JP5402561B2 - Counterbore drill - Google Patents

Description

  The present invention relates to a counterbored drill used for counterboring in which a stepped counterbored hole on which a bolt head is seated is formed in an opening of the bolt hole.

  As a drill used for such counterbore processing, for example, Patent Document 1 discloses that two secondary cutting edges that are paired and extend outward from the chisel by thinning with a tip angle of 170 ° to 190 °, each secondary. There have been proposed ones having a concave primary cutting edge extending outward from the cutting edge, and an outer cutting edge extending from each primary cutting edge to the leading edge and retreating in the drill rotation direction.

  Further, for example, as described in Patent Document 2, the cutting edge at the tip is formed such that the outer peripheral side region is substantially perpendicular to the axis, and the inner peripheral side region inside the outer peripheral side region is closer to the axis. A so-called candle-type drill that protrudes, or a drill that retreats with a radius R on the outer periphery as described in Patent Document 3, and has a through hole in the work material, such as a drill that protrudes in a straight line. Drills intended to prevent burrs and burrs when forming are also sometimes used for such spot facing.

JP 2009-56534 A JP 2004-188509 A JP-A-8-300209

  However, first, as described in Patent Document 2, when the inner peripheral region of the cutting blade protrudes as it approaches the axis, the outer peripheral region that should be perpendicular to the axis is slightly increased as it approaches the axis due to manufacturing errors or the like. However, if it is tilted so that it protrudes, the bottom surface of the counterbore hole will be recessed toward the bolt hole as a whole, and the head of the bolt will be in contact with the bottom surface of the counterbore hole only at its outermost periphery. The fastening force may be lost. In particular, when the bolt head has a hexagonal hexagonal bolt, only the hexagonal corner may come into contact with the counterbore hole bottom, and the fastening force is further lost.

  On the other hand, in the drill described in Patent Document 3, there is a possibility that the head of the bolt may come into contact only with the opening edge of the bolt hole on the inner periphery side of the counterbore hole, and the contact area is reduced and the fastening force is also reduced. May be damaged. Further, the drill described in Patent Document 3 has a problem in that the cutting performance is poor because the cutting edge is linear except for the portion retreating at the radius R.

  This problem of poor machinability is also the same in the drill described in Patent Document 1 because the tip angle is as large as 170 ° to 190 °, and is particularly noticeable in the secondary cutting edge at the center extending from the chisel by thinning. It becomes. Moreover, when the tip angle is large in this way, the secondary cutting edge may be formed to be recessed as it goes to the center side due to thinning, and the center part of the counterbore hole bottom surface is convex, If you try to form a bolt hole after forming a counterbore, the tip of the drill for forming the bolt hole rides on the center of the bottom of the counterbore hole that is convex, causing the drill to bend and bend, and the bolt hole is highly accurate. May not be able to be drilled, and in some cases, the drill for forming the bolt hole may be broken.

  Furthermore, in the counterbore drill described in Patent Document 1, the outer cutting edge extending to the leading edge is formed so as to recede when viewed in the direction of drill rotation. When the bolt head comes into contact with the outer periphery, the head comes into contact with the counterbore only at the outermost periphery, and the fastening force is lost. Furthermore, when the tip angle is large as described above, there is a problem that the force for bending the chips generated during cutting in the axial direction is weakened, and the chip breaking property is also impaired.

  The present invention was made under such a background, and while ensuring the fastening force by the bolt by increasing the contact area with the bolt head, it is possible to improve the machinability and chip breaking properties, Furthermore, a counterbored drill capable of forming a counterbore that can form a bolthole with high accuracy without causing breakage in the bolthole drill even after the counterbore is formed is provided. The purpose is to do.

  In order to solve the above-described problems and achieve such an object, the present invention is directed toward the rear end side in the axial direction toward the rear end side in the drill rotation direction toward the distal end portion of the drill body rotated around the axis line. A tip flank with a clearance angle is formed on the outer peripheral side of the drill body as viewed from the front side of the drill rotation direction. A first concave curved cutting blade extending toward the axial rear end side after being bent toward the inner peripheral side from the outer peripheral end of the cutting blade in order from the first, The second concave curved cutting edge that extends to the tip end side in the axial direction while being further concavely curved toward the inner peripheral side, and an obtuse angle to the second concave curved cutting edge The above axial direction as it crosses so as to be bent and goes toward the inner circumference A center cutting edge that extends linearly toward the tip side beyond the outer peripheral edge of the cutting edge, and the first and second concave curved cutting edges have a concave curve shape in the axial front end view, A radius of curvature of the first concave curved cutting edge in the axial front end view is larger than a curvature radius of the second concave curved cutting edge.

