JP2014159094A - Drill bit for diameter expansion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drill bit for diameter expansion which can cope with a small-diameter prepared hole by a simple structure.SOLUTION: A drill bit 10 for diameter expansion, which is used by being inserted into a prepared hole H bored in a skeleton A and partially expands the diameter of the prepared hole H by grinding includes: a bit part 11 which has a plurality of individual bit parts 51 inserted into the prepared hole H and each provided with a cutting blade part 53 at a tip part of a shank part 52 and annularly arranges the plurality of individual bit parts 51; and a holder shaft part 12 which is detachably mounted to a power source-side rotary shaft 3a at its base end side and coaxially holds a base part of the bit part 11 at its tip side. The holder shaft part 12 holds the bit part 11 so that the tip side of the plurality of individual bit parts 51 expands radially outward by a centrifugal force due to rotation.

Description

  The present invention mainly relates to a diameter expanding drill bit for expanding the diameter of a part of a pilot hole drilled in a housing such as concrete.

Conventionally, as this type of diameter expansion drill bit, an undercut drill device is known which is inserted into a straight-shaped prepared hole drilled in a concrete body or the like and expands the innermost part of the prepared hole. (See Patent Document 1).
This undercut drill device includes a hollow cylindrical cylindrical body that is inserted into a pilot hole, a contact member that sits on the opening edge of the pilot hole and rotatably supports the cylindrical body via a bearing, A shaft that slidably engages with the cylindrical body and rotates integrally with the cylindrical body, a truncated cone-shaped cone portion provided on the distal end side of the cylindrical body and having four guide grooves on the outer peripheral surface, and a distal end portion of the shaft Four arms that are attached and engage with each guide groove, and two cutting blades and two guide portions that are alternately provided on the outer surface of the front end of the four arms are provided.
The cutting blade and the guide part are located inside the cylindrical body with the shaft pulled up. When the cylindrical body and the shaft inserted into the prepared hole are integrally rotated and the shaft is moved downward, the four arms are opened outward while being moved downward by the guide groove of the cone portion. Thereby, a cutting blade grinds the internal peripheral surface of a pilot hole, and forms an enlarged diameter part in the bottom part (deepest part) of a pilot hole.

JP 2005-280243 A

  Such a conventional undercut drill device has a structure in which the arm having the cutting edge is guided by the outer peripheral surface of the cone portion, so the cone portion must be supported by the cylindrical body, and the structure is extremely complicated. There was a problem. In addition, since the arm, the cone portion, and the cylindrical body are arranged outside the shaft, the whole has a large diameter, and there is a problem that it cannot be used for a relatively small diameter pilot hole.

  An object of the present invention is to provide a drill bit for expanding the diameter that has a simple structure and can also accommodate a pilot hole having a small diameter.

  The diameter-expanding drill bit of the present invention is used by being inserted into a pilot hole drilled in a casing, and is used for expanding a part of the pilot hole by grinding, and is inserted into the pilot hole. In addition to having a plurality of individual bit portions provided with a cutting edge portion at the distal end portion of the shank portion, a plurality of individual bit portions are arranged in a ring shape, and can be detachably attached to the rotating shaft on the power source side at the base end A holder shaft portion that is mounted and holds the bit portion coaxially at the base portion on the distal end side, and the distal end side of the plurality of individual bit portions expands radially outward by a centrifugal force accompanying rotation. As described above, the bit part is held.

  According to this configuration, when the power source is driven to rotate with the bit portion inserted into the pilot hole, the holder shaft portion and the bit portion rotate integrally. By this rotation, each of the plurality of individual bit portions constituting the bit portion receives a centrifugal force and expands outward in the radial direction. That is, the rotating individual bit portions are expanded radially outward by centrifugal force, and the cutting edge portion of each individual bit portion grinds a part of the pilot hole to expand the diameter. In this case, since the plurality of individual bit portions are configured to be expanded by centrifugal force, the structure can be simplified. In addition, the plurality of individual bit portions (bit portions) inserted into the pilot holes can be arranged in a radial direction and do not require an outer cylinder as in the prior art. Therefore, it is possible to cope (expand the diameter) with a pilot hole with a small diameter.

  In this case, it is preferable that a weight is provided at the tip of each individual bit portion.

  According to this configuration, since a strong centrifugal force can be applied to each individual bit portion, grinding of the pilot hole can be promoted, and the diameter can be increased in a short time.

