Drill head and drill

Abstract

The drill bit head has a first mounting surface mounted to the holder, a head front end surface on the opposite side of the first mounting surface in the axial direction along the central axis, and a head outer peripheral surface connected to the first mounting surface and the head front end surface. A first chip flute and a second chip flute extending in a spiral shape around the central axis in a manner reaching from the head front end surface to the first mounting surface are formed in the head outer peripheral surface. The first chip flute and the second chip flute are symmetrically formed with respect to the central axis. The first chip flute and the second chip flute each have a first end and a second end facing each other at intervals in the circumferential direction along a circumference centered on the central axis. The first mounting surface has a first ridge, a second ridge, and a third ridge extending in a radial direction orthogonal to the axial direction.

Description

TECHNICAL FIELD

[0001] The present application relates to a drill head and a drill. This application claims priority from Japanese Patent Application No. 2020-208320 filed on December 16, 2020. The entire contents of the Japanese Patent Application are incorporated herein by reference. BACKGROUND

[0002] A drill is described in Patent Literature 1 (International Publication No. 2002 / 005990). The drill of Patent Literature 1 has a cutting head and a holder. The cutting head has a support surface. The holder has a front surface.

[0003] A plurality of protrusions extending in a radial direction are formed on the support surface. The plurality of protrusions each rise as they go toward the radial outside. A plurality of recesses are formed in the radial direction on the front surface. The plurality of recesses each deepen as they go toward the radial outside. The cutting head is mounted to the holder with the plurality of protrusions each fitting into the plurality of recesses respectively.

[0004] Patent Literature 1: International Publication No. 2002 / 005990 SUMMARY

[0005] The drill head of the present application rotates around a center axis. The drill head has a first mounting surface that is mounted to a holder, a head front end surface that is on the opposite side of the first mounting surface in the axial direction along the center axis, and a head outer peripheral surface that is continuous with the first mounting surface and the head front end surface. A first chip flute and a second chip flute that extend in a spiral shape around the center axis in such a way as to reach the first mounting surface from the head front end surface are formed on the head outer peripheral surface. The first chip flute and the second chip flute are symmetrically formed with respect to the center axis. When the first mounting surface is viewed in the axial direction along the center axis and in the direction from the first mounting surface toward the head front end surface, the first chip flute and the second chip flute each have a first end and a second end that face each other at a spaced interval in the circumferential direction along a circumference centered on the center axis, on the first mounting surface. A first ridge, a second ridge, and a third ridge that extend in a radial direction orthogonal to the axial direction are formed on the first mounting surface. The first ridge is between the first end of the first chip flute and the second end of the second chip flute in the circumferential direction. The second ridge and the third ridge are between the second end of the first chip flute and the first end of the second chip flute in the circumferential direction. The second ridge is closer to the second end of the first chip flute than the third ridge in the circumferential direction. The angle that an imaginary straight line passing through the center of the first ridge in the circumferential direction makes with an imaginary straight line passing through the center axis and the first end of the first chip flute is equal to the angle that the imaginary straight line passing through the center of the first ridge in the circumferential direction makes with an imaginary straight line passing through the center axis and the second end of the second chip flute. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 is an oblique view of the drill 100.

[0007] Figure 2 is a front view of the drill head 10.

[0008] Figure 3 is a rear view of the drill head 10.

[0009] Figure 4 is a side view of the drill head 10.

[0010] Figure 5 is a front view of the holder 20.

[0011] Figure 6 is an oblique view of the holder 20.

[0012] Figure 7 is an enlarged oblique view of the drill 100. DETAILED DESCRIPTION

[0013] [Problems to be Solved by the Invention]

[0014] In the drill described in Patent Literature 1, as the outer diameter of the drill (the outer diameter of the cutting head) becomes smaller, the maximum value of the depth of the recess and the maximum value of the height of the protrusion become smaller. Therefore, according to the drill described in Patent Literature 1, as the outer diameter of the drill becomes smaller, the fitting force between the recess and the protrusion decreases, and the support of the cutting head by the holder can become unstable. In addition, the drill is a rotary tool, and therefore it is necessary to maintain not only the stability of the support of the cutting head by the holder but also the tool balance. Here, the tool balance refers to the distribution of the mass of the rotary tool. The tool balance is determined by the distance from the center axis of the rotary tool to the mass and the arrangement of the mass in a cross section perpendicular to the center axis of the rotary tool. The tool balance is good if the centrifugal force that the rotary tool receives when the rotary tool is rotated at a prescribed rotational speed is small. Maintaining the tool balance means that the tool balance is good even if the outer diameter of the rotary tool becomes smaller.

[0015] The present application provides a drill head that can maintain the stability of the support by the holder and the tool balance even if the outer diameter becomes smaller.

[0016] [Effects of the Invention]

[0017] The drill head according to the present application can maintain the stability of the support by the holder and the tool balance even if the outer diameter becomes smaller.

[0018] [Explanation of Embodiments of the Invention]

[0019] First, an embodiment of the present application will be described.

