Drill

Abstract

To make breakage of a cutting edge in which a honing surface is formed, in particular a thinning cutting edge, less likely to occur in a drill in which the honing surface for inhibiting breakage is provided in the cutting edge.SOLUTION: A drill 1 has a plurality of cutting edges 4, in each of which a cutting part 4 at an axial tip side of a shank part 2 is made of a main cutting edge 41 at an outer periphery side in a radial direction and a thinning cutting edge 42 at a center side which continues to the main cutting edge 41, and honing surfaces 41a, 42a are formed at the main cutting edge 41 and the thinning cutting edge 42, respectively. In the drill 1, when the cutting edge 4 is viewed from an end surface side, a transition section 44 transiting from the main cutting edge 41 to the thinning cutting edge 42 draws a convex curved line toward a front side in a rotation direction. A border line 43 inclining relative to an axial direction and a direction orthogonal to the axial direction appears between the honing surface 41a and the honing surface 42a. A grinding line 45 is formed in a direction along the border line 43 on the honing surface 42a.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a drill that is used primarily for metal processing and has a honing surface formed on the cutting edge to prevent breakage. [Background technology]

[0002] A honing surface is often formed on the cutting edge of a drill such as a small-diameter long drill used for metal processing to prevent breakage during cutting (see Patent Documents 1 to 6). The cutting edge is divided into a main cutting edge on the radially outer periphery and a thinning cutting edge located on the radially central side of the main cutting edge, and a honing surface is formed continuously on each of the two cutting edges (Patent Documents 1 to 6).

[0003] Generally, for drills with cutting edge diameters of 4 mm or more, the honed surface is formed by mechanical honing, but for small diameter drills with cutting edge diameters of less than 4 mm, the honed surface is often formed by hand honing. When using hand honing, the grinding lines that appear on the honed surface are uneven in the length direction of the thinning cutting edge (along the thinning cutting edge), and the honing width is also prone to variation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 60-175513 (Claim 1, specification, page 6, line 11 to page 9, line 5, Figures 4 to 11) [Patent Document 2] JP 2003-39220 A (Claim 1, paragraphs 0016 to 0021) [Patent Document 3] JP 2003-266225 A (Claim 2, paragraphs 0011 to 0013, Figure 2) [Patent Document 4] JP 2006-212724 A (paragraph 0018) [Patent Document 5] JP 2009-18360 A (Claim 1, paragraphs 0016 to 0025, Figures 3 to 5) [Patent Document 6] JP 2015-131384 A (Claim 4, paragraphs 0019-0020, 0041, Figures 2-4) [Patent Document 7] JP 2021-88007 A (paragraphs 0006 to 0008) Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have confirmed that when machining high-hardness materials with a small-diameter long drill, breakage of the thinning cutting edge cannot be sufficiently suppressed by simply increasing the honing angle.

[0006] In view of the above-mentioned background, the present invention proposes a drill having a configuration in which the cutting edge having a honing surface, particularly the thinning cutting edge, is less likely to break. [Means for solving the problem]

[0007] The drill of the invention described in claim 1 is a drill having a cutting portion on the axial tip side of a shank portion, the cutting edges being provided with a plurality of cutting edges and a chip discharge groove between the cutting edges adjacent in the circumferential direction, a thinning portion facing the chip discharge groove is formed on the rotational rear side of the flank face of each of the cutting edges, the cutting edges being comprised of a main cutting edge on the radial outer periphery side and a thinning cutting edge continuous with the main cutting edge and positioned on the radial center side of the main cutting edge, and a honing surface is formed on each of the main cutting edges and the thinning cutting edge, Between the honing surface of the main cutting edge and the honing surface of the thinning cutting edge, a boundary line appears that is inclined with respect to both the axial direction of the shank portion and a direction perpendicular to the axial direction, and grinding lines are formed on the honing surface of the thinning cutting edge in a direction along the boundary line, When the cutting portion is viewed from the end face side in the axial direction, the transition section from the main cutting edge to the thinning cutting edge forms a convex curve toward the forward side in the rotational direction, and the angle between the tangent to the main cutting edge at the portion closest to the thinning cutting edge and the tangent to the thinning cutting edge at the portion closest to the main cutting edge is a minor angle greater than 150°.

[0008] "When the cutting portion 3 is viewed from the end face side in the axial direction" refers to the end face when the tip face 30 of the cutting portion 3 of the drill 1 shown in Figures 1 to 3 and 9 is viewed from that side in the axial direction (the direction of the rotation axis O) toward the shank portion 2.

