Drill

Abstract

This drill comprises a body (1) and a coolant hole (3) extending within the body. The coolant hole (3) includes: a spiral hole (31) that is disposed inside the body (1) and extends in a drill rotation direction toward the tip side; and a branch hole (32) that branches from the spiral hole (31) and opens to a relieving surface (14) at a position separated from a tip surface (1a) toward the rear end side. The flow path cross-sectional area of the branch hole (32) increases from the location of branching (33) from the spiral hole (31) toward an opening section (34) of the relieving surface (14).

Description

Drill

[0001] The present invention relates to a drill. This application claims priority based on Japanese Patent Application No. 2025-008445 filed in Japan on January 21, 2025, and incorporates its content herein by reference.

[0002] Conventionally, a drill having a body (blade part) extending in the axial direction around a central axis, a shank connected to the rear end part in the axial direction of the body, and a coolant hole extending inside the body and the shank is known. Further, the body has a cutting edge disposed at the tip end of the body, a chip discharge groove that opens to the tip end surface and the outer peripheral surface of the body and extends in the counter-drill rotation direction around the central axis as it goes from the tip end surface toward the rear end side in the axial direction, a margin disposed on the outer peripheral surface of the body and extending along the chip discharge groove, and a secondary cutting surface disposed on the outer peripheral surface of the body and located radially inward of the margin.

[0003] For example, in the drill described in Patent Document 1, a coolant hole extending inside the body branches inside the body and opens to the tip end surface and the outer peripheral surface of the body.

[0004] European Patent Application Publication No. 1941960

[0005] When drilling a work material that is likely to expand during cutting, such as a stainless alloy or a titanium alloy, for example, the inner diameter dimension of the machined hole tends to contract due to cutting heat. In such a case, there is a risk that welding is likely to occur due to excessive vanishing of the margin of the drill on the inner peripheral surface of the machined hole, or that sludge due to chips is likely to accumulate on the secondary cutting surface. Welding occurring on the margin or sludge accumulating on the secondary cutting surface is not preferable because it affects the accuracy of the drilling operation.

[0006] An object of the present invention is to provide a drill that can suppress excessive vanishing between the inner peripheral surface of a machined hole and the margin, can stably discharge sludge on the secondary cutting surface, and can maintain good accuracy in drilling operations.

[0007] To solve the above problems, the present invention provides the following means.

[0008] [Aspect 1 of the present invention] A drill comprising a body extending axially with respect to a central axis, and a coolant hole extending inside the body, wherein the body has a cutting edge disposed at the tip of the body, a chip discharge groove opening on the tip surface and outer circumferential surface of the body and extending in the anti-drill rotation direction around the central axis as it moves from the tip surface toward the rear end in the axial direction, a margin disposed on the outer circumferential surface of the body and extending along the chip discharge groove, and a secondary beveling surface disposed on the outer circumferential surface of the body and located radially inward from the margin, wherein the coolant hole is disposed inside the body and has a spiral hole extending in the drill rotation direction around the central axis as it moves toward the tip in the axial direction, and a branch hole branching from the spiral hole and opening on the secondary beveling surface at a position away from the tip surface of the body toward the rear end in the axial direction, wherein the cross-sectional area of ​​the flow path of the branch hole increases as it moves from the branching point with the spiral hole toward the opening of the secondary beveling surface.

[0009] In a drill according to an embodiment of the present invention, the coolant hole has a spiral hole and branch holes that branch off from the spiral hole. The tip of the spiral hole opens, for example, to the front surface of the body. The area near the cutting edge is efficiently cooled by the coolant ejected from the spiral hole.

[0010] Furthermore, the branch holes open onto the secondary beveling surface, and the coolant ejected from the branch holes is supplied to the margin through the space between the inner circumferential surface of the machined hole in the workpiece and the secondary beveling surface, cooling and lubricating the margin. In addition, the coolant ejected from the branch holes pushes away sludge accumulated on the secondary beveling surface and discharges it from above, while also generating hydraulic pressure (hydraulic pressure) between the outer circumference of the drill and the inner circumferential surface of the machined hole.

[0011] In an embodiment of the present invention, the cross-sectional area of ​​the flow path of the branch hole is increased from the connecting portion (branching portion) connected to the spiral hole toward the opening that opens to the secondary fraying surface. As a result, the coolant ejected from the branch hole is supplied over a wide area on the secondary fraying surface and also to the margin. This allows for efficient cooling and lubrication of the margin. Furthermore, since the coolant acts over a wide area on the sludge accumulated on the secondary fraying surface, the sludge can be efficiently discharged from the secondary fraying surface. Therefore, wall friction between the outer circumference of the drill and the inner circumference of the machined hole can be suppressed.

[0012] Furthermore, by ensuring a large area for the branch holes to open onto the secondary fringing surface, hydraulic pressure can be generated over a wide area between the inner circumferential surface of the machined hole and the secondary fringing surface. This makes it easier to float the outer circumference of the drill radially inward from the inner circumferential surface of the machined hole. According to the embodiment of the present invention, excessive burnishing between the inner circumferential surface of the machined hole and the margin can be stably suppressed. Welding to the margin can be suppressed, and the tool life of the drill can be extended. In addition, since drilling can be performed while maintaining a state in which the central axis of the machined hole and the central axis of the drill are coaxially positioned, machining accuracy can be stably improved.

[0013] Furthermore, the branch holes open onto the secondary furring surface at a position away from the front end of the body towards the rear end in the axial direction. Therefore, while the excellent effects described above are obtained, any interference with the regrinding process of the cutting edge is suppressed. Specifically, the branch holes are prevented from being exposed to the drill tip surface too early due to regrinding of the cutting edge, thus limiting the number of regrinding cycles that can be performed due to the presence of the branch holes.

[0014] Furthermore, as the cross-sectional area of ​​the branch holes increases from the branching point towards the opening, it becomes easier to stably connect the branch holes to the spiral hole when forming them through cutting or grinding processes during drill manufacturing. This simplifies the manufacturing of the drill.

[0015] As described above, according to the embodiments of the present invention, excessive burnishing of the inner circumferential surface of the machined hole and the margin can be suppressed, sludge on the secondary cutting surface can be stably discharged, and the accuracy of the drilling process can be maintained well. Furthermore, according to the embodiments of the present invention, the tool life of the drill can be extended. In addition, the manufacturing of the drill is easy.

[0016] [Aspect 2 of the present invention] The drill according to aspect 1, wherein the opening of the branch hole is elongated in the direction of the drill rotation as it extends toward the tip side in the axial direction.

[0017] In this case, since the opening of the branch hole is elongated, it is easy to secure a large opening area for the branch hole to the secondary chamfering surface. In addition, it is easy to stably supply the coolant ejected from the branch hole to the secondary chamfering surface and margin over a wide area in the axial direction.

