JP6653835B2 - Drill bit for diameter expansion - Google Patents

Description

  The present invention relates to a diameter-enlargement drill bit for enlarging a part of a pilot hole formed in a body such as concrete.

2. Description of the Related Art Conventionally, as a drill bit for this kind of diameter expansion, a cutting tool for forming a cutting part in a pilot bore drilled in concrete or the like is known (see Patent Document 1).
This cutting-down tool includes a tool main body attached to a tip of a shaft, and six wedges connected to the tool main body. The connection point between the tool body and the wedge is constituted by a connection member (hinge pin) on the tool body side and a connection portion on the wedge side, and the wedge is rotatably connected to the tool body in the radial direction. . As the devaluation tool rotates through the shaft, centrifugal forces displace the six wedges outward. Due to this rotation and outward displacement, the cutting surface provided on the outer surface of the wedge grinds the inner surface of the bore and the bore is cut down.

JP-T-2013-525647A

  In such a conventional undercutting tool, each wedge is supported on the tool body only at a hinge-type connection point. For this reason, the force (cutting resistance) received by each wedge at the time of cutting down acts intensively on the connection point. Therefore, there is a problem that the connection member and the connection portion forming the connection point are easily fatigued, and the tool life is shortened.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a diameter-enlargement drill bit capable of dispersing a force received by a cutting blade and improving durability.

The diameter-enlargement drill bit of the present invention is used by being inserted into a prepared hole drilled in a body, and is a diameter-enlarged drill bit for enlarging a part of the prepared hole by grinding. A plurality of cutting blades that rotate outward in the radial direction to grind a part of the pilot hole, a cutting blade holding unit that holds the plurality of cutting blades rotatably in the radial direction, and a cutting blade. A shank portion that supports a holding portion, wherein the plurality of cutting edge portions are disposed at point-symmetric positions around the axis, and each cutting edge portion has a cutting edge body having an outer peripheral portion having an arc-shaped cross section. A cutting edge holding portion having a rib-shaped support portion for supporting the cutting blade body from the inside, an arm portion extending in the axial direction from the rib-shaped support portion, and a rotation support portion connected to the arm portion and serving as a rotation base point; Is a guide holding portion in which the rib-shaped support portion is slidably engaged with the rotation, and a rotation supporting portion is rotatably held. Characterized in that it comprises a base holding unit.

  According to this configuration, when the cutting blade holding unit rotates via the shank, the plurality of cutting blade units held by the cutting blade holding unit rotate radially outward. Due to this rotation and rotation, the plurality of cutting blades contact and grind the inner peripheral surface of the prepared hole. That is, the diameter of a part of the pilot hole is increased by grinding the plurality of cutting blades. In this case, each of the rotating cutting blade portions is guided by the guide holding portion of the cutting blade holding portion via the rib-shaped support portion. For this reason, the force received by each cutting blade portion during cutting is mainly received by the guide holding portion via the rib-shaped support portion, and does not concentrate on the rotation support portion or the base point holding portion. That is, the forces received by the plurality of cutting blades can be dispersed and act on the cutting blade holding unit, and the durability can be improved as a whole.

  In this case, it is preferable that the guide holding section includes a cylindrical cylindrical guide section and a guide slit formed in the cylindrical guide section in the axial direction and the rib-shaped support section is slidably engaged.

  According to this configuration, the height of the rib-shaped support portion can be increased, and the forces received by the plurality of cutting blade portions can be further dispersed and act on the cutting blade holding portion.

  Further, it is preferable that the rotation supporting portion includes an arc-shaped outer peripheral surface, and the arc-shaped outer peripheral surface rotatably contacts the inner surface of the base holding portion.

  According to this configuration, it is not necessary to provide a shaft serving as a rotation center in the rotation support portion, and the structure around the rotation support portion and the base point holding portion that comes into contact with the rotation support portion can be simplified. Thereby, the whole can be formed with a small diameter, and it is possible to cope with a pilot hole having a relatively small diameter.