[0009] "The transition section 44 from the main cutting edge 41 to the thinning cutting edge 42 forms a convex curve toward the forward side in the direction of rotation" means that, when the cutting portion 3 is viewed from the end face (tip face 30), the transition section (transition portion) 44 shown in Figures 4 to 7 which transitions from the main cutting edge 41 to the thinning cutting edge 42 forms a convex curve toward the forward side in the direction of rotation, and the main cutting edge 41 and the thinning cutting edge 42 are formed so as to transition in a continuous curve.

[0010] This has the significance of ensuring a larger width in the rotational direction of the flank 7 (second surface 71) of the thinning cutting edge 42. A "convex curve" means an overall convex curve, and may include a flat surface in part. The flank 7 of the thinning cutting edge 42 is also the flank 7 of the main cutting edge 41. By ensuring a larger width in the rotational direction of the flank 7 of the thinning cutting edge 42, the rigidity of the portion that supports the thinning cutting edge 42 on the rear side in the rotational direction is increased, improving safety against breakage of the thinning cutting edge 42.

[0011] One indicator for expressing the degree of curvature of the curve that is convex toward the front side in the rotation direction described by the transition section 44 is that "the angle α between the tangent to the main cutting edge at the portion closer to the thinning cutting edge and the tangent to the thinning cutting edge at the portion closer to the main cutting edge is a minor angle greater than 150° (150°<α<180°)" (claim 1 and claim 5). The minor angle is an angle smaller than 180°.

[0012] "The angle α between the tangent L1 at the portion of the main cutting edge 41 closer to the thinning cutting edge 42 and the tangent L2 at the portion of the thinning cutting edge 42 closer to the main cutting edge 41 is a minor angle greater than 150°" represents a measure of how gentle and not abrupt the curve of the transition section 44 from the main cutting edge 41 to the thinning cutting edge 42 is when viewed from the end face side of the cutting portion 3.

[0013] "Tangent line L1 at the portion of main cutting edge 41 close to thinning edge 42" refers to the tangent line at the portion of the section of main cutting edge 41 that transitions from main cutting edge 41 to thinning edge 42 (portion that enters transition section 44) as shown in Figures 5 to 7. "Tangent line L2 at the portion of thinning cutting edge 42 close to main cutting edge 41" refers to the tangent line at the portion of the section of thinning cutting edge 42 that transitions from thinning edge 42 to main cutting edge 41 (Figure 7), or the tangent line at the portion of transition section 44 that transitions to thinning edge 42 (Figures 5 and 6).

[0014] The angle between the two tangents L1, L2 being 150° is a standard for preventing the curvature of the curve described by the transition section 44 when the cutting portion 3 is viewed from the end face side from becoming large, and for preventing breakage of the transition section 44 when cutting a workpiece in the transition section 44. In other words, "the angle between the two tangents L1, L2 being greater than 150°" is a measure (guideline) for preventing breakage of the transition section 44. This is because if the angle between the two tangents L1, L2 is 150° or less, the curve of the transition section 44 becomes closer to an angular shape, making it easier for breakage to occur in the transition section 44.

[0015] As described above, in claim 1, when the cutting portion 3 is viewed in the axial direction, the transition section 44 forms a convex curve toward the forward side in the direction of rotation, and the angle between the tangent L1 of the main cutting edge 41 and the tangent L2 of the thinning cutting edge 42 is made a minor angle greater than 150°, so that the curvature of the curve formed by the transition section 44 does not become large, making it possible to make it less likely for the transition section 44 to break when cutting the workpiece in the transition section 44.

[0016] Another measure to prevent breakage of transition section 44 and thinning edge 42 when cutting a workpiece in the section from transition section 44 to thinning edge 42 is to "make the angle β between the extension line of the boundary line between the honing surface of the main cutting edge and the honing surface of the thinning edge and the tangent line of the portion of the thinning edge beyond transition section 44 where the transition occurs from the main cutting edge to the thinning edge a soft angle exceeding 170° (170°<θ<360°)" (Claim 2, Claim 6).

[0017] The boundary line 43 between the honing surface 41a of the main cutting edge 41 and the honing surface 42a of the thinning cutting edge 42 is approximately the start position of the transition section 44, and the extension line L3 of the boundary line 43 is a line on the boundary line 43. The tangent line L4 at the portion of the thinning cutting edge 42 beyond the transition section 44 where the main cutting edge 41 transitions to the thinning cutting edge 42 is approximately the end position of the transition section 44, and is an index showing the degree of curvature of the curve in the section from the transition section 44 to the thinning cutting edge 42. The curve in this section is the part with the largest curvature in the section from the main cutting edge 41 to the thinning cutting edge 42. The angle β is the angle when the cutting portion 3 is viewed from the end face side. The "relief angle" refers to the angle taken on the side where the curve is convex, and is an angle greater than 170°.

