JP2016106041A - drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drill that is able to drill for a long life or highly efficiently into a steel material of about 45 to 55 HRC hardness, which is mainly used for a metal mold, by increasing the rigidity of the drill.SOLUTION: In a drill, a land has two margins arranged on a cutting blade side and a heel side of a groove. Between the two margins, relieving face is provided. In a cross-section axially at right angles, relieving depth gradually increases toward the heel-side margin from the cutting blade side margin. After reaching the maximum relieving depth, the relieving depth gradually decreases toward the heel-side margin.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a drill suitable for drilling a material having high hardness.

  A variety of holes are drilled in the mold, such as ejector pins for removing products, cooling water for passing water to cool the mold, and screws for assembling parts such as inserts. These drilling is generally performed using a drill before the heat treatment performed to obtain a predetermined hardness of the mold material. There are the following proposals for such drills.

  In Patent Document 1, two margins are provided in the land portion, and the second margin provided on the rear side in the rotation direction includes an outer peripheral end located at the land portion at the intersection ridge line of the flank and the thinning portion, and the heel of the blade edge portion A double margin type drill is proposed in which the hole position accuracy is improved by a guide effect by disposing it at a predetermined interval from the front part in the drill rotation direction.

  In Patent Document 2, by providing two margins in the land portion and providing a recess whose depth gradually increases from the first margin provided on the rear side in the rotation direction toward the second margin on the heel side, Drilling tools suitable for drilling aluminum castings have been proposed because chips are easy to flow and chips are discharged quickly.

  Further, in Patent Document 3, two margins are provided in the land portion almost equally, a portion having a predetermined width including a portion constituting the core thickness of the torsion groove is formed as a concave curved surface, and a portion from the concave curved surface toward the heel side is rotated. A drilling tool suitable for drilling has been proposed in which the chip discharge performance is improved by using a convex curved surface protruding backward in the direction.

JP 2005-305610 A Japanese Utility Model Publication No. 5-85509 Japanese Utility Model Publication No. 5-24218

  In recent years, in the manufacturing industry in which competition is intensifying, the necessity for cost reduction and short delivery time is further increased, and molds used for manufacturing parts and the like are no exception. As one of the means to lower the mold manufacturing cost, in order to reduce the number of setups and the number of man-hours required for post-processing correction, cutting is performed after heat treatment of the material from the conventional method of cutting before heat treatment of the material. There is a means to switch to direct carving. However, since the cutting process is performed on the material after the heat treatment to be a high hardness material, the load applied to the cutting tool is increased. In recent years, direct engraving is progressing due to advances in cutting tools.

  With regard to drilling in the mold, direct engraving after heat treatment is progressing, but with high-hardness materials of around 50 HRC and materials with higher hardness, which are often used in hot forging and die casting, There are still many processes using electric discharge. Especially for deep holes where the ratio of tool diameter to hole depth is large, machining by cutting is small, and even when cutting, cutting is performed over a long time while setting the cutting conditions low and inserting steps. Therefore, there is a demand for a high-performance drill capable of drilling with a long life or high efficiency.

  In the drilling of a hard material, a large cutting resistance is generated as compared with a material before heat treatment. For this reason, when drilling is carried out using a steel processing drill that processes machine parts and automobile parts manufactured with conventional carbon steel or alloy steel, the drill vibrates violently during cutting, resulting in chipping. It tends to reach the end of its life. This tendency is particularly noticeable in deep hole machining where the protruding length of the tool becomes long. For this reason, when drilling a high-hardness material, it is necessary to increase the rigidity of the drill to suppress vibrations and to prevent chipping caused by vibrations.

  In the double margin type drill described in Patent Document 1, it is disclosed that guideability can be improved by providing a plurality of margins in the land. However, in such a configuration, the rigidity of the drill is lowered and vibration is generated. Cannot be suppressed sufficiently. Therefore, when cutting a hard material, chipping may occur at an early stage.

  Further, Patent Document 2 describes a drilling tool provided with a recess whose depth gradually increases. However, it is possible to expel chips quickly by providing a deep recess between the first margin and the second margin. However, since the rigidity of the drill is significantly reduced, a high-hardness material has a long life or It is not enough for high-efficiency processing.

  Further, by simply improving the chip discharge groove as in the drilling tool described in Patent Document 3, it is possible to improve guideability and suppress chip clogging in cutting of a soft material such as aluminum. However, since the rigidity of the drill cannot be sufficiently obtained, drilling or breaking of the drill may occur when drilling a high-hardness material with a long life or high efficiency.

  The present invention provides a drill capable of drilling a steel with a hardness of about 45 to 55 HRC, which is mainly used for molds, with a longer life or higher efficiency by increasing the rigidity of the drill. With the goal.

  In view of the above problems, the present invention improves the rigidity of a drill to suppress vibration during cutting, and further reduces the occurrence of chipping of the cutting edge by suppressing vibration, thereby achieving a high hardness material of about 45 to 55 HRC. It is a drill that can be processed with high efficiency.

  That is, in the drill having a cutting edge at the front end portion of the cutting edge portion, a cutting edge portion having a groove and a land extending from the front end side toward the rear end side is formed on the front end side portion of the drill body rotated around the axis. The land provided continuously from the leading edge has two margins arranged on the cutting edge side and the heel side of the groove, and a two-sided surface is provided between the two margins, which is perpendicular to the axis. In the cross section, the second cutting depth gradually increases from the cutting edge side margin toward the heel side margin, and reaches the maximum second cutting depth, then the second cutting depth toward the heel side margin. The drill is characterized in that the cutting depth gradually becomes shallower.

  In the present invention, by setting the maximum second cutting depth in the range of 2.0% or more and 6.0% or less of the blade diameter, the rigidity of the drill is further improved and the high hardness material is processed with high efficiency. This is desirable because it increases stability at times.

  In the present invention, the second facet is provided in a region surrounded by the two margins, a virtual arc having a diameter, and a virtual arc having a diameter of 94% to 98% of the blade diameter. Accordingly, the rigidity of the drill is further improved, and vibrations can be suppressed even in deep hole machining where the protruding length of the tool becomes long, and the occurrence of chipping of the cutting edge can be reduced, which is more desirable.

  In the present invention, the second picking surface includes a planar first second picking surface formed from a rotation rear side end portion of the cutting edge side margin toward a rotation rear side of the drill, and a heel side margin. A second planar second surface formed from the end of the rotational front side toward the rotational front side of the drill, and a curved second surface connecting the first second surface and the second second surface. 3 Since it is formed from the second picking surface, the rigidity of the second picking surface is improved and vibration during cutting can be suppressed, which is desirable.

