JP2012030306A - Drill and drilling method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drill which prevents chips from being curled to improve separability and forms small-curl chips to remarkably improve discharge efficiency of the chips.SOLUTION: The drill has two cutters, and has a point angle of 170° to 190°, and groove widths of 75° to 85°. A first groove bottom curve is concave, a gap between the deepest position of the first groove bottom curve and the axis O of the drill is 0.35 to 0.70 times the drill's diameter, and the maximum depth of the first groove bottom curve is 0.03 to 0.07 times the drill diameter. A second groove bottom curve is concave, a gap between the deepest position of the second groove bottom curve and the axis O of the drill is 1.5 to 2.5 times the drill core thickness, and the maximum depth of the second groove bottom curve is more than 0 times to less than 0.04 times the drill diameter. The maximum depth of the second groove bottom curve is determined to be smaller than the maximum depth of the first groove bottom curve.

Description

  The present invention relates to a drill used for machining a guide hole or a counterbore, and a method for drilling or spotting a surface or a curved surface that is inclined with respect to the center axis of the drill using the drill. . In particular, the present invention uses a drill capable of preventing the enlargement of the entrance diameter of the hole and obtaining a good surface roughness, in addition to high position accuracy machining with very little deviation from the center of the targeted hole. The purpose is to provide a drilling method.

  When deep hole drilling or counterbore drilling is required on a slope, it has been common practice to pre-process the seating surface with a two-blade square end mill and then drill with a drill. FIG. 10 schematically shows problems in the conventional seat milling process using an end mill and the drilling process using a drill. In FIG. 10, the process from the bearing surface processing by the conventional end mill to the hole processing by the drill is performed in the order of (a), (b), (c).

  However, as shown in FIG. 10 (a), when the workpiece W is thrust with a conventional two-blade square end mill 1, the bottom edge of the square end mill has a watermark angle so that the center is recessed from the outer periphery. Therefore, as shown in FIG. 10B, the processed surface 2 formed by the conventional end mill has a convex shape. Therefore, after forming a seating surface on a slope with a square end mill having 2 to 4 blades, when a conventional drill 3 is used to drill a hole in the seating surface formed on the slope with the square end mill 1, a conventional convex shape is obtained. Since the processed surface 2 formed by the end mill of FIG. 10 bends the traveling direction of the conventional drill 3 along the direction 4 in which the conventional drill is displaced as shown in FIG. There is a problem that bending occurs.

  For this reason, holes may be drilled into the slope using only a square end mill with 2 to 4 blades. However, the square end mill has a smaller chip pocket than drills, so chip discharge is poor and position accuracy is due to chip clogging. As a result, chipping and chipping occurred at the cutting edge of the tool, and in the worst case, there was a problem of breakage. In order to prevent chip discharge, step feed processing is known in which a tool is processed by repeating a plurality of steps on a workpiece. This method requires time for the tool to leave the workpiece. Since substantial machining is not performed, it is difficult to increase machining efficiency, and there has been a demand for machining at once without steps.

In response to these problems, several tools have been proposed particularly for the purpose of counterbore machining.
In Patent Document 1, as an end mill for counterbore processing to suppress chip clogging, the core thickness is 15% to 40% of the tool diameter, the helix angle is 15 ° to 35 °, and the bottom blade rake angle is 2 ° to 15%. A two-blade end mill at ° is described.

  In Patent Document 2, as a counterbore drill, two secondary cutting edges extending outward from the chisel by thinning with a tip angle of 170 ° to 190 °, and a concave shape extending outward from each secondary cutting edge A primary cutting edge and an outer cutting edge extending from each primary cutting edge to the leading edge and retreating in the direction of drill rotation, the drill core thickness being 0.20 to 0.40 times the drill diameter D; For counterbore machining, the amount of the inner recess of the inner concave primary cutting edge is 0.01 to 0.06 times the drill diameter D, and the receding angle of the retreating outer cutting edge is -1 ° to -20 °. A drill is described. The counterbore drill of Patent Document 2 is described as being excellent in chip disposal and being less prone to chipping of the blade portion.

  In the drill, Patent Document 3 describes a proposal in which the shape of the curved surface portion of the chip discharge groove is devised. However, the drill described in Patent Document 3 is not for spot facing, but is suitable for high-speed dry cutting. In the drill described in Patent Document 3, the characteristic of the curved surface portion is that the margin portion side cutting edge has a convex curved surface on the outer peripheral end side, and the curvature of the second concave curved surface portion close to the heel side is the convex curved surface. It is characterized by being larger than the curvature of the following first concave curved surface portion.

  Further, Patent Document 4 proposes a device that devises the groove width shape of the chip discharge groove. However, this is also a drill made of cemented carbide suitable for general drilling, not for spot facing.

JP 2005-111642 A JP 2009-56534 A JP 2003-25124 A JP 59-219108 A

  To perform drilling or counterbore on a slope or curved surface that is inclined with respect to the axis of the drill, the center of the drilled hole is displaced due to the drill moving along the slope or curved surface during cutting. There is a problem that the drill breaks due to poor chip dischargeability, enlarges the diameter of the processed hole, and decreases the surface roughness of the processed hole.

  The tool described in Patent Document 1 is an end mill for counterbore machining, and is premised on performing counterbore machining by thrusting in which the endmill is axially fed. However, in the end mill, since the leading edge forms an acute angle, the strength is weak and chipping or chipping is likely to occur due to piercing. In addition, when the end mill described in Patent Document 1 is used to thrust a slope, the tool is liable to generate lateral vibration, and the end mill is chipped and chipped, so that there remains a problem that it cannot be processed with high efficiency. FIG. 9 is a diagram showing an end mill described in Patent Document 1. In FIG. In the conventional end mill 1 described in Patent Document 1, since the groove surface a connected from the groove bottom to the second surface as shown in FIG. 9 is formed in a convex shape, the chips are not curled and connected for a long time. Since the chips are discharged, there is a problem that chip stagnation occurs and the work surface is deteriorated and the workpiece is damaged, and in the worst case, the end mill is broken. In particular, regarding the drilling position accuracy, which is a major object of the present invention, the above-mentioned end mill has an unsatisfactory result in terms of both the drilling position accuracy and the surface roughness of the hole due to the application of vibrations to the end mill by chips and the large abrasion to the workpiece. I can't get it.