  Furthermore, it is preferable that the cutting blade holding unit has a rotation restricting unit that restricts a radially outer turning end position of each cutting blade unit via the arm unit.

  According to this configuration, the turning restricting portion can restrict the turning angle of each cutting blade portion to the radially outward side, and can appropriately adjust the diameter-expanding dimension of the enlarged diameter portion to be ground. .

  On the other hand, it is preferable that the cutting blade holding portion has a spire portion protruding so as to be coaxial with the tip portion, and the spire portion is preferably made of a super-steel material.

  According to this configuration, by rotating the spire section against the bottom of the prepared hole and rotating the spire section, the enlarged diameter portion can be formed at a predetermined depth position with respect to the bottom of the prepared hole. Further, since the spire section makes point contact with the center of the hole bottom, the friction with the hole bottom can be reduced as much as possible during rotation, and the rotational shake of the cutting blade section can be suppressed as much as possible. Further, since the spire portion is made of a super-steel material, wear of the spire portion can be suppressed. Therefore, the enlarged diameter portion can always be formed at a predetermined position from the bottom of the pilot hole.

  Further, the cutting blade holding portion preferably has a flange-shaped portion that is fitted into the prepared hole and has a larger diameter than the plurality of cutting blade portions in the non-expanded state.

  According to this configuration, since the flange-shaped portion that rotates as a part of the cutting blade holding portion is formed to have a diameter that can be inserted into the pilot hole, it can function as a member that prevents rotation blur. . Therefore, the rotation of the cutting blade holding portion and the cutting blade portion during grinding is stabilized, and the work of expanding the prepared hole by the plurality of cutting blade portions can be performed smoothly in a short time.

  Further, it is preferable that the plurality of cutting blades are constituted by two cutting blades disposed at 180 ° point symmetric positions around the axis.

  According to this configuration, the periphery of the cutting edge can be compactly configured with a simple structure without impairing the cutting performance.

  Still further, the shank portion communicates with the shank main body having the shank internal flow path and the shank main body flow path for supplying the coolant to the plurality of cutting edge portions via the cutting edge holding portion, and the shank main body. And a coolant pipe extending from the tip to the vicinity of the tips of the plurality of cutting blades.

  According to this configuration, the coolant discharged from the tip of the coolant pipe is supplied to the tip of each cutting blade via the cutting blade holder. Thus, the coolant flows from the tip of each cutting blade toward the opening of the pilot hole, so that the cutting blade can be efficiently cooled. In particular, even when the diameter-enlargement drill bit is used facing upward, the coolant can be appropriately supplied to the cutting edge portion. When the coolant is a liquid, the coolant subjected to the centrifugal force presses the tip of each cutting blade so as to scatter radially. Thereby, the expansion of the plurality of cutting blades can be promoted.

It is an outline view of a diameter expansion device including a drill bit for diameter expansion concerning an embodiment. It is a side view in the periphery of the bit part of the drill bit for diameter expansion. It is a half sectional view (a) of a non-expanded state around a bit part of a drill bit for diameter expansion, and a half sectional view (b) of an expanded state. FIG. 3 is an exploded perspective view around a bit portion of the drill bit for diameter expansion.

  Hereinafter, a drill bit for diameter expansion concerning one embodiment of the present invention is explained with reference to an accompanying drawing. This drill bit for diameter expansion is to expand a part of the pilot hole formed in the skeleton of concrete or the like mainly for driving the post-installed anchor, and it can increase the pull-out strength of the anchor after driving. Things. In other words, in order to make the anchor constructed after being driven into the pilot hole exhibit a theoretical wedge effect, the drill bit for diameter expansion forms an enlarged diameter part in a part of the pilot hole.