[0020] (1) In one embodiment, a drill bit head rotates around a central axis. The drill bit head has a first mounting surface mounted to a holder, a head front end surface on an opposite side of the first mounting surface in an axial direction along the central axis, and a head outer peripheral surface connected to the first mounting surface and the head front end surface. A first chip flute and a second chip flute are formed in the head outer peripheral surface so as to extend in a spiral shape around the central axis from the head front end surface to the first mounting surface. The first chip flute and the second chip flute are symmetrically formed with respect to the central axis. When the first mounting surface is viewed in the axial direction along the central axis and in a direction from the first mounting surface toward the head front end surface, each of the first chip flute and the second chip flute has a first end and a second end facing each other at a spaced interval in a circumferential direction along a circumference centered on the central axis in the first mounting surface. A first ridge, a second ridge, and a third ridge are formed in the first mounting surface so as to extend in a radial direction orthogonal to the axial direction. The first ridge is between the first end of the first chip flute and the second end of the second chip flute in the circumferential direction. The second ridge and the third ridge are between the second end of the first chip flute and the first end of the second chip flute in the circumferential direction. The second ridge is closer to the second end of the first chip flute than the third ridge in the circumferential direction. An angle formed by an imaginary straight line passing through the center of the first ridge in the circumferential direction and an imaginary straight line passing through the central axis and the first end of the first chip flute is equal to an angle formed by the imaginary straight line passing through the center of the first ridge in the circumferential direction and an imaginary straight line passing through the central axis and the second end of the second chip flute.

[0021] According to the drill bit head of (1) described above, stability of support by the holder and tool balance can be maintained even if the outer diameter is reduced.

[0022] (2) In the drill bit head of (1) described above, the angle formed by the imaginary straight line passing through the center of the first ridge in the circumferential direction and the imaginary straight line passing through the central axis and the first end of the first chip flute can be 30° or more and 70° or less.

[0023] (3) In the drill bit head of (1) or (2) described above, an angle formed by an imaginary straight line passing through the center of the first ridge in the circumferential direction and an imaginary straight line passing through the center of the second ridge in the circumferential direction can be 150° or more and 170° or less, and an angle formed by the imaginary straight line passing through the center of the first ridge in the circumferential direction and an imaginary straight line passing through the center of the third ridge in the circumferential direction can be 150° or more and 170° or less.

[0024] (4) In the drill bit head of (3) described above, an angle formed by an imaginary straight line passing through the center of the second ridge in the circumferential direction and an imaginary straight line passing through the center of the third ridge in the circumferential direction can be 20° or more and 60° or less.

[0025] According to the drill bit head of (3) and (4) described above, the first ridge, the second ridge, and the third ridge in the circumferential direction are arranged close to an equal arrangement, and thus tool balance is improved.

[0026] (5) In the drill bit head of the above (4), the first fluted channel can be twisted in a manner that the intersection line of the first fluted channel and the outer peripheral surface of the head extends clockwise from the second end of the first fluted channel, when the first mounting surface is viewed in the direction along the central axis and from the first mounting surface toward the head front end surface. The angle formed by an imaginary straight line passing through the center of the second protrusion in the circumferential direction and an imaginary straight line passing through the central axis and the second end of the first fluted channel can be larger than the angle formed by an imaginary straight line passing through the center of the third protrusion in the circumferential direction and an imaginary straight line passing through the central axis and the first end of the second fluted channel.

[0027] According to the drill bit head of the above (5), the stress applied to the groove engaged with the second protrusion and the stress applied to the groove engaged with the third protrusion are equalized, and thus it is possible to suppress the wear from being biased toward the groove engaged with the second protrusion.

[0028] (6) In the drill bit head of the above (5), the width of the first protrusion can be 1.1 times or more and 2.0 times or less of the width of the second protrusion and the width of the third protrusion.

[0029] According to the drill bit head of the above (6), the stress applied to the groove engaged with the first protrusion and the stress applied to the groove engaged with the second protrusion and the groove engaged with the third protrusion are equalized, and thus it is possible to suppress the wear from being biased toward the groove engaged with the first protrusion.

[0030] (7) A drill bit according to an embodiment of the present application includes a holder and the drill bit head of the above (1) to (6). The holder has a second mounting surface that contacts the first mounting surface. The second mounting surface has a first groove, a second groove, and a third groove that extend in the radial direction. The first groove, the second groove, and the third groove are engaged with the first protrusion, the second protrusion, and the third protrusion, respectively.

[0031] (8) The drill bit according to another aspect of the present application has a drill bit head, a holder, and a fixing member. The drill bit head has a first mounting surface that is mounted to the holder, a head front end surface that is on the opposite side of the first mounting surface in the axial direction along the central axis of the drill bit head, a head outer peripheral surface that is continuous with the first mounting surface and the head front end surface, and a shank shaft that extends in the axial direction from the first mounting surface. The first mounting surface has a first chip flute and a second chip flute formed therein so as to extend in a spiral shape around the central axis from the head front end surface to the first mounting surface. The first chip flute and the second chip flute are symmetrically formed with respect to the central axis. When the first mounting surface is viewed in the direction along the central axis and toward the head front end surface from the first mounting surface, each of the first chip flute and the second chip flute has a first end and a second end that face each other at a circumferential interval along a circumference centered on the central axis in the first mounting surface. The first mounting surface has a first protrusion, a second protrusion, and a third protrusion formed therein so as to extend in a radial direction orthogonal to the axial direction. The first protrusion is between the first end of the first chip flute and the second end of the second chip flute in the circumferential direction. The second protrusion and the third protrusion are between the second end of the first chip flute and the first end of the second chip flute in the circumferential direction. The second protrusion is closer to the second end of the first chip flute than the third protrusion in the circumferential direction. An angle formed by an imaginary straight line that passes through the center of the first protrusion in the circumferential direction and an imaginary straight line that passes through the center of the second protrusion in the circumferential direction is larger than an angle formed by an imaginary straight line that passes through the center of the first protrusion in the circumferential direction and an imaginary straight line that passes through the center of the third protrusion in the circumferential direction. The shank shaft has a cutout. The holder has a second mounting surface that is in contact with the first mounting surface, and a holder outer peripheral surface that is continuous with the second mounting surface. The second mounting surface has a first hole into which the shank shaft is inserted, and a first groove, a second groove, and a third groove that extend in the radial direction. The first groove, the second groove, and the third groove are respectively fitted with the first protrusion, the second protrusion, and the third protrusion. The holder outer peripheral surface has a second hole that is continuous with the first hole. The fixing member is inserted into the second hole so as to be in contact with the cutout.