  In the counterbore drill with such a configuration, the first concave curved cutting edge first extends toward the rear end side in the axial direction while bending toward the inner peripheral side from the outer peripheral end of the cutting edge, and then the front end side. Since both the second concave curved cutting edge and the central cutting edge on the inner peripheral side than the first concave curved cutting edge extend toward the distal end side in the axial direction toward the inner peripheral side, The cutting edge reaches the position most retracted in the axial direction in the first concave curved cutting edge. Here, the first concave curved cutting edge has a radius of curvature larger than that of the second concave curved cutting edge in the axial front end view, and the drill rotates on the tip flank where the cutting edge is formed. Since the clearance angle is given so as to go to the rear end side in the axial direction as it goes to the rear side in the direction, the radius of curvature of the concave curve formed by the first concave curved cutting blade as viewed from the front side in the drill rotation direction is also It becomes larger than the second concave curved cutting edge.

  For this reason, the outer peripheral portion of the bottom surface of the counterbore formed by such a cutting blade is convex so as to form a convex curve with a larger curvature radius toward the inner peripheral side in the cross section along the center line. However, since the bolt head is formed so as to recede through the protruding end portion, the bolt head has a large curvature radius by forming a bolt hole on the inner peripheral side of the protruding end portion. It is made to contact | abut to the near flat protrusion part of the bottom surface outer peripheral side part which makes a cross-sectional convex curve shape, and can ensure large contact area with the counterbore hole bottom face. According to the concave curved cutting blade as described above, even if a slight inclination occurs due to a manufacturing error or the like, the cross section of the bottom surface of the counterbore hole is only slightly shifted from the position of the projecting end portion as described above. Therefore, it is possible to ensure a contact area and improve the fastening force.

  On the other hand, if the first concave curved cutting edge whose radius of curvature is increased in this way occupies the entire cutting edge, the machinability is reduced as in the drill described in Patent Document 1. However, in the counterbore drill according to the present invention, the axis of the second concave curved cutting edge having a small curvature radius toward the inner peripheral side toward the inner peripheral side of the first concave curved cutting edge. A central cutting edge that intersects with the second concave curved cutting edge and forms an obtuse angle with the second concave curved cutting edge is formed on the inner peripheral side. It is formed so as to extend linearly toward the front end side in the axial direction as it goes, that is, it is formed in a convex shape with the central portion on the inner peripheral side protruding from the first concave curved cutting edge toward the front end side.

  For this reason, it is possible to ensure good machinability particularly in the central portion, and since the central portion is convex, the center portion of the bottom surface of the counterbore hole does not become convex even if thinning is performed. It is possible to prevent the bolt hole forming drill from being bent, bent, broken or the like when forming the bolt hole after forming the bore hole, and to make the bolt hole with high accuracy. Further, since the second concave curved cutting edge does not contact the linear central cutting edge so as to be bent at an obtuse angle, the central cutting edge and the second concave curved shape are intersected. Stress can be applied to the chips generated across the cutting edge, and the chips can be easily bent in the axial direction to improve chip separation.

  Here, the curvature radius R1 of the concave curve formed by the first concave curved cutting edge as viewed from the front in the axial direction is in a range of 0.8 × D to 2.0 × D with respect to the outer diameter D of the cutting blade. If it is larger than this, the cutting edge may become nearly linear and the machinability may be impaired, or it may not be possible to secure the contact area when tilting due to manufacturing errors occurs. Even if it is smaller, the curvature radius of the convex curve formed by the cross-section of the bottom face of the counterbore hole is also reduced, so that there is a possibility that the bolt head is close to the line and stable fastening is prevented. Moreover, it is desirable that the radius of curvature R2 of the concave curve formed by the second concave curved cutting edge as viewed from the front in the axial direction is in the range of 0.2 × D to 0.5 × D, and if smaller than this, On the other hand, there is a possibility that a sufficient cutting edge length cannot be ensured, while on the other hand, if it is large, there is a possibility that good cutting properties cannot be obtained.