  The counterbore drill described in Patent Document 2 has a wide groove width, so chip clogging is reduced. However, since the groove width is wide, the cutting effect of the chips is small, and curled chips are connected, so that the chips are not discharged out of the hole during processing and remain in the groove. For this reason, there is a problem that chips are scraped and damaged on the inner wall surface of the processed hole, and the surface roughness of the processed hole of the workpiece is deteriorated. Moreover, since it has the big feature of having the cutting edge which retreats -1 degree--20 degrees on the reverse side of a rotation direction on the outer peripheral side of a cutting edge, although the chipping of a blade part is suppressed, biting property is suppressed. However, since the hole diameter is enlarged, the position of the target hole is shifted and the drilling position accuracy is deteriorated.

  The drill described in Patent Document 3 has a convex curved surface on the outer peripheral end side of the cutting edge on the margin side, and a second concave curved surface portion closer to the heel side than the curvature of the first concave curved surface portion following the convex curved surface. Is characterized by a large curvature. Therefore, when this drill is used for spot facing, a large amount of chips do not slide on the second concave curved surface, and chips curled only by the first concave curved surface are grooves near the second concave curved surface. It tends to lose directionality or stay in the groove. As a result, the chips collide with the drill in a narrow space where there is no place in the traveling direction of the drill, and give vibration in the swing direction to the drill. This not only has a great influence on the deterioration of the target position accuracy, but also has a problem that the surface roughness of the machined surface deteriorates because chips are damaged on the inner wall surface of the machined hole.

  In addition, the drill described in Patent Document 4 has poor chip breaking property, so that the chips curled several times in a spiral form are connected for a long time. There was a problem that chips were abraded and scratched on the inner wall surface, and the processed surface deteriorated.

  In particular, the present invention relates to a drill specialized for drilling holes on a slope or curved surface and counterbore drilling, and particularly to provide a new drill shape and drilling method created to greatly improve the drilling position accuracy. It is. The object of the present invention is to solve the problems in the conventional tools as described in the problem to be solved by the invention, and particularly in comparison with a conventional counterbore drilling end mill or a counterbore drill. By controlling the curling of the chips in a spiral manner, the chip breaking property is improved, and by further curling the chips as small as possible, the chip discharging performance is improved. It is intended to provide a drill capable of suppressing an increase in the diameter of the inlet and simultaneously improving the hole position accuracy and machining surface roughness, and a machining method using the drill. In addition, according to the present invention, chipping and chipping of the drill blade tip due to chip clogging can be suppressed, so that drilling in a slope or curved surface or a counterbore drill has an effect of extending the life.

  An important feature of the drill of the present invention is that a small drill core thickness and an appropriate groove width ensure a large chip pocket and the chip curl can be finely divided by controlling the chip curl. The groove bottom shape greatly improves the discharge performance. A new shape of the drill of the present invention and its peripheral shape are manufactured, and the position accuracy of the hole in drilling, the degree of enlargement of the hole entrance diameter, and the work surface roughness of the work are evaluated for the drills. The shape of the concave curved surface of the groove bottom of this drill was optimized to a new drill shape that has never existed before.

  That is, the first aspect of the present invention is a drill having two cutting edges, and the drill has a tip angle of 170 ° to 190 ° and a core thickness of 0.15 to 0.25 times the drill diameter. In the figure when the drill is viewed from the drill tip in the axial direction of the drill, a groove straight line on the margin portion side connecting the drill axis O and the outer peripheral end of the inner wall surface on the margin portion side, and the drill axis O The groove width is in the range of 75 ° to 85 ° when the angle formed by the outer peripheral end of the inner wall surface on the heel portion side, that is, the groove straight line on the heel side connecting the heel, is in the range of 75 ° to 85 °, The first groove bottom curve from the groove bottom to the heel is a concave curve, and the first groove bottom curve is the most recessed position of the first groove bottom curve with respect to the straight line connecting the heel from the drill axis and the drill. The distance of the axis O is a straight distance from the drill axis to the heel direction. The maximum depth of the first groove bottom curve is 0.03 to 0.07 times the diameter, and the outer peripheral edge of the inner wall surface on the margin side The second groove bottom curve from the groove bottom to the groove bottom is a concave curve, and the maximum groove position of the second groove bottom curve where the second groove bottom curve is most recessed with respect to the groove straight line on the margin side and the axis O of the drill The interval of the straight line from the drill axis to the inner wall surface on the margin side is 1.5 to 2.5 times the core thickness, and the maximum depth of the second groove bottom curve is 0 times the drill diameter. And the maximum depth of the second groove bottom curve is set smaller than the maximum depth of the first groove bottom curve.

  In particular, in the first aspect of the invention, it is preferable that the relief angle of the thinning is in the range of 35 ° to 50 °. This is the second invention of the present invention.

  A third aspect of the present invention is a hole drilling method characterized by processing a slope or a curved surface inclined with respect to the axis of the drill using the drill of the first or second aspect of the present invention.

  According to a fourth aspect of the present invention, there is provided a counterboring process, wherein the counterboring process is performed on a surface or a curved surface inclined with respect to the axis of the drill using the drill according to the first or second aspect of the present invention. Is the method.

  According to the present invention, with respect to drilling on a slope or curved surface, and counterbore drilling, the cutting performance is controlled by controlling the curl of the chip as compared with a conventional counterbore end mill and counterbore drill. The chip discharge performance can be greatly improved by curling the chips small. Therefore, if the drill of the present invention is used to drill and counterbore a workpiece having a slope or a curved surface, good hole position accuracy can be obtained and the hole entrance diameter can be prevented from being increased. Roughness can be greatly improved.

It is a front view of the axial direction front end view of the drill which concerns on this invention. It is sectional drawing orthogonal to the axis line O of a drill in the part which has the chip | tip discharge groove | channel of the drill of this invention shown in FIG. It is a general view of the side surface of the drill shown in FIG. It is the figure which expanded the inner wall surface vicinity by the heel part side in the drill of this invention shown in FIG. It is the figure which expanded the inner wall surface vicinity in the margin part side in the drill of this invention shown in FIG. It is a figure which shows the shape of the typical chip with the drill of this invention. It is a figure which shows the shape of the typical chip in the conventional counterbore end mill. It is the figure which expanded and rotated 90 degree | times the cutting blade vicinity of the drill of this invention shown in FIG. It is a figure which shows the end mill of patent document 1. It is a figure which shows typically the problem of the seat surface processing by the conventional end mill, and the hole processing by a drill. It is a figure which shows the measurement direction of the shift | offset | difference of the work material used for the Example, and the hole center. It is sectional drawing when it sees from the arrow A in the workpiece shown in FIG.