  On the other hand, it is preferable to further include an adjustment attachment attached to the holder shaft portion and capable of adjusting the insertion depth of the bit portion into the prepared hole by contacting the opening edge of the prepared hole.

  According to this configuration, the insertion depth of the bit portion into the prepared hole can be adjusted by the adjustment attachment, and the diameter can be increased at an arbitrary depth position of the prepared hole.

  The plurality of individual bit portions are each formed in an arcuate cross section so as to form a circular cross section as a whole, and the engagement base portion held by the holder shaft portion is narrow and the outer arcuate step is formed. The holder shaft portion has an outer holder that comes into contact with each engagement base portion from the outside and an inner holder that comes into contact with the inside from the inside. An annular latching part is formed to latch the stepped part in the retaining state, and an annular protrusion is formed on the outer peripheral surface of the inner holder so as to face the annular latching part and serve as the expansion center of each individual bit part. It is preferable that

  According to this configuration, each individual bit portion maintains its retaining state so that the arc-shaped step portion is latched by the annular latching portion of the outer holder. Moreover, each individual bit part which expands rotates centering on the part which contacts the annular projection part of an inner holder. The engagement base portion of the individual bit portion is held in a state of being lifted by the annular projection portion of the inner holder, and this lifting allowance becomes a space for rotation of each individual bit portion. In this manner, the plurality of individual bit portions can be smoothly expanded centering on the base side. Moreover, since each cutting edge part makes circular arc shape, the grinding | polishing site | part of each cutting edge part transfers to the intermediate part from the whole circular arc-shaped peripheral surface as expansion progresses. That is, as the grinding progresses, the frictional resistance of the cutting edge portion decreases, so that the grinding can proceed smoothly.

  In this case, it is preferable that a plurality of guide projections for guiding the side surfaces of the respective engagement bases are formed on the outer peripheral surface of the inner holder when the individual bit portions are expanded.

  According to this configuration, the individual bit portions that are expanded (rotated) can be expanded outward against the rotational reaction force (twist) by the plurality of guide protrusions.

  Further, the plurality of individual bit portions are each formed in an arc-shaped cross section so as to form a circular cross-section as a whole, and are integrally formed in a cylindrical base portion held by the holder shaft portion, and each shank portion is It preferably has a spring property.

  According to this structure, the bit part which formed the cutting blade part in the peripheral surface whole region of a front-end | tip part can be formed as thin as possible. Moreover, since each cutting edge part makes circular arc shape, the grinding | polishing site | part of each cutting edge part transfers to the intermediate part from the whole circular arc-shaped peripheral surface as expansion progresses. That is, as the grinding progresses, the frictional resistance of the cutting edge portion decreases, so that the grinding can proceed smoothly. Furthermore, it is possible to maintain the integrity of the bit portion composed of a plurality of individual bit portions, and to smoothly expand the plurality of individual bit portions.

  On the other hand, the holder shaft portion has a flow passage in the shaft for supplying a coolant to the shaft center portion, and is attached to the holder shaft portion and disposed inside the bit portion, and is connected to the flow passage in the shaft. It is preferable to further provide an agent pipe.

  According to this configuration, the coolant can be supplied from the power source side to the distal end portion (cutting edge portion) of the bit portion (a plurality of individual bit portions) via the in-shaft flow path and the coolant pipe. For this reason, the diameter of the pilot hole can be smoothly and efficiently increased. Further, the expansion force can be applied to the individual bit portions by the coolant discharged from the coolant pipe. In addition, it is preferable to use a cooling fluid, compressed air, cooling gas, etc. as a coolant.

It is an external view of the state which mounted | wore the drilling apparatus with the drill bit for diameter expansion which concerns on embodiment. It is a structural diagram of the drill bit for diameter expansion concerning a 1st embodiment. It is a perspective view of the bit part circumference (a) and each individual bit part (b) of the drill bit for diameter expansion. It is explanatory drawing which shows the diameter expansion operation | movement of the drill bit for diameter expansion. FIG. 6 is a structural diagram of a bit part according to a modification of the first embodiment. It is a structural diagram of the drill bit for diameter expansion concerning a 2nd embodiment. It is a structural diagram of the drill bit for diameter expansion concerning a 3rd embodiment.