  In the present invention, the widths of the first first and second straight surfaces that are linear when viewed in a cross section perpendicular to the axis are the widths of the first and second second surfaces in the cross section perpendicular to the axis. When measuring in a direction parallel to the diameter, the range of 15% to 25% of the blade diameter is taken, so that the material is removed when grinding the second picking surface with a grindstone during the manufacture of the drill. Since the volume is reduced, manufacturing is facilitated, and a decrease in the rigidity of the drill can be suppressed, which is desirable.

  In the present invention, the radius of curvature of the third second face in the cross section perpendicular to the axis is in the range of 75% to 125% of the blade diameter, so that the rigidity at the position where the depth of the second face is maximum is obtained. It is desirable to improve.

  By using the drill of the present invention, drilling of a high hardness material after heat treatment can sufficiently ensure the rigidity of the drill, so that vibration generated by cutting resistance can be suppressed, and drilling to a high hardness material can be performed with a long service life. Or it can be performed highly efficiently. In particular, in the processing of deep holes where the protruding length of the tool becomes long, a remarkable effect is seen.

  Further, according to the present invention, it is possible to suppress chipping of the cutting edge that is likely to occur when drilling a high-hardness material. Therefore, it is possible to perform cutting with higher efficiency compared to a conventional drill. it can.

It is a front view of the drill of this invention. It is the side view to which the cutting blade vicinity of the drill of this invention was expanded. It is sectional drawing when cut | disconnecting in the orthogonal | vertical direction to the tool axis | shaft of the drill of this invention. FIG. 4 is an enlarged view of the vicinity of the second face in a cross section when cut in a direction perpendicular to the tool axis of the drill of the present invention shown in FIG. 3. It is a figure which shows another Example of this invention. It is sectional drawing when cut | disconnecting in the orthogonal | vertical direction to the tool axis | shaft of the conventional drill. It is an enlarged view near the second picking surface in the cross section when cut in the direction perpendicular to the tool axis of the conventional drill. It is sectional drawing when cut | disconnecting in the orthogonal | vertical direction with respect to the tool axis | shaft in another Example of this invention. FIG. 9 is an enlarged view of the vicinity of the second picking surface in a cross section when cut in a direction perpendicular to the tool axis of the drill of the present invention shown in FIG. 8.

  An example of the present invention will be described with reference to FIGS. FIG. 1 is a front view of a drill according to the present invention. As shown in FIG. 1, the drill 1 of the present invention has a cutting edge 2, a cutting edge part 3, and a shank 4, and the cutting edge part 3 is provided with a groove 5 and a land for discharging chips. A cutting edge 2 is provided at the tip of the blade edge portion 3. Since the drill 1 of the present invention is a drill having two margins, that is, a double margin drill, a margin 6 on the cutting edge side and a margin 7 on the heel side are provided on the outer periphery of the drill 1. The margin 6 on the cutting edge side and the margin 7 on the heel side are connected by a second picking surface 8.

  FIG. 2 is an enlarged side view of the vicinity of the cutting edge of the drill of the present invention. As shown in FIG. 2, the land 10 is provided with a margin 6 on the cutting edge side and a margin 7 on the heel side, and a second catching surface 8 is provided between the two margins. FIG. 2 shows a double margin drill provided with a coolant hole 11. By providing the coolant hole 11, it is possible to suppress a sharp rise in the cutting temperature and delay the progress of wear of the cutting edge even when cutting a hard material, but when the coolant hole 11 is not provided. Also has the advantageous effects of the present invention.

  Further, as shown in FIG. 2, on the outer peripheral side of the drill, by chamfering the outer peripheral corner 9 that connects the groove 5 and the margin 6 on the cutting edge side, or the heel that connects the groove 5 and the margin 7 on the heel side, Although it is desirable because the rigidity is improved, the advantageous effects of the present invention can be obtained even when the outer peripheral corner 9 and chamfering are not performed.

  In the present invention, the margin 6 on the cutting edge side refers to a margin disposed on the front side in the rotational direction of the land 10, and the margin 7 on the heel side refers to a margin disposed on the rear side in the rotational direction in the land 10. The example shown in FIG. 2 shows an example in which the margin 6 on the cutting edge side is connected to the outer peripheral corner 9, but the margin 6 on the cutting edge side may be provided so that the margin 6 on the cutting edge side contacts the leading edge. good. Similarly, for the heel side margin 7, the example shown in FIG. 2 shows an example in which the heel side margin 7 is connected to the chamfer, but the margin on the cutting edge side so that the heel side margin 7 is in contact with the heel. 6 may be provided.

  FIG. 3 is a cross-sectional view of the drill of the present invention cut in a direction perpendicular to the tool axis. As shown in FIG. 3, the drill of the present invention is a distance between a circular arc 12 having a diameter virtually drawn with a blade diameter as a diameter from a margin 6 on the cutting edge side toward a margin 7 on the heel side and the second face 8. The second picking depth, which is the depth when measured in the radial direction, gradually increases, and after reaching the maximum second picking depth, the second picking depth gradually increases toward the margin 7 on the heel side. A major feature is the shallow shape. In FIG. 3, d1 is the thickness of the core, w1 is the width of the margin 6 on the cutting edge side when measured in the rotational direction, and w2 is the width of the margin 7 on the heel side when measured in the rotational direction.

  FIG. 4 is an enlarged view of the vicinity of the second face in the cross section when cut in the direction perpendicular to the tool axis of the drill of the present invention shown in FIG. The drill of the present invention shown in FIG. 4 is a double margin drill in which the second face 8 is formed in the shape of an arc having a diameter larger than the blade diameter d. In the present invention, as described with reference to FIG. 3, the second picking depth h gradually increases from the cutting edge side margin 6 toward the heel side margin 7, and the value of the second picking depth h is maximum. The second feature is that the second picking depth h gradually decreases toward the heel side margin 7 after reaching the maximum second picking depth hmax. This makes it possible to ensure sufficient drill rigidity when drilling high-hardness materials after heat treatment, so that vibration caused by cutting resistance can be suppressed, and drilling high-hardness materials with a long life or high efficiency. Can do. In addition, the 2nd taking depth in this invention is a depth when the distance of the circular arc 12 of the diameter drawn virtually with the blade diameter as the diameter and the 2nd taking surface 8 is measured in the radial direction.