  Hereinafter, an embodiment for carrying out the present invention will be described with reference to FIGS. FIG. 1 is a front view of the drill according to the present invention when viewed from the front end in the axial direction. The drill body 5 includes at least a portion including the cutting edge 6 in terms of material, which is made of a hard material such as cemented carbide, CBN, or cermet, and is formed in a substantially cylindrical shape having a diameter D with the axis of the drill as the center. Further, the drill shown in FIG. 1 is provided with two cutting edges 6. A pair of substantially concave curved chip discharge grooves 7 (hereinafter also simply referred to as grooves) that twist to the rear side in the drill rotation direction L at a constant twist angle are drilled at a portion starting from the tip of the drill and reaching the rear side of the drill. Are provided symmetrically with respect to the axis O. The cutting edge 6 of the drill is provided at the ridge line portion where the inner wall surface 8 and the tip clearance surface 9 on the margin portion side facing the drill rotation direction L of the chip discharge groove 7 intersect. Furthermore, the drill of the present invention is provided with a thinning surface 27.

  FIG. 2 is a cross-sectional view perpendicular to the axis O of the drill at the portion having the chip discharge groove of the drill of the present invention shown in FIG. The shape characteristics of the inner wall surface 8 on the margin portion side and the inner wall surface 11 on the heel portion side of the chip discharge groove of the present invention can be well understood in FIG. In FIG. 2, the groove width θ in the present invention refers to the groove straight line 10 on the margin portion side connecting the drill axis O and the outer peripheral edge 18 of the inner wall surface on the margin portion side, the drill axis O and the heel portion side. The angle formed by the heel-side groove straight line 12 connecting the outer peripheral end of the inner wall surface 11, that is, the heel 15. In the present invention, the diameter of the core thickness circle 14 passing through the groove bottoms 13 of the two chip discharge grooves is defined by the core thickness d.

  In the present invention, the core thickness d is 0.15 to 0.25 times the diameter D. Thereby, a chip pocket sufficient for discharging chips can be ensured without significantly impairing the rigidity of the drill. If the core thickness d is less than 0.15 times the diameter D, the drilling position may deteriorate due to insufficient rigidity of the drill or the drill may be bent, resulting in problems such as poor drilling position accuracy or bending or breakage. If the core thickness d exceeds 0.25 times the diameter D, a chip pocket sufficient for chip discharge cannot be secured, so that the drilling position accuracy due to chip clogging deteriorates and the machined surface roughness deteriorates.

  The groove width θ of the present invention is 75 ° to 85 ° and is an acute angle. Referring to FIG. 2, the outer peripheral end of the inner wall surface 11 on the heel side, that is, the heel 15 is perpendicular to the groove straight line 10 on the margin side connecting the drill axis O and the outer peripheral end 18 of the inner wall surface on the margin side. It is located in a direction narrowing the groove rather than the straight line 17. If the groove width θ is less than 75 °, sufficient chip pockets required for chip discharge cannot be obtained, and chip clogging occurs, leading to breakage in the worst case. If the groove width θ is larger than 85 °, a chip pocket sufficient for chip discharge can be obtained. However, since the chip curl becomes large, the chip comes into contact with the inner wall surface of the processing hole and the processing surface roughness deteriorates. Further, since the cutting effect of the chips is reduced, the chips connected in a multi-layered manner are not easily discharged out of the groove, and the risk of breakage due to clogging of the chips increases.

  FIG. 3 is an overall side view of the drill shown in FIG. In the drill of the present invention, a substantially concave curved chip discharge groove 7 is provided in a portion starting from the tip of the drill and reaching the rear side of the drill. In the present invention, at least a portion including the cutting edge 6 is made of a hard material such as cemented carbide, CBN, cermet or the like, and the drill body 5 is formed in a substantially cylindrical shape having a diameter D centering on the axis of the drill. ing. The angle formed by the two cutting edges 6 is defined by the tip angle 26.

  In the present invention, the tip angle 26 is set to 170 ° to 190 °. Thereby, it can process, without deteriorating the drilling position precision at the time of processing of an inclined surface. If the tip angle 26 is less than 170 °, the biting of the drill is poor and the drill slides along the inclined surface of the workpiece, so that the drilling position accuracy is deteriorated or the hole is bent. If the tip angle 26 exceeds 190 °, the strength of the corner portion of the drill becomes weak, so that the drill is damaged.

4 is an enlarged view of the vicinity of the inner wall surface on the heel portion side in the drill of the present invention shown in FIG. 2, and FIG. 5 is an enlarged view of the vicinity of the inner wall surface on the margin portion side of the drill of the present invention shown in FIG. FIG.
As shown in FIG. 2, the groove of the drill of the present invention has an inner wall surface on the heel side from the contact point between the groove bottom 13 and the core thickness circle 14 when the core thickness d of the drill is the diameter. 11 and the inner wall surface on the margin side from the contact point between the groove bottom 13 and the core thickness circle 14 when the core thickness d of the drill is the diameter. A second groove bottom curve 19 extending to the outer peripheral end 18 is provided.

  In the present invention, as shown in FIG. 4, the groove shape on the heel side has a first groove bottom curve 16 in a direction perpendicular to the groove line 12 on the heel side, which is a straight line connecting the axis O of the drill and the heel 15. The most recessed position is defined as the maximum recessed position 20 of the first groove bottom curve, and the position where the maximum recessed position 20 of the first groove bottom curve is located is measured along the groove straight line 12 on the heel side from the drill axis to the heel direction. The distance 22 between the maximum recess position of the first groove bottom curve and the drill axis O is 0.35 to 0.70 times the diameter. Further, the first groove bottom curve 16 is a concave curve, and the maximum recess amount 21 of the first groove bottom curve from the groove straight line 12 on the heel side is in the range of 0.03 to 0.07 times the diameter. It is characterized by being.