[0018] [Aspect 3 of the present invention] The drill according to aspect 2, wherein the direction in which the opening of the branch hole extends and the direction in which the spiral hole extends are different from each other.

[0019] In this case, for example, when viewing the body radially, the branch hole opening and the spiral hole can be extended so that they intersect. During drill manufacturing, when forming the branch hole by cutting or grinding, it becomes easier to connect the branch hole and the spiral hole. Also, regardless of the direction in which the spiral hole extends, the direction in which the branch hole opening extends can be set as appropriate, increasing the degree of freedom in the shape of the branch hole opening.

[0020] [Aspect 4 of the present invention] The drill according to aspect 2 or 3, wherein the direction in which the opening of the branch hole extends and the direction in which the margin extends are the same.

[0021] In this case, the coolant ejected from the branch holes is more easily supplied to the margin over a wide area and evenly along the direction in which the margin extends. As a result, burnishing and welding of the margin can be suppressed more stably.

[0022] [Aspect 5 of the present invention] The drill according to any one of aspects 1 to 4, wherein the branch hole is arranged on the inner circumferential surface of the branch hole and has a first inclined surface that extends toward the tip side as it moves from the branch portion toward the opening.

[0023] In this case, the first inclined surface positioned on the inner circumferential surface of the branch hole causes the coolant flowing through the branch hole to be ejected toward the drill tip. This allows the coolant to flow toward the drill tip in the space between the inner circumferential surface of the machined hole and the secondary beveling surface. Specifically, the coolant on the secondary beveling surface flows from the branch hole toward the drill tip, is supplied to the vicinity of the cutting edge for cooling and lubrication, then changes direction axially and flows toward the rear end of the drill through the chip evacuation groove. Therefore, the direction of the coolant flowing on the secondary beveling surface (flow toward the tip) and the direction of the coolant flowing in the chip evacuation groove (flow toward the rear end) are different from each other.

[0024] This allows for a rectifying effect on the coolant flowing through the secondary bevel face and chip evacuation groove, increasing the flow velocity and pressure (hydraulic pressure), and further improving the cooling and lubricating effects of the coolant. The outer circumference of the drill can be stably floated away from the inner circumference of the machined hole, further suppressing friction between the inner circumference of the machined hole and the outer circumference of the drill.

[0025] [Aspect 6 of the present invention] The drill according to aspect 5, wherein the branch hole has a second inclined surface arranged on the inner circumferential surface of the branch hole and on the opposite side from the first inclined surface with the branch portion in between, and the second inclined surface extends toward the rear end or the front end as it moves from the branch portion toward the opening.

[0026] When the second inclined surface extends towards the rear end as it moves from the branching point towards the opening, a large and stable opening area can be secured for the secondary beveling surface of the branch hole opening. Furthermore, when the second inclined surface extends towards the tip as it moves from the branching point towards the opening, the coolant ejected from the branch hole can be directed more easily toward the drill tip.

[0027] [Aspect 7 of the present invention] The drill according to aspect 6, wherein the second inclined surface extends toward the rear end as it moves from the branch portion toward the opening, and in a cross-sectional view of the branch hole passing through the branch portion and the opening, the first angle at which the first inclined surface is inclined toward the front end with respect to a virtual line passing through the center of the branch portion and perpendicular to the spiral hole is greater than the second angle at which the second inclined surface is inclined toward the rear end with respect to the virtual line.

[0028] In this case, a large opening area for the secondary bevel face of the branch hole can be secured, while also making it easier to direct the coolant ejected from the branch hole toward the drill tip.

[0029] According to the above-mentioned aspect of the present invention, a drill is provided that can suppress excessive burnishing of the inner circumferential surface of the machined hole and the margin, stably discharge sludge from the secondary cutting surface, and maintain good accuracy in drilling.

[0030] Figure 1 is a perspective view showing a drill according to the first embodiment. Figure 2 is a front view of the drill according to the first embodiment, viewed from the tip side. Figure 3 is a side view showing a part of the body of the drill according to the first embodiment. Figure 4 is a perspective view showing a cylindrical cross-section obtained by cutting a part of the body with a virtual cylindrical surface having a diameter smaller than the cutting edge diameter. Figure 5 is a perspective view showing a cylindrical cross-section obtained by cutting a part of the body with a virtual cylindrical surface having a diameter smaller than the cutting edge diameter and larger than the virtual cylindrical surface in Figure 4. Figure 6 is a cross-sectional view showing the VI-VI section in Figure 3. Figure 7 is a side view showing a part of the body of the drill according to the second embodiment. Figure 8 is a perspective view showing a cylindrical cross-section obtained by cutting a part of the body with a virtual cylindrical surface having a diameter smaller than the cutting edge diameter. Figure 9 is a perspective view showing a cylindrical cross-section obtained by cutting a part of the body with a virtual cylindrical surface having a diameter smaller than the cutting edge diameter and larger than the virtual cylindrical surface in Figure 8. Figure 10 is a cross-sectional view showing the X-X section in Figure 7. Figure 11 is a perspective view showing a part of the body of a drill according to a modified example of the first embodiment.

[0031] <First Embodiment> A drill 10 according to the first embodiment of the present invention will be described with reference to Figures 1 to 6. As shown in Figure 1, the drill 10 of this embodiment is columnar in shape with a central axis O. The drill 10 comprises a body 1, a shank 2, and a coolant hole 3. The body 1 and the shank 2 are positioned at different locations from each other in the direction in which the central axis O of the drill 10 extends. The body 1 may be referred to as the cutting edge or the like.

[0032] [Definition of Direction] In this embodiment, the direction in which the central axis O of the drill 10 extends is called the axial direction. Of the axial directions, the direction from the shank 2 toward the body 1 is called the axial tip side or simply the tip side, and the direction from the body 1 toward the shank 2 is called the axial rear end side or simply the rear end side.

[0033] Furthermore, the direction perpendicular to the central axis O is called the radial direction. Within the radial direction, the direction approaching the central axis O is called the radially inward direction, and the direction moving away from the central axis O is called the radially outward direction. The direction of rotation around the central axis O is called the circumferential direction. Within the circumferential direction, the direction in which the drill 10 is rotated during drilling (cutting) is called the drill rotation direction T. Also, within the circumferential direction, the rotation direction opposite to the drill rotation direction T is called the opposite side of the drill rotation direction T, or the anti-drill rotation direction.

[0034] Furthermore, if there are any directions other than those mentioned above that need to be defined, they will be defined separately when describing each component.

[0035] [Shank] The shank 2 is columnar in shape, extending axially around the central axis O, and in this embodiment, it is cylindrical. The shank 2 is located at least at the rear end of the drill 10. The shank 2 is connected to the axial rear end of the body 1. The shank 2 is detachably held by, for example, the spindle of a machine tool (not shown) or the chuck of a drilling machine (hereinafter sometimes referred to as the spindle, etc.). The drill 10 is fed towards the tip in the axial direction while the shank 2 is rotated in the drill rotation direction T by the spindle, etc., so that the body 1 cuts into the workpiece and performs drilling.

