantially flat plate shape is formed in these recessed portions. The hard sintered body to be formed is joined and attached by brazing the other surface facing the one surface to the concave portion with one surface thereof directed in the drill rotation direction. In the hard sintered body thus provided, one surface on the front side in the drill rotation direction is flush with the wall surface of the chip discharge groove, and a corner on the tip side constitutes a cutting blade.

In such a drill having a cutting edge made of a hard sintered body, the resistance of the cutting edge, which is used for cutting a workpiece and has a large cutting resistance, is compared with a drill that does not have a hard sintered body. It is possible to improve wearability. Thereby, it is possible to improve the durability of the drill.
JP 2003-205413 A

  On the other hand, in a drill in which the above-mentioned cutting blade is formed of a hard sintered body, in addition to improving the durability of the cutting blade used for cutting a workpiece, a relatively expensive hard sintered body Therefore, it has also been desired that the cutting surface be machined with high surface accuracy. On the other hand, in the above drill, since each hard sintered body constituting the plurality of cutting blades is provided at substantially the same position in the axial direction, each hard sintered body is cut when cut into the work piece. The bonded body is brought into contact with the work piece almost simultaneously and cuts the work piece. For this reason, there is a problem that the hard sintered body does not contribute to the finishing of the machined cutting surface, and the machining can be performed only with the same surface accuracy as that without the hard sintered body.

  In view of the above circumstances, an object of the present invention is to provide a drill capable of cutting with high surface accuracy.

  In order to achieve the above object, the present invention provides the following means.

The drill of the present invention is provided with a plurality of chip discharge grooves extending from the front end toward the rear end on the outer periphery of a substantially cylindrical drill body that rotates about an axis, and the front end relief that forms the front end surface of the drill main body A drill having a cutting edge at a cross ridge line portion between a surface and a wall surface facing the front side in the drill rotation direction of the chip discharge groove, wherein the plurality of cutting edges are rearward in the axial direction from the axis toward the outer periphery. The other cutting blade that is inclined toward the end side and is located on the rear side in the drill rotation direction with respect to one of the cutting blades as a reference is referred to as the reference cutting blade. On the other hand, at least the outer peripheral side of the drill body is sequentially arranged on the rear end side of the drill body as it is positioned on the rear side in the rotation direction of the drill, and is further disposed on the rear end side of the drill body among the other cutting blades. The above-mentioned cutting blade includes Hard sintered body is provided on an outer peripheral side of the drill body even without a plurality of the cutting edge is located within the circle of 1/2 the diameter of the outer diameter of the cutting edge around the said axis The portion is formed so that the rotation trajectories around the axis coincide with each other.

  Further, in the drill according to the present invention, the outer peripheral side of the drill main body is sequentially placed on a plane perpendicular to the axis as the other cutting blade is positioned on the rear side in the drill rotation direction with respect to the reference cutting blade. It is more desirable that it is formed with a large inclination angle.

  Further, in the drill of the present invention, the other cutting blades are positioned on the rear side in the rotation direction of the drill with respect to the reference cutting blade, and the inclination angle on the outer peripheral side of the drill body is made substantially the same. It may be formed so as to be sequentially positioned on the rear end side in the axial direction.

  According to the drill of the present invention, the hard sintered body is provided on the outer peripheral side of the drill body of the cutting blade that is located on the rear side in the drill rotation direction and is arranged closest to the rear end side of the drill body. The workpiece can be sequentially cut with a cutting blade located on the front side in the drill rotation direction with respect to the hard sintered body, and the cut surface thus cut can be finally processed with the hard sintered body. As a result, the cutting surface can be finished with a hard sintered body, and cutting with high surface accuracy can be performed. In addition, by providing the hard sintered body only on the cutting edge arranged on the rear end side of the drill body, it is possible to improve surface accuracy while effectively arranging relatively expensive hard sintered bodies. It is said.

  Further, in the drill of the present invention, the portions of the plurality of cutting blades that are located within a circle having a diameter that is ½ of the outer diameter of the drill body are formed in substantially the same shape so that the rotation trajectories around the axis coincide. Therefore, even when the position of the outer peripheral side of the drill body is sequentially retreated to the rear end side of the drill body, when the drill is cut into the work piece, the above-mentioned substantially the same shape is first used. Since the cutting blade portion formed in the above can be brought into contact with the work piece, the biting property to the work piece can be maintained. Thereby, it is possible to prevent the drill from swinging during cutting, and the hard sintered body can reliably finish the cutting surface with high surface accuracy.