[0018] "Boundary line 43 appears" means that, when the honing surfaces 41a, 42a of main cutting edge 41 and thinning cutting edge 42 are viewed in detail in a direction perpendicular to rotation axis O as shown in Fig. 4, boundary line 43 is formed as a boundary line that separates both honing surfaces 41a, 42a. Transition section 44 refers to the section that forms a convex curve from boundary line 43 to the tangent line at thinning cutting edge 42 in Figs. 5 to 7.

[0019] "A boundary line 43 appears between honing surface 41a and honing surface 42a, which is inclined both in the axial direction of shank portion 2 and in the direction perpendicular to this axial direction" means that a boundary line 43 appears between honing surface 41a of main cutting edge 41 and honing surface 42a of thinning cutting edge 42, and that the direction of this boundary line 43 is inclined with respect to the axial direction of shank portion 2 (direction of tool axis O) and is also inclined with respect to the direction perpendicular to the axial direction of shank portion 2.

[0020] When the angle between the extension line L3 of the boundary line 43 and the tangent line L4 at the portion beyond the transition section 44 of the thinning cutting edge 42 is greater than 170°, this means that the degree of curvature of the curve in the transition section 44 is greater than when the angle is less than 170°. This means that the angle from the main cutting edge 41 to the thinning cutting edge 42 is more toward the chisel edge 46 than when the angle is less than 170°, and this means that it is easier to ensure a larger width d of the honing surface 42a of the thinning cutting edge 42 than when the angle is less than 170°. Because the width d of the honing surface 42a can be easily ensured, the safety of the thinning cutting edge 42 against breakage is improved.

[0021] Specifically, in the case of a small-diameter long drill with cutting diameter D of 1 mm≦D≦4 mm and L / D (total length / cutting diameter) of 20 or more, the honing width d of the thinning cutting edge 42 shown in Fig. 8 is 0.020 mm or more, and the difference between the maximum and minimum values ​​of the honing width d of the thinning cutting edge 42 is within 0.005 mm (claim 7). In terms of honing angle γ, when cutting diameter D and L / D satisfy the above conditions, it is appropriate that 30°≦γ≦40° (claim 8). "Honing width d" is the width of honing surface 42a when viewed in the direction of tool axis O, as shown in Fig. 8.

[0022] "The honing width d of the thinning edge 42 is 0.020 mm or more, and the difference between the maximum and minimum values ​​of the honing width d is within 0.005 mm" and "30°≦γ≦40°" are derived from the fact that, when 1 mm≦D≦4 mm and 20≦L / D, "the angle between the extension line L3 of the boundary line 43 and the tangent L4 at the part beyond the transition section 44 of the thinning edge 42 is greater than 170°."

[0023] In claim 1, "grinding lines 45 are formed on the honing surface 42a of the thinning edge 42 in a direction along the boundary line 43" means that the grinding lines 45 are formed facing in a direction along the boundary line 43. "Along the boundary line 43" means that, when the grinding lines 45 are viewed from the front in a direction perpendicular to the rotation axis O as shown in Fig. 4, they are arranged substantially parallel to the boundary line 43 if they are projected onto a plane perpendicular to the viewing direction.

[0024] More specifically, this can be said to mean that the grinding streaks 45 are arranged uniformly (evenly) at substantially constant intervals in the arrangement direction. The state in which the grinding streaks 45 are arranged substantially uniformly in the arrangement direction can be obtained by machining the honing surface 42a (mechanical honing). The grinding streaks 45 may also be formed on the honing surface 41a of the main cutting edge 41. This makes the surface properties of the honing surface 41a of the thinning cutting edge 42 uniform, which is thought to stabilize tool damage.

[0025] Specifically, when the cutting part 3 is viewed from the side as shown in FIG. 4 and the boundary line 43 is viewed from the front, the angle θ between the boundary line 43 (grinding line 45) and the axial direction is 15° or more (15°≦θ), and the angle η between the boundary line 43 (grinding line 45) and a plane perpendicular to the axial direction is 15° or more (15°≦η) (claim 3), which is more reasonable. The angles θ and η refer to the acute angle side. "The angle between the boundary line 43 (grinding line 45) and the axial direction is 15° or more, and the angle between the boundary line 43 and a plane perpendicular to the axial direction is 15° or more" means that the boundary line (grinding line) is located within a 60° range centered on a 45° direction relative to the axial direction and the direction perpendicular to the axial direction.