  Hereinafter, a drill bit for diameter expansion according to an embodiment of the present invention will be described with reference to the accompanying drawings. This diameter-expanding drill bit mainly expands the deepest part of the pilot hole formed in the frame of concrete or stone to drive the anchor, and can increase the pullout strength of the anchor It is. A straight-shaped pilot hole drilled with a diamond core drill or the like is drilled on the side of the opening and narrowed on the back side by a minute axial blur, and has a substantially tapered shape. For this reason, if a large force due to an earthquake or the like is repeatedly applied to the anchor that has been driven in, the pullout strength decreases with time. The diameter-expanding drill bit expands a part of the pilot hole in the same manner as the pilot hole in order to prevent such a decrease in the pullout strength of the anchor over time.

  FIG. 1 is an external view of a state in which a drill bit for diameter expansion is mounted on a drilling device. As shown in the figure, the drilling device 1 has a hand-held electric drill 2 and a coolant attachment 3 attached to the electric drill 2, and a drill bit 10 for expanding the diameter is attached to the coolant attachment 3. . That is, the drill bit for diameter expansion 10 is used by being detachably mounted on the rotary shaft 3a in the coolant attachment 3 of the drilling device 1 (electric drill 2) constituting the power source.

  A coolant flow path 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 to the coolant attachment. 3 is supplied to the distal end portion of the diameter-expanding drill bit 10. In the drilling device 1 of the embodiment, a drill bit for drilling (for example, a diamond core bit) is mounted on the coolant attachment 3 to drill the pilot hole H, and then a drill bit 10 for expanding the diameter is mounted instead of the drill bit for drilling. In addition, the innermost portion Ha (hole bottom portion) of the prepared hole H is expanded in diameter.

  FIG. 2 is a structural diagram of the diameter-expansion drill bit 10 according to the first embodiment. As shown in the figure, the drill bit 10 for expanding the diameter is attached to and detached from the bit portion 11 for expanding the diameter of the pilot hole H at the distal end portion and the rotating shaft 3a (coolant attachment 3) of the drilling device 1 at the proximal end side. A holder shaft portion 12 that is freely mounted and that holds the bit portion 11 coaxially at the base portion on the distal end side. The diameter-expanding drill bit 10 is provided with a coolant pipe 13 (coolant pipe) that is provided coaxially at the tip of the holder shaft portion 12 and extends forward in the bit portion 11. In this diameter-expanding drill bit 10, the bit part 11 is expanded by centrifugal force by rotating the diameter-expanding drill bit 10 with the drilling device 1 in a state where the bit part 11 is inserted into the pilot hole H (FIG. 4).

  The holder shaft portion 12 includes a shaft main body 21 that is detachably attached to the drilling device 1 (coolant attachment 3), a holder attachment portion 22 that extends coaxially from the tip of the shaft main body 21, and a holder attachment portion 22 that is coaxial. And an outer holder 24 attached to the holder attachment portion 22 in a state of surrounding the inner holder 23. In the gap between the inner holder 23 and the outer holder 24, the bit portion 11 is held at the base portion.

  The shaft main body 21 has a female screw portion 31 that is recessed in the small opening, and this female screw portion 31 is screwed into a male screw portion (see FIG. 1) of the rotating shaft 3 a of the coolant attachment 3. Although not shown in the drawings, a tool hooking portion for a spanner is formed on the shaft main body 21, and the holder shaft portion 12 is detachably attached to the coolant attachment 3, that is, the perforating apparatus 1 at the female screw portion 31.

  The shaft main body 21, the holder mounting portion 22, and the inner holder 23 are integrally formed, and an in-shaft flow path 35 for cooling liquid is formed in these axial centers. The in-shaft flow path 35 communicates with the coolant attachment 3 on the proximal end side, and communicates with the coolant pipe 13 on the distal end side. When the holder shaft portion 12 is attached to the rotating shaft 3 a of the coolant attachment 3, the in-shaft flow path 25, the coolant pipe 13, and the coolant attachment 3 communicate with each other, and the coolant flows from the coolant attachment 3. Is possible.

  The coolant pipe 13 may be formed integrally with the holder shaft portion 12 (inner holder 23), or may be fixed to the inner holder 23 by screwing or the like (separate body). Moreover, it is preferable that the front-end | tip of the cooling fluid pipe 13 is made into the structure where a cooling fluid is discharge | released toward the inner side of the cutting blade part 53 mentioned later (it mentions later for details). Note that compressed air or cooling gas can be used instead of the cooling liquid (details will be described later).