  In the drill of the present invention, the second picking depth h gradually increases from the cutting edge side margin 6 toward the heel side margin 7 and reaches the maximum second picking depth hmax. However, it is desirable that the position at which the maximum second picking depth hmax is reached is provided near the center of the second picking surface 8. Specifically, when viewed from the straight line A connecting the end of the second picking surface 8 that contacts the margin 7 on the heel side and the tool axis O, the end of the second picking surface 8 that contacts the margin 6 on the cutting edge side At a position corresponding to 40 to 60% of the angle a formed by the straight line B connecting the tool axis O and the straight line A connecting the tool axis O and the end portion in contact with the margin 7 on the heel side of the second surface 8. It is desirable to reach the second sampling depth hmax.

  The drill shown in FIG. 4 has a straight line B connecting the end 6 of the second picking surface 8 that contacts the margin 6 on the cutting edge and the tool axis O, and an end of the second picking surface 8 that contacts the margin 7 on the heel side. The angle a formed by the straight line A connecting the tool axis O is 79 °, and the maximum second picking depth hmax is a straight line A connecting the end of the second picking surface 8 contacting the heel side margin 7 and the tool axis O. In this example, the angle reaches 42 °, which is 53% of the angle a.

  Further, in the present invention, by setting the maximum second cutting depth hmax in the range of 2.0% to 6.0% of the blade diameter d, the rigidity of the drill is further improved, and the high hardness material is made highly efficient. This is desirable because it increases stability when processed. When the maximum double-cutting depth hmax is smaller than 2.0% of the blade diameter d, the possibility of contact between the tool and the machined surface increases due to tool wobbling during machining. There is a possibility that the performance becomes unstable when it is processed efficiently. In addition, when the maximum double-cutting depth hmax exceeds 6.0% of the blade diameter d, the rigidity of the tool cannot be sufficiently ensured and vibration during machining increases, resulting in chipping when machining with high efficiency. There is a tendency for performance to become unstable.

  Further, as shown in FIG. 4, the second face 8 has two margins, a margin 6 on the cutting edge side and a margin 7 on the heel side, a circular arc 12 with a diameter, and 94% or more of the blade diameter d 98 or more. It is provided in the area | region enclosed with the virtual arc 13 with a diameter below%. As a result, the rigidity of the drill is further improved, and vibrations can be suppressed even in the drilling of deep holes where the protruding length of the tool is long, and the occurrence of chipping of the cutting edge can be reduced, which is more desirable. When the second picking surface 11 is provided in an area exceeding 98% (that is, when the value of the diameter of the virtual arc 13 exceeds 98% of the blade diameter d), when fine chips enter the second picking, An increase in vibration is considered. When the second picking surface 11 is provided in an area smaller than 94% (that is, when the value of the diameter of the virtual arc 13 is less than 94% of the blade diameter d), the rigidity of the tool becomes small and vibration suppression is insufficient. There is a tendency to become.

  FIG. 5 is a diagram showing another embodiment of the present invention. The drill of the present invention shown in FIG. 4 is a double margin drill in which the second face 8 is formed by a plurality of planes. Even when the second picking surface 8 is formed by a plurality of flat surfaces, the second picking depth h gradually increases from the margin 6 on the cutting edge side toward the margin 7 on the heel side. The second picking surface 8 is formed in the shape of an arc having a diameter larger than the blade diameter d by gradually decreasing the second picking depth h toward the heel side margin 7 after reaching hmax. The same advantageous effects as those of the present invention can be obtained.

  FIG. 8 is a cross-sectional view when cut in a direction perpendicular to the tool axis in another embodiment of the present invention. As the shape of other second picking surfaces 8 where the second picking depth gradually increases and reaches the maximum second picking depth and then the second picking depth gradually decreases toward the margin 7 on the heel side. As shown in FIG. 8, the straight first first picking surface 16 formed from the end 19 on the rear side of the margin on the cutting edge side toward the rear side of the drill as shown in FIG. And a linear second second picking surface 17 formed from the end 20 on the rotation front side of the margin on the heel side toward the rotation front side of the drill, the first second picking surface 16 and the second Some of them are configured with a curved third second-hand surface 18 connecting the second-hand surface 17.

  FIG. 9 is an enlarged view of the vicinity of the second picking surface in the cross section when cut in the direction perpendicular to the tool axis of the drill of the present invention shown in FIG. As described above, the second picking surface 8 in another embodiment of the present invention, when viewed in a cross section perpendicular to the axis, from the end 19 on the rotation rear side of the margin on the cutting edge side toward the rotation rear side of the drill. A linear first second picking surface 16 formed, and a linear second second picking surface 17 formed from the rotation front side end 20 of the heel side margin toward the rotation front side of the drill, The first second picking surface 16 and the curved second second picking surface 18 connecting the second second picking surface 17. Even in such a case, the second picking depth in the second picking surface 8 gradually increases, and after reaching the maximum second picking depth hmax, the second picking depth gradually increases toward the heel side margin 7. If it is a shallower shape, the advantageous effects of the present invention can be obtained. In particular, by providing the first first second surface 16 and the second second second surface 17 that are linear on the second surface 8, the edge 19 on the rotation rear side of the margin on the cutting edge side and the margin on the heel side are provided. Since it is possible to easily avoid contact between the second picking surface 8 and the machining surface while sufficiently securing the rigidity of the end portion 20 on the rotation front side, the vibration of the drill is suppressed and stable cutting is performed. Is possible.

  In addition, the width w3 of the first second picking surface and the width w4 of the second second picking surface, which are the widths of the first second picking surface 16 and the second second picking surface 17, are the first in the cross section perpendicular to the axis. When measured in a direction parallel to the second picking surface 16 and the second second picking surface 17, it is desirable that the blade diameter is in the range of 15% to 25% of the blade diameter. Thereby, when grinding the second picking surface with a grindstone at the time of manufacture of a drill, since the volume which removes a raw material reduces, manufacture becomes easy and the fall of the rigidity of a drill can be controlled.

  In another embodiment of the present invention, the curvature radius R of the third second picking surface which is the radius of curvature of the third second picking surface 18 in the cross section perpendicular to the axis is in the range of 75% to 125% of the blade diameter. Is desirable. Thereby, at the position where the value of the second picking depth h is maximum, that is, at the position where the most base material is removed by grinding in the direction of the second picking depth h when forming the second picking surface 8. The rigidity necessary for suppressing the vibration of the drill can be secured.