  On the other hand, the crossing angle in the projection view on the plane including the axis of the rotation trajectory of the cutting edge around the axis of the second concave curved cutting edge and the center cutting edge intersecting so as to bend and bend at an obtuse angle However, if this is too large, there is a risk that sufficient stress will not be applied to the chip and it will not be possible to improve the chip breaking property. Conversely, if it is too small, the tilt angle with respect to the axis of the center cutting edge will be too small. It is desirable that the angle is in the range of 140 ° to 160 °. The intersection of the second concave curved cutting edge and the central cutting edge so as to bend and bend at an obtuse angle is the outer peripheral edge of the cutting edge (the outer peripheral edge of the first concave curved cutting edge). It may be on the front end side in the axial direction or on the rear end side, but within the range of 0.002 × D with respect to the outer diameter D of the cutting edge in the axial direction from the outer peripheral end of the cutting edge. It is desirable that they are in substantially equal positions, so that the intersection is larger than the outer peripheral end on the front end side in the axial direction, or conversely on the rear end side in the axial direction. If the position in the direction is shifted, it may be difficult to form the cutting edge so as to be the most retracted position in the axial direction on the first concave curved cutting edge having a large radius of curvature.

  Further, when the center cutting edge is formed by thinning the tip flank of the drill body, the center cutting edge has an obtuse angle with respect to the second concave curved cutting edge in the axial front end view. However, the crossing angle between the second concave curved cutting edge and the central cutting edge in the axial front end view is too small. If the intersection angle is too large, the force for bending the chips may be insufficient. Therefore, the intersection angle is preferably in the range of 130 ° to 150 °. . The crossing angle between the second concave curved cutting edge and the central cutting edge when viewed from the direction of drill rotation and when viewed from the front in the axial direction is the second angle at the intersection of each other when viewed from the respective directions. This is the intersection angle between the tangent line of the concave curved cutting edge and the straight central cutting edge.

  Furthermore, the inner diameter of the bolt hole drilled on the bottom face of the counterbore hole is about 0.3 to 0.6 times the inner diameter of the counterbore hole, that is, the outer diameter D of the cutting blade, depending on the type of bolt. , The radial range from the axis of the drill body to the portion where the second concave curved cutting edge having a small curvature radius is formed, that is, the drill up to the position of the connecting portion of the first and second concave curved cutting blades The radius R3 from the axis of the main body is preferably in the range of 0.2 × D to 0.25 × D with respect to the outer diameter D. On the other hand, the position where the first concave curved cutting edge is most retracted toward the rear end side in the axial direction is that the protruding end portion of the bottom face of the counterbore hole is located on the outer peripheral side to some extent from the bolt hole. It is desirable that the radius R4 from the axis is in the range of 0.25 × D to 0.4 × D with respect to the outer diameter D so that the contact area is secured. Of course, R3 <R4.

  As described above, according to the present invention, a counterbore hole that can secure a large contact area with the bolt head and obtain a high fastening force while maintaining good cutting performance and chip breaking performance. It can be reliably formed. Also, when the bolt hole is drilled after the counterbore hole is formed in this way, it is possible to prevent the bolt hole forming drill from being bent, bent, broken or the like and to form a highly accurate bolt hole. Become.

It is a side view of the front-end | tip part of the drill main body which shows one Embodiment of this invention. It is an enlarged front view of the axial direction front end view of embodiment shown in FIG. FIG. 2 is an enlarged projection view onto a plane including an axis of a rotation locus around the axis of the cutting edge in the embodiment shown in FIG. 1.

  1 to 3 show an embodiment of the present invention. In the present embodiment, the drill body 1 is formed in a substantially cylindrical shape centering on the axis O by a hard material such as high-speed steel or cemented carbide, and its rear end (right side portion in FIG. 1) is cylindrical. The end portion (left side portion in FIG. 1) is the cutting blade portion 3, and the shank portion 2 is attached to the main spindle of the machine tool and rotated in the drill rotation direction T around the axis O. While being sent out to the front end side in the direction of the axis O, a counterbore with a bottom is formed in the work material by the cutting edge portion 3.

  In the cutting edge portion 3, a pair of chip discharge grooves 5 that are twisted to the rear side in the drill rotation direction T around the axis O as it goes from the front end flank 4 to the rear end side are formed symmetrically with respect to the axis O. The cutting edges 6 are also symmetrically formed with respect to the axis O at the intersecting ridge line portions of the wall surfaces of the chip discharge grooves 5 facing the drill rotation direction T and the tip flank 4. A margin 7 is formed on the outer peripheral flank of the cutting edge 3 so as to be continuous with the outer peripheral edge of the chip discharge groove 5 on the drill rotation direction T side.