  The holder attachment portion 22 is formed to have a smaller diameter than the shaft main body 21, and is formed to extend forward from the tip of the shaft main body 21. A male screw is formed on the outer peripheral surface of the holder mounting portion 22, and the outer holder 24 is screwed into this portion.

  As shown in FIGS. 2 and 3, the inner holder 23 is formed so as to have a smaller diameter than the holder mounting portion 22 and extends from the holder mounting portion 22 to the front. The inner holder 23 includes a cylindrical inner main body 41, an annular protrusion 42 having a wedge-shaped cross-section protruding from the outer peripheral surface of the inner main body 41, and four guide protrusions protruding from the outer peripheral surface of the inner main body 41. Part 43. Each guide projection 43 is formed in an oval shape that is long in the axial direction, and the four guide projections 43 are equally arranged in the circumferential direction. As will be described in detail later, the engagement base portion 57 of the individual bit portion 51 is disposed so that the inner surface thereof is in contact with the annular projection portion 42 and is sandwiched between two adjacent guide projection portions 43.

  The outer holder 24 has a cylindrical outer main body 45 and an annular latching portion 46 projecting from the inner peripheral surface of the distal end portion of the outer main body 45. A female screw is formed on the inner peripheral surface of the base portion side of the outer main body 45, and the outer holder 24 is detachably screwed to the holder mounting portion 22 at this portion. Although not shown, a tool hook portion for screwing the outer holder 24 is formed on the outer peripheral surface of the outer main body 45.

  The annular latching portion 46 is formed in a wedge shape in cross section, and protrudes inward at the distal end portion of the outer main body 45. Although details will be described later, an arc-shaped stepped portion 58 connected to the engagement base portion 57 of the individual bit portion 51 is engaged with the annular latching portion 46 to prevent the individual bit portions 51 (bit portions 11) from coming off. It has come to be. And the annular latching | locking part 46 of the outer holder 24 with which the holder attaching part 22 was mounted | worn is arrange | positioned in the vicinity in the axial direction so that the annular projection part 42 of the inner holder 23 may be opposed.

  As shown in FIG. 2 and FIG. 3, the bit unit 11 is configured by arranging a plurality (four in the figure) of individual bit units 51 in a ring shape. Specifically, the bit part 11 has the form which divided the bit which provided the cylindrical cutting blade in the front-end | tip part of a cylindrical shank into 4 in the circumferential direction. Each individual bit portion 51 includes a shank portion 52 having a ¼ arc cross section that is held by the holder shaft portion 12, and a cutting edge portion 53 having a ¼ arc cross section provided (welded) at the tip of the shank portion 52. (See FIG. 3B). That is, the plurality of individual bit portions 51 are each formed in an arcuate cross section so that the whole has a circular cross section. The plurality of individual bit portions 51 configured in this way expands around the base portion of each shank portion 52 by centrifugal force generated by rotation.

  As shown in FIG. 3, each shank portion 52 includes a shank portion main body 55 that extends in the axial direction and an engagement base portion 57 that continues to the proximal end side of the shank portion main body 55. The engagement base portion 57 is a portion that is held by the holder shaft portion 12, and is formed narrower than the shank portion main body 55. Thereby, the four engagement bases 57 can be inserted into the outer holder 24.

  Further, the engagement base portion 57 is formed thick with respect to the shank portion main body 55 with an arc-shaped step portion 58 formed outside. In this case, in a state where the plurality of individual bit portions 51 are closed (non-expanded state), the engagement base portion 57 of each shank portion 52 comes into contact with the inner peripheral surface of the outer holder 24 (outer main body 45), and the expanded state. Regardless of the unexpanded state, the arc-shaped stepped portion 58 is hooked on the annular hooking portion 46 of the outer holder 24.

  On the other hand, each engagement base 57 contacts the annular protrusion 42 of the inner holder 23 on the inner peripheral surface at the front end side (substantially the position of the arc-shaped stepped portion 58), and both side surfaces are two guide protrusions of the inner holder 23. Contact is made so as to be sandwiched between the portions 43. The engagement base 57 may be configured by stacking and welding arc-shaped members constituting the arc-shaped stepped portion 58 on the base of the shank portion main body 55 formed narrow.