[0026] As described above, the boundary line 43 between the honing surface 41a of the main cutting edge 41 and the honing surface 42a of the thinning cutting edge 42 is the start position of the "transition section 44", and is located in a position continuous with the boundary portion between the rake face 41a of the main cutting edge 41 and the rake face 42a of the thinning cutting edge 42. On the other hand, since the main cutting edge 41 and the thinning cutting edge 42 have angles α and β when viewed from the end face side as described above, the rake face 41a and the rake face 42a are unlikely to be continuous surfaces, and a clear boundary line is likely to appear as a convex ridgeline in the intermediate section 47 between the rake face 41a of the main cutting edge 41 and the rake face 42a of the thinning cutting edge 42 (Patent Documents 1, 5 to 7).

[0027] The intermediate section 47, which is the boundary between the cutting face 41a of the main cutting edge 41 and the cutting face 42a of the thinning cutting edge 42, serves as a section that supports the main cutting edge 41 and the thinning cutting edge 42 on their respective axial rear sides (rear sides in the direction of travel) when the main cutting edge 41 and the thinning cutting edge 42 cut a workpiece. For this reason, the intermediate section 47 serves as a section that can play a role in stiffening the main cutting edge 41 and the thinning cutting edge 42 against breakage via the transition section 44. If a convex ridge appears on the surface of the intermediate section 47 that can serve as this stiffening section, and if there is a sharp portion, stress is likely to concentrate in that portion and it is likely to become a weak point, and the function of stiffening the cutting edge 4 may be impaired.

[0028] For example, in Patent Documents 1 and 5 to 7, a boundary line (ridge line) clearly appears between the main cutting edge rake face and the thinning cutting edge rake face (Figure 5 of Patent Document 1, Figure 1 of Patent Document 5, Figure 4 of Patent Document 6, and Figure 13 of Patent Document 7).

[0029] When the main cutting edge 41 and the thinning cutting edge 42 cut a workpiece, the resistance (reaction force) received by the main cutting edge 41 and the thinning cutting edge 42 can be borne by the intermediate section 47, which is the boundary between the rake faces 41b, 42b including the honing faces 41a, 42a, which are the axially rear portions. If the intermediate section 47 has a sharp portion with low rigidity, stress will be concentrated in the sharp portion of the intermediate section 47 due to compressive stress generated in the main cutting edge 41 and the thinning cutting edge 42, and the influence (stress burden) of the cutting edge 41 when it breaks will extend to the cutting edge 42, and it cannot be said that there is no possibility of breakage.

[0030] Therefore, at least a portion of the intermediate section 47 transitioning from the boundary line 43 between the honing surface 41a of the main cutting edge 41 and the honing surface 42a of the thinning cutting edge 42 to the cutting surface 41b of the main cutting edge 41 and the cutting surface 42b of the thinning cutting edge 42, near the honing surfaces 41a, 42a, is formed to have a flat or curved surface without a convex ridge (claim 4), thereby eliminating any sharp portions.

[0031] In other words, there are no sharp portions in a portion of the intermediate section 47 between the rake face 41b of the main cutting edge 31 and the rake face 42b of the thinning cutting edge 42 on the sides of the honing faces 41a, 42a. As a result, the rigidity of the entire intermediate section 47 is easier to increase than when a convex ridgeline appears, so the function of compensating for the rigidity of the main cutting edge 41 and the thinning cutting edge 42 is improved, and it is possible to reduce the possibility of the main cutting edge 41 and the thinning cutting edge 42 breaking.

[0032] "No sharp parts" means that when the intermediate section 47 is viewed in a cross section perpendicular to the rotation axis O, there are no parts that form an acute angle on the surface side. However, it is preferable that the intermediate section 47 only has parts that form an obtuse angle on the surface side on a cross section perpendicular to the rotation axis O.

[0033] In this way, in claim 4, at least a part of the intermediate section 47 from the boundary line 43 is formed to have a flat or curved surface, so that the rigidity of the intermediate section 47 can be increased compared to when a convex ridgeline appears. As a result, the function of compensating for the rigidity of the main cutting edge 41 and the thinning cutting edge 42 is improved, and as a result, the possibility of breakage of the main cutting edge 41 and the thinning cutting edge 42 can be reduced. Effect of the Invention

[0034] In claim 1, when the blade portion is viewed from the end face side in the axial direction, the transition section from the main cutting edge to the thinning cutting edge forms a convex curve toward the forward side in the direction of rotation, and the angle between the tangent to the main cutting edge at the part of the main cutting edge closer to the thinning cutting edge and the tangent to the part of the thinning cutting edge closer to the main cutting edge is a minor angle greater than 150°.This prevents the curvature of the curve formed by the transition section from becoming large, making it less likely for the transition section to break when cutting a workpiece in the transition section.