  Here, the tip flank 4 is formed so as to have a predetermined flank angle toward the rear end side in the axis O direction from the cutting edge 6 toward the rear side in the drill rotation direction T. The tip edge on the side of the cutting edge 6 is formed so as to extend perpendicularly to the axis O from the outer periphery of the drill body 1 toward the inner periphery, and then toward the tip in the vicinity of the axis O toward the inner periphery. Thus, a mountain-shaped convex portion 8 is formed at the center of the tip flank 4.

  Furthermore, a concave thinning is applied to the tip flank 4 so as to reach the heel along the wall surface from the convex portion 8 toward the rear side in the drill rotation direction T of the chip discharge groove 5 to form a thinning portion 9. Therefore, the cutting edge 6 is formed at the ridge line portion on the tip side of the convex portion 8 with the wall surface facing the drill rotation direction T side of the thinning portion 9 as a rake face at the center portion of the tip flank 4. In addition, the chisel 10 is formed in the top part of the convex part 8 so that it may orthogonally cross the axis line O so that the inner peripheral end of a pair of cutting blade 6 may be tied.

  On the other hand, the wall surface facing the drill rotation direction T side of the chip discharge groove 5 serving as the rake face of the portion other than the portion formed on the convex portion 8 of the cutting blade 6 is at least the axis O at the tip edge on the cutting blade 6 side. The cross section orthogonal to is formed in a shape in which two concave curves having different curvature radii are connected, so that the cutting edge 6 also has two concaves having different curvature radii as shown in FIG. It is formed so as to form a concave curve shape that is recessed backward in the drill rotation direction T with the curved lines.

  The cutting blade 6 formed other than the convex portion 8 includes a first concave curved cutting blade 11 having a radius of curvature R1 as viewed from the front in the axis O direction extending from the outer peripheral end 6A of the cutting blade 6 toward the inner peripheral side, The first concave curved cutting edge 11 includes a second concave curved cutting edge 12 having a radius of curvature R2 as viewed from the front end in the direction of the axis O and continuing to the inner peripheral side and continuing to the connecting portion 6B. Further, the second concave curved cutting edge 12 is connected to the center cutting edge 13 formed on the convex portion 8 at the center of the tip flank 6 of the cutting edge 6 in the direction of drill rotation at the intersection 6C in the front view of the axis O. It is made to cross | intersect so that it may protrude at an angle toward the T side.

  And these 1st, 2nd concave curve-shaped cutting blades 11 and 12 are set so that the curvature radii R1 and R2 in the axis line O direction front-end | tip view may become R1> R2. In the present embodiment, the first concave curved cutting edge 11 is 0.8 × D to 2.0 × with respect to the outer diameter D of the cutting edge 6 (the diameter of the circle formed by the outer peripheral end 6A around the axis O) D. The radius of curvature R1 is in the range of D, and the second concave curved cutting blade 12 has a radius of curvature in the range of 0.2 × D to 0.5 × D with respect to the outer diameter D of the cutting blade 6. R2. The first and second concave curved cutting edges 11 and 12 may be concave arcs having constant radii of curvature R1 and R2 within the above-mentioned range when viewed from the front in the axis O direction. A concave curve shape in which the curvature radii R1 and R2 change may be used. In the present embodiment, the first and second concave curved cutting blades 11 and 12 are connected so as to smoothly contact at the connecting portion 6B.

  By being configured in this way, the first and second concave curved cutting blades 11 and 12 are in relation to a straight line connecting the outer peripheral end 6A of the cutting blade 6 and the intersection 6C in the front view in the direction of the axis O. The first concave curved cutting edge 11 extends from the outer peripheral end 6A to the inner peripheral side while being bent backward in the drill rotation direction T, and then retreats most backward in the drill rotation direction T with respect to the straight line. After passing through the last retreat point 6D, it extends further to the inner peripheral side while being bent in the drill rotation direction T side, and then comes into contact with the second concave curved cutting edge 12 at the connecting portion 6B. The shaped cutting blade 12 is formed so as to extend toward the inner peripheral side while being further bent in the drill rotation direction T side to reach the intersection 6C.

