JP2017087352A - Drill bit for enlarging diameter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drill bit for enlarging a diameter which is configured so that large cutting resistance is not generated when starting to rotate.SOLUTION: A drill bit 10 for enlarging a diameter, which enlarges a diameter of a part of a lower hole H by cutting the part, comprises: a plurality of cutting blade portions 21 which are slid to outside in a radial direction by centrifugal force caused by rotation to grind the part of the lower hole H; a cutting blade holding portion 22 which holds slidably the plurality of cutting blade portions 21 individually in a radial direction; and a shank portion 12 that supports the cutting blade holding portion 22. Each of the cutting blade portions 21 has a cutting blade main body 51 formed in a shape in which a part in an axial direction is formed to cut into the lower hole H preceding to the other part, and a rib-like support portion 52 that supports the cutting blade main body 51 from inside and engages slidably with the cutting blade holding portion 22.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a drill bit for expanding a diameter for forming an enlarged diameter portion (undercut portion) for a pilot hole drilled in a casing such as concrete.

Conventionally, in order to form an anchor hole for driving an anchor, a diameter-expanding drill bit is known in which a diameter-expanded portion is formed in a prepared hole formed in a concrete frame (see Patent Document 1).
This diameter-expanding drill bit includes two cutting blade portions that grind the inner peripheral surface of the pilot hole, a cutting blade holding portion that holds the two cutting blade portions so as to be movable in the radial direction, and a cutting blade holding portion. And a shank portion for supporting. The cutting edge portion has a cutting blade main body having an arcuate cross section composed of a diamond cutting blade, a rib portion protruding from the inside of the cutting blade main body, and a retaining portion provided at the tip of the rib portion. ing. Two slit portions are formed in the 180 ° point symmetrical position in the cutting blade holding portion, and the two cutting blade portions are slidably engaged with the slit portions, respectively.
When the diameter-expanding drill bit rotates, the two cutting blade portions are guided by the slit portion in parallel with the centrifugal force and are translated in the radially outward direction. Thereby, two cutting blade parts grind the inner peripheral surface of a pilot hole, and a cylindrical enlarged diameter part is formed in a pilot hole.

International publication WO2014 / 129119A1

By the way, this type of drill bit for diameter expansion is used by being mounted on an electric drill as a power source. The electric drill incorporates an overcurrent circuit breaker that shuts off the power supply during overload in order to prevent seizure of the motor that is the power source.
On the other hand, in the conventional diameter-expanding drill bit, when the rotation is started, the outer peripheral surface of the cutting blade main body, which is a diamond cutting blade, instantaneously contacts the inner peripheral surface of the pilot hole by centrifugal force. That is, the cutting blade body that receives the centrifugal force comes into full contact with the inner peripheral surface of the pilot hole and starts grinding. For this reason, when the contact area of the cutting blade body is large (when the pilot hole has a large diameter), a large load (cutting resistance) is instantaneously generated when the motor (electric drill) is started, and the starting current and In addition, overcurrent may flow. In such a case, there is a problem that the overcurrent circuit breaker works to shut off the power source and the motor does not start.

  An object of the present invention is to provide a drill bit for diameter expansion that does not cause a large cutting resistance at the start of rotation.

  The diameter expansion drill bit of the present invention is a diameter expansion drill bit that is inserted into a pilot hole drilled in a housing and expands a part of the pilot hole by grinding, and is radial by centrifugal force accompanying rotation. A plurality of cutting blade portions that slide outward and grind a part of the pilot hole, a plurality of cutting blade portions that hold each of the plurality of cutting blade portions so as to be slidable in the radial direction, and support the cutting blade holding portion. A cutting blade main body formed in a shape in which a part in the axial direction is cut in advance with respect to the pilot hole, and the cutting blade main body from the inside. And a rib-like support portion that is slidably engaged with the cutting blade holding portion.

  According to this configuration, when the cutting blade holding portion rotates via the shank portion, the plurality of cutting blade portions held by the cutting blade holding portion slide and move outward in the radial direction. That is, the plurality of cutting blade portions that rotate together with the cutting blade holding portion move so as to expand outward in the radial direction under the centrifugal force, and a part of the pilot hole is ground and diameter-expanded. In this case, the cutting blade body of each cutting blade part is formed in a shape in which a part in the axial direction is cut in advance of the other part, so that the cutting blade body comes into full contact with the pilot hole at the start of rotation. No large cutting resistance is generated at the start of rotation. Therefore, even if an overcurrent circuit breaker is incorporated in the motor serving as the power source, it can be avoided that this operates.

  In this case, it is preferable that the cutting blade body is formed in a shape in which the tip side, which is a part in the axial direction, is cut into the pilot hole in advance of the other part.

  According to this configuration, a diameter-expanded portion having a shape whose back side is widened compared to the front side can be formed in the pilot hole, and a diameter-expanded shape suitable for a general post-installed anchor that exhibits a wedge effect. The part can be formed.

  In this case, the cutting blade main body is connected to the first grinding portion on the distal end side facing the parallel hole in the axial direction and the proximal end side of the first grinding portion, and is opposed to the bottom hole inclined in the axial direction. And 2 grinding parts.

  According to this configuration, when rotation is started, first, the entire region of the first grinding portion on the tip side comes into contact with the prepared hole. On the other hand, the second grinding portion starts contact with the prepared hole from the distal end side and gradually increases the contact area toward the proximal end side. In this case, since the first grinding part parallel to the pilot hole proceeds before the second grinding part, the contact with the pilot hole of the cutting blade body is stabilized and the diameter-enlarged part can be formed smoothly.

  Moreover, it is preferable that the cross section orthogonal to an axial direction is formed in the circular arc shape in the cutting-blade main body.