[0036] [Body] Body 1 extends axially around the central axis O and is roughly columnar in shape. Body 1 is located at least at the tip of the drill 10. Body 1 is connected to the axial tip of the shank 2. As shown in Figure 2, the diameter dimension (outer diameter dimension) D of body 1 corresponds to the diameter dimension D of the rotational trajectory of the cutting edge 7 around the central axis O, which will be described later. For this reason, the diameter dimension D of body 1 may be rephrased as the cutting edge diameter dimension D.

[0037] As shown in Figures 2 and 3, the body 1 has a front surface 1a facing the tip side of the body 1, an outer peripheral surface 1b facing radially outward of the body 1, a chip discharge groove 4, a thinning 5, a cutting edge 7, a margin 13, a leading edge 12, and a secondary beveling surface 14. In this embodiment, a plurality of margins 13 are provided spaced apart from each other in the circumferential direction, and the plurality of margins 13 include a first margin 13A and a second margin 13B.

[0038] Multiple chip evacuation grooves 4, thinning 5, cutting edge 7, first margin 13A, second margin 13B, leading edge 12, and secondary bevel face 14 are provided on the body 1 at intervals from each other in the circumferential direction. In this embodiment, two sets of chip evacuation grooves 4, thinning 5, cutting edge 7, first margin 13A, second margin 13B, leading edge 12, and secondary bevel face 14 are provided at equal pitches in the circumferential direction. In other words, the drill 10 of this embodiment is a two-blade twist drill with two sets of cutting edge 7.

[0039] The chip evacuation groove 4 opens to the front surface 1a and the outer peripheral surface 1b of the body 1 and is groove-shaped, extending from the front surface 1a toward the rear end. Specifically, the chip evacuation groove 4 extends in the anti-drill rotation direction as it moves from the front surface 1a toward the rear end in the axial direction. That is, the chip evacuation groove 4 extends in a spiral twist around the central axis O.

[0040] The chamfer 5 is disposed at the tip of the body 1 and is connected to the chip discharge groove 4 and the tip surface 1a. The chamfer 5 is recessed radially inward from the chip discharge groove 4 and recessed toward the rear end side from the tip surface 1a. That is, the chamfer 5 has a concave shape and is formed so as to notch a part of each of the chip discharge groove 4 and the tip surface 1a.

[0041] As shown in FIG. 2, the tip surface 1a has a first relief surface 1c and a second relief surface 1d. A plurality of sets of the first relief surface 1c and the second relief surface 1d are provided on the body 1 at intervals in the circumferential direction. In the present embodiment, two sets of the first relief surface 1c and the second relief surface 1d are provided at equal pitches in the circumferential direction.

[0042] The first relief surface 1c has a substantially polygonal surface shape that extends elongated in the radial direction. The first relief surface 1c extends toward the rear end side in the axial direction as it goes in the counter-drill rotation direction.

[0043] The second relief surface 1d is disposed adjacent to the first relief surface 1c in the counter-drill rotation direction of the first relief surface 1c. The second relief surface 1d has a substantially fan shape, and the circumferential dimension increases as it goes toward the outer side in the radial direction. Also, the second relief surface 1d extends toward the rear end side in the axial direction as it goes in the counter-drill rotation direction. The amount of displacement in the axial direction per unit length along the circumferential direction (the inclination corresponding to the relief angle) on the second relief surface 1d is made larger than the amount of displacement on the first relief surface 1c.

[0044] In the present embodiment, the tip surface 1a has two types of inclined surfaces (the first relief surface 1c and the second relief surface 1d) with different relief angles from each other, but it is not limited to this. Although not particularly shown, the tip surface 1a may have one type of inclined surface (relief surface) with a constant relief angle, or may have three or more types of inclined surfaces (relief surfaces) with different relief angles from each other.

[0045] The cutting edge 7 is disposed at the tip of the body 1. The cutting edge 7 is disposed at a ridge line portion where the wall surfaces facing the respective drill rotation directions T of the chip discharge groove 4 and the thinning 5 are connected to the tip surface 1a. The cutting edge 7 includes a thinning blade 71 disposed at the radially inner end portion of the cutting edge 7, and a main cutting edge 72 disposed radially outside the thinning blade 71. In this embodiment, some of the components near the cutting edge 7 may be omitted from illustration.

[0046] Although not particularly shown, at least a part of the cutting edge 7 may have honing on the cutting edge tip. The honing is, for example, chamfer honing, round honing, or the like.

[0047] As shown in FIGS. 2 and 3, the margins 13 (first margin 13A, second margin 13B) are disposed on the outer peripheral surface 1b of the body 1 and extend along the chip discharge groove 4. Specifically, the first margin 13A is disposed at an end portion in the drill rotation direction T of the outer peripheral surface 1b of the body 1. In other words, the first margin 13A is disposed at a portion of the outer peripheral surface 1b adjacent to the non-drill rotation direction of the chip discharge groove 4. The first margin 13A extends in the non-drill rotation direction as it goes toward the rear end side in the axial direction. The first margin 13A has a curved surface shape that protrudes outward in the radial direction. The first margin 13A extends in an arc shape centered on the central axis O in a cross-sectional view perpendicular to the central axis O.

[0048] The second margin 13B is disposed away from the first margin 13A in the non-drill rotation direction. Specifically, the second margin 13B is disposed at an end portion in the non-drill rotation direction of the outer peripheral surface 1b of the body 1. In other words, the second margin 13B is disposed at a portion of the outer peripheral surface 1b adjacent to the drill rotation direction T of the chip discharge groove 4. The second margin 13B extends in the non-drill rotation direction as it goes toward the rear end side in the axial direction. The second margin 13B has a curved surface shape that protrudes outward in the radial direction. The second margin 13B extends in an arc shape centered on the central axis O in a cross-sectional view perpendicular to the central axis O.

[0049] The leading edge 12 is positioned on the ridge where the wall surface of the chip evacuation groove 4 facing the drill rotation direction T connects to the first margin 13A. The leading edge 12 extends along the wall surface of the chip evacuation groove 4 facing the drill rotation direction T and the first margin 13A. Specifically, the leading edge 12 extends in the direction opposite to the drill rotation direction as it approaches the rear end in the axial direction.

[0050] The leading edge 12 may also be provided with a back taper. In this case, the leading edge 12 extends so that it is slightly radially inward as it approaches the rear end in the axial direction.