[0035] In claim 4, at least a part of the intermediate section that transitions from the boundary between the honing surface of the main cutting edge and the honing surface of the thinning cutting edge to the rake surface of the main cutting edge and the rake surface of the thinning cutting edge is formed to be a flat or curved surface, so that the rigidity of the boundary part can be increased compared to when a convex ridgeline appears. As a result, the function of compensating for the rigidity of the main cutting edge and the thinning cutting edge is improved, and as a result, the possibility of breakage of the main cutting edge and the thinning cutting edge can be reduced. [Brief description of the drawings]

[0036] [Figure 1] FIG. 2 is an end view showing an example of a drill cutting edge of the drill of the present invention as viewed in the axial direction from the tip face side. [Diagram 2] FIG. 2 is a view taken along line xx in FIG. [Diagram 3] FIG. 2 is a view taken along line yy in FIG. [Figure 4] FIG. 3 is an enlarged view of a portion including a main cutting edge and a thinning cutting edge in FIG. 2. [Diagram 5]FIG. 11 is an end view showing an example in which, when the blade portion is viewed from the end face side in the axial direction, the angle α between the tangent to the main cutting edge at a portion closer to the thinning cutting edge and the tangent to the thinning cutting edge at a portion closer to the main cutting edge is a minor angle greater than 150°. [Figure 6] FIG. 11 is an end view showing another example in which the angle α between the tangent to the main cutting edge at a portion closer to the thinning cutting edge and the tangent to the thinning cutting edge at a portion closer to the main cutting edge is a minor angle greater than 150°. [Figure 7] FIG. 11 is an end view showing another example in which the angle α between the tangent to the main cutting edge at a portion closer to the thinning cutting edge and the tangent to the thinning cutting edge at a portion closer to the main cutting edge is a minor angle greater than 150°. [Figure 8] 6 is a cross-sectional view taken along line zz in FIG. 5. [Figure 9] FIG. 2 is an elevational view showing the entire drill. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] 1 to 3 show an example of a drill 1 shown in Fig. 9, which has a cutting portion 3 having multiple cutting edges 4 and chip discharge grooves 5 between adjacent cutting edges 4, 4 in the circumferential direction at the axial tip side of a shank portion 2, and a thinning portion 6 facing the chip discharge groove 5 is formed on the rear side in the rotational direction of a flank face 7 of each cutting edge 4. The axis of the shank portion 2 corresponds to the rotation axis O of the drill body (drill 1).

[0038] 9, the drill 1 is divided axially into a shank portion 2 located on the axial rear side of the drill body and a cutting portion 3 formed axially further towards the tip side thereof, and a pair (two) cutting edges 4, 4 are mainly formed on a tip surface 30 at the axial tip of the cutting portion 3. The drawing shows an example of a solid type drill 1 in which the cutting portion 3 is integrated with the drill body, but there may also be a case where the drill 1 is an indexable type in which the cutting portion 3 is fixed and held in a detachable manner relative to the drill body.

[0039] The "tip face 30" refers to the area (portion) excluding the chip groove 5 and the thinning surface 61 when the tip face 30 of the drill body is viewed in the direction of the rotation axis O, and refers to the area of ​​the flank 7. The drawing shows an example in which the second face 71 is continuously formed as the flank 7 on the rear side in the rotation direction of the cutting edge 4, and the third face 72 is continuously formed on the rear side in the rotation direction of the second face 71. In this case, the flank 7 is the area consisting of the second face 71 and the third face 72.

[0040] As shown in Fig. 1, the cutting edge 4 is formed from the end of the chisel edge 46 to the radially outer periphery of the tip face 30, and in the radial direction, it is composed of a main cutting edge 41 on the radially outer periphery side and a thinning cutting edge 42 that is continuous with the main cutting edge 41, is located on the radially central side of the main cutting edge 41, and is in contact with the end of the chisel edge 46. The thinning portion 6 is composed of a rake face 42b (to be described later) of the thinning cutting edge 42 and a thinning surface 61 that is a curved surface that continues to the second chamfering surface 8 or a continuous curved surface on the forward side of the rake face 42b in the rotational direction. As shown in Fig. 4, which is an enlarged view of Fig. 2, the main cutting edge 41 and the thinning cutting edge 42 are formed with honing surfaces 41a and 42a, respectively.