  FIG. 1 is an external view of a diameter expanding device in which a diameter expanding portion is formed in a pilot hole. As shown in FIG. 1, the diameter expanding device 1 includes an electric drill 2 on hand, a coolant attachment 3 attached to the electric drill 2, and a drill bit 10 for diameter enlargement attached to the coolant attachment 3. ing. That is, the drill bit 10 for diameter expansion is used by being detachably attached to the rotating shaft 3a of the coolant attachment 3 connected to the electric drill 2 constituting the power source.

  A coolant passage is formed on the rotating shaft 3a, and a coolant supply device (not shown) is connected to the coolant attachment 3, and the coolant is supplied from the coolant supply device. It is supplied to the drill bit 10 for diameter expansion via the attachment 3. The coolant attachment 3 is provided with a valve (not shown) for opening and closing a coolant passage (not shown). The valve is formed by abutting a drill bit 10 for diameter expansion against the bottom Ha of the pilot hole H. "Open" and "closed" by separating from the hole bottom Ha. The prepared hole H is formed by a vibration drill, a hammer drill, a core bit, or the like.

  The drill bit 10 for diameter enlargement is detachably attached to the bit part 11 forming the enlarged diameter part Hb in the prepared hole H and the rotating shaft 3a of the diameter enlargement device 1 (coolant attachment 3) at the base end side. And a shank portion 12 that coaxially supports the bit portion 11 on the side. The shank portion 12 is formed integrally with a shank body 15 that supports the bit portion 11 and a large-diameter shaft portion 16 that is mounted on the rotating shaft 3a. A coolant pipe 17 (coolant pipe) is attached to the tip of the shank body 15 (see FIG. 4). On the other hand, the bit portion 11 includes two (a pair of) cutting blade portions 21 and a cutting blade holding portion 22 that rotatably holds the two cutting blade portions 21. In this case, the bit 11 is unitized, and is detachably attached to the tip of the shank 12 (the shank main body 15) by screw connection.

  The shaft portion 16 has a fastening portion 16a formed by a female screw on a small edge thereof, and the fastening portion 16a is screwed to the rotating shaft 3a of the coolant attachment 3 formed by a male screw. Further, at the tip of the shank body 15, a tip male screw portion 15a to which the bit portion 11 is screwed is formed, and the cutting edge holding portion 22 of the bit portion 11 is screwed to the tip male screw portion 15a. A shaft 18 for the coolant is formed in a shaft portion of the shaft portion 16 and the shank body 15.

  The cooling liquid pipe 17 is attached to the distal end portion (the distal male screw portion 15a) of the shank main body 15 so as to communicate with the flow path 18 in the shank (see FIG. 4). The coolant pipe 17 is made of stainless steel or the like, and its base end is press-fitted into the axial center portion of the male screw portion 15a at the tip of the shank body 15 (the portion where the flow passage 18 in the shank is expanded by the thickness of the coolant pipe 17). Installed. The tip of the coolant pipe 17 extends to near the tips of the two cutting blades 21 in the cutting blade holder 22. The coolant supplied from the coolant attachment 3 is supplied to the distal end side of the bit portion 11 through the shank flow path 18 and the coolant pipe 17 to cool the two cutting blades 21 during grinding.

  The diameter expanding device 1 is a wet type using a cooling liquid, but a dry type using no cooling liquid is also available. Although not particularly shown, the dry diameter expanding device 1 has no shank channel 18 in the shank portion 12, and the diameter expanding drill bit 10 is directly connected to the electric drill 2. Further, in another dry type diameter expanding device 1, compressed air or cooling gas is introduced instead of the cooling liquid. The unitized bit portion 11 is used as a common component in the wet type and dry type drill bit 10 (diameter expanding device 1).