  Further, the tip flank 4 on which the first and second concave curved cutting blades 11 and 12 having such a configuration are formed at the tip edge moves toward the rear side in the drill rotation direction T, and the rear end side in the axis O direction. Since the leading edge extends substantially perpendicular to the axis O, the first and second concave curved cutting blades 11 and 12 are formed so as to have a predetermined clearance angle toward Even when viewed from the front side of the drill rotation direction T, the first concave curved cutting edge 11 is bent with a large curvature radius from the outer peripheral end 6A of the cutting edge 6 toward the inner peripheral side, while being in the axis O direction. It extends to the rear end side, retreats most in the direction of the axis O at the last retreat point 6D, further extends toward the front end side in the direction of the axis O while bending toward the inner peripheral side, and then the second recess in the connecting portion 6B. The first concave curved cutting edge 11 is connected to the curved cutting edge 12 and goes toward the inner periphery. Remote extending in the axial O direction leading end side while the concave with a small radius of curvature is formed so as to extend in the intersection 6C.

  Furthermore, the center cutting edge 13 that intersects the second concave curved cutting edge 12 at the intersection 6C has an angle toward the drill rotation direction T at the intersection 6C in the front view of the axis O as described above. When intersected so as to be bent and formed on the mountain-shaped convex portion 8, the obtuse angle at the intersection 6C is formed on the first concave curved cutting edge 12 when viewed from the front in the drill rotation direction T. Are formed so as to extend in a straight line in the direction of the axis O beyond the outer peripheral end 6A of the cutting edge 6 toward the inner peripheral side.

  In addition, when viewed from the front in the drill rotation direction T, the crossing angle between the second concave curved cutting edge 12 and the central cutting edge 13 intersecting to form a concave bend at the intersection 6C is as shown in FIG. As shown in FIG. 4, the crossing angle α in the projection view on the plane including the axis O of the rotation locus of the cutting edge 6 around the axis O is in the range of 140 ° to 160 °. In addition, the crossing angle between the second concave curved cutting edge 12 and the central cutting edge 13 which are crossed so as to be bent toward the drill rotation direction T side at an angle at the intersection 6C when viewed from the front in the axis O direction. β is in the range of 130 ° to 150 °.

  The position of the intersection 6C between the second concave curved cutting edge 12 and the center cutting edge 13 in the direction of the axis O is on the tip side in the direction of the axis O with respect to the position of the outer peripheral end 6A of the cutting edge 6. Alternatively, it may be on the rear end side, but it is desirable that the position is substantially equal to the outer peripheral end 6A of the cutting edge 6. In this embodiment, the outer peripheral end 6A and the intersection 6C are in the direction of the axis O in the direction of the axis O. The outer diameter D of the blade 6 is set within a range of 0.002 × D. As long as it is within this range, either the outer peripheral end 6A or the intersection 6C may be the front end side in the axis O direction. In addition, for example, when the intersection 6C is located on the distal end side in the axis O direction from the outer peripheral end 6A, the connecting portion 6B is also at the same position in the axis O direction as the outer peripheral end 6A or Although it may be located on the front end side in the O direction, when the outer peripheral end 6A and the intersection point 6C are at substantially the same position in the direction of the axis O as in the present embodiment, the axis line is longer than the outer peripheral end 6A and the intersection point 6C. It is located on the rear end side in the O direction.

  Further, the connecting portion 6B of the first concave curved cutting edge 11 and the second concave curved cutting blade 12 has a radius R3 from the axis O to the connecting portion 6B in the radial direction with respect to the axis O. The cutting blade 6 is disposed at a position in the range of 0.2 × D to 0.25 × D with respect to the outer diameter D of the cutting blade 6. On the other hand, the radial position of the last retraction point 6D of the first concave curved cutting edge 11 arranged on the outer peripheral side of the connecting portion 6B is such that the radius R4 from the axis O is the outer diameter of the cutting edge 6. It is made to become the range of 0.25 * D-0.4 * D with respect to D. Of course, R4> R3.