  Furthermore, in the drill of the present invention, the outer peripheral side of the other cutting edge positioned on the rear side in the drill rotation direction is orthogonal to the axis so that the outer peripheral side of the other cutting edge located on the rear side in the drill rotation direction is positioned on the rear side in the drill rotation direction. By forming with a large inclination angle with respect to the plane, the outer peripheral part where each cutting edge and the outer periphery of the drill body contact is sequentially arranged on the rear end side of the drill body as it is positioned on the rear side in the drill rotation direction can do. As a result, a hard sintered body can be provided on the outer peripheral portion of the cutting edge located closest to the rear end side of the drill body, and the hard sintered body can surely finish the cutting surface with high surface accuracy. .

  Furthermore, in the drill of the present invention, the outer peripheral side of the drill body of the other cutting blade is sequentially positioned on the rear end side in the axial direction while making the inclination angle substantially the same as the reference cutting blade, By providing the hard sintered body on the outer peripheral portion of the cutting blade located most rearward in the drill rotation direction, the cutting surface can be finished with high surface accuracy.

  Hereinafter, a drill according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 2. 1st Embodiment of this invention is related with the drill used for the drilling process of a workpiece, and is related with the drill provided with the hard sintered compact in the front end side especially.

  As shown in FIGS. 1 to 2, the drill A of the present embodiment includes a drill body 1 having a substantially cylindrical shape centered on the axis O <b> 1 with a hard material such as cemented carbide. On the rear end 1a side, for example, a shank portion 2 that is held by a chuck of a machine tool or the like is provided, and on the front end 1b side, three cutting blades 3, 4, and 5 that are used for cutting a workpiece are provided. A blade edge portion 6 is formed.

  Further, the drill body 1 extends linearly from the tip 1b to the shank 2 on the outer periphery 6a of the cutting edge portion 6 in parallel with the axis O1, and in the circumferential direction in a plan view in the direction of the axis O1 from the tip 1b side. Three strip discharge grooves 7 provided at equal intervals are formed. The chip discharge groove 7 is a cross-sectional view orthogonal to the axis O1, and a wall surface 7a facing the front side of the drill rotation direction T, and a wall surface 7b connected to the wall surface 7a while being substantially orthogonal to each other and facing the drill rotation direction T rear side. It is composed of For this reason, the drill main body 1 is formed so as to exhibit a substantially three-blade windmill shape in a plan view in the direction of the axis O1 from the tip 1b.

  Further, the tip surfaces of the drill A connected to the respective wall surfaces 7a and 7b of the respective chip discharge grooves 7 are set as the tip flank surfaces 8, 9, and 10. These tip flank surfaces 8 to 10 are respectively separated from the axis O1. Inclined toward the rear end 1a in the direction of the axis O1 toward the outer periphery 6a of the drill body 1, and a clearance angle is given toward the rear side in the drill rotation direction T. Here, the three tip flank surfaces 8 to 10 defined by the adjacent chip discharge grooves 7 and extending in the radial direction from the axis O1 are respectively the first tip flank surface 8, the second tip flank surface 9, and the third tip flank surface. 10, the second tip flank 9 is located behind the first tip flank 8 in the drill rotation direction T, and the third tip flank 10 is located behind the second tip flank 9 in the drill rotation direction T. Is located.

  Further, the inclination angles of the second and third tip flank surfaces 9 and 10 with respect to the plane orthogonal to the axis O1 change to a position that is ½ of the outer diameter D of the drill body 1 with the axis O1 as the center. The bent portion 11 is provided, and the portion from the bent portion 11 to the outer periphery 6a (hereinafter referred to as the outer peripheral side flank) rather than the portion from the axis O1 to the bent portion 11 (hereinafter referred to as the axial flank). The inclination angle with respect to a plane orthogonal to the axis O1 is increased. Further, the axial flank surfaces of the second and third tip flank surfaces 9 and 10 have the same inclination angle, while the inclination angle θ2 of the outer peripheral flank surface of the second tip flank surface 9 is The inclination angle θ3 of the outer peripheral side flank of the third front end flank 9 is greater than the inclination angle θ2 of the outer peripheral side flank of the second front end flank 9. Is also formed at a large angle.