[0051] The secondary chamfering surface 14 is positioned on the outer peripheral surface 1b of the body 1. In the circumferential direction, the secondary chamfering surface 14 is positioned between the first margin 13A and the second margin 13B. The secondary chamfering surface 14 is formed recessed radially inward from the first margin 13A and the second margin 13B. That is, the secondary chamfering surface 14 is located radially inward from the margin 13.

[0052] The secondary chamfering surface 14 has a curved shape that is convex radially outward. The secondary chamfering surface 14 is formed to constitute a part of a cylindrical surface centered on the central axis O. In a cross-sectional view perpendicular to the central axis O, the secondary chamfering surface 14 extends in a substantially arc shape centered on the central axis O. During drilling, the secondary chamfering surface 14 faces the inner circumferential surface of the machined hole in the workpiece with a radial gap between them. In this embodiment, the entire outer circumferential surface 1b, including the secondary chamfering surface 14 and the margins 13 (first margin 13A, second margin 13B), may be referred to as the land 1b.

[0053] [Coolant Holes] The coolant holes 3 extend throughout the interior of the body 1 and the shank 2. As shown in Figure 1, in this embodiment, the coolant holes 3 are provided through the drill 10 in the axial direction and open to the front end surface 1a and rear end surface 1e of the drill 10. Multiple coolant holes 3 are provided spaced apart from each other in the circumferential direction, and in this embodiment, two are provided at equal pitches in the circumferential direction. The two coolant holes 3 have a shape that is 180° rotationally symmetrical with respect to the central axis O.

[0054] The coolant holes 3 are arranged throughout the interior of the body 1 and the shank 2 and include spiral holes 31 that extend in the drill rotation direction T as they approach the tip in the axial direction, and branch holes 32 that branch off from the spiral holes 31 and open to the secondary beveling surface 14 at a position away from the tip surface 1a of the body 1 in the axial direction towards the rear end. In this embodiment, one branch hole 32 branches off from each spiral hole 31. The spiral holes 31 may also be referred to as main holes 31.

[0055] The spiral hole 31 is provided so that it penetrates the drill 10 in the axial direction. Specifically, the tip of the spiral hole 31 opens into the tip surface 1a of the body 1, and the rear end of the spiral hole 31 opens into the rear end surface 1e of the shank 2. Coolant is supplied to the rear end opening of the spiral hole 31 from a spindle or the like (not shown).

[0056] As shown in Figure 2, in this embodiment, the tip opening of the spiral hole 31 is positioned on the second relief surface 1d of the tip surface 1a. The spiral hole 31 extends in the anti-drill rotation direction as it moves from the tip surface 1a toward the rear end in the axial direction. The spiral hole 31 is a coolant flow path that twists and extends spirally around the central axis O.

[0057] The spiral hole 31 is located inside the body 1, between a pair of circumferentially adjacent chip discharge grooves 4. In this embodiment, the cross-sectional shape of the flow path of the spiral hole 31 is substantially triangular. However, it is not limited to this, and the cross-sectional shape of the flow path of the spiral hole 31 may be circular, for example. In this embodiment, the flow path cross-sectional area of ​​the spiral hole 31 is constant along the direction in which the spiral hole 31 extends. More specifically, the flow path cross-sectional area of ​​the spiral hole 31 is constant along the entire length of the spiral hole 31.

[0058] The branch holes 32 will be explained in detail with reference to Figures 3 to 6. Figure 3 is a side view of the body 1 as seen from the radial direction, and more specifically, it is a side view of the body 1 as seen from the front with the branch holes 32. Figure 4 is a perspective view showing a cylindrical cross-section obtained by cutting a part of the body 1 with a virtual cylindrical surface having a diameter smaller than its cutting diameter D, and Figure 5 is a perspective view showing a cylindrical cross-section obtained by cutting a part of the body 1 with a virtual cylindrical surface having a diameter smaller than its cutting diameter D and larger than the virtual cylindrical surface in Figure 4. Figure 6 is a cross-sectional view showing the VI-VI section in Figure 3.

[0059] The branch hole 32 is a coolant flow path extending in the radial direction. The radial inner end of the branch hole 32 is connected to the spiral hole 31. In this embodiment, the portion where the branch hole 32 and the spiral hole 31 are connected, that is, the portion where the branch hole 32 branches off from the spiral hole 31, is called the branch portion 33. The branch portion 33 may also be referred to as the connection portion 33 or the linking portion 33. In this embodiment, the branch portion 33 of the branch hole 32 is connected to one side (one side of the triangle) of the spiral hole 31 that faces radially outward, and the flow path cross-section of the spiral hole 31 is triangular. The radial outer end of the branch hole 32 opens to the second bevel surface 14. In this embodiment, the portion where the branch hole 32 opens to the second bevel surface 14 is called the opening 34.

[0060] As shown in Figures 3 to 6, the cross-sectional area of ​​the branch hole 32 increases as it moves from the branching point 33 with the spiral hole 31 toward the opening 34 of the secondary beveling surface 14. In other words, the cross-sectional area (opening area) of the branch hole 32 perpendicular to the direction in which the branch hole 32 extends (radial direction) increases as it moves from the branching point 33 toward the opening 34. To put it another way, the cross-sectional area of ​​the branch hole 32 increases as it moves radially outward. The branching point 33 is a hole that is approximately circular or approximately elliptical in shape. The opening 34 is an elongated hole that extends in the drill rotation direction T as it moves toward the tip side in the axial direction. In this embodiment, the branch hole 32 is formed during drill manufacturing by cutting the body 1 using, for example, a ball end mill.

[0061] Here, the imaginary straight line indicated by reference numeral C1 in Figure 3 represents the direction in which the spiral hole 31 extends at the point where the spiral hole 31 and the branch hole 32 connect (branching section 33). More specifically, the direction in which the spiral hole 31 extends corresponds to the direction in which the center line C1 of the spiral hole 31 extends at the branching section 33. The direction in which the spiral hole 31 extends may also be referred to as the spiral hole extension direction.

[0062] Furthermore, the imaginary straight line indicated by the symbol C2 in Figure 3 represents the direction in which the opening 34 of the branch hole 32 extends in this side view. More specifically, the direction in which the opening 34 extends corresponds to the direction in which the center line C2, which passes through the center of the opening 34 in the width direction and is aligned with the extension direction of the opening 34, extends in a side view of the body 1 with the branch hole 32 viewed from the radially outside, as shown in Figure 3. Note that the direction in which the opening 34 extends may also be referred to as the opening extension direction.

[0063] As shown in Figure 3, in this embodiment, the direction in which the opening 34 of the branch hole 32 extends (the direction in which the center line C2 of the opening 34 extends) and the direction in which the spiral hole 31 extends (the direction in which the center line C1 of the spiral hole 31 extends) are different from each other. Specifically, in the side view of the body 1 shown in Figure 3, the angle formed between the center line C2 of the opening 34 of the branch hole 32 and the central axis O of the drill 10 (corresponding to the inclination angle of the branch hole 32) is larger than the angle formed between the center line C1 at the branch portion 33 of the spiral hole 31 and the central axis O of the drill 10 (corresponding to the inclination angle of the spiral hole 31).