  Next, the bit unit 11 will be described in detail with reference to FIGS. As described above, the bit portion 11 has two (a pair) of cutting blade portions 21 for grinding the prepared hole H, and a cutting blade that holds the two cutting blade portions 21 rotatably in the radial direction. And a holding unit 22. The cutting blade holding part 22 is connected to the shank part 12, and as the shank part 12 rotates, the cutting blade holding part 22 and the two cutting blade parts 21 held by the cutting blade holding part 22 rotate. When the cutting blade holder 22 rotates, the two cutting blades 21 rotate so as to expand radially outward under centrifugal force. When the two cutting blades 21 are expanded, the pilot hole H is ground to form an enlarged diameter portion Hb having a truncated cone shape.

  The two cutting blades 21 are disposed at 180 ° point symmetrical positions around the axis, and the outer diameter in the non-expanded state is formed to be slightly smaller than the diameter of the pilot hole H. Correspondingly, the cutting blade holding portion 22 holds the two cutting blade portions 21 at 180 ° point symmetrical positions and rotatably around the shank portion 12 side in the axial direction. As a result, the two cutting blades 21 expand in a well-balanced skirt shape.

  Each of the cutting blades 21 has a cutting blade main body 31 having an outer peripheral portion having an arc-shaped cross section, and a plate-shaped cutting blade supporting portion for supporting the cutting blade main body 31 from the inside so as to be rotatable (strictly, circularly movable). 32. Correspondingly, the cutting blade holding unit 22 includes a holding unit main body 41 slidably engaged with the rotating cutting blade support unit 32 and a holding unit rotatably holding the base side of the cutting blade support unit 32. And a receiver 42. The holding portion main body 41 is configured to be screwable with the holding portion receiver 42 on the shank portion 12 side, and the holding portion main body 41 incorporating the two cutting blade portions 21 is screwed into the holding portion receiver 42. , The bit unit 11 is assembled.

  The cutting blade body 31 is formed of a diamond cutting blade having an arc-shaped cross section. That is, the cutting blade main body 31 has a base 51 having an arc-shaped cross section along the outer peripheral surface of the holding part main body 41, and a diamond grinding portion 52 applied to the outer peripheral portion of the base 51. Thus, when the cutting blade 21 rotates by centrifugal force, the grinding unit 52 comes into contact with and grinds the inner peripheral surface of the prepared hole H. In the present embodiment, the grinding portion 52 is provided on the entire outer peripheral surface of the base 51, but may be provided on a part thereof. Also, after grinding, the upper end of the cutting blade main body 31 in the drawing is preferably chamfered or tapered so that the cutting blade 21 can be easily pulled out from the prepared hole H.

  The cutting blade support portion 32 includes a rib-shaped support portion 54 that supports the cutting blade main body 31 from the inside, an arm portion 55 that extends in the axial direction from the rib-shaped support portion 54, A moving support 56. In addition, the arm portion 55 is provided with a regulated portion 57 that regulates the position of the radially outer turning end of the cutting blade portion 21 in cooperation with the holding portion receiver 42. The rib-shaped support portion 54, the arm portion 55, the regulated portion 57, and the rotation support portion 56 are integrally formed in a plate shape.

  The rib-shaped support portion 54 is preferably formed in a plate shape so as to have the same height as the cutting blade main body 31, and the cutting blade main body 31 (base 51) is welded to an end surface thereof at an intermediate position in the circumferential direction. ing. Further, the rib-shaped support portion 54 is slidably engaged with a guide slit 77 (see FIG. 4) of the holding portion main body 41 described later. That is, the rib-shaped support portion 54 connects the cutting blade main body 31 located outside the holding portion main body 41 and the arm portion 55 positioned inside, and reduces the cutting resistance acting on the cutting blade main body 31 with the guide slit 77. Has a function to escape to the holding portion main body 41 via the.