  On the other hand, cutting edges 3, 4, and 5 are formed on the intersecting ridge line portion 12 between each tip flank 8 to 10 and the wall surface 7 a facing the front side in the drill rotation direction T of each chip discharge groove 7. In these cutting edges 3 to 5, the cutting edge formed at the crossed ridge line portion 12 between the first tip flank 8 and the wall surface 7 a of the chip discharge groove 7 is the first cutting edge (reference cutting edge) 3. The cutting edge of the intersecting ridge line portion 12 between the second tip flank 9 and the wall surface 7 a of the chip discharge groove 7 is a second cutting edge (other cutting edge) 4. Similarly, the cutting edge formed at the crossing ridge line portion 12 between the third tip flank 10 and the wall surface 7 a of the chip discharge groove 7 is a third cutting edge (other cutting edge) 5.

  Thereby, the 2nd cutting blade 4 and the 3rd cutting blade 5 are provided in order in the drill rotation direction T back side on the basis of the 1st cutting blade 3, These cutting blades 3-5 are respectively the front-end | tips of the axis line O1 vicinity. From the center to the cutting edge bent portion 13 that is ½ of the outer diameter D of the drill body 1 is formed in the same shape with the same inclination angle θ1. Further, a portion from the cutting edge bent portion 13 to the outer periphery 6a of the drill body 1 (a range of 1/2 or more of the outer diameter D of the drill body 1 around the axis O1) is an inclination of the first cutting edge 3. In a cross-sectional view in the direction orthogonal to the axis O1 such that the inclination angle θ2 of the second cutting edge 4 is larger than the angle θ1 and the inclination angle θ3 of the third cutting edge 5 is larger than the inclination angle θ2 of the second cutting edge 4. Each is formed to have a straight line shape. Accordingly, the second cutting edge 4 and the third cutting edge 5 positioned on the rear side in the drill rotation direction T with respect to the first cutting edge 3 are sequentially moved toward the rear side in the drill rotation direction T with respect to the first cutting edge 3. The outer peripheral portion 14 that is positioned and continues to the outer periphery 6 a of the drill main body 1 is sequentially disposed on the rear end 1 a side of the drill main body 1.

  On the other hand, the third cutting edge 5 arranged closest to the rear end 1a side of the drill body 1 is, for example, a diamond sintered body or CBN (cubic boron nitride) provided on the outer peripheral portion 14 in contact with the outer periphery 6a of the drill body 1. It is formed on a hard sintered body 15 such as a sintered body. The hard sintered body 15 is formed in a substantially flat plate shape having a fan shape in a plan view, and is fixed to a recess formed in the chip discharge groove 7. The concave portion is recessed in one step from the wall surface 7a on the tip 1b side of the wall surface 7a facing the front side of the drill rotation direction T of the chip discharge groove 7, and opens to the third tip flank 10 and the outer periphery 6a. The hard sintered body 15 is fixed by, for example, brazing the other surface to the recess, with one surface facing the front side of the drill rotation direction T. Further, the hard sintered body 15 has the one surface flush with the wall surface 7a of the chip discharge groove 7 and the surface facing the tip 1b side in the axis O1 direction is connected to the third tip flank 10 in the above-described manner. It is fixed to the outer peripheral side with respect to the bent portion 11.

  Next, a method for cutting a work using the drill A having the above-described configuration will be described.

  First, the shank portion 2 is fixed while being held by a chuck of a machine tool, for example, and the drill A is rotated around the axis O1 at high speed. And the blade edge | tip part 6 formed in the front-end | tip 1b side of the drill main body 1 is advanced while maintaining the direction of an axis O1, and is cut into a workpiece.

  At this time, in the drill A of the present embodiment, the first to third cuttings of the axial flank surfaces of the respective tip flank surfaces 8 to 10 having the same inclination angle θ1 of the cutting edge portion 6 rotated about the axis O1 are made. The part of the blade 3 to 5 in the range of ½ of the outer diameter D of the drill body 1 (the part from the center of the tip to the cutting edge bent part 13) first contacts the work piece, and the work pieces are almost at the same time. It is cut into. For this reason, the drill A bites the workpiece while reliably maintaining the direction of the axis O1 and starts cutting.