[0032] According to the drill bit of the above (8), the shank shaft can be positioned at a position where the fixing member can be fixed by mounting the first mounting surface to the second mounting surface.

[0033] [Details of Embodiments of the Present Application]

[0034] Details of embodiments of the present application will be described with reference to the accompanying drawings. In the following drawings, the same reference numerals are applied to the same or equivalent parts and repeated descriptions are omitted.

[0035] (Structure of Drill Bit According to Embodiments)

[0036] The structure of a drill bit according to embodiments (hereinafter referred to as "drill bit 100") will be described.

[0037] Figure 1is an oblique view of the drill bit 100. As shown in Figure 1 The drill bit 100 has a drill bit head 10, a holder 20, and a fixing member 30. The drill bit 100 rotates around a center axis A, thereby performing cutting. The drill bit head 10 is formed of, for example, super hard alloy. The holder 20 and the fixing member 30 are formed of, for example, steel. In the direction along the center axis A, the drill bit head 10 is on the front end side of the drill bit 100, and the holder 20 is on the base end side of the drill bit 100. In the direction along the center axis A, the base end side of the drill bit 100 is on the opposite side of the front end side of the drill bit 100. The drill bit 100 rotates around the center axis A with the holder 20 mounted to a spindle of a working machine.

[0038] <Drill bit head 10>

[0039] The drill bit head 10 rotates around a center axis Al when the drill bit 100 rotates around the center axis A. The center axis Al coincides with the center axis A. Hereinafter, the direction along the center axis A is referred to as the axial direction, the direction orthogonal to the center axis A is referred to as the radial direction, and the direction in the plane orthogonal to the center axis A along the circumference centered on the center axis A is referred to as the circumferential direction. Figure 2 is a front view of the drill bit head 10. Figure 3 is a rear view of the drill bit head 10. Figure 4 is a side view of the drill bit head 10. As shown in Figure 2 , Figure 3 and Figure 4 The drill bit head 10 has a first mounting surface 11, a head front end surface 12, and a head outer peripheral surface 13.

[0040] The first mounting surface 11 and the head front end surface 12 are end surfaces of the drill bit head 10 in the axial direction. The drill bit head 10 is mounted to the holder 20 at the first mounting surface 11. The head front end surface 12 is located at the front end of the drill bit 100. The head front end surface 12 is the opposite surface of the first mounting surface 11 in the axial direction. The head outer peripheral surface 13 is continuous with the first mounting surface 11 and the head front end surface 12.

[0041] The first chip flute 14 and the second chip flute 15 are formed in the head outer peripheral surface 13. The head outer peripheral surface 13 is recessed toward the center axis Al at the portions where the first chip flute 14 and the second chip flute 15 are formed. The first chip flute 14 and the second chip flute 15 extend in a spiral shape around the center axis Al in such a manner as to reach the first mounting surface 11 from the head front end surface 12. The first chip flute 14 and the second chip flute 15 are formed in symmetrical shapes with respect to the center axis Al. In Figure 2 , Figure 3 and Figure 4In the illustrated example, the first flutes 14 and the second flutes 15 are twisted clockwise as they progress from the head front face 12 toward the first mounting face 11 as viewed in the axial direction. From another viewpoint, the first flutes and the second flutes are right-handed. From yet another viewpoint, the first flutes and the second flutes are formed in a helical shape.

[0042] The head front face 12 has a rear clearance face 12a and a rear clearance face 12b. The rear clearance face 12a intersects the first flutes 14. The rear clearance face 12b intersects the second flutes 15. An intersection ridge line of the rear clearance face 12a and the first flutes 14 becomes a cutting edge 16, and an intersection ridge line of the rear clearance face 12b and the second flutes 15 becomes a cutting edge 17. The cutting edge 16 and the cutting edge 17 extend from the head peripheral face 13 toward the center of the head front face 12 (the front end of the drill 100). The cut material (chips) cut by the cutting edge 16 and the cutting edge 17 are discharged through the first flutes 14 and the second flutes 15, respectively. That is, the first flutes 14 and the second flutes 15 are grooves formed for discharging the chips.

[0043] The first flutes 14 have a first end 14a and a second end 14b. The second end 14b is circumferentially spaced apart from the first end 14a. If moving from the second end 14b toward the head front face 12 side in the direction in which the first flutes 14 extend on the head peripheral face 13, the second end 14b is connected to the end of the head peripheral face 13 side of the cutting edge 16.

[0044] The second flutes 15 have a first end 15a and a second end 15b. The second end 15b is circumferentially spaced apart from the first end 15a. If moving from the second end 15b toward the head front face 12 side in the direction in which the second flutes 15 extend on the head peripheral face 13, the second end 15b is connected to the end of the head peripheral face 13 side of the cutting edge 17.

[0045] The first mounting face 11 has a first ridge 11a, a second ridge 11b, and a third ridge 11c. The first ridge 11a, the second ridge 11b, and the third ridge 11c extend in the radial direction. The first ridge 11a, the second ridge 11b, and the third ridge 11c extend from the head peripheral face 13 toward the center axis Al side. The first ridge 11a, the second ridge 11b, and the third ridge 11c protrude in the axial direction from the first mounting face 11.