[0041] When the cutting portion 3 is viewed in the axial direction from the tip surface 30 side, the transition section 44 that transitions from the main cutting edge 41 to the thinning cutting edge 42 describes a convex curve toward the front side in the rotational direction as shown in Figs. 1 and 5 to 7. The transition section 44 is the transition section of the cutting edge 4 as shown in Figs. 4 and 5, and refers to a short section to the thinning cutting edge 42. The curvature of the convex curve described by the transition section 44 is specifically adjusted as follows. Figs. 2 and 4 show the honing surfaces 41a, 42a when viewed from the front. The convex curve includes a combination of straight lines.

[0042] In order to prevent breakage of the thinning edge 42 from the transition section 44 when cutting a workpiece in the transition section 44, it is appropriate that when the cutting portion 3 is viewed in the axial direction from the tip face 30 side, the angle α between the tangent L1 of the main cutting edge 41 at the portion closer to the thinning edge 42 and the tangent L2 of the thinning cutting edge 42 at the portion closer to the main cutting edge 41 be a minor angle greater than 150° (150°<α<180°) as shown in Figures 5 to 7. The angle α indicates the degree of curvature of the transition section 44, and represents a measure of how gentle and not abrupt the curvature of the curve when the cutting portion 3 is viewed in the axial direction from the tip face 30 side.

[0043] In addition, in order to ensure that the width d of the honing surface 42a of the thinning edge 42 shown in Figure 8 is a size effective for preventing breakage of the thinning edge 42, it is appropriate that the angle β between the extension line L3 of the boundary line 43 shown in Figure 4 between the honing surface 41a of the main cutting edge 41 and the honing surface 42a of the thinning edge 42, as shown in Figures 5 to 7, and the tangent L4 of the thinning edge 42 beyond the transition section 44 where the main cutting edge 41 transitions to the thinning edge 42, is a soft angle exceeding 170° (170°<β<360°).

[0044] Boundary line 43 is a boundary line that separates honing surface 41a of main cutting edge 41 from the honing surface in transition section 44 described above, and extension line L3 refers to an extension line of boundary line 43 itself. 170°<β<360° means that the degree of curvature of the curve in transition section 44 is greater than when angle β is 170° or less (β≦170°), and this is a measure that makes it easier to ensure a larger width d of honing surface 42a of thinning edge 42 than when angle β is 170° or less.

[0045] As a specific example, FIG. 5 shows an example in which the angle α is 165° and the angle β is 193.5°, which satisfies the requirements of 150°<α<180° and 170°<β<360°. FIG. 6 shows an example in which the angle α is 162° and the angle β is 212°, which satisfies the requirements of 150°<α<180° and 170°<β<360°. FIG. 7 shows an example in which the angle α is 152° and the angle β is 177°, which satisfies the requirements of 150°<α<180° and 170°<β<360°. In both examples, the width d of the honing surface 42a is secured to be large enough to suppress breakage of the thinning cutting edge 42. Focusing on the examples of FIG. 5 and FIG. 6, it can be said that it is more preferable for the angle β to strictly satisfy the requirement of 180°<β<360°.

[0046] Specifically, in the case of a small-diameter long drill with cutting diameter D of 1 mm≦D≦4 mm and L / D (total length / cutting diameter) of 20 or more, it is appropriate that the honing width d of the thinning cutting edge 42 shown in Figure 8 is 0.020 mm or more and the difference between the maximum and minimum values ​​of the honing width d of the thinning cutting edge 42 is within 0.005 mm. Expressed in terms of honing angle γ shown in Figure 8, it is appropriate that 30°≦γ≦40°.

[0047] "The honing width d of thinning edge 42 is 0.020 mm or more, and the difference between the maximum and minimum values ​​of honing width d is within 0.005 mm" and "30°≦γ≦40°" are derived from the numerical requirement that, when 1 mm≦D≦4 mm and 20≦L / D, "the angle β between extension line L3 of boundary line 43 and tangent L4 at the portion beyond transition section 44 of thinning edge 42 is greater than 170°" and the specific requirement that "the width d of honing surface 42a is ensured to be large enough to prevent breakage of thinning edge 42."

[0048] Between the honing surface 41a of the main cutting edge 41 and the honing surface 42a of the thinning cutting edge 42, when both honing surfaces 41a, 42a are viewed in an enlarged front view as shown in FIG. 4, a boundary line 43 appears that is inclined both in the direction of the rotation axis O and in a direction perpendicular to the direction of the rotation axis O. On the honing surface 42a of the thinning cutting edge 42, uniform or evenly spaced grinding lines 45 are formed in a direction along the boundary line 43. The boundary line 43 is not necessarily a line that draws a convex ridge on the surface side, but appears to separate the honing surface 41a and the honing surface 42a. The grinding lines 45 in a direction along the boundary line 43 are formed by machining.