  Further, according to the present invention, the groove shape on the margin portion side is a second groove bottom curve 19 from the contact point between the groove bottom 13 and the core thickness circle 14 to the outer peripheral edge 18 of the inner wall surface on the margin portion side as shown in FIG. Is provided. In the present invention, as shown in FIG. 5, the second groove bottom curve 19 is measured when measured in a direction perpendicular to the groove straight line 10 on the margin portion side connecting the outer peripheral end 18 of the inner wall surface on the margin portion side from the drill axis O. The most recessed position is the maximum recess position 23 of the second groove bottom curve, and the position where the maximum recess position 23 of the second groove bottom curve is located is from the drill axis to the outer peripheral edge 18 of the inner wall surface on the margin section side. The distance 24 between the maximum recess position of the second groove bottom curve and the axis O of the drill when measured along the groove straight line 10 is 1.5 to 2.5 times the core thickness. Further, the second groove bottom curve 19 is a concave curve, and the maximum depression amount 25 of the second groove bottom curve from the groove straight line 10 on the margin side is a range of more than 0 times and less than 0.04 times the diameter. It is characterized by being smaller than the maximum depression amount 21 of the first groove bottom curve.

When the maximum recess position 20 of the first groove bottom curve is at a position where the distance 22 between the maximum recess position of the first groove bottom curve and the drill axis O is less than 0.35 times the diameter, the point touching the core thickness Since the chips are bent sharply at the portion from the first groove bottom curve to the recess of the first groove bottom, the chips are not curled smoothly and chip clogging is likely to occur.
When the maximum dent position 20 is at a position where the distance 22 between the maximum dent position of the first groove bottom curve and the drill axis O exceeds 0.70 times the diameter, the curl of the swarf increases, so that the swarf is increased. Comes into contact with the inner wall surface of the machined hole and the machined surface roughness deteriorates. In addition, since the cutting effect of the chips is reduced, the chips connected in multiple layers in a spiral form are not easily discharged out of the groove, and are easily broken due to chip clogging.

  The maximum recess 21 of the first groove bottom curve is in the range of 0.03 to 0.07 times the drill diameter. If the maximum recess 21 of the first groove bottom curve is less than 0.03 times the drill diameter, the chips cannot be curled sufficiently, resulting in poor chip evacuation and the maximum recess 21 of the first groove bottom curve of 0. If it exceeds .07 times, the chips are strongly curled, resulting in multiple chips connected in a spiral, resulting in poor chip evacuation, and the heel of the drill becomes too sharp. There is a greater risk of chipping in the part.

  If the maximum depression position 23 of the second groove bottom curve is less than 1.5 times the core thickness, the chips curl abruptly at the groove bottom portion in contact with the core thickness, so that the chips are not curled smoothly and become clogged. When it exceeds 2.5 times, the chips are smoothly curled, but the cutting effect of the chips is reduced, and the chips are connected in multiple layers in a spiral shape, resulting in poor chip discharge.

Furthermore, in the present invention, when the maximum groove amount 25 of the second groove bottom curve is 0 or less, the angle formed by the outer peripheral portion of the drill and the second groove curve becomes an obtuse angle. The position accuracy deteriorates. Here, the case where the maximum dent amount 25 of the second groove bottom curve is a negative value means that the second groove bottom curve 19 has a convex curve shape.
When the maximum dent amount 25 of the second groove bottom curve is 0.04 times or more of the drill diameter, the chips are smoothly curled, but the angle formed by the outer periphery and the second groove bottom curve becomes an acute angle, so there is a crack due to insufficient strength. Arise. In the drill of the present invention, the maximum depression amount 25 of the second groove bottom curve is made smaller than the maximum depression amount 21 of the first groove bottom curve. When the maximum depression amount 25 of the second groove bottom curve is the same as the maximum depression amount 21 of the first groove bottom curve or the maximum depression amount 25 of the second groove bottom curve is larger than the maximum depression amount 21 of the first groove bottom curve, Since the chips of the chips are strongly curled at the curved portion of the second groove surface, the curling effect at the curved portion of the first groove is reduced, so that the chip cutting effect is reduced, and the chips are connected in a spiral manner. This is because the chip dischargeability becomes worse.

  Usually, in order to divide the chips, when the chips curled by the shape of the twisted groove of the drill cannot be curled as the cutting progresses, the bottom of the groove forming the drill core thickness is divided as a shearing origin. However, as the curl of the chips is closer to a beautiful circle, the generated chips are connected in a spiral manner, so that the cutting effect of the chips is reduced.

  The feature of the groove bottom curve of the present invention is that the groove width seems to be unexpectedly narrow, but the second groove bottom curve on the margin side and the first groove bottom curve on the heel side are recessed in a concave shape by a specific width. Therefore, the combination of the groove width and the groove bottom curve ensures a chip pocket large enough for the chips to move. Chips gently curled by the concave curved second groove curve are strongly curled by the concave curved first groove bottom curved portion. As a result, the chip is not a beautiful circle but a triangular shape close to a circle, so that the curling of the chip can be forcibly terminated when the chip curls once. As a result, small curled and finely divided chips are smoothly discharged to the outside without giving vibration to the drill and damaging the work surface. That is, the feature of the groove bottom curve of the present invention is to ensure good positional accuracy that the center position targeted by drilling using the drill of the present invention does not shift and to have a good surface roughness of the drilled hole. It greatly contributes to securing of this.

The position accuracy of the drilled hole depends on the shape of the chips. Relatively long and continuous chips may become violent in the groove of the drill, become bitten or entangled, and cause vibration of the drill. The shape of the chips generated and discharged by the drill of the present invention is divided into small parts so as not to affect the accuracy of the hole. The shape of the chips with the drill of the present invention confirmed in the following examples is shown in FIGS. 6 and 7 in comparison with the chips with a conventional counterbore end mill.
FIG. 6 is a diagram showing a typical chip shape in the drill of the present invention. FIG. 7 is a view showing a typical chip shape in a conventional counterbore end mill. 6 and 7, (a) is a top view and (b) is a side view. As shown in FIG. 7, the chips 30 in the conventional counterbore end mill have a continuous shape, whereas the chips 29 of the drill of the present invention are divided into small pieces as shown in FIG. I understand. The present invention is largely characterized by the optimum combination of the shapes of the groove bottom curves of the drill where the chips from the drilling process are curled and divided into small pieces as described above. This is the first drill that can drill holes on curved surfaces and curved surfaces, and counterbore holes.

  FIG. 8 is an enlarged view of the vicinity of the cutting edge of the drill of the present invention shown in FIG. 3 rotated 90 degrees. The drill body 5 is provided with a thinning surface 27, and an angle formed by the cutting edge 6 and the thinning surface 27 becomes a thinning clearance angle 28. In the present invention, it is desirable that the thinning clearance angle 28 is 35 ° to 50 °. Thereby, the curled chips can be discharged more efficiently.