  The counterbore drill configured as described above is transferred in the direction of the axis O while being rotated in the drill rotation direction T around the axis O as described above, thereby transferring the shape of the cutting edge 6. A counterbore having a bottom surface having a cross-sectional shape is formed in the work material. That is, the cross section of the bottom surface of the counterbore hole is directed from the outer peripheral end toward the inner peripheral side so that the projected view formed by the rotation locus around the axis O of the cutting edge 6 with respect to the plane including the axis O is reversed. Then, while drawing a convex curve with a large radius of curvature corresponding to the first concave curved cutting edge 11, it reaches a tip corresponding to the last retreat point 6D, and then retreats so as to be recessed at the same radius of curvature, then From the position corresponding to the connecting portion 6B, it is recessed with a small radius of curvature corresponding to the second concave curved cutting edge 12, and from the position corresponding to the intersection 6C, it is recessed more linearly with a steeper slope than this. It is formed.

  Therefore, by drilling a bolt hole on the inner peripheral side from the protruding end portion of the counterbore hole bottom formed in this way, the head of the bolt inserted into the bolt hole becomes the protruding end portion of the counterbore hole bottom surface. Will abut. And this protrusion part makes the cross section of the convex curve shape with a large curvature radius corresponding to the 1st concave curve-shaped cutting blade 11 as mentioned above, and since it is made flat, it contacts with a bolt head. A large area can be secured, and the fastening force by the bolt can be improved. Moreover, since the first concave curved cutting edge 11 has a concave curved shape from the outer peripheral end 6A of the cutting edge 6 and retreats toward the rear end side in the axis O direction, even with a hexagon bolt, the outer peripheral portion of the counterbore hole bottom surface. The bolt head does not come into contact with each other.

  Further, like the first concave curvilinear cutting edge 11, it is concaved from the outer peripheral end 6 </ b> A of the cutting edge 6 toward the inner peripheral side, toward the rear end side in the axis O direction, and further concaved via the final retreat point 6 </ b> D. However, even if the cutting edge that reaches the connecting portion 6B with the second concave curved cutting edge 12 toward the tip side is inclined in the profile in the projection view due to a manufacturing error or the like, the position of the last retreat point 6D Is slightly displaced in the radial direction, for example, the position of the last retreat point does not become the outer peripheral edge or inner peripheral edge of the cutting edge depending on the tilting direction like a linear cutting edge perpendicular to the axis. . Therefore, according to the counterbored drill having the above-described configuration, it is possible to form a counterbore hole that can ensure a large contact area with the bolt head even if such a manufacturing error occurs.

  On the other hand, when the cutting edge 6 is only the first concave curved cutting edge 11 having such a large radius of curvature, the cutting edge length particularly when this extends along the direction perpendicular to the axis O. Is shortened and the load on the cutting edge 6 per unit length is increased, so that the feed cannot be increased, and the pushing force when applying the feed is also increased, so that the machinability is inevitably impaired. . However, in the counterbore drill having the above configuration, the second concave curved cutting edge 12 having a smaller radius of curvature than the first concave curved cutting edge 11 is connected to the inner peripheral side of the first concave curved cutting edge 11. In addition, since a linear center cutting edge 13 extending toward the distal end is formed on the further inner peripheral side of the second concave curved cutting edge 12, the second concave curved cutting edge 12 and The sharpness of the cutting edge 6 can be improved by the center cutting edge 13, and good machinability can be obtained.

  Further, since the center cutting edge 13 is formed on the mountain-shaped convex portion 8 formed at the center portion of the tip flank 4 as described above, the center portion is thinned as in this embodiment. Even when the central cutting edge 13 is formed by the thinning portion 9, the central cutting edge 13 does not have a concave shape, and therefore, the central portion of the bottom surface of the counterbore does not have a convex shape. For this reason, when the bolt hole is drilled after the counterbore is formed as described above, the bolt hole forming drill rides on the bottom center portion of the convex counterbore hole and is bent or bent. In some cases, it will not break.

  Furthermore, the second concave curved cutting edge 12 and the central cutting edge 13 are concavely bent so as to intersect with an obtuse angle at an intersection 6C when viewed from the drill rotation direction side. Chips generated across the second concave curved cutting edge 12 and the central cutting edge 13 are also generated by receiving bending stress so as to be bent. For this reason, it is possible to easily fold the generated chips in the direction of the axis O of the drill main body 1 to improve the chip breaking property, thereby facilitating smooth chip disposal.

  Moreover, in the present embodiment, the second concave curved cutting edge 12 and the central cutting edge 13 are formed so as to be bent with a crossing angle β at the same intersection 6C when viewed from the front in the axis O direction. Therefore, the chips are generated in a cross-sectional shape that is bent in a V shape. Therefore, by applying the bending stress as described above to such chips, the stress can be concentrated on the V-shaped folds to make it easier to divide the chips, thereby further improving the chip disposability. Is possible.