  The present invention can be applied to a drill having any shape, but it is particularly effective to apply to a drill having 2 to 3 blades and a blade diameter d of about 1 mm to 20 mm. In addition, the second picking depth h, the maximum second picking depth hmax, the first second picking surface width w3, the second second picking surface width w4, and the third second are important elements in the present invention. The curvature radius R of the winding surface can be obtained by a known measurement method. As a specific example, the drill 1 of the present invention is cut in a direction perpendicular to the tool axis O, a measurement sample having a thickness of about 5 mm is prepared, and a method of measuring with an optical microscope or a contact type There is a method in which the shape of a land is traced using a shape measuring instrument, and the measurement is performed from the shape of the second surface of the traced land.

  FIG. 6 is a cross-sectional view when cut in a direction perpendicular to the tool axis of a conventional drill. As shown in FIG. 6, in the conventional drill, the second cutting depth suddenly becomes deeper from the margin 6 on the cutting edge side toward the margin 7 on the heel side. After reaching the depth, the second picking surface 8 is formed at a constant second picking depth from the vicinity of the heel side margin 18, and the second picking depth suddenly extends from the vicinity of the heel side margin 18 to the heel side margin 18. Is getting shallower. In other words, it can be said that the second picking surface 8 in the conventional drill is formed in an arc shape that is smaller than the blade diameter d and is arranged concentrically with the arc 12 of the diameter. On the other hand, since the second face 8 in the drill of the present invention is formed by a plurality of straight lines or an arc having a diameter larger than the blade diameter d when viewed in cross section, the drill of the present invention and the conventional drill It can be said that the shape of the second catching surface 8 is greatly different.

  FIG. 7 is an enlarged view of the vicinity of the second face in a cross section when cut in a direction perpendicular to the tool axis of a conventional drill. As shown in FIG. 7, the conventional drill is provided with a step 15 in which the second cutting depth h suddenly increases from the cutting edge side margin 6 toward the heel side margin 7, and the maximum second cutting depth. After reaching hmax, the shape is provided with a step 15 that suddenly becomes shallower toward the heel side margin 18. In such a configuration, the rigidity of the drill is lowered and the occurrence of vibration cannot be sufficiently suppressed. Therefore, when cutting a hard material, chipping may occur at an early stage. The maximum drilling depth in the conventional drill shown in FIG. 7 is a radial measurement of the distance between an arc 12 having a diameter virtually drawn with the blade diameter as a diameter and an arc 14 having an extended second catching surface. Is the depth of time.

  In the drill of the present invention, the position at which the maximum double depth hmax at which the maximum double depth h is reached is only one position when the secondary surface 8 is seen in the cross-sectional view. It is a big feature. In other words, the number of straight lines connecting the tool axis O and the position reaching the maximum second picking depth hmax on the second picking surface 8 is only one per land 10.

  On the other hand, in the conventional drill, the second face 8 is provided between the two steps 15, and the shape thereof is smaller than the blade diameter d and is provided concentrically with the arc 12 of the diameter. There are an infinite number of straight lines that connect the tool axis O and the position where the maximum second picking depth hmax is reached on the second picking surface 8. Since the second picking surface 8 is formed in this way, the conventional drill has a very low rigidity because more material is removed because the second picking surface 8 is formed.

  In the drill of the present invention, the material to be removed to form the second picking surface 8 is formed by forming the second picking surface 8 so that the position reaching the maximum second picking depth hmax is one. Therefore, the rigidity can be kept very high.

  In the shape of the drill of the present invention, since a new shape of the second picking surface is provided, the cross section of the tool becomes larger than that of the conventional drill, so that the rigidity of the tool can be increased. Generally, in drilling a hard material, a large cutting resistance is generated as compared with a material before heat treatment. In the drill according to the present invention, since the vibration generated by the cutting resistance can be suppressed by increasing the tool rigidity, chipping and tool loss due to the cutting vibration can be prevented. This makes it possible to perform drilling with a long life or high efficiency.

  Hereinafter, the present invention will be described in detail by the following examples, but the present invention is not limited thereto.

Example 1
Using the present invention example 1 and the conventional example 2, a life comparison test was performed according to the difference in the shape of the second face.

  As a common specification of the present invention example 1 and the conventional example 2, it has an oil hole for supplying coolant through the tool body, the blade diameter d is 6.0 mm, and the length when the groove 5 is measured in the direction of the tool axis. The groove length L is 198 mm (L / d = 33 times), the total length is 250 mm, the twist angle of the groove 5 is 20 °, the core thickness d1 is 2.4 mm, the shank diameter D is 6.0 mm, FIG. 3 and FIG. In the drill in which the width w1 of the cutting edge side margin of the land is set to 0.5 mm and the width w2 of the heel side margin is set to 0.5 mm, the maximum second cutting depth hmax is set to 4.0 of the cutting edge diameter d. %, That is, 0.24 mm.

  As specifications other than the common specifications in Example 1 of the present invention, as shown in FIG. 3 and FIG. 4, in the cross section when cut in the direction perpendicular to the tool axis, the end on the rotational rear side of the margin 6 on the cutting edge side and the heel By forming an arcuate second-handing surface 8 that connects the rotation front side end of the side margin 7, the second-handing depth h gradually increases from the cutting edge side margin toward the heel side margin. The drill was made deeper, and after reaching the maximum second-handing depth hmax, the second-handing depth h gradually decreased toward the heel side margin. As described above, the maximum double-cutting depth hmax in Invention Example 1 was 4.0% of the blade diameter d, that is, 0.24 mm.

  As a specification other than the common specification in Conventional Example 2, as shown in FIGS. 6 and 7, it is smaller than the blade diameter d and provided concentrically with the diameter arc 12 in the cross section when cut in the direction perpendicular to the tool axis. By forming the circular arc-shaped second-handed surface 8, a step is formed from the cutting edge side margin 6 to suddenly reach the maximum second-handing depth hmax, and a step is suddenly formed toward the heel side margin 7. In this way, a drill with a second chamfering surface 8 was made so that the second happing depth h was shallow. As described above, the maximum double-cutting depth hmax in Conventional Example 2 is 4.0% of the blade diameter d, that is, 0.24 mm.

  The test conditions were that the work material was SKD61, the hardness was HRC50, and a plate material having a width of 50 mm, a depth of 200 mm, and a height of 150 mm was used. At the horizontal machining center, the cutting conditions are as follows: rotational speed 1600 min-1 (cutting speed approx. 30.2 m / min), feed amount per rotation 0.06 mm / rotation, drilling depth 180 mm (30 times the blade diameter d) The blind hole was processed in the depth direction. The coolant supplied water-soluble cutting fluid through the oil hole.