  Next, by further feeding the workpiece into the work piece while rotating the drill A, the tip 1b side of the drill main body 1 is located most together with the portion from the tip center of the first to third cutting blades 3 to 5 to the cutting blade bent portion 13. A portion from the cutting edge bent portion 13 to the outer periphery 6a of the first cutting edge 3 located in the position is used for cutting and cutting the work piece. And while this 1st cutting blade 3 carries out 1 rotation of the circumferential direction, the part from the cutting edge bending part 13 of the 2nd cutting blade 4 and the 3rd cutting blade 5 to the outer periphery 6a cuts into a workpiece sequentially. It will be rare.

  At this stage, the cut surface of the cut workpiece is in a state of low surface accuracy. On the other hand, in this embodiment, the hard sintered body of the third cutting edge 5 arranged on the most rear end 1a side of the drill body 1 by further cutting the cutting edge 6 of the drill A into the work piece. 15 is brought into contact with the cutting surface. Since the hard sintered body 15 is harder than the drill body 1 on which the first and second cutting edges 3 and 4 are formed, the third cutting edge 5 can be cut with a sharp edge. In addition, while rotating at high speed around the axis O1, for example, the surface facing radially outward is slidably contacted with a cutting surface with low surface accuracy to polish the cutting surface, and thereby the processed hole diameter Is finished to a predetermined hole diameter to form a hole with high surface accuracy.

  Therefore, in the above drill A, 1/2 of the outer diameter D of the drill body 1 from the cutting edge bent portion 13 of the first cutting edge 3, the second cutting edge 4, and the third cutting edge 5 to the outer periphery 6a. The portions in the above range are formed at different inclination angles, so that they can be sequentially arranged on the rear end 1a side in the axis O1 direction as they are positioned rearward in the drill rotation direction T. By providing the hard sintered body 15 on the outer peripheral portion 14 of the third cutting blade 5 arranged on the 1a side, the cutting surface cut mainly by the first cutting blade 3 and the second cutting blade 4 is used. Finally, the hard sintered body 15 of the third cutting edge 5 can be brought into contact. As a result, it is possible to perform cutting with a sharp sharpness of the hard sintered body 15 and to polish the cut surface, thereby making it possible to finish to a predetermined hole diameter. Therefore, it is possible to form a hole with high surface accuracy.

  Moreover, in said drill A, 1/2 of the outer diameter D of the drill main body 1 from the front-end | tip center of the 1st cutting blade 3, the 2nd cutting blade 4, and the 3rd cutting blade 5 to the cutting blade bending part 13 is shown. Are formed in substantially the same shape with substantially the same inclination angle θ1, the rotation trajectories of these portions around the axis O1 can be made coincident with each other. Thereby, since these portions can be cut into the work piece substantially simultaneously at the start of cutting, it is possible to prevent the drill A from swinging and to perform cutting while reliably maintaining the direction of the axis O1. By being able to perform, the hard sintered body 15 can be reliably cut into the cutting surface and brought into sliding contact in a suitable state, and a hole with high surface accuracy can be processed.

  In addition, this invention is not limited to said 1st Embodiment, In the range which does not deviate from the meaning, it can change suitably. For example, in the present embodiment, the three chip discharge grooves 7 are formed and the first to third three cutting edges 3, 4, and 5 are provided. As shown in FIG. 4, a drill B in which two pieces of chip discharge grooves 7 are formed and two cutting edges 16 and 17 are provided may be used. In the drill B including the two cutting edges 16 and 17, the inclination angle θ 5 of the outer peripheral portion 14 of the other cutting edge 17 is formed larger than the inclination angle θ 4 of the one cutting edge 16, and the outer peripheral portion 14. Is arranged on the rear end 1a side in the direction of the axis O1, and the hard sintered body 15 is provided on the outer peripheral portion 14 of the other cutting edge 17, so that the same effect as in the present embodiment can be obtained. . Therefore, the present invention is applicable to any drill having a plurality of cutting edges.

  Moreover, in this embodiment, the cutting edge bending part 13 of the 1st cutting edge 3, the 2nd cutting edge 4, and the 3rd cutting edge 5 is 1/2 of the outer diameter D of the drill main body 1 centering on the axis line O1. In each of the cutting blades 3 to 5, the portions from the axis O <b> 1 to the cutting edge bent portion 13 are formed in substantially the same shape with substantially the same inclination angle θ <b> 1. The range formed in the shape of the above-mentioned shape is only required to be a range of 1/2 or more of the outer diameter D of the drill body 1 around the axis O1. On the other hand, when the drill body 1 is within 1/2 of the outer diameter D of the drill body 1, the biting of the work piece is worsened and the straightness of the drill may not be ensured.