  The plurality of individual bit parts 51 in the non-expanded state are hooked in the retaining state in the outer holder 24 in each shank part 52 and are in contact with the tip part of the inner holder 23. Further, a gap corresponding to the projecting dimension of the annular protrusion 42 is formed between the inner main body 41 and the engagement base 57. When the state shifts from this state to the expanded state by centrifugal force, each of the shank portions 52 rotates around the annular protrusion 42 and is guided by the guide protrusion 43. Thereby, the base end side of the engagement base 57 that has been in contact with the outer main body 45 moves to the inner main body 41 side, and the rotation of the shank portion 52 (each individual bit portion 51) is allowed.

  Each cutting edge portion 53 is constituted by a diamond cutting edge having an arc cross section, and the diamond for grinding is provided only on the outer peripheral surface. Thereby, the innermost peripheral surface Ha of the pilot hole H is ground and diameter-expanded to a predetermined dimension. In addition, since the diameter expansion of the pilot hole H in the embodiment is intended to prevent the anchor from coming off, the diameter expansion dimension may be minute. Therefore, it is preferable that the movement of the cutting edge portion 53 is about 0.1 to 2 mm. Further, it is preferable that a strong centrifugal force acts on the cutting edge portion 53 during the grinding. For this reason, it is preferable to provide the weight 61 on the inner surface of the cutting edge portion 53 (indicated by a virtual line in FIG. 3). The weight 61 is assumed to have a heavy specific gravity, such as lead or tungsten. A weight 61 is preferably provided at the tip of the shank portion 52.

  Since each cutting edge 53 has an arc shape, as the spread progresses, the grinding portion shifts from the entire arc-shaped peripheral surface to the intermediate portion (see FIG. 4). That is, as the grinding progresses, the frictional resistance of the cutting edge portion 53 decreases, so that the grinding can proceed smoothly. Moreover, in order to reduce the grinding resistance in the initial stage of grinding, it is preferable that the circumferential front end side (front end side in the rotation direction) of the cutting blade body 61 is chamfered. In the circumferential direction, the diameter of this portion in the state where the four cutting edge portions 53 are in contact with each other (initial state) is formed to be smaller than the diameter of the pilot hole H by about 0.5 to 1.0 mm. The bit portion 11 can be smoothly inserted into the prepared hole H.

  Next, with reference to FIG. 1 and FIG. 4, the diameter expansion work of the pilot hole H by the diameter expansion drill bit 10 is demonstrated. In this diameter expansion work, it is assumed that a pilot hole H is formed in advance in a target concrete frame A or the like. In addition, the concrete frame A in this case includes a foundation, a beam, and the like in addition to a concrete outer wall, an inner wall, and a slab. The pilot hole H is formed by, for example, a drilling operation in which a diamond core bit is mounted on the drilling device 1 described above.

  In the diameter expansion work, first, the diameter expansion drill bit 10 is mounted on the drilling device 1, and the bit portion 11 is inserted into the pilot hole H (see FIG. 4A). When the bit portion 11 is inserted so as to abut against the bottom of the pilot hole H, the electric drill 2 is driven to rotate the diameter-expanding drill bit 10. At the same time or in succession, the coolant is supplied to the cutting blade portion 53 via the in-shaft channel 35 and the coolant pipe 13.

  When the diameter-expanding drill bit 10 rotates, centrifugal force acts on the four individual bit portions 51 to expand the four individual bit portions 51 outward (see FIG. 4B). In addition, the coolant discharged from the coolant pipe 13 also spreads radially at the inner portions of the four cutting blade portions 53, and promotes the expansion of the individual bit portions 51. Thereby, the cutting edge part 53 of each rotating individual bit part 51 grinds the inner surface of the pilot hole H, and the innermost part Ha of the pilot hole H is expanded in diameter. Then, when a predetermined time (about 10 to 20 seconds) elapses from the rotation start of the diameter expanding drill bit 10, the innermost portion Ha is expanded to a predetermined size.

  Here (after a predetermined time has elapsed), the operator turns off the electric drill 2 and stops the rotation of the diameter-expanding drill bit 10 (the supply of the coolant is also stopped). As a result, the centrifugal force acting on the four individual bit portions 51 becomes zero, and the initial state is restored so that the four individual bit portions 51 are closed. Subsequently, the bit part 11 is pulled out.