[0049] As shown in Fig. 4, the rake face 41b of the main cutting edge 41 is formed on the chip groove 5 side of the honing surface 41a, and the main cutting edge side boundary line W1 appears between the honing surface 41a and the rake face 41b. Similarly, the rake face 42b of the thinning cutting edge 42 is formed on the thinning portion 6 side of the honing surface 42a, and the thinning cutting edge side boundary line W2 appears between the honing surface 42a and the rake face 42b. In Fig. 4, the main cutting edge side boundary line W1 and the thinning cutting edge side boundary line W2 are drawn to be convex ridgelines, but both W1 and W2 are not necessarily convex ridgelines and may form curved surfaces.

[0050] The rake face 41b of the main cutting edge 41 is continuous with the chip groove 5, and the rake face 42b of the thinning cutting edge 42 is continuous with the thinning surface 61 as described above. A thinning portion boundary line W3 appears between the chip groove 5 and the thinning surface 61, except for an intermediate section 47 described below, which is a portion closer to the boundary line 43 between the honing surfaces 41a, 42a. The thinning portion boundary line W3 is not necessarily a convex ridgeline either. At least the intermediate section 47 closer to the boundary line 43 does not form a convex ridgeline.

[0051] In order to suppress wear of the honing surfaces 41a, 42a during cutting by the main cutting edge 41 and the thinning cutting edge 42, particularly wear of the grinding streaks 45, it is appropriate that when the cutting portion 3 is viewed from the side and the boundary line 43 is viewed from the front, the angle θ between the extension line L3 of the boundary line 43 and the direction of the rotation axis O is 15° or more on the acute angle side, as shown in Figure 4. At the same time, it is appropriate that the angle η between the plane perpendicular to the direction of the rotation axis O and the boundary line 43 is 15° or more on the acute angle side.

[0052] In other words, when boundary line 43 is viewed from the front, it is appropriate for boundary line 43 to be located within a 60° range sandwiched between a straight line inclined 15° in a direction perpendicular to the direction of rotation axis O, and a straight line inclined 15° from the perpendicular direction toward the direction of rotation axis O.

[0053] In addition, in order to increase the rigidity of at least a portion of the intermediate section 47 shown in Figure 4, which transitions from the boundary line 43 between the rake face 41b of the main cutting edge 41 and the rake face 42b of the thinning cutting edge 42, near the honing surfaces 41a, 42a, and to provide this portion with a stiffening effect on the main cutting edge 41 and the thinning cutting edge 42 via the transition section 44, it is effective to eliminate any sharp portions in the intermediate section 47.

[0054] In order to provide a stiffening effect to intermediate section 47, an area including a part of intermediate section 47 is formed to have a flat or curved surface without a convex ridge, as shown in Fig. 4. This portion is at least a part of intermediate section 47 near honing surfaces 41a, 42a that transitions from boundary line 43 between honing surfaces 41a and honing surfaces 42a to between rake surface 41b of main cutting edge 41 and rake surface 42b of thinning cutting edge 42.

[0055] In the direction of the rotation axis O, the intermediate section 47 is located on the rear side when the main cutting edge 41 and the thinning cutting edge 42 cut the workpiece, and thus plays a role in supporting the main cutting edge 41 and the thinning cutting edge 42 and stiffening the main cutting edge 41 and the thinning cutting edge 42 against breakage. For this reason, it is appropriate that a part or the whole of the intermediate section 47 be formed in a shape that does not show a convex ridge on the surface side on a cross section perpendicular to the rotation axis O, in particular, in a curve such that the angle between two nearby tangents in any part on the surface side is an obtuse angle. [Explanation of symbols]

[0056] 1... Drill (drill body), O... Rotating shaft, 2...Shank part, 3...Blade part, 30...Tip surface, 4... cutting edge, 41: main cutting edge; 41a: honing surface; 41b: rake surface; 42... thinning cutting edge, 42a... honing surface, 42b... rake surface, 43...Boundary line, 44...Transition section, 45...Grinding line, 46...Chisel edge, 47...Middle section, 5...Chip discharge groove, 6: thinning portion; 61: thinning surface; 7...flank, 71...second, 72...third, 8...2nd cut surface, W1: Boundary line on the main cutting edge side, W2: Boundary line on the thinning cutting edge side, W2: Boundary line on the thinning part, L1: Tangent to the part of the main cutting edge closer to the thinning cutting edge, L2: Tangent to the part of the thinning cutting edge closer to the main cutting edge, L3: Extension of the boundary line between the honing surface of the main cutting edge and the honing surface of the thinning cutting edge; L4: Tangent at the part beyond the transition area where the main cutting edge transitions to the thinning cutting edge; d……honing width of thinning cutting edge, γ……honing angle of thinning cutting edge, α: the angle between the tangent L1 at the portion of the main cutting edge closer to the thinning cutting edge and the tangent L2 at the portion of the thinning cutting edge closer to the main cutting edge, β: the angle between the extension line L3 of the boundary line between the honing surface of the main cutting edge and the honing surface of the thinning cutting edge and the tangent line L4 at the portion of the thinning cutting edge beyond the transition area from the main cutting edge to the thinning cutting edge; θ...The angle between the boundary line and the rotation axis O, η...The angle between the boundary line and a plane perpendicular to the rotation axis O.