  In the present embodiment, the chip discharge groove 7 extends in a straight line parallel to the axis O1 from the front end 1b to the shank portion 2 toward the rear end 1a. For example, a plurality of chip discharge grooves 7 may be formed in a spiral shape so as to twist toward the rear side in the rotational direction T while moving toward the rear end 1a in the direction of the axis O1.

  Furthermore, in this embodiment, each bending part 11 of each front-end flank 8-10 is formed on the concentric circle centering on the axis O1, and each cutting edge bending part 13 according to this is also concentric on the axis O1 center. However, as shown in FIGS. 5 to 6, for example, as shown in FIGS. 5 to 6, the cutting edge bent portion 13 is different in the center of the axis O <b> 1 in which the diameter decreases in the order of the second and third tip flank surfaces 9 and 10. It may be provided on a circle. Also in this case, each of the cutting edges 3, 4, 5 is inclined at an appropriate inclination angle θ 6, θ 7, θ 8 from the cutting edge bent portion 13 to the outer periphery 6 a, and the hard cutting of the third cutting edge 5 is performed. By arranging the ligature 15 closest to the rear end 1a in the direction of the axis O1, the same effect as described above can be obtained. In this case, the inclination angle θ7 of the second cutting edge 4 and the inclination angle θ8 of the third cutting edge 5 may be the same inclination angle.

  Next, a drill according to a second embodiment of the present invention will be described with reference to FIGS. In the description of the present embodiment, the same reference numerals are assigned to configurations common to the first embodiment, and the detailed description thereof is omitted.

  As in the first embodiment, this embodiment includes three chip discharge grooves 7 and three cutting blades 3, 4, 5 and three tip flank surfaces 8, 9, and 10, and each tip flank surface. 8 to 10 relate to the drill D in which the axial flank from the axis O1 to the bent portion 11 is formed in substantially the same shape with the substantially same inclination angle θ1.

  On the other hand, the second tip flank 9 and the third tip flank 10 are stepped portions 20 in which the respective bent portions 11 are extended toward the rear end 1a along the direction of the axis O1. 20 are formed with wall surfaces 21 facing outward in the radial direction. These wall surfaces 21 make the flank side and the outer flank side of the second tip flank 9 and the third tip flank 10 continuous. Further, the length H1 of the wall surface 21 formed on the third tip flank 10 in the direction of the axis O1 is larger than the length H2 of the wall surface 21 formed on the second tip flank 9 in the direction of the axis O1. Thus, the outer peripheral flank of the third front flank 10 is positioned closer to the rear end 1a in the axis O1 direction than the outer flank of the second front flank 9. Further, the wall surface 21 is not formed on the bent portion 11 (20) of the first tip flank 8 and is the same as that of the first embodiment, while the outer flank of the first tip flank 8 and the first The outer peripheral flank of the second front flank 9 and the outer peripheral flank of the third front flank 10 are formed so as to be parallel to each other.

  Cutting edges 3, 4, 5 are provided on the intersecting ridge line portion 12 between the respective tip flank surfaces 8, 9, 10 formed as described above and the wall surface 7 a facing the front side of the drill rotation direction T of the chip discharge groove 7. Therefore, the portion from the cutting edge bent portion 13 to the outer periphery 6a of the second cutting blade 4 is the rear end in the axis O1 direction than the portion from the cutting blade bent portion 13 to the outer periphery 6a of the first cutting blade 3. It is arranged on the 1a side. Further, the portion from the cutting edge bent portion 13 to the outer periphery 6a of the third cutting blade 5 is closer to the rear end 1a side in the axis O1 direction than the portion from the cutting blade bent portion 13 to the outer periphery 6a of the second cutting blade 4. It is arranged in. Thereby, the outer peripheral part 14 of the 3rd cutting blade 5 is arrange | positioned rather than the outer peripheral part 14 of the other cutting blades 3 and 4 at the rear-end 1a side of the drill main body 1, and is the same as that of 1st Embodiment in this part. A hard sintered body 15 is provided.