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

  In each example in the following table, the present invention example, the conventional example, and the comparative example are shown as classifications, and the sample numbers are indicated by consecutive serial numbers for each of the present invention example, the conventional example, and the comparative example.

The present invention is a cemented carbide drill having two cutting edges. As a result of experiments, a new shape of the groove bottom curve is required for the significant improvement in the hole position accuracy and the hole entrance diameter of the present invention. However, in addition to the groove bottom curve, the drill tip angle, the drill core thickness, and the groove width can be used as the basic shape of the drill to maximize its effectiveness. Optimization is essential as a component of the present invention.
Therefore, in the following examples, the tip angle of the drill, the drill core thickness, based on a unified specification in which a hard coating containing Si in a (TiAl) N system as a surface treatment is applied to a cemented carbide drill, Examples of carrying out the present invention to investigate the influence of the groove width and groove shape and comparative examples compared with those other than the conditions of the present invention are shown below.

Example 1
The tip angles were compared by cutting tests using Invention Examples 1 to 5 and Comparative Examples 1 and 2. In Inventive Examples 1 to 5, the tip angles were 170 °, 175 °, 180 °, 185 °, and 190 °, respectively. The tip angles of Comparative Examples 1 and 2 were 165 ° and 195 °, respectively.
All the seven types of drills used in Example 1 are made of cemented carbide, the number of blades is two, the diameter is 6 mm, the groove length is 19 mm, the shank diameter is 6 mm, the helix angle is 30 °, the core thickness Is 0.20 times the diameter and the groove width is 80 °. Further, the shape of the first groove bottom curve is a concave curve, the distance between the maximum recess position of the first groove bottom curve and the drill axis O is 0.50 times the diameter, and the maximum recess amount of the first groove bottom curve is the diameter. 0.05 times, the shape of the second groove bottom curve is a concave curve, the distance between the maximum recess position of the second groove bottom curve and the drill axis O is 2.0 times the core thickness, the maximum of the second groove bottom curve The amount of dents was 0.02 times the diameter, and these specifications were unified in Invention Examples 1 to 5 and Comparative Examples 1 and 2.

FIG. 11 is a diagram showing the measurement direction of the deviation of the work material and the hole center used in the example. The work material is S50C. As shown in FIG. 11, a rectangular parallelepiped having a width of 120 mm, a depth of 100 mm, and a height of 80 mm is cut, and a shape having a slope with a gradient of 30 ° in the height direction is used for the cutting test. Using.
12 is a cross-sectional view of the work material shown in FIG. 11 when viewed from the arrow A. As a test method, the cutting speed is 75 m / min, the blade feed is 0.09 mm / rev, the tool protrusion amount is 36 mm, and the machining hole depth is a position where the inclined surface and the cutting edge of the drill come into contact as shown in FIG. As a reference, under the cutting conditions of 18 mm in the height direction, 10 holes were cut at a hole interval of 10 mm by dry cutting without using any coolant.

After the cutting test, the position accuracy and the enlarged diameter of the processed hole were measured. As a measuring method of the positional accuracy, a positional deviation (hereinafter also referred to as “deviation”) from the theoretical position at the center of each of the 10 holes was measured using an optical microscope. First, the average value of the deviations in the width direction at the center of the 10 holes was set as the deviation in the X direction, and the workpiece having a gradient was placed on the upper side as shown in FIG. In this case, the upward direction was defined as + and the downward direction was defined as-. Furthermore, when the average value of the deviations in the depth direction at the center of the 10 holes is defined as the deviation in the Y direction, and the workpiece with a gradient is placed on the higher side, the right direction is-, the left direction Was defined as +.
As a method of measuring the enlarged diameter of the processed hole, the diameter of the processed hole on the upper surface side of the work material is measured using an optical microscope, the diameter of the processed hole on the upper surface side of the work material, the tool diameter of the drill used, and The enlarged diameter of the processed hole was determined from the difference between the two.
As evaluation criteria, both the deviation in the X direction and the deviation in the Y direction are in the range of +0.1 mm to −0.1 mm, and the enlarged diameter of the processed hole is 5 μm or less. Table 1 shows the results of the cutting test.

  As shown in Table 1, in Examples 1 to 5 of the present invention, both the deviation in the X direction and the deviation in the Y direction are in the range of +0.1 mm to −0.1 mm, and the enlarged diameter of the processed hole is within 5 μm. Therefore, the result was good. On the other hand, in Comparative Example 1, the tip angle is small, the corner angle is obtuse, and the work material is less likely to bite, so the X-direction deviation is 0.4 mm and the Y-direction deviation is 0.18 mm. The enlarged diameter of the hole was 5.9 μm. Further, in Comparative Example 2, the tip angle is large and the corner portion is too sharp, the strength is reduced, and chipping occurs at the blade edge at the first hole. Therefore, the deviation in the X direction is 0.55 mm, and the deviation in the Y direction is The diameter of the processed hole was 5.1 μm.

(Example 2)
Examples 6 to 8 of the present invention are examples in which core thicknesses were compared by a cutting test in comparison with Comparative Examples 3 and 4. The core thicknesses were 0.15 times, 0.20 times, and 0.25 times the diameter D in Examples 6 to 8 of the present invention, respectively. In Comparative Examples 3 and 4, the diameter D was 0.10 and 0.30 times, respectively. In addition, the specifications were unified with the same specifications as Example 3 except for the thickness.

The work material and the test method were the same as in Example 1. In the cutting test, the number of holes processed and the position accuracy were measured. The evaluation method of the number of processed holes was evaluated by measuring the number of holes that could be processed in a cutting test in which up to 10 holes were cut. As a measuring method of the positional accuracy, a positional deviation (hereinafter also referred to as “deviation”) from the theoretical position at the center of each of the 10 holes was measured using an optical microscope. The measurement item is that the average value of the deviation in the width direction at the center of the 10 holes is defined as the deviation in the X direction. The downward direction is-. Furthermore, when the average value of the deviations in the depth direction at the center of the 10 holes is defined as the deviation in the Y direction, and the workpiece with a gradient is placed on the higher side, the right direction is-, the left direction Was defined as +.
As the evaluation criteria, the number of holes to be processed was 10 holes, and both the deviation in the X direction and the deviation in the Y direction were in the range of +0.1 mm to -0.1 mm. Table 2 shows the cutting test results.