  If the radius of curvature R1 of the concave curve formed by the first concave curved cutting edge 11 as viewed from the front in the direction of the axis O is too large, the first concave curved cutting edge 11 becomes close to a straight line and the machinability is improved. There is a risk that the contact area between the bottom face of the counterbore hole and the bolt head cannot be secured when tilting occurs due to manufacturing errors. On the other hand, even if the radius of curvature R1 is too small, the convex curve formed by the cross section of the counterbore hole bottom has a small radius of curvature, and the contact area may not be secured. Is preferably in the range of 0.8 × D to 2.0 × D with respect to the outer diameter D of the cutting edge 6 as in this embodiment.

  In addition, if the radius of curvature R2 of the second concave curved cutting edge 12 in the end view in the direction of the axis O is too large, the cutting ability cannot be improved. There is a possibility that the second concave curved cutting edge 12 cannot be secured. For this reason, it is desirable that the radius of curvature R2 of the second concave curved cutting edge 12 is also in the range of 0.2 × D to 0.5 × D as in this embodiment.

  Furthermore, when the crossing angle between the second concave curved cutting edge 12 and the central cutting edge 13 intersecting so as to bend and bend at an intersecting point 6B when viewed from the front side of the drill rotation direction T is too large, a straight line is obtained. If the center cutting edge 13 is close to the tangent line that smoothly touches the second concave curved cutting edge 12, it may not be possible to apply sufficient bending stress to the chips. The inclination angle formed by the axis 13 with respect to the axis O is also small, and the tip of the convex portion 8 may become too sharp and may cause a defect. For this reason, it is desirable that this intersection angle is in the range of 140 ° to 160 ° as the intersection angle α in the projection view in which the rotation locus of the cutting edge 6 around the axis O is projected onto the plane including the axis O.

  On the other hand, as in the case where the central cutting edge 13 is formed by thinning as in the present embodiment, the second concave curved cutting edge 12 and the central cutting edge 13 are projected at the intersection 6C in the front view of the axis O direction. When formed so as to be bent, if the crossing angle β in the end view in the direction of the axis O is too small, the cutting edge 6 is liable to be broken at the intersection 6C, and conversely if the crossing angle β is too large, the force of bending the chips. There is a risk of shortage. Therefore, it is desirable that the crossing angle β is also in the range of 130 ° to 150 ° as in the present embodiment.

  Further, the intersection 6C of the second concave curved cutting edge 12 and the central cutting edge 13 and the outer peripheral edge 6A of the cutting edge 6 are within the range of 0.002 × D in the axis O direction as in this embodiment. In this case, if the deviation in the direction of the axis O between the outer peripheral edge 6A and the intersection 6C is larger than this, it will retreat last on the first concave curved cutting edge 11 having a large curvature radius R1. It may be difficult to position the point 6D. For example, if the outer peripheral end 6A is located on the tip side larger than the intersection 6C, the connecting portion 6B becomes the last retreat point, and the curvature radius on the bottom face of the counterbore hole is smaller on the inner peripheral side than the protruding end portion. The contact area with the head may be reduced.

  Furthermore, the radius R3 from the axis O to the position of the connecting portion 6B of the first and second concave curved cutting blades 11 and 12 is 0.2 × D to 0.25 × D with respect to the outer diameter D. It is desirable to be within the range. This is because the inner diameter of the bolt hole generally drilled on the bottom face of the counterbore is about 0.3 to 0.6 times the inner diameter of the counterbore, that is, with respect to the outer diameter D of the cutting edge 6. Is a radius of 0.15 × D to 0.3 × D, and therefore, if the connecting portion 6B is within this range, the cross-sectional convex curve shape having a large curvature radius with which the bolt head abuts on the outer peripheral side of the bolt hole. This is because the bottom face of the counterbore can be reliably formed.

  Furthermore, the radial position of the last retraction point 6D in the first concave curved cutting edge 11 must be located on the outer peripheral side with respect to the bolt hole formed in this way. The radius R4 from the axis O is preferably in the range of 0.25 × D to 0.4 × D with respect to the outer diameter D of the cutting blade 6 so as to be larger than the radius of the bolt hole. Of course, the radius R3 is larger than the radius R4 up to the position of the connecting portion 6B.