  As an evaluation method, evaluation was performed by measuring the maximum flank wear width of the cutting edge after processing 25 holes and 75 holes with an optical microscope by 100 times magnification. When chipping or chipping occurred during cutting, the processing was stopped at that time and the number of holes to be processed at that time was entered.

   As an evaluation standard, no chipping or chipping occurred after machining 75 holes, and the maximum flank wear width after machining 75 holes was 0.30 mm or less. The evaluation results are shown in Table 1.

  As a result, Example 1 of the present invention was able to machine up to 75 holes, and the flank maximum wear width after machining 75 holes was 0.30 mm or less, which was a good result. When drilling high-hardness materials, vibration occurs with a large cutting force, but with the drill of the present invention, the second cutting depth gradually increases from the cutting edge side margin to the heel side margin. The shape of the second picking depth that gradually decreases toward the heel side margin after reaching the maximum second picking depth increases the rigidity of the tool and suppresses the occurrence of vibration, so chipping occurs during machining. The tool life was good without. In the conventional example 2, chipping occurred on the cutting edge after processing 15 holes, and the test was stopped. It is considered that chipping occurred in the cutting edge due to vibration because the tool cutting surface of the second picking surface in the conventional example 2 suddenly reaches the maximum second picking depth hmax and the tool rigidity is reduced.

(Example 2)
Next, Examples 3 to 13 of the present invention in which the maximum double punching depth was changed to 1.0% to 7.0% were manufactured, and a life test was performed according to the difference in the maximum double punching depth.

  As a common specification of Examples 3 to 13 of the present invention, it is an length having an oil hole for supplying coolant through the tool body, the blade diameter d is 6.0 mm, and the groove 5 is measured in the direction of the tool axis. The groove length L is 198 mm (L / d = 33 times), the total length is 250 mm, the twist angle of the groove 5 is 20 °, the core thickness d1 is 2.4 mm, the shank diameter D is 6.0 mm, as shown in FIG. 3 and FIG. Thus, the width w1 of the cutting edge side margin of the land is set to 0.5 mm, the width w2 of the heel side margin is set to 0.5 mm, and the shape of the second face 8 is the end portion on the rotation rear side of the margin 6 on the cutting edge side. And the circular arc shape which connects the edge part of the rotation front side of the margin 7 on the heel side was used.

In Inventive Example 3, the maximum double cutting depth hmax was 1.0% of the blade diameter d, that is, 0.06 mm.
In Inventive Example 4, the maximum double cutting depth hmax was 1.5% of the blade diameter d, that is, 0.09 mm.
In Invention Example 5, the maximum double cutting depth hmax was 2.0% of the blade diameter d, that is, 0.12 mm.
In Invention Example 6, the maximum double cutting depth hmax was 2.5% of the blade diameter d, that is, 0.15 mm.
In Invention Example 7, the maximum double cutting depth hmax was 3.0% of the blade diameter d, that is, 0.18 mm.
In Example 8 of the present invention, the maximum double cutting depth hmax was 4.0% of the blade diameter d, that is, 0.24 mm.
In Invention Example 9, the maximum double cutting depth hmax was 5.0% of the blade diameter d, that is, 0.30 mm.
In Example 10 of the present invention, the maximum double cutting depth hmax was 5.5% of the blade diameter d, that is, 0.33 mm.
In Invention Example 11, the maximum double cutting depth hmax was 6.0% of the blade diameter d, that is, 0.36 mm.
In Invention Example 12, the maximum double cutting depth hmax was 6.5% of the blade diameter d, that is, 0.39 mm.
In Invention Example 13, the maximum double-cutting depth hmax was 7.0% of the blade diameter d, that is, 0.42 mm.

  Test conditions, evaluation methods, and evaluation criteria were the same as in Example 1. The evaluation results are shown in Table 2.

  In Examples 3 to 13 of the present invention, chipping and chipping did not occur after machining 75 holes, and the maximum wear width of the flank after machining 75 holes was 0.30 mm or less. If the maximum double punching depth hmax is within this range, the rigidity of the tool is ensured, so that it is considered that the occurrence of vibration can be suppressed.

(Example 3)
Inventive Examples 14 to 18 in which the width w3 of the first second picking surface was changed to a range of 10% to 30% of the blade diameter were manufactured, and the lifetimes were compared by the difference in the width w3 of the first second picking surface. Tested.

  As a common specification of Examples 14 to 18 of the present invention, it is the length when having an oil hole for supplying coolant through the tool body, the blade diameter d is 10.0 mm, and the groove 5 is measured in the direction of the tool axis. The groove length L is 330 mm (L / d = 33 times), the total length is 390 mm, the twist angle of the groove 5 is 20 °, the core thickness d1 is 4.0 mm, the shank diameter D is 10.0 mm, and the land as shown in FIG. The width w1 of the cutting edge side margin was set to 0.8 mm, and the width w2 of the heel side margin was set to 0.8 mm.

  In addition, as a common specification of other Examples 14 to 18 of the present invention, the shape of the second picking surface 8 is a straight line formed from the end portion on the rotating rear side of the margin on the cutting edge side toward the rotating rear side of the drill. The first second picking surface 16, the linear second second picking surface 17 formed from the rotation front end of the margin on the heel side toward the rotation front side of the drill, and the first second picking surface 17 It was made into the shape comprised from the chamfering surface 16 and the curved 3rd 2nd picking surface 18 which connects the said 2nd 2nd picking surface 17. FIG. Further, in Examples 14 to 18 of the present invention, the width w4 of the second second picking surface is 20% of the blade diameter d, that is, 2.00 mm, and the curvature radius R of the third second picking surface is 95% of the blade diameter d, that is, 9.50 mm.

As the specifications of the respective inventive examples, in the inventive example 14, the width w3 of the first second facet was 10% of the blade diameter d, that is, 1.00 mm.
In Example 15 of the present invention, the width w3 of the first second facet was 15% of the blade diameter d, that is, 1.50 mm.
In Invention Example 16, the width w3 of the first second facet was 20% of the blade diameter d, that is, 2.00 mm.
In Example 17 of the present invention, the width w3 of the first second facet was 25% of the blade diameter d, that is, 2.50 mm.
In Example 18 of the present invention, the width w3 of the first second facet was 30% of the blade diameter d, that is, 3.00 mm.

  The test condition was that the work material was a SKD61 material, the hardness was HRC50, and a plate material having a width of 50 mm, a depth of 320 mm, and a height of 150 mm was used. At the horizontal machining center, the cutting conditions are as follows: the rotation speed is 1,000 min-1 (cutting speed of about 31.4 m / min), the feed amount per rotation is 0.10 mm / rotation, and the drilling depth is 300 mm (blade diameter d 30). Double) blind holes were processed in the depth direction. The coolant supplied water-soluble cutting fluid through the oil hole.