  As can be seen from Table 2, Examples 6 to 8 of the present invention have 10 processed holes, and both the X-direction deviation and the Y-direction deviation are both in the range of +0.1 mm to -0.1 mm. It was a result. On the other hand, since the comparative example 3 had a small core thickness and low rigidity, it was broken by vibration during the processing of the second hole. Therefore, the deviation in the X direction and the deviation in the Y direction were not measurable. Moreover, although the comparative example 4 had a high core thickness and high rigidity, the chip dischargeability deteriorated, and breakage occurred at the sixth hole due to chip clogging. Therefore, the deviation in the X direction and the deviation in the Y direction were not measurable.

(Example 3)
The groove width was compared by a cutting test using Invention Examples 9 to 11 and Comparative Examples 5 and 6. The groove width was 75 °, 80 °, and 85 ° in Examples 9 to 11 of the present invention, respectively. In Comparative Examples 5 and 6, the drill diameter was set to 70 ° and 90 °, respectively. In addition, the specifications were unified with the same specifications as Example 3 except for the groove width.

The work material and the test method were the same as in Example 1. In the cutting test, the number of processed holes and the processed surface roughness of the work material were measured. The evaluation method of the number of processed holes was evaluated by measuring the number of holes that could be processed in a cutting test in which up to 10 holes were cut. The processed surface roughness of the work material is measured by measuring the surface roughness of the inner wall surface of the hole processed using a surface roughness measuring instrument (manufactured by Tokyo Seimitsu Co., Ltd., SURFCOM 1500DX) from the back of the hole toward the entrance. Evaluation was performed.
As evaluation criteria, the number of processed holes was 10 and the processed surface roughness of the work material was 10 μm or less. Table 3 shows the results of the cutting test.

  As can be seen from Table 3, since the inventive examples 9 to 11 were finely divided, the number of processed holes was 10 and the processed surface roughness of the work material was 10 μm or less, which was a good result. . On the other hand, Comparative Example 5 was broken at the third hole due to chip clogging because the chip pocket was narrow. Moreover, the trace which the chip | wound was damaged by the chip | tip clogging remained on the inner wall face of the processing hole, and the processing surface roughness of the work material was 16.1 micrometers. In Comparative Example 6, the number of processed holes was 10, but the processed surface roughness of the work material was 12.2 μm due to the effect that the chips were not cut and the connected chips remained in the groove. Met.

Example 4
By the cutting test using Examples 12 to 19 of the present invention, Comparative Examples 7 and 8, and Conventional Example 1, the shape of the first groove bottom curve from the groove bottom to the heel, and the maximum depression position of the first groove bottom curve A comparison was made of the spacing of the drill axis O.
In Examples 1 to 5, the shape of the first groove bottom curve is a concave curve, and the distance between the maximum depression position of the first groove bottom curve and the drill axis O is a linear distance from the drill axis to the heel direction, respectively. The positions were 0.35 times, 0.40 times, 0.45 times, 0.50 times, 0.55 times, 0.60 times, 0.65 times, and 0.70 times the diameter D.
In Comparative Examples 7 and 8, the shape of the first groove bottom curve is a concave curve, and the distance between the maximum recess position of the first groove bottom curve and the drill axis O is a linear distance from the drill axis to the heel direction, with a linear distance. It was set as the position which becomes 0.30 times and 0.75 times.
In Conventional Example 1, the shape of the first groove bottom curve is a convex curve, and the distance between the maximum recess position of the first groove bottom curve and the drill axis O is 0 in diameter at a linear distance from the drill axis to the heel direction. It was set as the position which becomes .55 times.
Further, in the inventive examples 12 to 19, comparative examples 7 and 8, and the conventional example 1, the example 3 of the invention except for the shape of the first groove bottom curve and the interval between the maximum groove position of the first groove bottom curve and the axis O of the drill. The specifications were unified with the same specifications.

The work material and the test method were the same as in Example 1. In the cutting test, the position accuracy and the machined surface roughness of the work material were measured. As a measuring method of the positional accuracy, a positional deviation (hereinafter also referred to as “deviation”) from the theoretical position at the center of each of the 10 holes was measured using an optical microscope. The measurement item is that the average value of the deviation in the width direction at the center of the 10 holes is defined as the deviation in the X direction. The downward direction is-. Furthermore, when the average value of the deviations in the depth direction at the center of the 10 holes is defined as the deviation in the Y direction, and the workpiece with a gradient is placed on the higher side, the right direction is-, the left direction Was defined as +. The processed surface roughness of the work material is measured by measuring the surface roughness of the inner wall surface of the hole processed using a surface roughness measuring instrument (manufactured by Tokyo Seimitsu Co., Ltd., SURFCOM 1500DX) from the back of the hole toward the entrance. Evaluation was performed.
As evaluation criteria, both the deviation in the X direction and the deviation in the Y direction are in the range of +0.1 mm to −0.1 mm, and the processed surface roughness of the work material is 10 μm or less. Table 4 shows the results of the cutting test.

As shown in Table 4, in Examples 12 to 19 of the present invention, both the deviation in the X direction and the deviation in the Y direction are in the range of +0.1 mm to -0.1 mm, and the processed surface roughness of the work material Was in the range of 10 μm or less at the maximum height (Rz value), showing good results.
In Comparative Examples 7 and 8, the chips were not properly curled, and the tool moved greatly along the slope when in contact with the work material. As a result, in Comparative Example 7, the deviation in the X direction was −0.15 mm, the deviation in the Y direction was 0.11 mm, and in Comparative Example 8, the deviation in the X direction was −0.14 mm, and the deviation in the Y direction was 0.12 mm. . Further, in Comparative Examples 7 and 8, chips were clogged during the cutting process, so the processed surface roughness of the work material was 16.1 μm in Comparative Example 7 and 19.2 μm in Comparative Example 8.
In Conventional Example 1, since the shape of the first groove bottom curve is a convex curve, the cutting effect of the chips is small, and the curled chips are connected. Therefore, also in the cutting results, the deviation in the X direction was -0.16 mm, and the deviation in the Y direction was -0.18 mm. Further, since the connected chips rubbed the processed surface, the processed surface roughness of the work material was 21.6 μm.

  (Example 5)

  By the cutting test using Invention Examples 20 to 24, Comparative Examples 9, 10 and Conventional Example 2, the maximum dent amount of the first groove bottom curve from the groove bottom to the heel was compared.