[0064] Furthermore, the direction in which the opening 34 of the branch hole 32 extends and the direction in which the margin 13 (first margin 13A, second margin 13B) extends are the same. Also, the axial dimension in which the branch hole 32 moves away from the front surface 1a of the body 1 toward the rear end is, for example, 1D or more and 5D or less, preferably 0.5D or more and 4D or less, where D is the cutting diameter dimension of the body 1 (the diameter dimension of the rotational trajectory around the central axis O of the cutting edge 7).

[0065] In this embodiment, the distance (circumferential dimension) between the chip discharge groove 4 located in the drill rotation direction T of the branch hole 32 and the branch hole 32 is different from the distance (circumferential dimension) between the chip discharge groove 4 located in the opposite direction of the drill rotation of the branch hole 32 and the branch hole 32. Specifically, the distance between the chip discharge groove 4 located in the drill rotation direction T of the branch hole 32 and the branch hole 32 is greater than the distance between the chip discharge groove 4 located in the opposite direction of the drill rotation of the branch hole 32 and the branch hole 32. However, this is not limited to this, and the distance between the chip discharge groove 4 located in the drill rotation direction T of the branch hole 32 and the branch hole 32 may be smaller than the distance between the chip discharge groove 4 located in the opposite direction of the drill rotation of the branch hole 32 and the branch hole 32. Alternatively, the distance between the chip discharge groove 4 located in the drill rotation direction T of the branch hole 32 and the branch hole 32 may be the same as the distance between the chip discharge groove 4 located in the opposite direction of the drill rotation of the branch hole 32 and the branch hole 32.

[0066] In this embodiment, the opening area of ​​the branch portion 33 of the branch hole 32 that opens into the spiral hole 31 is smaller than the opening area of ​​the spiral hole 31 that opens into the front end surface 1a of the body 1 (see Figure 4). Also, the opening area of ​​the opening 34 of the branch hole 32 that opens into the second bevel surface 14 is larger than the opening area of ​​the spiral hole 31 that opens into the front end surface 1a of the body 1. With respect to the branch portion 33 of the branch hole 32, the dimension of the direction C1 in which the spiral hole 31 extends is preferably 1D or more and 3D or less, where D is the blade diameter dimension of the body 1 (the diameter dimension of the rotational trajectory around the central axis O of the cutting edge 7).

[0067] As shown in Figures 3 and 6, the branch hole 32 has a first inclined surface 35, a second inclined surface 36, and a pair of side wall surfaces 37. The first inclined surface 35, the second inclined surface 36, and the pair of side wall surfaces 37 are each located on the inner circumferential surface of the branch hole 32.

[0068] The first inclined surface 35 extends toward the tip as it moves from the branching portion 33 toward the opening 34 (i.e., radially outward). More specifically, the first inclined surface 35 extends toward the drill rotation direction T as it moves toward the tip in the axial direction. That is, the first inclined surface 35 extends toward the tip in the axial direction and toward the drill rotation direction T as it moves radially outward. Furthermore, in the side view of the body 1 shown in Figure 3, the first inclined surface 35 extends along the extending direction of the opening 34 (the direction in which the center line C2 extends).

[0069] The first inclined surface 35 has a concave curved shape. Although not specifically shown in the figures, in a cross-sectional view perpendicular to the center line C2 of the opening 34, the first inclined surface 35 has a concave curved shape that is recessed radially inward. Also, as shown in Figure 6, in a cross-sectional view along the center line C2 of the opening 34, the first inclined surface 35 has a straight shape that extends towards the tip as it is directed radially outward.

[0070] The second inclined surface 36 is located on the inner circumferential surface of the branch hole 32, on the side opposite to the first inclined surface 35, with the branch portion 33 in between. The second inclined surface 36 extends toward the rear end or the front end as it moves from the branch portion 33 toward the opening 34 (i.e., radially outward), and in this embodiment, it extends toward the rear end as it moves radially outward.

[0071] More specifically, the second inclined surface 36 extends in the direction opposite to the drill rotation as it approaches the rear end in the axial direction. That is, the second inclined surface 36 extends towards the rear end in the axial direction and in the direction opposite to the drill rotation as it approaches the radially outward direction. Furthermore, in the side view of the body 1 shown in Figure 3, the second inclined surface 36 extends along the direction in which the opening 34 extends (the direction in which the center line C2 extends).

[0072] The second inclined surface 36 has a concave curved shape. Although not specifically shown in the figures, in a cross-sectional view perpendicular to the center line C2 of the opening 34, the second inclined surface 36 has a concave curved shape that is recessed radially inward. Also, as shown in Figure 6, in a cross-sectional view along the center line C2 of the opening 34, the second inclined surface 36 has a straight shape that extends towards the rear end as it is directed radially outward.

[0073] Here, the symbol VL shown in Figure 6 represents a virtual straight line VL that passes through the center (opening center) of the branching portion 33 and is perpendicular to the spiral hole 31. As shown in Figure 6, in a cross-sectional view of the branching portion 33 and opening 34 of the branch hole 32, the first angle θ1 in which the first inclined surface 35 is inclined toward the tip side with respect to the virtual straight line VL is greater than the second angle θ2 in which the second inclined surface 36 is inclined toward the rear end side with respect to the virtual straight line VL. The aforementioned cross-sectional view is a cross-sectional view along the center line C2 of the opening 34, and more specifically, it corresponds to a cross-sectional view that includes the center line C2 and the virtual straight line VL in the plane. In this embodiment, the first angle θ1 is, for example, 1° or more and 89° or less. The first angle θ1 is preferably 35° or more and 70° or less. The second angle θ2 is preferably 25° or more and 60° or less.

[0074] The pair of side wall surfaces 37 are positioned opposite each other with a gap between them in the width direction of the opening 34. Each of the pair of side wall surfaces 37 is planar. Each side wall surface 37 is triangular in shape. Each side wall surface 37 is located between the first inclined surface 35 and the second inclined surface 36 in the extending direction of the opening 34. Each side wall surface 37 is connected to the first inclined surface 35 and the second inclined surface 36. In this embodiment, the pair of side wall surfaces 37 are parallel to each other.

[0075] [Effects of this embodiment] In the drill 10 of this embodiment described above, the coolant hole 3 has a spiral hole 31 and branch holes 32 that branch off from the spiral hole 31. In this embodiment, the tip of the spiral hole 31 opens onto the tip surface 1a of the body 1. The area around the cutting edge 7 is efficiently cooled by the coolant ejected from the spiral hole 31.