[0046] The first ridge 11a is between the first end 14a of the first chip flute 14 and the second end 15b of the second chip flute 15 in the circumferential direction. The second ridge 11b and the third ridge 11c are between the second end 14b of the first chip flute 14 and the first end 15a of the second chip flute 15 in the circumferential direction. The second ridge 11b is closer to the second end 14b of the first chip flute 14 than the third ridge 11c in the circumferential direction. From another viewpoint, the first ridge 11a, the second ridge 11b, and the third ridge 11c are formed asymmetrically with respect to the center axis Al.

[0047] As shown in FIG. 1, an imaginary straight line passing through the center of the circumferential direction of the first ridge 11a is set as an imaginary straight line VL1 in the first mounting surface 11. Similarly, an imaginary straight line passing through the center of the circumferential direction of the second ridge 11b is set as an imaginary straight line VL2, and an imaginary straight line passing through the center of the circumferential direction of the third ridge 11c is set as an imaginary straight line VL3. The imaginary straight lines VL1, VL2, and VL3 are orthogonal to the center axis Al, respectively. Figure 3

[0048] As shown in FIG. 1, an imaginary straight line passing through the first end 14a of the first chip flute 14 and the center axis Al is set as an imaginary straight line VL4. Similarly, an imaginary straight line passing through the second end 14b of the first chip flute 14 and the center axis Al is set as an imaginary straight line VL5. Similarly, an imaginary straight line passing through the first end 15a of the second chip flute 15 and the center axis Al is set as an imaginary straight line VL6. Similarly, an imaginary straight line passing through the second end 15b of the second chip flute 15 and the center axis Al is set as an imaginary straight line VL7. The imaginary straight lines VL4, VL5, VL6, and VL7 are orthogonal to the center axis Al, respectively. Figure 3

[0049] The angle θ1 formed by the imaginary straight line VL1 and the imaginary straight line VL4 is equal to the angle θ2 formed by the imaginary straight line VL1 and the imaginary straight line VL7. However, a slight angular error between the angle θ1 and the angle θ2 is allowed as long as the effects of the present application are obtained. The angle θ1 and the angle θ2 are, for example, 30° or more and 70° or less.

[0050] The angle θ3 formed by the imaginary straight line VL1 and the imaginary straight line VL2 is preferably greater than the angle θ4 formed by the imaginary straight line VL1 and the imaginary straight line VL3. That is, the second ridge 11b and the third ridge 11c are preferably formed asymmetrically with respect to the imaginary straight line VL1. The angle θ3 and the angle θ4 are preferably 150° or more and 170° or less.

[0051] The angle θ5 formed by the imaginary straight line VL2 and the imaginary straight line VL3 is preferably 20° or more and 60° or less. Furthermore, the sum of the angle θ3, the angle θ4, and the angle θ5 becomes 360°.

[0052] ​​As described above, the first chip discharge groove 14 and the second chip discharge groove 15 are formed in a clockwise spiral shape when viewed from the front end face 12 side of the head. Therefore, when the first mounting surface 11 is viewed along the central axis A1 and in the direction from the first mounting surface 11 toward the front end face 12 of the head, the first chip discharge groove 14 is located at the intersection of the first chip discharge groove 14 and the outer peripheral surface 13 of the head ( Figure 3 The first chip discharge groove 14 (CL1) extends circumferentially and clockwise from the second end 14b of the first chip discharge groove 14. Similarly, the second chip discharge groove 15 is twisted at the intersection of the second chip discharge groove 15 and the outer peripheral surface 13 of the head ( Figure 3 The CL2 in the second chip discharge groove 15 extends clockwise in the circumferential direction from the second end 15b of the second chip discharge groove 15. The angle θ6 formed by the imaginary straight line VL2 and the imaginary straight line VL5 is preferably greater than the angle θ7 formed by the imaginary straight line VL3 and the imaginary straight line VL6.

[0053] The widths of the first protrusion 11a, the second protrusion 11b, and the third protrusion 11c are respectively designated as the first width, the second width, and the third width. The first width, the second width, and the third width are widths in directions orthogonal to the extending direction of each protrusion, and are measured at the ends of the outer peripheral surfaces 13 of the heads of each protrusion. The first width is preferably greater than the second width and the third width. More specifically, the first width is preferably 1.1 times to 2.0 times the second width and the third width. Furthermore, the second width is, for example, equal to the third width.

[0054] like Figure 4 As shown, a shank 18 is formed on the first mounting surface 11. The shank 18 extends axially from the center of the first mounting surface 11. The portion with the cutout 18a described later is removed, and the cross-section of the shank 18 orthogonal to the axial direction is, for example, circular.

[0055] A notch 18a is formed on the outer peripheral surface of the shank 18. The notch 18a has an inclined surface 18b. The inclined surface 18b is inclined relative to the axial direction (the direction in which the shank 18 extends). More specifically, when the normal vector of the inclined surface 18b is set as V1, and the unit vector in the direction from the front end of the shank 18 (the end opposite to the first mounting surface 11) towards the base end of the shank 18 (the end on the side of the first mounting surface 11) is set as V2, the angle between V1 and V2 is less than 90°. From another point of view, the area of ​​the cross section of the shank 18, which intersects the inclined surface 18b and is orthogonal to the axial direction of the shank 18, decreases monotonically as it travels along the central axis A1 from the front end side of the shank 18 towards the base end side of the shank 18.