  Thus, in the first embodiment, the innermost portion Ha of the pilot hole H can be expanded in a short time simply by inserting the bit part 11 into the pilot hole H and rotating it for a predetermined time. In addition, since the plurality of individual bit portions 51 are configured to be expanded by centrifugal force, the device configuration can be simplified. Furthermore, since the plurality of individual bit portions 51 can be arranged in the radial direction, it is possible to appropriately expand the diameter of the small-diameter prepared hole H.

FIG. 5 shows a bit part 11A according to a modification of the first embodiment. As shown in the figure, in this bit portion 11A, four individual bit portions 51 are configured to mesh with each other in the shank portions 52. That is, both side surfaces 52a of each shank part 52 are formed in a concavo-convex shape, and adjacent shank parts 52 are meshed with each other on the side surface 52a.
In such a configuration, the shank portions 52 mesh with each other, so that torsional deformation generated in the four rotating individual bit portions 51 is suppressed, and the strength of the bit portion 11A against rotation can be increased.

  Next, with reference to FIG. 6, about the diameter-expansion drill bit 10A which concerns on 2nd Embodiment, a different part from 1st Embodiment is mainly demonstrated. As shown in the figure, the diameter-expanding drill bit 10A is different from the diameter-expanding drill bit 10 of the first embodiment in which the innermost portion Ha of the prepared hole H is expanded, and has an arbitrary depth of the prepared hole H. It is intended to expand the position. For this reason, 10 A of diameter-expansion drill bits of 2nd Embodiment are further provided with the adjustment attachment 70 which can adjust the insertion depth to the pilot hole H of the bit part 11. FIG.

  The adjustment attachment 70 is provided at a cylindrical attachment main body 71 that is screwed to the holder shaft portion 12, a set screw portion 72 that is screwed to the holder shaft portion 12 adjacent to the attachment main body 71, and a distal end portion of the attachment main body 71. And an annular rotation receiving portion 73.

  A male screw is formed on the outer peripheral surface of the shaft main body 31. Correspondingly, a female screw is formed on the inner peripheral surface of the attachment main body 71 and the inner peripheral surface of the set screw portion 72. After the set screw portion 72 is deeply screwed into the shaft main body 31, the attachment main body 71 is screwed to adjust the insertion depth of the bit portion 11 into the pilot hole H. When the adjustment is completed, the set screw portion 72 is returned and tightened so as to come into contact with the attachment main body 71 so that the attachment main body 71 does not loosen. In addition, it is preferable to form a scale for indicating the insertion depth on the outer peripheral surface of the shaft body 31.

  The rotation receiving portion 73 is constituted by a thrust bearing, for example, and comes into contact with the opening edge portion of the pilot hole H. The attachment main body 71 and the set screw portion 72 rotate together with the holder shaft portion 12, but the rotation is received by the rotation receiving portion 73 so that the rotational power is not transmitted to the opening edge portion of the pilot hole H.

  In such a configuration, the insertion depth of the bit portion 11 into the prepared hole H can be adjusted by the screwing depth of the attachment main body 71. That is, an enlarged diameter portion can be formed at an arbitrary depth position of the pilot hole H.

  Next, with reference to FIG. 7, with respect to the diameter-expanding drill bit 10B according to the third embodiment, portions different from the first embodiment will be mainly described. As shown in the drawing, in this diameter-expanding drill bit 10B, the bit portion 11B has a base portion provided with a cylindrical cutting edge at a tip end portion of a cylindrical shank by a plurality of axial cuts. And has a form divided into a plurality of parts in the circumferential direction. That is, the bit portion 11B includes a cylindrical base portion 81, four shank portions 52 extending from the cylindrical base portion 81 and arranged in an annular shape with a split slit 82, and four cut portions formed at the tip of the shank portion 52. And a blade portion 53. A male screw member 83 for attaching the bit portion 11B to the holder shaft portion 12 is welded to the outside of the cylindrical base portion 81. Furthermore, each shank part 52 has a spring property so that it can be expanded by centrifugal force.

  On the other hand, the holder shaft portion 12 in this case does not have the inner holder 33 and the outer holder 34, and has the shaft main body 31 and a bit attachment portion 85 that is connected to the shaft main body 31 and has an internal thread formed on the inner peripheral surface. The bit portion 11B is detachably screwed to the bit attachment portion 85 of the holder shaft portion 12 by a male screw member 83 provided at the base portion.