  The arm portion 55 extends in the axial direction from the upper end in the drawing of the rib-shaped support portion 54, and constitutes a rotating arm for rotating the cutting blade body 31 at a predetermined curvature. Further, on the rib-shaped support portion 54 side of the arm portion 55, a regulated portion 57 is integrally provided so as to protrude outward in the radial direction. The regulated portion 57 is in contact with a front edge portion (a rotation regulating portion 67 described later) of the holding portion receiver 42 to regulate an outer rotation end position of the cutting blade portion 21. In other words, the position where the cutting blade main body 31 extends along the outside of the holding portion main body 41 is the inner rotation end position (non-expanded state) of the cutting blade portion 21, and the position where the regulated portion 57 contacts the holding portion receiver 42. , The outer rotating end position of the cutting blade 21 (in the expanded state). In the present embodiment, the regulated portion 57 may be configured as a projecting step provided on the arm portion 55, or the arm portion 55 may be wide. Further, the distal end (rotation restricting portion 67) of the holding portion receiver 42 may be extended so that the arm portion 55 also serves as the restricted portion 57.

  The rotation supporting portion 56 is a portion serving as a starting point of rotation of the cutting blade portion 21, and a contact portion with the holding portion receiver 42 is formed in an arc shape. Specifically, the rotation supporting portion 56 has an arc-shaped outer peripheral surface 56a, and the arc-shaped outer peripheral surface 56a rotatably contacts an inner surface of a base point holding portion 66 of the holding portion receiver 42 described later. . That is, there is no member such as a hinge pin or the like in the rotation supporting portion 56, and the arc-shaped outer peripheral surface 56 a slidably contacts the inner surface of the base holding portion 66 in a state where centrifugal force is applied.

  As described above, each of the cutting edge portions 21 is roughly held by the cutting edge holding portion 22 inside the cutting edge holding portion 22, and when a centrifugal force is applied, the cutting edge portion 21 radially outwards around the rotation support portion 56. Rotate. Further, the rotation of each cutting blade 21 is guided by the cutting blade holder 22 in the radial direction.

  On the other hand, the cutting blade holding portion 22 has the holding portion main body 41 that is the main body as described above, and the holding portion receiver 42 on the shank portion 12 side with which the holding portion main body 41 is screwed. The outer diameter of the holding portion receiver 42 is formed to have the same diameter as the two cutting blade portions 21 in the non-spreading state. In the present embodiment, the holding portion main body 41 and the holding portion receiver 42 are joined by screws, but they may be joined by welding or the like. That is, the holding part main body 41 and the holding part receiver 42 may be in a detachable joint form or may be in a fixed joint form (fixed after the cutting blade 21 is assembled).

  The holding portion receiver 42 is integrally formed by a frusto-conical shank connecting portion 61 connected to the shank portion 12 and a cylindrical main body connecting portion 62 connected to the shank connecting portion 61 and connected to the holding portion main body 41. Is formed. A small-diameter first female screw portion 64 is formed in the shank connection portion 61. The first female screw portion 64 is screwed into the male screw portion 15a at the tip of the shank portion 12, whereby the bit portion 11 is detachably mounted on the shank portion 12.

  On the inner peripheral surface of the main body connection portion 62, a second female screw portion 65 is formed on the distal end side. The base end side of the holding portion main body 41 is screwed into the second female screw portion 65, whereby the holding portion main body 41 is detachably incorporated in the holding portion receiver 42. The tip of the second female screw portion 65 constitutes a rotation restricting portion 67 described in the claims, and the rotation restricting portion 67 cooperates with the above-described restricted portion 57 to move the outer side of the cutting blade portion 21. Restrict the rotation end position (spreading state). The depth of cut into the pilot hole H regulated by the rotation restricting portion 67, that is, the enlarged diameter (radius) of the enlarged diameter portion Hb is preferably about 3 to 5 mm on the distal end side.