[0056] Let the outer diameter of the drill bit head 10 be defined as the outer diameter D. The outer diameter D is as follows: Figure 2 The figure shows the diameter of the circumscribed circle of the drill head 10 when viewed axially from the front face 12 side. The outer diameter D is preferably 15 mm or less. For example, the outer diameter D is 6 mm or more.

[0057] <Holder 20 and fixing member 30>

[0058] Figure 5 Fig. 4 is an elevational view of the holder 20. Figure 6 Fig. 5 is an oblique view of the holder 20. As shown in Figs. 4 and 5, the holder 20 extends in the axial direction. The holder 20 has a second mounting surface 21 and a holder outer peripheral surface 22. The holder 20 rotates around a center axis A2. The center axis A2 coincides with the center axis A. Figure 5 Figure 6

[0059] The second mounting surface 21 is an end surface of the holder 20 in the axial direction. The first slot 21a, the second slot 21b, and the third slot 21c are formed in the second mounting surface 21. The first slot 21a, the second slot 21b, and the third slot 21c extend in the radial direction. The first slot 21a, the second slot 21b, and the third slot 21c extend from the head outer peripheral surface 13 toward the center side of the second mounting surface 21. The first slot 21a, the second slot 21b, and the third slot 21c are recessed from the second mounting surface 21 in the axial direction.

[0060] The holder outer peripheral surface 22 is continuous with the second mounting surface 21. The chip flutes 23 and 24 are formed in the holder outer peripheral surface 22. The holder outer peripheral surface 22 is recessed toward the center axis A2 at portions where the chip flutes 23 and 24 are formed. The chip flutes 23 and 24 are formed in a spiral shape around the center axis of the holder 20. The chip flutes 23 and 24 extend from the second mounting surface 21 toward the base end side of the drill bit 100. The chip flutes 23 and 24 are twisted in the same direction as the first chip flute 14 and the second chip flute 15 when viewed from the second mounting surface 21 side. That is, the chip flutes 23 and 24 are twisted clockwise when viewed from the second mounting surface 21 side. The chip flutes 23 and 24 are connected to the first chip flute 14 and the second chip flute 15, respectively.

[0061] The chip flute 23 has a first end 23a and a second end 23b. The second end 23b is opposite the first end 23a at a circumferential interval. The first end 23a is a circumferential end of the chip flute 23 corresponding to the first end 14a, and the second end 23b is a circumferential end of the chip flute 23 corresponding to the second end 14b.

[0062] The chip flute 24 has a first end 24a and a second end 24b. The second end 24b is opposite the first end 24a at a circumferential interval. The first end 24a is a circumferential end of the chip flute 24 corresponding to the first end 15a, and the second end 24b is a circumferential end of the chip flute 24 corresponding to the second end 15b.

[0063] ​​The first groove 21a is between the first end 23a of the chip discharge groove 23 and the second end 24b of the chip discharge groove 24 in the circumferential direction. The second groove 21b and the third groove 21c are between the second end 23b of the chip discharge groove 23 and the first end 24a of the chip discharge groove 24 in the circumferential direction. The second groove 21b is closer to the second end 23b of the chip discharge groove 23 than the third groove 21c in the circumferential direction. From another viewpoint, the first groove 21a, the second groove 21b, and the third groove 21c are formed asymmetrically with respect to the center axis A2.

[0064] As shown in FIG. 8, an imaginary straight line passing through the center of the circumferential direction of the first groove 21a is set as an imaginary straight line VL8 in the second mounting surface 21. Similarly, an imaginary straight line passing through the center of the circumferential direction of the second groove 21b is set as an imaginary straight line VL9. Similarly, an imaginary straight line passing through the center of the circumferential direction of the third groove 21c is set as an imaginary straight line VL10. The imaginary straight line VL8, the imaginary straight line VL9, and the imaginary straight line VL10 are each orthogonal to the center axis A2. Figure 5 As shown in FIG. 8, an imaginary straight line passing through the center of the circumferential direction of the first groove 21a is set as an imaginary straight line VL8 in the second mounting surface 21. Similarly, an imaginary straight line passing through the center of the circumferential direction of the second groove 21b is set as an imaginary straight line VL9. Similarly, an imaginary straight line passing through the center of the circumferential direction of the third groove 21c is set as an imaginary straight line VL10. The imaginary straight line VL8, the imaginary straight line VL9, and the imaginary straight line VL10 are each orthogonal to the center axis A2.

[0065] Figure 5 As shown in FIG. 8, an imaginary straight line passing through the center of the circumferential direction of the first groove 21a is set as an imaginary straight line VL8 in the second mounting surface 21. Similarly, an imaginary straight line passing through the center of the circumferential direction of the second groove 21b is set as an imaginary straight line VL9. Similarly, an imaginary straight line passing through the center of the circumferential direction of the third groove 21c is set as an imaginary straight line VL10. The imaginary straight line VL8, the imaginary straight line VL9, and the imaginary straight line VL10 are each orthogonal to the center axis A2.

[0066] The angle θ8 formed by the imaginary straight line VL8 and the imaginary straight line VL11 and the angle θ9 formed by the imaginary straight line VL8 and the imaginary straight line VL14 are each equal to the angle θ1 and the angle θ2, respectively. The angle θ10 formed by the imaginary straight line VL8 and the imaginary straight line VL9 and the angle θ11 formed by the imaginary straight line VL8 and the imaginary straight line VL10 are each equal to the angle θ4 and the angle θ5, respectively. As a result, in a case where the first groove 21a opposes the first protrusion 11a, the second groove 21b and the third groove 21c oppose the second protrusion 11b and the third protrusion 11c, respectively. Further, the angle θ12 formed by the imaginary straight line VL9 and the imaginary straight line VL10 is equal to the angle θ5.