[0076] Furthermore, the branch holes 32 open into the secondary beveling surface 14, and the coolant ejected from the branch holes 32 is supplied to the margin 13 through the space between the inner circumferential surface of the machined hole in the workpiece and the secondary beveling surface 14, cooling and lubricating the margin 13. In addition, the coolant ejected from the branch holes 32 pushes away the sludge accumulated on the secondary beveling surface 14 and discharges it from above the secondary beveling surface 14, while also generating hydraulic pressure (hydraulic pressure) between the outer circumference of the drill and the inner circumferential surface of the machined hole.

[0077] In this embodiment, the cross-sectional area of ​​the flow path of the branch hole 32 is increased from the connection portion (branching portion 33) connected to the spiral hole 31 toward the opening 34 that opens toward the secondary beveling surface 14. As a result, the coolant ejected from the branch hole 32 is supplied over a wide area on the secondary beveling surface 14, and also to the margin 13. This allows for efficient cooling and lubrication of the margin 13. Furthermore, since the coolant acts over a wide area on the sludge accumulated on the secondary beveling surface 14, the sludge can be efficiently discharged from the secondary beveling surface 14. Therefore, wall friction between the outer circumference of the drill and the inner circumference of the machined hole can be suppressed.

[0078] Furthermore, because the area of ​​the branch hole 32 opening onto the secondary beveling surface 14 is large, hydraulic pressure can be generated over a wide area between the inner circumferential surface of the machined hole and the secondary beveling surface 14. This makes it easier to float the outer circumference of the drill radially inward from the inner circumferential surface of the machined hole. According to this embodiment, excessive burnishing between the inner circumferential surface of the machined hole and the margin 13 can be stably suppressed. Welding to the margin 13 can be suppressed, and the tool life of the drill 10 can be extended. In addition, since drilling can be performed while maintaining a state in which the central axis of the machined hole and the central axis O of the drill are coaxially arranged, machining accuracy can be stably improved.

[0079] Furthermore, the branch hole 32 opens into the secondary cutting surface 14 at a position away from the front end surface 1a of the body 1 towards the rear end in the axial direction. Therefore, while the above-mentioned excellent effects can be obtained, any obstruction to the regrinding process of the cutting edge 7 can be suppressed. Specifically, since the branch hole 32 is prevented from being exposed to the drill tip surface 1a too early due to the regrinding of the cutting edge 7, the provision of the branch hole 32 does not limit the number of regrinding cycles.

[0080] Furthermore, as the cross-sectional area of ​​the branch holes 32 increases from the branching section 33 towards the opening 34, it becomes easier to stably connect the branch holes 32 to the spiral holes 31 when forming the branch holes 32 by cutting or grinding (in this embodiment, cutting with a ball end mill, etc.) during drill manufacturing. This makes it easier to manufacture the drill 10.

[0081] As described above, according to this embodiment, excessive burnishing between the inner circumferential surface of the machined hole and the margin 13 can be suppressed, sludge on the secondary cutting surface 14 can be stably discharged, and the accuracy of the drilling process can be maintained well. Furthermore, according to this embodiment, the tool life of the drill 10 can be extended. In addition, the manufacturing of the drill 10 is easy.

[0082] In this embodiment, the opening 34 of the branch hole 32 is elongated in the direction of drill rotation T as it approaches the tip in the axial direction.

[0083] In this case, since the opening 34 of the branch hole 32 is elongated, it is easy to secure a large opening area for the branch hole 32 to the secondary bevel surface 14. In addition, it is easy to stably supply the coolant ejected from the branch hole 32 to the secondary bevel surface 14 and the margin 13 over a wide area in the axial direction.

[0084] Furthermore, in this embodiment, the direction in which the opening 34 of the branch hole 32 extends and the direction in which the spiral hole 31 extends are different from each other.

[0085] In this case, as shown in Figure 3, the body 1 can be extended so that the opening 34 of the branch hole 32 and the spiral hole 31 intersect when viewed radially. When forming the branch hole 32 by cutting or grinding during drill manufacturing, it becomes easier to connect the branch hole 32 and the spiral hole 31. In addition, the direction in which the opening 34 of the branch hole 32 extends can be set as appropriate regardless of the direction in which the spiral hole 31 extends, thus increasing the degree of freedom in the opening shape of the branch hole 32.

[0086] In this embodiment, the direction in which the opening 34 of the branch hole 32 extends and the direction in which the margin 13 extends are the same.

[0087] In this case, the coolant ejected from the branch holes 32 is more easily supplied to the margin 13 over a wide area and evenly along the direction in which the margin 13 extends. As a result, burnishing and welding of the margin 13 can be suppressed more stably.

[0088] In this embodiment, the branch hole 32 has a first inclined surface 35 located on the inner circumferential surface of the branch hole 32, which extends toward the tip side as it moves from the branching portion 33 toward the opening 34.

[0089] In this case, the first inclined surface 35 positioned on the inner circumferential surface of the branch hole 32 causes the coolant flowing inside the branch hole 32 to be ejected toward the drill tip. This allows the coolant to flow toward the drill tip in the space between the inner circumferential surface of the machined hole and the secondary beveling surface 14. Specifically, the coolant on the secondary beveling surface 14 flows from the branch hole 32 toward the drill tip, is supplied to the vicinity of the cutting edge 7 for cooling and lubrication, then changes direction in the axial direction and flows toward the rear end of the drill through the chip discharge groove 4. For this reason, the direction of the coolant flowing on the secondary beveling surface 14 (flow toward the tip) and the direction of the coolant flowing in the chip discharge groove 4 (flow toward the rear end) are different from each other.

[0090] This provides a rectifying effect on the coolant flowing through the secondary beveling surface 14 and the chip discharge groove 4, increasing the flow velocity and pressure (hydraulic pressure), and further improving the cooling and lubrication effects of the coolant. The outer circumference of the drill can be stably floated away from the inner circumference of the machined hole, and friction between the inner circumference of the machined hole and the outer circumference of the drill can be further suppressed.

[0091] In this embodiment, the branch hole 32 has a second inclined surface 36 located on the inner circumferential surface of the branch hole 32, with the branch portion 33 in between, and positioned on the opposite side from the first inclined surface 35. The second inclined surface 36 extends towards the rear end or the front end as it moves from the branch portion 33 toward the opening 34.

[0092] In this embodiment, when the second inclined surface 36 extends toward the rear end as it moves from the branching portion 33 towards the opening 34, a large and stable opening area can be secured for the opening 34 of the branch hole 32 toward the secondary beveling surface 14. Also, although not shown in the figures, when the second inclined surface 36 extends toward the tip as it moves from the branching portion 33 towards the opening 34, the coolant ejected from the branch hole 32 can be directed more easily toward the drill tip.