  As an evaluation method, the flank maximum wear width of the cutting edge after processing 15 holes and 50 holes was measured with an optical microscope and magnified 100 times for evaluation. When chipping or chipping occurred during cutting, the processing was stopped at that time and the number of holes to be processed at that time was entered.

  As evaluation criteria, a chip in which chipping and chipping did not occur after 50 holes were processed, and the flank maximum wear width after 50 holes was processed was 0.50 mm or less. The evaluation results are shown in Table 3.

  As shown in Table 3, Examples 14 to 18 of the present invention did not cause chipping or chipping after processing 50 holes, and the flank maximum wear width after processing 50 holes was 0.50 mm or less, which was a favorable result. . In particular, when the width w3 of the first second picking surface is measured in a direction parallel to the first second picking surface and the second second picking surface in the cross section perpendicular to the axis, the blade diameter is 15% or more and 25% of the blade diameter. Examples 15 to 17 of the present invention having the following ranges had a flank maximum wear width of 0.40 mm or less after processing 50 holes, and showed further favorable results.

Example 4
Inventive Examples 19 to 23 in which the width w4 of the second second picking surface was changed to a range of 10% to 30% of the blade diameter were manufactured, and the lifespan was compared by the difference in the width w4 of the second second picking surface. Tested.

  As a common specification of Examples 19 to 23 of the present invention, it is the length when having an oil hole for supplying coolant through the tool body, the blade diameter d is 10.0 mm, and the groove 5 is measured in the direction of the tool axis. The groove length L is 330 mm (L / d = 33 times), the total length is 390 mm, the twist angle of the groove 5 is 20 °, the core thickness d1 is 4.0 mm, the shank diameter D is 10.0 mm, and the land as shown in FIG. The width w1 of the cutting edge side margin was set to 0.8 mm, and the width w2 of the heel side margin was set to 0.8 mm.

  Further, as a common specification of the other Examples 19 to 23 of the present invention, the shape of the second picking surface 8 is a straight line formed from the end portion on the rotation rear side of the margin on the cutting edge side toward the rotation rear side of the drill. The first second picking surface 16, the linear second second picking surface 17 formed from the rotation front end of the margin on the heel side toward the rotation front side of the drill, and the first second picking surface 17 It was made into the shape comprised from the chamfering surface 16 and the curved 3rd 2nd picking surface 18 which connects the said 2nd 2nd picking surface 17. FIG. Further, in Examples 19 to 23 of the present invention, the width w3 of the first second picking surface is 20% of the blade diameter d, that is, 2.00 mm, and the curvature radius R of the third second picking surface is 95% of the blade diameter d, that is, 9.50 mm.

As the specifications of the respective inventive examples, in the inventive example 19, the width w4 of the second second facet was 10% of the blade diameter d, that is, 1.00 mm.
In Example 20 of the present invention, the width w4 of the second second facet was 15% of the blade diameter d, that is, 1.50 mm.
In Example 21 of the present invention, the width w4 of the second second facet was 20% of the blade diameter d, that is, 2.00 mm.
In Invention Example 22, the width w4 of the second second facet was 25% of the blade diameter d, that is, 2.50 mm.
In Invention Example 23, the width w4 of the second second facet was 30% of the blade diameter d, that is, 3.00 mm.

  Test conditions, evaluation methods, and evaluation criteria were the same as in Example 3. The evaluation results are shown in Table 4.

  As shown in Table 4, Examples 19 to 23 of the present invention did not cause chipping or chipping after processing 50 holes, and the flank maximum wear width after processing 50 holes was 0.50 mm or less, which was a favorable result. . In particular, when the width w4 of the second second picking surface is measured in a direction parallel to the first second picking surface and the second second picking surface in the cross section perpendicular to the axis, it is 15% or more and 25% of the blade diameter. Inventive Examples 20 to 22 in the following range, the flank maximum wear width after drilling 50 holes was 0.40 mm or less, and even better results were shown.

(Example 5)
Examples 24 to 31 of the present invention were manufactured in which the curvature radius R of the third second facet was changed in the range of 65% to 135% of the blade diameter, and the life due to the difference in the curvature radius R of the third second facet. A comparative test was conducted.

  As a common specification of Examples 24-31 of the present invention, there is an oil hole for supplying coolant through the tool body, the blade diameter d is 10.0 mm, and the length when the groove 5 is measured in the direction of the tool axis. The groove length L is 330 mm (L / d = 33 times), the total length is 390 mm, the twist angle of the groove 5 is 20 °, the core thickness d1 is 4.0 mm, the shank diameter D is 10.0 mm, and the land as shown in FIG. The width w1 of the cutting edge side margin was set to 0.8 mm, and the width w2 of the heel side margin was set to 0.8 mm.

  Moreover, as a common specification of the other invention examples 24-31, the shape of the second picking surface 8 is a linear shape formed from the end portion on the rotating rear side of the margin on the cutting edge side toward the rotating rear side of the drill. The first second picking surface 16, the linear second second picking surface 17 formed from the rotation front end of the margin on the heel side toward the rotation front side of the drill, and the first second picking surface 17 It was made into the shape comprised from the chamfering surface 16 and the curved 3rd 2nd picking surface 18 which connects the said 2nd 2nd picking surface 17. FIG. Further, in the inventive examples 24-31, the width w3 of the first second picking surface is 20% of the blade diameter d, that is, 2.00 mm, and the width w4 of the second second picking surface is 20% of the blade diameter d, that is, 2 0.000 mm.

As the specifications of the respective inventive examples, in the inventive example 24, the radius of curvature R of the third second facet was 65% of the blade diameter d, that is, 6.50 mm.
In Invention Example 25, the radius of curvature R of the third second facet was 75% of the blade diameter d, that is, 7.50 mm.
In Invention Example 26, the radius of curvature R of the third second facet was 85% of the blade diameter d, that is, 8.50 mm.
In Invention Example 27, the radius of curvature R of the third second facet was 95% of the blade diameter d, that is, 9.50 mm.
In Inventive Example 28, the radius of curvature R of the third second facet was 105% of the blade diameter d, that is, 10.50 mm.
In Invention Example 29, the radius of curvature R of the third second facet was 115% of the blade diameter d, that is, 11.50 mm.
In Invention Example 30, the radius of curvature R of the third second facet was 125% of the blade diameter d, that is, 12.50 mm.
In Invention Example 31, the radius of curvature R of the third second facet was 135% of the blade diameter d, that is, 13.50 mm.