Claims

1. a drill comprising a cutting portion having a plurality of cutting edges at an axial tip end side of a shank portion and a chip discharge groove between adjacent cutting edges in a circumferential direction, a thinning portion facing the chip discharge groove is formed on the rotationally rear side of the flank face of each cutting edge, the cutting edges being composed of a main cutting edge on the radially outer periphery side and a thinning cutting edge continuous with the main cutting edge and positioned on the radially central side of the main cutting edge, and a honing surface is formed on each of the main cutting edges and the thinning cutting edge, Between the honing surface of the main cutting edge and the honing surface of the thinning cutting edge, a boundary line appears that is inclined with respect to both the axial direction of the shank portion and a direction perpendicular to the axial direction, and grinding lines are formed on the honing surface of the thinning cutting edge in a direction along the boundary line, A drill characterized in that, when the cutting portion is viewed from the end face side in the axial direction, a transition section from the main cutting edge to the thinning cutting edge describes a convex curve toward the forward side in the rotational direction, and an angle between a tangent to the main cutting edge at a portion closer to the thinning cutting edge and a tangent to the thinning cutting edge at a portion closer to the main cutting edge is a minor angle greater than 150°.

2. 2. The drill according to claim 1, wherein an angle between an extension of the boundary line and a tangent to the thinning edge at a portion beyond the transition section is an angle exceeding 170°.

3. The drill according to claim 1 or 2, characterized in that, when the cutting edge is viewed from the side and the boundary line is viewed from the front, an angle between the boundary line and the axial direction is 15° or more, and an angle between the boundary line and a plane perpendicular to the axial direction is 15° or more.

4. a drill comprising a cutting portion having a plurality of cutting edges at an axial tip end side of a shank portion and a chip discharge groove between adjacent cutting edges in a circumferential direction, a thinning portion facing the chip discharge groove is formed on the rotationally rear side of the flank face of each cutting edge, the cutting edges being composed of a main cutting edge on the radially outer periphery side and a thinning cutting edge continuous with the main cutting edge and positioned on the radially central side of the main cutting edge, and a honing surface is formed on each of the main cutting edges and the thinning cutting edge, When the cutting portion is viewed from the end face side in the axial direction, a transition section from the main cutting edge to the thinning cutting edge draws a convex curve toward the front side in the rotation direction, Between the honing surface of the main cutting edge and the honing surface of the thinning cutting edge, a boundary line appears that is inclined with respect to both the axial direction of the shank portion and a direction perpendicular to the axial direction, and grinding lines are formed on the honing surface of the thinning cutting edge in a direction along the boundary line, A drill characterized in that at least a portion of an intermediate section transitioning from the boundary line between the honing surface of the main cutting edge and the honing surface of the thinning cutting edge to the rake surface of the main cutting edge and the rake surface of the thinning cutting edge, closer to the honing surface, does not form a convex ridgeline but is flat or curved.

5. The drill according to claim 4, characterized in that, when the cutting edge is viewed from the end face side in the axial direction, an angle between a tangent to the main cutting edge at a portion closer to the thinning cutting edge and a tangent to the thinning cutting edge at a portion closer to the main cutting edge is a minor angle greater than 150°.

6. The drill according to claim 4 or claim 5, characterized in that an angle between an extension of the boundary line and a tangent to the thinning cutting edge at a portion beyond the transition section is an angle exceeding 170°.

7. The drill according to claim 1 or claim 4, characterized in that the drill is a small-diameter long drill having a cutting diameter D of 1 mm≦D≦4 mm and a total length L / cutting diameter D ratio of 20 or more, the honing width d of the thinning edge is 0.020 mm or more, and the difference between the maximum value and the minimum value of the honing width d of the thinning edge is within 0.005 mm.

8. The drill according to claim 1 or claim 4, characterized in that it is a small-diameter long drill having a cutting diameter D of 1 mm≦D≦4 mm, a total length L / cutting diameter D of 20 or more, and a honing angle γ of 30°≦γ≦40°.

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