[0067] ​The first groove 21a, the second groove 21b, and the third groove 21c are formed in shapes that can be fitted with the first protrusion 11a, the second protrusion 11b, and the third protrusion 11c, respectively. Therefore, the first mounting surface 11 is brought into contact with the second mounting surface 21 in a manner that the first groove 21a, the second groove 21b, and the third groove 21c are opposed to the first protrusion 11a, the second protrusion 11b, and the third protrusion 11c, respectively, whereby the drill head 10 is mounted to the holder 20.

[0068] The flutes 23 and 24 are formed in helical shapes in the clockwise direction as viewed from the second mounting surface 21 as described above. Therefore, as viewed in the direction along the central axis A2 and toward the base end side of the holder 20 (i.e., the base end side of the drill 100) from the second mounting surface 21, the flute 23 is twisted in a manner that the intersection line of the flute 23 and the holder outer peripheral surface 22 extends in the circumferential direction from the first end 23a of the flute 23 in the clockwise direction. Similarly, the flute 24 is twisted in a manner that the intersection line of the flute 24 and the holder outer peripheral surface 22 extends in the circumferential direction from the first end 24a of the flute 24 in the clockwise direction.

[0069] The angle θ13 formed by the imaginary straight line VL9 and the imaginary straight line VL12 and the angle θ14 formed by the imaginary straight line VL10 and the imaginary straight line VL13 are equal to the angle θ6 and the angle θ7, respectively.

[0070] The width of the first groove 21a, the width of the second groove 21b, and the width of the third groove 21c are set as a fourth width, a fifth width, and a sixth width, respectively. The fourth width, the fifth width, and the sixth width are widths in a direction orthogonal to the direction in which each groove extends, and are measured at the end on the holder outer peripheral surface 22 side of each groove. The fourth width is preferably greater than the fifth width and the sixth width. More specifically, the fourth width is preferably 1.1 times or more and 2.0 times or less of the fifth width and the sixth width. Further, the fifth width is equal to the sixth width, for example.

[0071] The first hole 21d is formed in the second mounting surface 21. The first hole 21d is formed in the central portion of the second mounting surface 21. The first hole 21d extends in the axial direction. In the state in which the drill head 10 is mounted to the holder 20, the shank shaft 18 is inserted into the first hole 21d.

[0072] The second hole 25 is formed in the holder outer peripheral surface 22. The second hole 25 is continuous with the first hole 21d. The second hole 25 extends in a direction intersecting the inclined surface 18b. As viewed in the direction in which the second hole 25 extends, the inclined surface 18b is exposed from the second hole 25.

[0073] The fixing member 30 is inserted into the second hole 25. More specifically, a screw groove is formed in the inner wall surface of the second hole 25, and the fixing member 30 is a bolt having a screw thread formed in a shaft. The fixing member 30 is inserted into the second hole 25 by screwing the fixing member 30 into the second hole 25. The fixing member 30 is rotated, whereby the fixing member 30 advances in the second hole 25 in the direction in which the second hole 25 extends and comes into contact with the inclined surface 18b. The shank 18 is thereby pulled toward the front end of the first hole 21d (the end on the side opposite the second mounting surface 21), and the drill bit head 10 is fixed to the holder 20.

[0074] (EFFECTS OF THE DRILL BIT)

[0075] Next, the effects of the drill bit 100 will be described.

[0076] The first protrusions 11a, 11b, 11c are formed in the first mounting surface 11 so as to be fitted into the first, second, and third grooves 21a, 21b, 21c, respectively. Therefore, the drill bit head 10 is supported at three points in the state of being mounted to the holder 20. Therefore, the drill bit head 10 is stably supported to the holder 20.

[0077] For example, as described in Patent Document 1, in order to ensure the fitting force with the holder 20, it is considered to form a plurality of protrusions that rise toward the radially outer side in the first mounting surface 11, and to form a plurality of grooves that deepen toward the radially outer side in the second mounting surface 21. However, for the following reasons, it becomes difficult to form a plurality of protrusions in the case of reducing the diameter of the drill bit head 10. If the number and height of the protrusions are maintained and the diameter of the drill bit head 10 is reduced, the width of the protrusions in the circumferential direction becomes small. Then, the mechanical strength of the protrusions decreases, and thus it is necessary to lower the protrusions with respect to the first mounting surface 11. In this case, the grooves corresponding to the lowered protrusions also become shallow. As a result, the fitting force between the protrusions and the grooves can decrease. That is, the support of the drill bit head 10 by the holder 20 can become unstable.

[0078] On the other hand, in the drill bit 100, the drill bit head 10 is supported to the holder 20 by the three-point support achieved by the three protrusions (the first protrusion 11a, the second protrusion 11b, and the third protrusion 11c) formed in the first mounting surface 11 and the three grooves (the first groove 21a, the second groove 21b, and the third groove 21c) formed in the second mounting surface 21, and thus the drill bit head 10 can be stably supported even in the case of a small outer diameter of the drill bit head 10.

[0079] In the drill head 10, the angle θ1 and the angle θ2 are equal. Also, in the holder 20, the angle θ8 and the angle θ9 are equal to the angle θ1 and the angle θ2, respectively. That is, in the drill 100, the first land 11a is disposed in the circumferential direction at the middle of the first chip flute 14 and the second chip flute 15, and the first groove 21a is disposed in the circumferential direction at the middle of the chip flute 23 and the chip flute 24. Therefore, according to the drill 100, the tool balance can be maintained.