  Test conditions, evaluation methods, and evaluation criteria were the same as in Example 3. The evaluation results are shown in Table 5.

  As shown in Table 5, Examples 24 to 31 of the present invention did not cause chipping or chipping after processing 50 holes, and the flank maximum wear width after processing 50 holes was 0.50 mm or less, which was a favorable result. . In particular, Examples 25 to 30 of the present invention in which the radius of curvature R of the third second face in the cross section perpendicular to the axis is in the range of 75% to 125% of the blade diameter have a maximum flank wear width after 50 holes are machined. It was 0.40 mm or less, and more favorable results were shown.

  By using the drill of the present invention, drilling of a high hardness material after heat treatment can sufficiently ensure the rigidity of the drill, so that vibration generated by cutting resistance can be suppressed, and drilling to a high hardness material can be performed with a long service life. Or it can be performed highly efficiently. Therefore, it is suitable for processing into a steel material having a hardness of about 45 to 55 HRC mainly used for a mold. Further, the effect of the present invention is remarkably observed in the machining of deep holes where the protruding length of the tool becomes long.

DESCRIPTION OF SYMBOLS 1 Drill of this invention 2 Cutting edge 3 Cutting edge part 4 Shank 5 Groove 6 Margin on the cutting edge side 7 Margin on the heel side 8 Rounding surface 9 Outer corner 10 Land 11 Coolant hole 12 Arc of diameter 13 Virtual arc 14 Second rounding Arc with extended surface 15 Step 16 First second picking surface 17 Second second picking surface 18 Third second picking surface 19 End of rotation of margin on cutting edge side 20 Front of rotation of margin on heel side End d edge diameter D shank diameter O tool axis L groove length d1 core thickness w1 cutting edge side margin width w2 heel side margin width w3 first second face width w4 second second face Width h Depth of cut hmax Maximum depth of cut A A straight line connecting the heel side margin of the second face and the tool axis B End of the second face of the edge in contact with the cutting edge side tool Angle R third double-dip up surface radius of curvature formed by the straight line a straight lines A and B which connects the

That is, according to the present invention, a cutting edge portion having a groove and a land extending from the front end side toward the rear end side is formed in the front end side portion of the drill body rotated about the axis, and the cutting edge is provided at the front end portion of the cutting edge portion. In the drill which has, the land provided continuously from the leading edge has two margins arranged on the cutting edge side and heel side of the groove, and the second surface is provided between the two margins In the cross section perpendicular to the axis, the second cutting surface is formed in the shape of an arc having a diameter larger than the blade diameter, and the second cutting depth is from the margin on the cutting edge side toward the margin on the heel side. The drill is characterized in that after the depth gradually increases and reaches the maximum second-handed depth, the second-handed depth gradually decreases toward the heel side margin.

In the present invention, the double-dip up surface, in the the two margins, and virtual circle with a diameter of the blade diameter to the diameter, the virtual circle having 98% or less of the diameter of 94% or more of the blade diameter By providing it in the enclosed area, the rigidity of the drill is further improved, and it is possible to suppress the occurrence of chipping of the cutting edge by suppressing vibration even when machining deep holes where the protruding length of the tool becomes long. So it is more desirable.

It is a front view of the drill of this invention. It is the side view to which the cutting blade vicinity of the drill of this invention was expanded. It is sectional drawing when cut | disconnecting in the orthogonal | vertical direction to the tool axis | shaft of the drill of this invention. FIG. 4 is an enlarged view of the vicinity of the second face in a cross section when cut in a direction perpendicular to the tool axis of the drill of the present invention shown in FIG. 3. It is a figure which shows the drill of the reference example of this invention. It is sectional drawing when cut | disconnecting in the orthogonal | vertical direction to the tool axis | shaft of the conventional drill. It is an enlarged view near the second picking surface in the cross section when cut in the direction perpendicular to the tool axis of the conventional drill. It is sectional drawing when cut | disconnected in the orthogonal | vertical direction with respect to the tool axis | shaft in another reference example of this invention. FIG. 9 is an enlarged view of the vicinity of the second picking surface in a cross section when cut in a direction perpendicular to the tool axis of the drill of the reference example shown in FIG. 8.

An embodiment of the present invention will be described with reference to FIG 1-4. FIG. 1 is a front view of a drill according to the present invention. As shown in FIG. 1, the drill 1 of the present invention has a cutting edge 2, a cutting edge part 3, and a shank 4, and the cutting edge part 3 is provided with a groove 5 and a land for discharging chips. A cutting edge 2 is provided at the tip of the blade edge portion 3. Since the drill 1 of the present invention is a drill having two margins, that is, a double margin drill, a margin 6 on the cutting edge side and a margin 7 on the heel side are provided on the outer periphery of the drill 1. The margin 6 on the cutting edge side and the margin 7 on the heel side are connected by a second picking surface 8.

Further, as shown in FIG. 4, the second face 8 has two margins, a margin 6 on the cutting edge side and a margin 7 on the heel side, an arc 12 having a diameter of the cutting edge, and a cutting edge diameter d. It is provided in a region surrounded by a virtual arc 13 having a diameter of 94% or more and 98% or less. As a result, the rigidity of the drill is further improved, and vibrations can be suppressed even in the drilling of deep holes where the protruding length of the tool is long, and the occurrence of chipping of the cutting edge can be reduced, which is more desirable. When the second face 8 is provided in an area exceeding 98% (that is, when the value of the diameter of the virtual arc 13 exceeds 98% of the blade diameter d), when a fine chip enters the second face, An increase in vibration is considered. When the second picking surface 11 is provided in an area smaller than 94% (that is, when the value of the diameter of the virtual arc 13 is less than 94% of the blade diameter d), the rigidity of the tool becomes small and vibration suppression is insufficient. There is a tendency to become.