In addition, an annular step is formed between the shank connecting portion 61 and the inner peripheral surface of the main body connecting portion 62 that is continuous with the second female screw portion 65, and the rotation of the cutting blade portion 21 is formed in this portion. A base point holding section 66 that holds the support section 56 is configured. The base holding portion 66 is a simple annular step, and the pivot support 56 of the cutting blade 21 contacts an arbitrary position in the circumferential direction of the base holding portion 66. As described above, the turning support 56 of the cutting blade 21 is disposed inside the holder receiver 42, that is, inside the cutting blade holder 22. Note that the inner peripheral surface of the base point holding portion 66 may have a cross-sectional shape complementary to the arc-shaped outer peripheral surface 56a of the rotation support portion 56.

  The holding portion main body 41 includes a guide holding portion 71 with which the cutting blade portion 21 is slidably engaged, a flange-shaped tip flange portion 72 (flange-shaped portion) connected to the tip side of the guide holding portion 71, and a tip flange portion 72. And a spire portion 73 provided at the tip side of In this case, the guide holding portion 71 and the distal end flange portion 72 are formed integrally. The holder main body 41 is mounted on the holder receiver 42 with the two cutting blades 21 incorporated therein.

  The distal flange 72 has a distal half formed in a tapered shape, and a spire 73 is attached to an axial center of this portion. The spire portion 73 is made of, for example, a super-steel alloy (super-steel material), and is integrally formed with a tip conical portion 73a and a cylindrical portion 73b connected thereto. Also, the cone angle of the tapered portion of the distal flange portion 72 and the cone angle of the distal cone portion 73a are formed at the same angle, and the distal cone portion 73a is positioned on the extension of the tapered portion of the distal flange portion 72. It has become.

  The distal end flange portion 72 is formed to have a somewhat larger diameter (larger diameter) than the holding portion receiver 42 and the two cutting blade portions 21 having the same diameter. That is, the distal end flange portion 72 is formed to have the largest diameter in the bit portion 11, and the diameter is slightly smaller than the diameter of the pilot hole H (about 0.5 mm). The diameter-enlargement drill bit 10 according to the embodiment is rotated while the spire portion 73 abuts against the bottom Ha of the prepared hole H, and forms an enlarged-diameter portion Hb at the back of the prepared hole H. That is, when forming the enlarged diameter portion Hb, the enlarged diameter drill bit 10 is rotated while the tip conical portion 73a is in contact with the center of the hole bottom Ha.

  Thereby, the tip conical portion 73a (the spire portion 73) makes point contact with the center of the hole bottom Ha, and the friction with the hole bottom Ha can be minimized during rotation. Further, since the spire portion 73 is made of a super steel alloy, wear of the spire portion 73 can be suppressed as much as possible. Furthermore, the spike portion 73 and the large-diameter distal end flange portion 72 can suppress the rotation blur of the bit portion 11 (the cutting blade portion 21). Therefore, the enlarged diameter portion Hb can always be formed at a predetermined position from the hole bottom Ha of the prepared hole H. The spire portion 73 is attached to the front flange portion 72 by welding or shrink fitting, but may be attached rotatably.

  The guide holding portion 71 is formed in a cylindrical shape and integrally with the distal end flange portion 72. The guide holding portion 71 includes a cylindrical guide portion 75 extending from the distal end flange portion 72, a cylindrical screw portion 76 connected to the cylindrical guide portion 75 and having the same diameter as the cylindrical guide portion 75, a cylindrical guide portion 75 and a cylindrical screw portion. 76 has two guide slits 77 formed therein (see FIG. 4). A male screw is formed on the outer peripheral surface of the cylindrical screw portion 76. This male screw is screwed into the second female screw portion 65 of the holding portion receiver 42, whereby the holding portion main body 41 is detachably attached to the holding portion receiver 42.

Each guide slit 77 extends in the axial direction to the cylindrical guide portion 75 so as to cut from the end of the cylindrical screw portion 76, and the slit width is determined by the cutting blade support portion 32 (rib-shaped support portion 54). In order to engage slidably, it corresponds to the thickness of the cutting blade support portion 32. Further, the two guide slits 77 are formed at 180 ° point symmetrical positions in the circumferential direction of the cylindrical guide portion 75 and the cylindrical screw portion 76. Therefore, the two cutting blades 21 are held at 180 ° point symmetrical positions by the guide holding unit 71. In this case, the two cutting blades 21 are incorporated into the guide holding unit 71 so as to slide from the end of the cylindrical screw part 76, that is, from the small edge.