In Examples 20 to 24 of the present invention, the shape of the first groove bottom curve is a concave curve, and the maximum dent amount of the first groove bottom curve is 0.03 times, 0.04 times, 0.05 times, 0. They were 06 times and 0.07 times.
In Comparative Examples 9 and 10, the shape of the first groove bottom curve was a concave curve, and the maximum depression amount of the first groove bottom curve was 0.02 times and 0.08 times the diameter.
Since the shape of the first groove bottom curve is a convex curve in Conventional Example 2, the maximum dent amount of the first groove bottom curve is a negative value, which is -0.05 times the diameter.
In addition, in Examples 20 to 24 of the present invention, Comparative Examples 9 and 10, and Conventional Example 2, the specifications were unified with the same specifications as Example 3 of the present invention except for the maximum depression amount of the first groove bottom curve.

  The work material, test method, evaluation method and evaluation criteria were the same as in Example 4. Table 5 shows the cutting test results.

As shown in Table 5, in Examples 20 to 24 of the present invention, both the deviation in the X direction and the deviation in the Y direction are in the range of +0.1 mm to -0.1 mm, and the processed surface roughness of the work material Was in the range of 10 μm or less, and good results were shown.
In Comparative Examples 9 and 10, the chips were not curled appropriately, and the tool moved greatly along the slope when in contact with the work material. As a result, in Comparative Example 9, the deviation in the X direction was 0.08 mm, the deviation in the Y direction was 0.11 mm, and in Comparative Example 10, the deviation in the X direction was 0.19 mm, and the deviation in the Y direction was 0.13 mm. Further, in Comparative Examples 9 and 10, chips were clogged during the cutting process, so the processed surface roughness of the work material was 13.2 μm in Comparative Example 9 and 11.5 μm in Comparative Example 10.
In Conventional Example 2, since the shape of the first groove bottom curve is a convex curve, the cutting effect of chips is small, and curled chips are connected. Therefore, also in the cutting results, the deviation in the X direction was -0.19 mm, and the deviation in the Y direction was -0.15 mm. Further, since the connected chips rubbed the processed surface, the processed surface roughness of the work material was 19.5 μm.

  (Example 6)

  By the cutting test using Invention Examples 25 to 29, Comparative Examples 11 and 12, and Conventional Example 3, the shape of the second groove bottom curve from the groove bottom to the outer corner portion and the maximum depression of the second groove bottom curve. The position and the distance between the drill axis O were compared.

In the inventive examples 25 to 29, the shape of the second groove bottom curve is a concave curve, and the interval between the maximum recess position of the second groove bottom curve and the drill axis O is 1.5 times the core thickness d, 1.75. The positions were doubled, 2.0 times, 2.25 times, and 2.5 times.
In Comparative Examples 11 and 12, the shape of the second groove bottom curve is a concave curve, and the distance between the maximum recess position of the second groove bottom curve and the drill axis O is 1.25 times and 2.75 times the core thickness d. It was set as the position.
In Conventional Example 3, the shape of the second groove bottom curve is a convex curve, and the distance between the maximum recess position of the second groove bottom curve and the drill axis O is 1.75 times the core thickness d.
Further, in Examples 25 to 29 of the present invention, Comparative Examples 11 and 12, and Conventional Example 3, the shape of the second groove bottom curve, the maximum groove position of the second groove bottom curve, and the distance between the drill axis O, Example 3 of the present invention. The specifications were unified with the same specifications.

  The work material, test method, evaluation method and evaluation criteria were the same as in Example 4. The cutting test results are shown in Table 6.

As shown in Table 6, in inventive examples 25 to 29, both the deviation in the X direction and the deviation in the Y direction are in the range of +0.1 mm to -0.1 mm, and the processed surface roughness of the work material Was in the range of 10 μm or less, and good results were shown.
In Comparative Examples 11 and 12, the chips were not properly curled, and the tool moved greatly along the slope when in contact with the work material. As a result, in Comparative Example 11, the deviation in the X direction was 0.11 mm and the deviation in the Y direction was 0.13 mm. In Comparative Example 12, the deviation in the X direction was 0.15 mm, and the deviation in the Y direction was 0.16 mm. Further, in Comparative Examples 11 and 12, since the chips were clogged during the cutting process, the processed surface roughness of the work material was 15.9 μm in Comparative Example 11 and 13.3 μm in Comparative Example 12.
In Conventional Example 3, the shape of the second groove bottom curve is a convex curve, so that the cutting effect of the chips is small and curled chips are connected. Therefore, also in the cutting results, the deviation in the X direction was -0.25 mm, and the deviation in the Y direction was -0.22 mm. Furthermore, since the connected chips rubbed the processed surface, the processed surface roughness of the work material was 25.5 μm.

(Example 7)
By the cutting test using Invention Examples 30 to 39, Comparative Examples 13 to 16 and Conventional Example 4, the maximum dent amount of the second groove bottom curve from the groove bottom to the outer peripheral corner portion was compared.

In the inventive examples 30 to 36, the shape of the second groove bottom curve is a concave curve, the maximum depression amount of the first groove bottom curve is 0.05 times the diameter D, and the maximum depression amount of the second groove bottom curve is the diameter. 0.005 times, 0.010 times, 0.015 times, 0.020 times, 0.025 times, 0.030 times, and 0.035 times D were set.
In Examples 37 to 39 of the present invention, the shape of the second groove bottom curve is a concave curve, the maximum depression amount of the first groove bottom curve is 0.03 times the diameter D, and the maximum depression amount of the second groove bottom curve is the diameter. 0.005 times, 0.015 times, 0.025 times, and 0.030 times D.
In Comparative Examples 13 and 14, the shape of the second groove bottom curve is a concave curve, the maximum depression amount of the first groove bottom curve is 0.05 times the diameter D, and the maximum depression amount of the second groove bottom curve is the diameter D, respectively. 0 times and 0.040 times.
In Comparative Examples 15 and 16, the shape of the second groove bottom curve is a concave curve, the maximum depression amount of the first groove bottom curve is 0.03 times the diameter D, and the maximum depression amount of the second groove bottom curve is the diameter D, respectively. 0 times and 0.030 times.
In Conventional Example 2, the maximum dent amount of the first groove bottom curve is 0.05 times the diameter D, and the shape of the second groove bottom curve is a convex curve. Therefore, the maximum dent amount of the second groove bottom curve is negative. The value was -0.05 times the diameter D.
In Examples 30 to 39 of the present invention, Comparative Examples 13 to 16 and Conventional Example 4, except for the maximum dent amount of the first groove bottom curve and the maximum dent amount of the second groove bottom curve, the specifications are the same as those of Example 3 of the present invention. Was unified.