[0080] In the case where the angle θ3 and the angle θ4 are 150° or more and 170° or less (in the case where the angle θ5 is 20° or more and 60° or less), the disposition of the circumferential direction of the first land 11a, the second land 11b, and the third land 11c (the first groove 21a, the second groove 21b, and the third groove 21c) is close to equal disposition. Therefore, in this case, the tool balance of the drill 100 is further improved.

[0081] Figure 7 is an enlarged oblique view of the drill 100. As shown in Figure 7 In the holder 20, the chip flute 23 is twisted in a manner that the intersection line of the chip flute 23 and the holder outer peripheral surface 22 extends in the circumferential direction clockwise from the first end 23a of the chip flute 23 when the second mounting surface 21 is viewed along the central axis A2 and in the direction DR from the second mounting surface 21 toward the base end side of the holder 20 (i.e., the base end side of the drill 100). Similarly, the chip flute 24 is twisted in a manner that the intersection line of the chip flute 24 and the holder outer peripheral surface 22 extends in the circumferential direction clockwise from the first end 24a of the chip flute 24.

[0082] The chip flutes 23 and 24 are disposed as described above, and therefore the wall thickness in the vicinity of the second groove 21b with respect to the chip flute 23 is smaller than the wall thickness in the vicinity of the third groove 21c with respect to the chip flute 24. More specifically, the thickness T23, which is the shortest distance between the deepest portion of the second groove 21b in the direction DR and the chip flute 23, is smaller than T24 (not shown), which is the shortest distance between the deepest portion of the third groove 21c in the direction DR and the chip flute 24. Therefore, the stress in the vicinity of the second groove 21b is easily larger than the stress in the vicinity of the third groove 21c. In order to alleviate the stress in the vicinity of the second groove 21b, the angle θ6 is made larger than the angle θ7 in the drill head 10, and correspondingly, in the case where the angle θ13 is made larger than the angle θ14 in the holder 20, the wall thickness in the circumferential direction and the axial direction in the vicinity of the second groove 21b with respect to the chip flute 23 is made larger. Therefore, in this case, the stress applied to the second groove 21b is alleviated. As a result, the wear is suppressed from being biased toward the second groove 21b.

[0083] The cutting force is supported by one flute (first flute 21a) between the first end 23a of the first flute 23 and the second end 24b of the second flute 24, and the cutting force is supported by two flutes (second flute 21b and third flute 21c) between the second end 23b of the first flute 23 and the first end 24a of the second flute 24, so stress is more likely to be applied to the first flute 21a than to the second flute 21b and the third flute 21c. Therefore, in the case where the first width is larger than the second and third widths (the fourth width is larger than the fifth and sixth widths), stress in the vicinity of the first flute 21a is mitigated. As a result, wear is inhibited from being biased toward the first flute 21a.

[0084] The first land 11a, the second land 11b, and the third land 11c are asymmetrically arranged with respect to the center axis Al. In the case where the angle θ3 and the angle θ4 are different from each other, the second land 11b and the third land 11c are asymmetrically arranged with respect to the imaginary straight line VLl. That is, the drill head 10 cannot be mounted to the holder 20 except in the case where the first land 11a, the second land 11b, and the third land 11c are fitted to the first flute 21a, the second flute 21b, and the third flute 21c, respectively.

[0085] Therefore, in the case where the angle θ3 and the angle θ4 are different from each other, the drill head 10 can be positioned with respect to the holder 20 by the first land 11a, the second land 11b, and the third land 11c. From another viewpoint, as long as the drill head 10 is mounted to the holder 20, the inclined surface 18b is necessarily exposed from the second hole 25, so it is not necessary to form the cutout 18a at a plurality of sites in order to secure the drill head 10 by pulling it in while securing it by the securing member 30. That is, it is possible to inhibit the decrease in the rigidity of the shank 18 accompanying the formation of the cutout 18a.

[0086] The embodiments disclosed this time are examples in all respects and are not limited to the contents thereof. The scope of the present application is not shown by the above embodiments but is shown by the claims, and includes all modifications equivalent in substance and scope to the claims.

[0087] Explanation of Reference Numerals

[0088] 100 drill, 10 drill head, 11 first mounting surface, 11a first ridge, 11b second ridge, 11c third ridge, 12 head front end surface, 12a, 12b rear clearance surface, 13 head outer peripheral surface, 14 first chip flute, 14a first end, 14b second end, 15 second chip flute, 15a first end, 15b second end, 16, 17 cutting edge, 18 shank shaft, 18a notch, 18b inclined surface, 20 holder, 21 second mounting surface, 21a first groove, 21b second groove, 21c third groove, 21d first hole, 22 holder outer peripheral surface, 23 chip flute, 23a first end, 23b second end, 24 chip flute, 24a first end, 24b second end, 25 second hole, 30 fixing member, A, A1, A2 center axis, D outer diameter, DR direction, T23, T24 thickness, VL1, VL2, VL3, VL4, VL5, VL6, VL7, VL8, VL9, VL10, VL11, VL12, VL13, VL14 imaginary straight line, θ1, θ2, θ3, θ4, θ5, θ6, θ7, θ8, θ9, θ10, θ11, θ12, θ13, θ14 angle.