  In such a structure, each shank part 52 bends and the four individual bit parts 51 are expanded by the centrifugal force accompanying rotation of the diameter expansion drill bit 10B. When the rotation is stopped from this state, the four individual bit portions 51 are closed by their own spring characteristics. In this case, the cylindrical base portion 81 maintains the integrity of the plurality of individual bit portions 51, and the plurality of individual bit portions 51 can be opened and closed smoothly. However, the shank part 52 may be separated and integrated with the male screw member 83.

  In the present embodiment, the number of individual bit units 51 is four, but it may be two, three, five, or the like. Moreover, although each shank part 52 was made into the circular-arc shaped cross section, a rectangular cross section etc. may be sufficient. Further, when compressed air or cooling gas is used instead of the cooling liquid, a compressed air supply device (compressor or the like) is connected to the cooling liquid attachment 3 instead of the cooling liquid supply device, or the cooling liquid attachment 3 is connected to the cooling liquid attachment 3. Instead, a cooling gas attachment capable of mounting a gas cylinder such as a liquefied gas is used.

  DESCRIPTION OF SYMBOLS 1 Drilling device, 2 Electric drill, 3 Coolant attachment, 3a Rotating shaft 10, 10A, 10B Diameter expansion drill bit, 11, 11A, 11B Bit part, 12 Holder shaft part, 13 Coolant pipe, 21 Shaft body, 22 Holder mounting portion, 23 Inner holder, 24 Outer holder, 35 In-shaft channel, 42 Annular projection, 43 Guide projection, 46 Annular latch, 51 Individual bit, 52 Shank, 53 Cutting edge, 57 Engagement base, 58 arc-shaped step, 61 weight, 70 adjustment attachment, 81 cylindrical base, A concrete frame, H pilot hole, Ha innermost part

Claims (7)

A drill bit for expanding the diameter, which is used by being inserted into a prepared hole drilled in a housing, for expanding a part of the prepared hole by grinding,
A bit portion inserted into the pilot hole and having a plurality of individual bit portions provided with a cutting edge portion at a tip portion of the shank portion, and a plurality of the individual bit portions arranged annularly,
A holder shaft portion that is detachably attached to the rotating shaft on the power source side at the base end side, and that holds the bit portion coaxially at the base portion at the tip end side;
The diameter increasing drill bit characterized in that the holder shaft portion holds the bit portion so that the distal end side of the plurality of individual bit portions expands radially outward by centrifugal force accompanying rotation. .   The diameter expanding drill bit according to claim 1, wherein a weight is provided at a distal end portion of each individual bit portion.   2. An adjustment attachment attached to the holder shaft portion and capable of adjusting an insertion depth of the bit portion into the pilot hole by contacting an opening edge of the pilot hole. Or the drill bit for diameter expansion of 2. The plurality of individual bit portions are each formed in an arc-shaped cross section so as to form a circular cross-section as a whole, and the engagement base portion held by the holder shaft portion is narrow and has an outer arc-shaped step. Part is formed thick,
The holder shaft portion has an outer holder that contacts each engagement base from the outside and an inner holder that contacts from the inside,
On the inner peripheral surface of the outer holder, an annular latching portion is formed on which each arc-shaped stepped portion is latched in a retaining state,
4. An annular projection that is an expansion center of each individual bit portion is formed on the outer peripheral surface of the inner holder so as to face the annular latching portion. The drill bit for diameter expansion as described in 1.   5. The expansion according to claim 4, wherein a plurality of guide protrusions are formed on an outer peripheral surface of the inner holder to guide side surfaces of the engagement bases when the individual bit portions are expanded. Diameter drill bit. The plurality of individual bit portions are each formed in an arcuate cross section so as to form a circular cross section as a whole, and are integrally formed in a cylindrical base portion held by the holder shaft portion,
The diameter-expanding drill bit according to any one of claims 1 to 3, wherein each of the shank portions has a spring property. The holder shaft portion has a flow path in the shaft for supplying a coolant to the shaft center portion,
The coolant pipe according to any one of claims 1 to 6, further comprising a coolant pipe attached to the holder shaft portion and disposed inside the bit portion and communicating with the flow path in the shaft. Drill bit for diameter expansion.

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