DESCRIPTION OF SYMBOLS 1 Drill main body 3 Cutting edge part 4 Tip flank 5 Chip discharge groove 6 Cutting edge 6A Outer edge of cutting edge 6 6B Connection part 6C of 1st concave curve-shaped cutting edge 11 and 2nd concave curve-shaped cutting edge 12 6C Intersection of second concave curved cutting edge 12 and center cutting edge 13 6D Last retreat point of cutting edge 6 8 Convex part 9 Thinning part 11 First concave curvilinear cutting edge 12 Second concave curvilinear cutting edge 13 Center cutting edge O Axis of drill body 1 T Drill rotation direction D Outer diameter of cutting edge 6 R1 First concave curve-shaped radius of curvature of first concave edge 11 viewed from the front of axis O direction R2 Second concave-curved shape The radius of curvature of the concave curve that the cutting edge 12 makes when viewed from the front in the direction of the axis O R3 The radius from the axis O to the connecting portion 6B R4 The radius from the axis O to the last retreat point 6D The rotation locus of the cutting edge 6 about the axis Of the second concave curved cutting edge 12 and the central cutting edge 13 in the projection onto the plane including the axis O Intersection angles between the second concave-curved cutting edge 12 and the center cutting edge 13 in the β axis O direction tip viewed

Claims (8)

  A tip flank is formed at the tip of the drill body that rotates about the axis toward the rear side in the direction of drill rotation. The cutting blade formed on the edge on the front side in the direction is bent from the outer peripheral end of the cutting blade toward the inner peripheral side in order from the outer peripheral side of the drill body as viewed from the front side in the drill rotation direction. The first concave curved cutting edge extending to the axial front end side after extending to the axial rear end side, and the first concave curved cutting edge connected to the first concave curved cutting edge and further bent toward the inner peripheral side A second concave curved cutting edge extending toward the distal end side in the axial direction and the second concave curved cutting edge intersecting the second concave curved cutting edge so as to be bent at an obtuse angle and moving toward the inner peripheral side, the cutting direction in the axial direction. Provided with a central cutting edge that extends straight beyond the outer peripheral edge of the blade toward the tip The first and second concave curved cutting edges have a concave curved shape in the axial front end view, and the radius of curvature of the first concave curved cutting edge in the axial front end view is the second radius. A counterbore drill having a larger radius of curvature than the concave curved cutting edge.   The radius of curvature R1 of the concave curve formed by the first concave curved cutting edge as viewed from the front in the axial direction is in a range of 0.8 × D to 2.0 × D with respect to the outer diameter D of the cutting blade. The counterbore drill according to claim 1, wherein:   The radius of curvature R2 of the concave curve formed by the second concave curved cutting edge when viewed from the front in the axial direction is in the range of 0.2 × D to 0.5 × D with respect to the outer diameter D of the cutting blade. The counterbore drill according to claim 1 or 2, wherein:   A crossing angle between the second concave curved cutting edge and the central cutting edge in a projection view on a plane including the axis of the rotation locus of the cutting edge around the axis is in a range of 140 ° to 160 °. The counterbore drill according to any one of claims 1 to 3, wherein the counterbore drill is provided.   The intersection of the second concave curved cutting edge and the central cutting edge is located within a range of 0.002 × D with respect to the outer diameter D of the cutting edge in the axial direction from the outer peripheral end of the cutting edge. The counterbore drill according to any one of claims 1 to 4, wherein the counterbore drill is provided.   The second concave curved cutting edge and the central cutting edge are formed so as to bend and bend toward the direction of drill rotation in the axial front end view. The second concave cutting edge in the axial front end view is formed. The counterbore drill according to any one of claims 1 to 5, wherein a crossing angle between the curved cutting edge and the center cutting edge is in a range of 130 ° to 150 °.   A radius R3 from the axis line to the connecting portion of the first concave curved cutting edge and the second concave curved cutting edge is 0.2 × D to 0. The counterbore drill according to any one of claims 1 to 6, wherein the drill has a range of 25 x D.   A radius R4 from the axis up to a position where the first concave curved cutting edge is most retracted toward the rear end side in the axial direction is 0.25 × D to 0.4 with respect to the outer diameter D of the cutting edge. The counterbore drill according to any one of claims 1 to 7, wherein x is in a range of D.

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