  Therefore, also in the drill D described above, the second cutting edge 4 and the third cutting edge 5 are arranged on the rear end 1a side in the axis O1 direction while being parallel to the first cutting edge 3, respectively. By providing the hard sintered body 15 on the outer peripheral portion 14 of the third cutting edge 5 arranged on the rear end 1a side, the hard sintered body 15 can be finally brought into contact with the cutting surface. The hard sintered body 15 can be cut with a sharp sharpness, and the cutting surface can be polished and finished to a predetermined hole diameter, so that a hole with high surface accuracy can be formed. .

  In addition, this invention is not limited to said 2nd Embodiment, In the range which does not deviate from the meaning, it can change suitably. For example, in the present embodiment, the three chip discharge grooves 7 are formed and the three cutting blades 3, 4, and 5 are provided. However, the present invention is not limited thereto, and the present invention can be applied to, for example, FIGS. As shown in FIG. 2, the present invention may be applied to a drill E in which two pieces of chip discharge grooves 7 are formed and two cutting blades 22 and 23 are provided. In this case, by providing a step in the bent portion 11 of one tip flank 24, one cutting edge 23 is disposed on the rear end 1a side in the axis O1 direction with respect to the other cutting edge 22, and By providing the hard sintered body 15 on the outer peripheral portion 14 of the cutting edge 23, it is possible to obtain the same effect as described above. Therefore, the present invention can be applied to any drill having a plurality of cutting edges.

1 is a side view of a drill according to a first embodiment of the present invention. It is a front view of the drill shown in FIG. It is the side view shown as a modification of the drill which concerns on 1st Embodiment of this invention. It is a front view of the drill shown in FIG. It is the side view shown as a modification of the drill which concerns on 1st Embodiment of this invention. It is a front view of the drill shown in FIG. It is a side view of the drill which concerns on 2nd Embodiment of this invention. It is a front view of the drill shown in FIG. It is the side view shown as a modification of the drill which concerns on 2nd Embodiment of this invention. FIG. 10 is a front view of the drill shown in FIG. 9.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Drill main body 1a Rear end 1b Front end 2 Shank part 3 1st cutting blade (cutting blade on the basis)
4 Second cutting edge (other cutting edges)
5 Third cutting edge (other cutting edges)
6 Cutting edge portion 6a Outer periphery 7 Chip discharge groove 7a Wall surface 7b facing forward in the direction of drill rotation Wall surface 8 facing rearward in the direction of drill rotation 8 First tip flank (tip flank)
9 Second tip flank (tip flank)
10 Third tip flank (tip flank)
11 bent portion 12 intersecting ridge line portion 13 cutting edge bent portion 14 outer peripheral portion 15 hard sintered body A to E drill O1 axis T drill rotating direction

Claims (3)

A plurality of chip discharge grooves extending from the front end toward the rear end are provided on the outer periphery of the substantially cylindrical drill body that rotates about the axis, and a tip flank that forms the tip surface of the drill body, and the chip discharge In the drill having a cutting edge in the crossing ridge line portion with the wall surface facing the front side in the drill rotation direction of the groove,
The plurality of cutting blades are inclined toward the rear end side in the axial direction from the axis toward the outer periphery, and one of the cutting blades is used as a reference, and the drill rotates more than the cutting blade based on the reference. The other cutting blade located on the rear side in the direction of the drill body is positioned at the rear side in the drill rotation direction with respect to the reference cutting blade. The hard cutting body is provided on the outer peripheral side of the drill body at least on the cutting blade disposed and further disposed on the rear end side of the drill body most among the other cutting blades ,
The plurality of cutting blades are formed such that portions located within a circle having a diameter of ½ of the outer diameter of the cutting blade centered on the axis are coincident with the rotation trajectory around the axis. drill, characterized in that there. The drill according to claim 1 ,
With respect to the reference cutting blade, as the other cutting blades are positioned on the rear side in the drill rotation direction, the outer peripheral side of the drill body is sequentially formed with a large inclination angle with respect to the plane perpendicular to the axis. A drill characterized by The drill according to claim 1 ,
With respect to the reference cutting edge, as the other cutting edge is positioned on the rear side in the drill rotation direction, the inclination angle on the outer peripheral side of the drill body is made substantially the same, and sequentially toward the rear end side in the axial direction. A drill characterized by being positioned and formed.

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