Claims

1. A drill bit head that rotates about a central axis, The drill bit head has: a first mounting surface that is mounted to a cage; a front end face that is located on the opposite side of the first mounting surface along the central axis; and an outer peripheral surface that is connected to the first mounting surface and the front end face. A first chip discharge groove and a second chip discharge groove are formed on the outer peripheral surface of the head, extending in a spiral shape around the central axis from the front end face of the head to the first mounting surface. The first chip discharge groove and the second chip discharge groove are formed symmetrically about the central axis. When the first mounting surface is viewed along the central axis and in a direction from the first mounting surface toward the front end face of the head, the first chip discharge groove and the second chip discharge groove each have a first end and a second end on the first mounting surface that are circumferentially spaced apart from each other along a circumference centered on the central axis and are opposite to each other. A plurality of protrusions, radially asymmetrical about the central axis, are formed on the first mounting surface. The plurality of protrusions include a first protrusion, a second protrusion, and a third protrusion extending radially orthogonal to the axial direction. The first protrusion is located circumferentially between the first end of the first chip discharge groove and the second end of the second chip discharge groove. The second and third protrusions are located circumferentially between the second end of the first chip discharge groove and the first end of the second chip discharge groove. The second protrusion is closer to the second end of the first chip discharge groove in the circumferential direction than the third protrusion. The angle formed by the imaginary straight line passing through the center of the first radial protrusion and the imaginary straight line passing through the central axis and the first end of the first chip discharge groove is equal to the angle formed by the imaginary straight line passing through the center of the first radial protrusion and the imaginary straight line passing through the central axis and the second end of the second chip discharge groove.

2. The drill bit head according to claim 1, wherein, The angle between the imaginary straight line passing through the center of the first radial protrusion and the imaginary straight line passing through the central axis and the first end of the first chip discharge groove is more than 30° and less than 70°.

3. The drill bit head according to claim 1 or 2, wherein, The angle between an imaginary straight line passing through the center of the first radial protrusion and an imaginary straight line passing through the center of the second radial protrusion is more than 150° and less than 170°. The angle between an imaginary straight line passing through the center of the first radial protrusion and an imaginary straight line passing through the center of the third radial protrusion is more than 150° and less than 170°.

4. The drill bit head according to claim 3, wherein, The angle between the imaginary straight line passing through the center of the second radial protrusion and the imaginary straight line passing through the center of the third radial protrusion is more than 20° and less than 60°.

5. The drill bit head according to claim 4, wherein, When viewed along the central axis and in a direction from the first mounting surface toward the front end face of the head, the first chip discharge groove is twisted in a clockwise direction from the second end of the first chip discharge groove along the circumferential direction, with the intersection line of the first chip discharge groove and the outer peripheral surface of the head. The angle formed by the imaginary straight line passing through the center of the second radial protrusion and the imaginary straight line passing through the central axis and the second end of the first chip discharge groove is greater than the angle formed by the imaginary straight line passing through the center of the third radial protrusion and the imaginary straight line passing through the central axis and the first end of the second chip discharge groove.

6. The drill bit head according to claim 5, wherein, The width of the first protrusion is more than 1.1 times and less than 2.0 times the width of the second protrusion and the width of the third protrusion.

7. A drill bit, comprising: cage; and The drill head as described in any one of claims 1 to 6, The cage has a second mounting surface that contacts the first mounting surface. A first groove, a second groove, and a third groove extending radially are formed on the second mounting surface. The first groove, the second groove, and the third groove are respectively engaged with the first protrusion, the second protrusion, and the third protrusion.

8. A drill bit having: Drill bit head; cage; and Fixed components The drill bit head has: a first mounting surface mounted on the cage; a front end face located axially opposite to the first mounting surface along the central axis of the drill bit head; an outer peripheral surface connected to the first mounting surface and the front end face; and a shank extending axially from the first mounting surface. A first chip discharge groove and a second chip discharge groove are formed on the outer peripheral surface of the head, extending in a spiral shape around the central axis from the front end face of the head to the first mounting surface. The first chip discharge groove and the second chip discharge groove are formed symmetrically about the central axis. When the first mounting surface is viewed along the central axis and in a direction from the first mounting surface toward the front end face of the head, the first chip discharge groove and the second chip discharge groove each have a first end and a second end on the first mounting surface that are circumferentially spaced apart from each other along a circumference centered on the central axis and are opposite to each other. A plurality of protrusions, radially asymmetrical about the central axis, are formed on the first mounting surface. The plurality of protrusions include a first protrusion, a second protrusion, and a third protrusion extending radially orthogonal to the axial direction. The first protrusion is located circumferentially between the first end of the first chip discharge groove and the second end of the second chip discharge groove. The second and third protrusions are located circumferentially between the second end of the first chip discharge groove and the first end of the second chip discharge groove. The second protrusion is closer to the second end of the first chip discharge groove in the circumferential direction than the third protrusion. The angle formed by an imaginary straight line passing through the center of the first radial protrusion and an imaginary straight line passing through the central axis and the first end of the first chip discharge groove is equal to the angle formed by an imaginary straight line passing through the center of the first radial protrusion and an imaginary straight line passing through the central axis and the second end of the second chip discharge groove. A cut is formed in the shank. The cage has a second mounting surface that contacts the first mounting surface and a cage outer peripheral surface that is connected to the second mounting surface. The second mounting surface has a first hole for inserting the shank shaft and a first groove, a second groove, and a third groove extending radially. The first groove, the second groove, and the third groove respectively engage with the first protrusion, the second protrusion, and the third protrusion. A second hole, connected to the first hole, is formed on the outer peripheral surface of the cage. The fixing component is inserted into the second hole, thereby contacting the cut.

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