FIG. 5 is a diagram showing a reference example for the embodiment shown in FIGS. The drill of the reference example shown in FIG. 5 is a double margin drill in which the second face 8 is formed by a plurality of planes. Even when the second picking surface 8 is formed by a plurality of flat surfaces, the second picking depth h gradually increases from the margin 6 on the cutting edge side toward the margin 7 on the heel side. The second picking surface 8 is formed in the shape of an arc having a diameter larger than the blade diameter d by gradually decreasing the second picking depth h toward the heel side margin 7 after reaching hmax. Has the same advantageous effect as

FIG. 8 is a sectional view when cut in a direction perpendicular to the tool axis in another reference example of the present invention. As the shape of other second picking surfaces 8 where the second picking depth gradually increases and reaches the maximum second picking depth and then the second picking depth gradually decreases toward the margin 7 on the heel side. As shown in FIG. 8, the straight first first picking surface 16 formed from the end 19 on the rear side of the margin on the cutting edge side toward the rear side of the drill as shown in FIG. And a linear second second picking surface 17 formed from the end 20 on the rotation front side of the margin on the heel side toward the rotation front side of the drill, the first second picking surface 16 and the second Some of them are configured with a curved third second-hand surface 18 connecting the second-hand surface 17.

FIG. 9 is an enlarged view of the vicinity of the second picking surface in the cross section when cut in the direction perpendicular to the tool axis of the drill of the present invention shown in FIG. As described above, the second picking surface 8 in another reference example of the present invention, when viewed in a cross-section perpendicular to the axis, from the end 19 on the rotation rear side of the margin on the cutting edge side toward the rotation rear side of the drill. A linear first second picking surface 16 formed, and a linear second second picking surface 17 formed from the rotation front side end 20 of the heel side margin toward the rotation front side of the drill, The first second picking surface 16 and the curved second second picking surface 18 connecting the second second picking surface 17. Even in such a case, the second picking depth in the second picking surface 8 gradually increases, and after reaching the maximum second picking depth hmax, the second picking depth gradually increases toward the heel side margin 7. If the shape is shallow , an advantageous effect can be obtained. In particular, by providing the first first second surface 16 and the second second second surface 17 that are linear on the second surface 8, the edge 19 on the rotation rear side of the margin on the cutting edge side and the margin on the heel side are provided. Since it is possible to easily avoid contact between the second picking surface 8 and the machining surface while sufficiently securing the rigidity of the end portion 20 on the rotation front side, the vibration of the drill is suppressed and stable cutting is performed. Is possible.

In another reference example of the present invention, the curvature radius R of the third second picking surface which is the radius of curvature of the third second picking surface 18 in the cross section perpendicular to the axis is in the range of 75% to 125% of the blade diameter. Is desirable. Thereby, at the position where the value of the second picking depth h is maximum, that is, at the position where the most base material is removed by grinding in the direction of the second picking depth h when forming the second picking surface 8. The rigidity necessary for suppressing the vibration of the drill can be secured.

FIG. 6 is a cross-sectional view when cut in a direction perpendicular to the tool axis of a conventional drill. As shown in FIG. 6, in the conventional drill, the second cutting depth suddenly becomes deeper from the margin 6 on the cutting edge side toward the margin 7 on the heel side. is a double-dip up surface 8 at a constant double-dip up depth from reaching the depth to the vicinity of the heel side margin 7 is formed, suddenly double-dip up depth from near to the heel side margin 7 of the heel side margin 7 Is getting shallower. In other words, it can be said that the secondary surface 8 in the conventional drill is formed in an arc shape that is smaller than the blade diameter d and is arranged concentrically with the arc 12 having the blade diameter as a diameter . On the other hand, since the second picking surface 8 in the drill of the present invention is formed by an arc having a diameter larger than the blade diameter d when viewed in a cross section, the second drill is the second in the drill of the present invention and the conventional drill. It can be said that the shape of the cut surface 8 is greatly different.

FIG. 7 is an enlarged view of the vicinity of the second face in a cross section when cut in a direction perpendicular to the tool axis of a conventional drill. As shown in FIG. 7, the conventional drill is provided with a step 15 in which the second cutting depth h suddenly increases from the cutting edge side margin 6 toward the heel side margin 7, and the maximum second cutting depth. After reaching hmax, the shape is provided with a step 15 that suddenly becomes shallower toward the heel side margin 7 . In such a configuration, the rigidity of the drill is lowered and the occurrence of vibration cannot be sufficiently suppressed. Therefore, when cutting a hard material, chipping may occur at an early stage. The maximum drilling depth in the conventional drill shown in FIG. 7 is a radial measurement of the distance between an arc 12 having a diameter virtually drawn with the blade diameter as a diameter and an arc 14 having an extended second catching surface. Is the depth of time.

On the other hand, in the conventional drill, the second face 8 is provided between the two steps 15, and the shape thereof is smaller than the blade diameter d and is provided concentrically with the arc 12 having the blade diameter as a diameter. Therefore, an infinite number of straight lines connecting the tool axis O and the position that reaches the maximum double depth hmax on the double face 8 are provided. Since the second picking surface 8 is formed in this way, the conventional drill has a very low rigidity because more material is removed because the second picking surface 8 is formed.

Hereinafter, the present invention will be described in detail by the following examples, but the present invention is not limited thereto. In these examples, Examples 14 to 31 of the present invention are drills of another reference example of the present invention based on FIGS. 8 and 9.

Claims (6)

  In a drill having a cutting edge at the tip end portion of the blade tip portion, a cutting edge portion having a groove and a land extending from the tip end side toward the rear end side is formed at the tip side portion of the drill body rotated about the axis. The land continuously provided from the side has two margins arranged on the cutting edge side and the heel side of the groove, and a two-sided surface is provided between the two margins. The second cutting depth gradually increases from the cutting edge side margin toward the heel side margin and reaches the maximum second cutting depth, and then the second cutting depth toward the heel side margin. A drill characterized by its shallowness gradually.   2. The drill according to claim 1, wherein the maximum double-cutting depth is in a range of 2.0% to 6.0% of a blade diameter.   In the cross section perpendicular to the axis, the second facet is provided in a region surrounded by the two margins, a circular arc having a diameter, and a virtual circular arc having a diameter of 94% to 98% of the blade diameter. The drill according to claim 1 or 2, wherein the drill is provided.   In the cross section perpendicular to the axis, the second surface is a straight first second surface formed from the end of the margin on the cutting edge side toward the rear side of the drill, and a heel side A linear second second face formed from the end on the rotation front side of the margin toward the rotation front side of the drill, and a curved surface connecting the first second face and the second second face. The drill according to any one of claims 1 to 3, wherein the drill is formed of a third second face.   The widths of the first second picking surface and the second second picking surface are determined by measuring the blade diameter when measured in a direction parallel to the first second picking surface and the second second picking surface in the cross section perpendicular to the axis. The drill according to any one of claims 1 to 4, wherein the range is 15% or more and 25% or less.   The drill according to any one of claims 1 to 5, wherein the radius of curvature of the third second face in the cross section perpendicular to the axis is in the range of 75% to 125% of the blade diameter.

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