  Each of the two cutting edges 21 of the bit 11 is incorporated into the cutting edge holding portion 22 with a small clearance. When the bit 11 rotates in this state, the two cutting blades 21 strongly contact the inner peripheral surface of the cutting blade holder 22 due to centrifugal force, and the cutting blade main body 31 expands in a skirt shape. This expansion is guided by the guide slit 77 of the guide holding portion 71, and the cutting resistance received by the cutting blade body 31 is received by the guide holding portion 71 through the guide slit 77. That is, the forces received by the two cutting blades 21 due to the formation of the enlarged diameter portion Hb are received by the cutting blade holder 22 in a distributed manner. According to an experiment, the rotation speed of the bit portion 11 is preferably 10,000 rpm or more, and the enlarged diameter portion Hb is cut in about 10 to 20 seconds.

  Next, with reference to FIG. 3, the operation of expanding the prepared hole H by the diameter expanding drill bit 10 will be described. In this diameter expanding operation, it is assumed that a pilot hole H is previously formed in the target concrete skeleton A or the like. In this case, the concrete skeleton A includes a foundation, a beam, and the like in addition to the concrete outer wall, the inner wall, and the slab.

  In the diameter expanding operation, first, the diameter expanding drill bit 10 attached to the diameter expanding device 1 is inserted into the prepared hole H, and the spire portion 73 of the bit portion 11 is brought into contact with the hole bottom Ha of the prepared hole H. When the bit portion 11 abuts against the hole bottom Ha, the supply of the cooling liquid is started. After confirming the supply of the cooling liquid, the electric drill 2 is driven to rotate the drill bit 10 for diameter expansion. When the diameter-enlargement drill bit 10 rotates, a centrifugal force acts on the two cutting blades 21, and the two cutting blades 21 expand in a skirt shape.

  Thus, the grinding portion 52 of the rotating cutting blade body 31 grinds the inner surface of the prepared hole H, and the enlarged diameter portion Hb is formed at the back of the prepared hole H. On the other hand, the cooling liquid supplied from the cooling liquid pipe 17 is discharged from the inside of the holding section main body 41 toward the tip of the cutting blade main body 31 via the guide slit 77. The released coolant flows toward the tip of the bit portion 11 and then flows toward the opening of the prepared hole H to cool the cutting blade portion 21 to be ground.

  When the enlarged diameter portion Hb having the predetermined shape is formed in this manner, the restricted portion 57 of the cutting blade portion 21 comes into contact with the rotation restricting portion 67 (the distal end portion) of the holding portion receiver 42 and is caused by centrifugal force. The rotation of the cutting blade 21 is restricted. Due to the rotation control of the cutting blade 21, the rotational load of the electric drill 2 is sharply reduced, and the formation of the enlarged diameter portion Hb is confirmed. Here, the operator stops driving the electric drill 2, and pulls out the drill bit 10 for diameter expansion from the prepared hole H (stops supply of the coolant).

  As described above, according to the diameter-enlargement drill bit 10 of the present embodiment, the two cutting edge portions 21 that expand with the rotation of the bit portion 11 are separated by the two guide slits 77 of the cutting edge holding portion 22. While being guided, the cutting resistance is received by the cutting blade holder 22 via the two guide slits 77. For this reason, the force received by the cutting blade 21 is dispersed and received by the cutting blade holder 22, and the durability of the bit 11 can be improved. In addition, since the cutting resistance is received by the cutting blade holder 22, a large force is not applied around the turning support 56 of the cutting blade 21, and the turning support 56 is connected to the cutting blade holder 22 with a hinge pin or the like. There is no need to fixedly provide the Therefore, the entire structure of the bit portion 11 including the structure around the rotation support portion 56 can be simplified.