[0093] In this embodiment, the second inclined surface 36 extends toward the rear end as it moves from the branching portion 33 toward the opening 34. As shown in Figure 6, in a cross-sectional view of the branch hole 32 passing through the branching portion 33 and the opening 34, the first angle θ1 at which the first inclined surface 35 inclins toward the front end with respect to a virtual straight line VL that passes through the center of the branching portion 33 and is perpendicular to the spiral hole 31 is greater than the second angle θ2 at which the second inclined surface 36 inclins toward the rear end with respect to the virtual straight line VL.

[0094] In this case, the opening area of ​​the branch hole 32 to the secondary beveling surface 14 can be made larger, while also making it easier to direct the coolant ejected from the branch hole 32 toward the drill tip.

[0095] In this embodiment, the tip of the spiral hole 31 opens to the front surface 1a of the body 1, and the opening area of ​​the branching portion 33 that opens to the spiral hole 31 is smaller than the opening area of ​​the spiral hole 31 that opens to the front surface 1a.

[0096] In this case, a sufficient supply of coolant is ensured from the spiral hole 31 to the tip surface 1a of the body 1. As a result, the excellent effects described above are obtained by the coolant ejection from the branch hole 32, while the cooling and lubrication conditions near the cutting edge 7 are maintained in good condition.

[0097] In this embodiment, the opening area of ​​the branch hole 32 opening to the secondary bevel surface 14 is larger than the opening area of ​​the spiral hole 31 opening to the tip surface 1a.

[0098] In this case, a large area is secured where the branch hole 32 opens onto the secondary cutting surface 14, so the above-mentioned effects of generating hydraulic pressure over a wide area between the inner circumferential surface of the machined hole and the secondary cutting surface 14, and efficiently lubricating and cooling the margin 13, can be enhanced more stably.

[0099] In this embodiment, the axial distance at which the branch hole 32 moves away from the front end surface 1a of the body 1 toward the rear end is set to be between 1D and 5D, where D is the cutting diameter of the body 1.

[0100] As described above, if the axial distance of the branch hole 32 from the front surface 1a of the body 1 toward the rear end is 1D or more, the limitation on the number of times the cutting edge 7 can be resharpened due to the provision of the branch hole 32 is further suppressed. Also, if the axial distance of the branch hole 32 from the front surface 1a of the body 1 toward the rear end is 5D or less, the branch hole 32 is prevented from being too far away from the front surface 1a, and the above-mentioned effects of the branch hole 32 are stably achieved.

[0101] <Second Embodiment> Next, a drill 20 according to a second embodiment of the present invention will be described with reference to Figures 7 to 10. In this embodiment, the same components as in the previously described embodiment may be given the same names and reference numerals and their descriptions may be omitted. The definition of direction is also the same as in the previously described embodiment unless otherwise specified. In Figures 7 to 10, at least some of the components arranged at the tip of the body 1 (thinning 5, first relief surface 1c, second relief surface 1d, cutting edge 7, etc.) are not shown.

[0102] The drill 20 of this embodiment differs from the drill 10 described in the first embodiment above in the shape of the branch holes 32. In the drill 20 of this embodiment, the branch holes 32 are formed during the manufacturing of the drill by grinding the body 1 using, for example, a disc-shaped grinding wheel. That is, the shape of the branch holes 32 is transferred from the shape of the grinding wheel.

[0103] The branch hole 32 of this embodiment will be described in detail with reference to Figures 7 to 10. Figure 7 is a side view of the body 1 as seen from the radial direction, and more specifically, it is a side view of the body 1 as seen from the front with the branch hole 32. Figure 8 is a perspective view showing a cylindrical cross-section obtained by cutting a part of the body 1 with a virtual cylindrical surface having a diameter smaller than its cutting diameter D, and Figure 9 is a perspective view showing a cylindrical cross-section obtained by cutting a part of the body 1 with a virtual cylindrical surface having a diameter smaller than its cutting diameter D and larger than the virtual cylindrical surface in Figure 8. Figure 10 is a cross-sectional view showing the X-X section in Figure 7.

[0104] In this embodiment as well, the cross-sectional area of ​​the flow path of the branch hole 32 increases as it moves from the branching portion 33 with the spiral hole 31 toward the opening 34 of the second beveling surface 14. The branching portion 33 is a roughly quadrilateral (roughly polygonal) hole that is roughly parallelogram-shaped or roughly rhombic-shaped. The opening 34 is an elongated hole that extends in the drill rotation direction T toward the tip side in the axial direction.

[0105] The first inclined surface 35 of the branch hole 32 has a concave curved shape. Although not specifically shown in the figures, in a cross-sectional view perpendicular to the center line C2 of the opening 34, the first inclined surface 35 has a straight shape extending in the width direction of the opening 34. Also, as shown in Figure 10, in a cross-sectional view along the center line C2 of the opening 34, the first inclined surface 35 has a concave curved shape that extends towards the tip as it moves from the branch portion 33 toward the opening 34 (radially outward).

[0106] The second inclined surface 36 of the branch hole 32 has a concave curved shape. Although not specifically shown in the figures, in a cross-sectional view perpendicular to the center line C2 of the opening 34, the second inclined surface 36 has a straight shape extending in the width direction of the opening 34. Also, as shown in Figure 10, in a cross-sectional view along the center line C2 of the opening 34, the second inclined surface 36 has a concave curved shape that extends toward the rear end as it moves from the branch portion 33 toward the opening 34 (as it moves radially outward).

[0107] In this embodiment, the dimensions of the first inclined surface 35 along the extending direction of the opening 34 (the direction in which the center line C2 extends) and the dimensions of the second inclined surface 36 along the same extending direction are approximately the same. Therefore, the branch portion 33 is positioned approximately in the center of the branch hole 32 in the extending direction of the opening 34.

[0108] [Effects of this Embodiment] The drill 20 of this embodiment described above provides the same effects as those of the previously described embodiment. Furthermore, in this embodiment, during drill manufacturing, the branch holes 32 can be formed by grinding along with the grinding process to form the cutting edge 7 of the body 1, making manufacturing easier.

[0109] [Other Configurations Included in the Invention] The present invention is not limited to the first and second embodiments described above, and the configuration can be modified as long as it does not depart from the technical requirements of the present invention, for example, as described below. In the illustration of modified examples, the same reference numerals are used for the same components as in the embodiments described above, and the differences will be mainly described below.

[0110] In the first and second embodiments described above, an example was given in which, in a side view of the body 1 shown in Figure 3 or Figure 7, the angle formed between the center line C2 of the opening 34 of the branch hole 32 and the central axis O of the drills 10 and 20 (corresponding to the inclination angle of the branch hole 32) is larger than the angle formed between the center line C1 of the branch portion 33 of the spiral hole 31 and the central axis O of the drills 10 and 20 (corresponding to the inclination angle of the spiral hole 31). However, the configuration is not limited to this. For example, the inclination angle of the branch hole 32 may be smaller than the inclination angle of the spiral hole 31. Alternatively, the inclination angles of the branch hole 32 and the spiral hole 31 may be the same.