  The work material, test method, evaluation method and evaluation criteria were the same as in Example 4. Table 7 shows the cutting test results.

As shown in Table 7, in inventive examples 30 to 39, both the deviation in the X direction and the deviation in the Y direction are in the range of +0.1 mm to -0.1 mm, and the processed surface roughness of the work material Was in the range of 10 μm or less, and good results were shown.
In Comparative Examples 13 to 15, the chips were not properly curled, and the tool moved greatly along the slope when in contact with the work material. As a result, the deviation in the X direction and the deviation in the Y direction both exceeded the range of +0.1 mm to −0.1 mm, and the work surface roughness of the work material exceeded 10 μm.
In Comparative Example 16 in which the maximum depression amount of the second groove bottom curve is the same value as the maximum depression amount of the first groove bottom curve, the deviation in the X direction and the deviation in the Y direction are in the range of +0.1 mm to -0.1 mm. there were. However, since the curl effect at the first groove bottom curve is small and the chip dischargeability is poor, the work surface roughness of the work material is 10.8 μm, which is poor.
In Conventional Example 4, since the shape of the second groove bottom curve is a convex curve, the cutting effect of the chips is small, and the curled chips are connected. Therefore, also in the cutting results, the deviation in the X direction was 0.19 mm and the deviation in the Y direction was -0.17 mm. Furthermore, since the connected chips rubbed the processed surface, the processed surface roughness of the work material was 20.2 μm.

(Example 8)
Comparison of thinning clearance angles by cutting tests using Examples 40 to 45 of the present invention was performed.
The thinning relief angles were 30 °, 35 °, 40 °, 45 °, 50 °, and 55 ° in the inventive examples 40 to 45, respectively.
In Inventive Examples 40 to 45, the specifications were unified with the same specifications as in Inventive Example 3 except for the clearance angle of the thinning.

The work material and the test method were the same as in Example 4. In the cutting test, the surface roughness of the work material was measured. The processed surface roughness of the work material is measured by measuring the surface roughness of the inner wall surface of the hole processed using a surface roughness measuring instrument (manufactured by Tokyo Seimitsu Co., Ltd., SURFCOM 1500DX) from the back of the hole toward the entrance. Evaluation was performed.
As an evaluation standard, a material having a work surface roughness of 10 μm or less was considered good. Table 8 shows the cutting test results.

  As can be seen from Table 8, Examples 40 to 45 of the present invention had good results because the machined surface roughness of the work material was in the range of 10 μm or less. In Invention Examples 41 to 44, the chips were smoothly curled from the beginning of cutting and the chips were finely divided, and the work surface roughness of the work material was in the range of 8 μm or less, and the results were particularly good.

  According to the present invention, for example, a crank portion formed of a curved surface of a crankshaft, and a required oil hole can be drilled in the shaft portion freely in an oblique direction and a vertical direction. In addition, holes and holes can be formed in molds and parts having inclined surfaces and curved surfaces without the need for conventional seating by an end mill.

DESCRIPTION OF SYMBOLS 1 Conventional end mill 2 Machining surface formed by conventional end mill 3 Conventional drill 4 Direction in which conventional drill is displaced 5 Drill body 6 Cutting edge 7 Chip discharge groove 8 Inner wall surface on margin side 9 Tip clearance surface 10 Margin Groove straight line on the heel side 11 Inner wall surface on the heel side 12 Groove straight line on the heel side 13 Groove bottom 14 Heart thickness circle 15 Heel 16 First groove bottom curve 17 Straight line 18 Outer peripheral edge of the inner wall surface on the margin side 19 Second Groove bottom curve 20 Maximum depression position of the first groove bottom curve 21 Maximum depression amount of the first groove bottom curve 22 Distance between the maximum depression position of the first groove bottom curve and the drill axis O 23 Maximum depression position of the second groove bottom curve 24 Distance between maximum recess position of second groove bottom curve and drill axis O 25 Maximum recess amount of second groove bottom curve 26 Tip angle 27 Thinning surface 28 Thinning clearance angle 29 With the drill of the present invention Rikuzu 30 chips W axis θ groove width D of the workpiece O Drill diameter L drill rotation direction d web thickness a groove surface of the conventional end mill

Claims (4)

  A drill having two cutting edges, wherein the drill has a tip angle of 170 ° to 190 °, a core thickness of 0.15 to 0.25 times the drill diameter, and the drill is inserted into the drill tip. In the figure seen from the axial direction of the drill, the groove straight line on the margin side connecting the drill axis O and the outer peripheral edge of the inner wall surface on the margin side, and the inner wall surface on the heel side of the drill axis O The groove width is in a range of 75 ° to 85 ° when an angle formed by a groove straight line on the heel side connecting the outer peripheral end, that is, the heel, is in a range of 75 ° to 85 °, and extends from the groove bottom and the groove bottom to the heel. The first groove bottom curve is a concave curve, and the distance between the maximum groove position of the first groove bottom curve where the first groove bottom curve is most recessed with respect to the straight line connecting the heel from the drill axis O and the axis O of the drill is The straight line distance from the axis of the heel to the heel direction is 0.35 times the diameter to 0. The maximum depression amount of the first groove bottom curve is in the range of 0.03 to 0.07 times the diameter, and the second groove from the outer peripheral edge of the inner wall surface on the margin side to the groove bottom. The groove bottom curve is a concave curve, and the distance between the maximum groove position of the second groove bottom curve where the second groove bottom curve is most recessed with respect to the groove straight line on the margin side and the axis O of the drill is a margin portion from the drill axis. In the direction of the inner wall surface on the side, the center thickness is 1.5 to 2.5 times the core thickness, and the maximum recess amount of the second groove bottom curve is more than 0 times less than the drill diameter and less than 0.04 times. The drill is characterized in that the maximum depression amount of the second groove bottom curve is set smaller than the maximum depression amount of the first groove bottom curve.   The drill according to claim 1, wherein a thinning relief angle is in a range of 35 ° to 50 °.   A guide hole machining method comprising machining a slope or a curved surface inclined with respect to the axis of the drill, using the counterbored drill according to claim 1.   A counterbore processing method, wherein the counterbore process is performed on a surface or a curved surface inclined with respect to the axis of the drill using the counterbore drill according to claim 1.

Images