  Note that the guide holding portion 71 and the holding portion receiver 42 may be integrally formed, and the distal end flange portion 72 may be screwed (joined) to the guide holding portion 71. The number of the cutting blades 21 may be three or more.

  1: Drilling device, 2: Electric drill, 3: Coolant attachment, 10: Drill bit for diameter expansion, 11: Bit part, 12: Shank part, 17: Coolant pipe, 18: Channel in shank, 21: Off Blade part, 22: Cutting blade holding part, 31: Cutting blade main body, 32: Cutting blade supporting part, 41: Holding part main body, 42: Holding part receiving part, 54: Rib-shaped supporting part, 55: Arm part, 56: Rotation Moving support portion, 56a: arc-shaped outer peripheral surface, 57: regulated portion, 66: base holding portion, 67: rotation regulating portion, 71: guide holding portion, 72: distal flange portion, 73: spire portion, 75: cylindrical guide Part, 77: guide slit, A: concrete frame, H: pilot hole, Ha: hole bottom, Hb: enlarged diameter part

Claims (8)

A drill bit for diameter expansion used to be inserted into a prepared hole drilled in a skeleton and for expanding a part of the prepared hole by grinding,
A plurality of cutting blades that rotate outward in the radial direction by centrifugal force due to rotation and grind a part of the pilot hole, and a cutting that holds the plurality of cutting blades rotatably in the radial direction. A blade holding portion, and a shank portion that supports the cutting blade holding portion,
The plurality of cutting blades are disposed at point-symmetric positions around the axis,
Each of the cutting blade portions has a cutting blade body having an outer peripheral portion having an arc-shaped cross section, a rib-shaped support portion for supporting the cutting blade body from the inside, an arm portion extending in the axial direction from the rib-shaped support portion, A rotation support portion connected to the arm portion and serving as a base point of the rotation,
The cutting blade holding portion has a guide holding portion in which the rib-shaped support portion is slidably engaged with the turning, and a base holding portion for holding the turning support portion in a freely rotatable manner. A drill bit for diameter enlargement. The guide holding unit includes:
A cylindrical guide section,
The drill bit according to claim 1, further comprising: a guide slit formed in the cylindrical guide portion in an axial direction, and the rib-shaped support portion slidably engaging the guide slit.   3. The enlarged diameter according to claim 1, wherein the rotating support portion includes an arc-shaped outer peripheral surface, and the arc-shaped outer peripheral surface rotatably contacts an inner surface of the base holding portion. 4. For drill bit.   The said cutting blade holding part has the rotation restricting part which regulates the rotation end position of the radial outside of each said cutting blade part via the said arm part, The rotation control part characterized by the above-mentioned. 4. The drill bit for diameter expansion according to any one of 3. The cutting blade holding portion has a spire portion protruded and located coaxially at the tip portion,
The drill bit for diameter expansion according to any one of claims 1 to 4, wherein the spire portion is made of a super-steel material.   The said cutting blade holding part is fitted in the said pilot hole, and has a flange-shaped part formed in the non-expanded state with a larger diameter than the some cutting blade part, The characterized by the above-mentioned. The drill bit for diameter expansion according to any one of claims 1 to 5.   The expansion according to any one of claims 1 to 6, wherein the plurality of cutting blades are constituted by two of the cutting blades disposed at 180 ° point symmetrical positions around an axis. Drill bit for diameter. The shank portion is
For supplying a coolant to the plurality of cutting blades via the cutting blade holding unit, a shank body having a shank internal flow path,
8. A coolant pipe which communicates with the flow path in the shank and extends from a tip end of the shank main body to a vicinity of a tip end of the plurality of cutting blades. The drill bit for diameter expansion according to claim 1.

Images