[0111] Furthermore, although an example was given in which the second inclined surface 36 of the branch hole 32 extends inclined toward the rear end or the front end as it moves from the branching portion 33 toward the opening 34 (as it moves radially outward), the configuration is not limited to this. Although not specifically shown, the axial position of the second inclined surface 36 may be kept constant between the branching portion 33 and the opening 34. In this case, the second inclined surface 36 may be referred to as the rear wall surface 36, etc.

[0112] In the drills 10 and 20 of the first and second embodiments described above, the two coolant holes 3 are formed in a shape that is 180° rotationally symmetrical with respect to the central axis O, and therefore the axial positions of the two branch holes 32 are the same. However, this is not limited to this, and for example, the axial positions of the branch holes 32 of the two (or more) coolant holes 3 may be different from each other. Alternatively, for example, in the two (or more) branch holes 32, the axial positions of the openings 34 may be the same, and the axial positions of the branch portions 33 may be different. In other words, the two coolant holes 3 do not have to be formed in a shape that is 180° rotationally symmetrical with respect to the central axis O.

[0113] Furthermore, multiple branch holes 32 may be provided at intervals from each other in the axial direction. That is, multiple branch holes 32 may branch off from each spiral hole 31. In this case, the shapes (opening shapes) of the multiple branch holes 32 may be the same or different from each other.

[0114] Furthermore, although an example was given in which the tip of the spiral hole 31 opens to the front surface 1a of the body 1, the spiral hole 31 may also open to the tip of the chip discharge groove 4 or the like, either in conjunction with or instead of opening to the front surface 1a.

[0115] Furthermore, although an example was given in which the second margin 13B is located at the end of the outer circumferential surface 1b of the body 1 in the direction opposite to the drill rotation, the configuration is not limited to this. The second margin 13B may also be located at a position away from the end of the outer circumferential surface 1b of the body 1 in the direction opposite to the drill rotation, in the direction T of the drill rotation.

[0116] Furthermore, in the first and second embodiments described above, the drills 10 and 20 are double margin drills, and examples were given in which they have two types of margins 13 (first margin 13A and second margin 13B) that are spaced apart from each other in the circumferential direction, but the configuration is not limited to this. The drill may be a single margin drill having one type of margin, or a triple margin drill having three types of margins that are spaced apart from each other in the circumferential direction, etc.

[0117] Here, Figure 11 shows a part of the body 1 of a drill 30, which is a modified version of the drill 10 described in the first embodiment above. In the drill 30 shown in Figure 11, the body 1 has only a first margin 13A as the margin 13, and does not have a second margin 13B. The present invention may also be applied to such a single-margin type drill 30.

[0118] Furthermore, in the first embodiment, the second embodiment, and the modified examples described above, the drills 10, 20, and 30 are two-blade twist drills having two cutting edges 7, but the invention is not limited to these. The drill may be, for example, a three-blade or more drill having three or more cutting edges.

[0119] Furthermore, the drills 10, 20, and 30 described in the first embodiment, second embodiment, and modifications are solid drills in which the body 1 and shank 2 are integrally formed from a single material, but are not limited to this. For example, the body 1 and shank 2 may be manufactured separately and then integrated into a solid drill by brazing or the like.

[0120] Alternatively, although not specifically illustrated, the drill may be an indexable drill with a body detachably attached to the shank. In this case, the shank may be referred to as a holder. Furthermore, the drill may consist only of a body and not have a shank. In this case, the drill may be referred to as a drill head, etc.

[0121] The present invention may be combined in any way that does not depart from the technical requirements of the present invention, and the configurations described in the above embodiments and modifications may be added, omitted, substituted, or otherwise modified. Furthermore, the present invention is not limited by the above embodiments, but is limited only by the claims.

[0122] According to the drill of this embodiment of the present invention, excessive burnishing of the inner circumferential surface and margin of the machined hole can be suppressed, sludge on the secondary cutting surface can be stably discharged, and the accuracy of the drilling process can be well maintained. Therefore, it has industrial applicability.

[0123] 1...Body 1a...Tip surface 1b...Outer surface 3...Coolant hole 4...Chip discharge groove 7...Cutting edge 10, 20, 30...Drill 13...Margin 14...Second beveling surface 31...Spiral hole 32...Branch hole 33...Branching section 34...Opening 35...First inclined surface 36...Second inclined surface O...Center axis T...Drill rotation direction VL...Virtual straight line θ1...First angle θ2...Second angle.

Claims

1. A drill comprising: a body extending axially with respect to a central axis; and coolant holes extending inside the body, wherein the body has: a cutting edge positioned at the tip of the body; a chip evacuation groove opening on the tip surface and outer circumferential surface of the body, extending in the anti-drill rotation direction around the central axis as it moves from the tip surface toward the rear end in the axial direction; a margin positioned on the outer circumferential surface of the body, extending along the chip evacuation groove; and a secondary beveling surface positioned on the outer circumferential surface of the body, located radially inward from the margin, wherein the coolant holes have: a spiral hole positioned inside the body, extending in the drill rotation direction around the central axis as it moves toward the tip in the axial direction; and a branch hole branching from the spiral hole, opening into the secondary beveling surface at a position away from the tip surface of the body toward the rear end in the axial direction, wherein the cross-sectional area of ​​the flow path of the branch hole increases as it moves from the branching point with the spiral hole toward the opening of the secondary beveling surface.

2. The drill according to claim 1, wherein the opening of the branch hole is elongated in the direction of the drill rotation as it extends toward the tip in the axial direction.

3. The drill according to claim 2, wherein the direction in which the opening of the branch hole extends and the direction in which the spiral hole extends are different from each other.

4. The drill according to claim 2 or 3, wherein the direction in which the opening of the branch hole extends and the direction in which the margin extends are the same.

5. The drill according to any one of claims 1 to 3, wherein the branch hole is arranged on the inner circumferential surface of the branch hole and has a first inclined surface that extends toward the tip side as it moves from the branch portion toward the opening.

6. The drill according to claim 5, wherein the branch hole has a second inclined surface disposed on the inner circumferential surface of the branch hole and disposed on the opposite side from the first inclined surface with the branch portion in between, and the second inclined surface extends toward the rear end or the front end as it moves from the branch portion toward the opening.

7. The drill according to claim 6, wherein the second inclined surface extends toward the rear end as it moves from the branch portion toward the opening, and in a cross-sectional view of the branch hole passing through the branch portion and the opening, the first angle at which the first inclined surface is inclined toward the front end with respect to a virtual line passing through the center of the branch portion and perpendicular to the spiral hole is greater than the second angle at which the second inclined surface is inclined toward the rear end with respect to the virtual line.

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