  According to this configuration, the length of the cutting blade body in the circumferential direction can be sufficiently taken, and grinding can be performed efficiently. Thereby, an enlarged diameter part can be formed in a short time.

  Furthermore, the cutting blade portion may further include a retaining portion that is continuous with the rib-shaped support portion and that contacts the cutting blade holding portion and restricts the position of the moving end of the cutting blade body radially outward. preferable.

  According to this configuration, the retaining portion can regulate the movement of each cutting blade portion in the radial direction, and the diameter expansion dimension of the diameter expanding portion to be ground can be adjusted appropriately.

  On the other hand, it is preferable that a cutting blade holding | maintenance part is coaxially located in a front-end | tip part, has a spire part, and a spire part is comprised with the super steel material.

  According to this configuration, the diameter-enlarged portion can be formed at a predetermined depth position with the spire portion pressed against the hole bottom of the pilot hole and rotated, with the hole bottom of the pilot hole used as a reference. In addition, since the spire portion makes point contact with the center of the hole bottom, friction with the hole bottom can be minimized as much as possible during rotation, and rotational blurring of the cutting edge portion can be suppressed as much as possible. Furthermore, since the spire portion is made of 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 prepared hole.

  Moreover, it is preferable that the cutting-blade holding part has a flange-shaped part that is inserted into the pilot hole and has a larger diameter than the plurality of non-expanded cutting blade parts.

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

  Furthermore, it is preferable that the plurality of cutting blade portions are composed of two cutting blade portions disposed at 180 ° point symmetrical positions around the axis.

  According to this configuration, the cutting blade portion and its surroundings can be configured compactly with a simple structure without impairing the cutting performance.

It is an external view of the diameter expansion apparatus containing the drill bit for diameter expansion of embodiment. It is a half cutting side surface around the bit in the drill bit for diameter expansion. It is the side view (a) of the non-expanded state around the bit of the drill bit for diameter expansion, and the side view (b) of the expanded state. It is an exploded perspective view around the bit in the drill bit for diameter expansion. It is the half part cutting side surface around the bit in the drill bit for diameter expansion of 2nd 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 diameter of the pilot hole formed in the frame of concrete or the like to drive the post-installed anchor, and can increase the pullout strength of the post-installed anchor Is. That is, in order to make the post-installed anchor driven into the prepared hole exhibit a theoretical wedge effect, this diameter-expanding drill bit forms an expanded portion in a part of the prepared hole.

  FIG. 1 is an external view of a diameter expansion device that forms a diameter expansion portion in a pilot hole. As shown in the figure, the diameter expansion device 1 has a hand-held electric drill 2, a coolant attachment 3 attached to the electric drill 2, and a diameter expansion drill bit 10 attached to the coolant attachment 3. ing. That is, the diameter-expanding drill bit 10 is used by being detachably mounted on the rotating shaft 3a of the coolant attachment 3 connected to the 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. It is supplied to the drill bit 10 for diameter expansion through the attachment 3. The coolant attachment 3 incorporates a valve for opening and closing the coolant flow path (not shown), and the valve is configured by abutting the diameter-expanding drill bit 10 against the hole bottom Ha of the pilot hole H. “Open” and “closed” when separated from the hole bottom Ha. The pilot hole H is drilled by a vibration drill, a hammer drill, a core bit, or the like.

  The drill bit 10 for expanding the diameter is detachably mounted on the rotating shaft 3a of the diameter expanding device 1 (coolant attachment 3) on the base end side and the bit portion 11 that forms the expanded diameter portion Hb in the pilot hole H. And a shank portion 12 that coaxially supports the bit portion 11 on the side. The shank portion 12 is integrally formed with a shank body 15 that supports the bit portion 11 and a large-diameter shaft portion 16 that is attached to the rotating shaft 3a. On the other hand, the bit part 11 is comprised by the two (a pair) cutting blade part 21 and the cutting blade holding | maintenance part 22 which hold | maintains the two cutting blade parts 21 so that sliding movement is possible. In this case, the bit part 11 is unitized, and is attached to the front-end | tip part of the shank part 12 (shank main body 15) so that attachment or detachment is possible.

  The shaft portion 16 has a fastening portion 16a formed with a female screw at its small end, and this fastening portion 16a is screwed to the rotating shaft 3a of the coolant attachment 3 formed with a male screw. Moreover, the front-end | tip male screw part 15a in which the bit part 11 is screwed together is formed in the front-end | tip part of the shank main body 15, The cutting blade holding | maintenance part 22 of the bit part 11 is screwing in this front-end | tip male screw part 15a. In addition, an in-shank flow path 18 for the coolant is formed in the shaft portion 16 and the axial center portion of the shank body 15. The coolant supplied from the coolant attachment 3 is supplied to the bit portion 11 through the in-shank flow path 18 to cool the two cutting blade portions 21 being ground.

  In addition, a coolant pipe communicating with the in-shank flow path 18 may be attached to the tip portion (tip male screw portion 15a) of the shank body 15. In this case, the coolant pipe is preferably extended to the vicinity of the tips of the two cutting blade portions 21 in the cutting blade holding portion 22. As a result, the coolant discharged from the coolant pipe circulates toward the tip side of the bit portion 11 and then flows toward the opening of the pilot hole H, so that the cutting blade portion 21 being ground is efficiently cooled.

  By the way, the above-mentioned diameter expanding device 1 is a wet type using a coolant, but a dry type using no coolant is also prepared. Although not particularly illustrated, in the dry-type diameter expanding device 1, the shank portion 12 does not have the in-shank flow path 18, and the diameter expanding drill bit 10 is directly connected to the electric drill 2. Further, in other dry-type diameter expanding apparatuses 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 these wet and dry diameter expanding drill bits 10 (diameter expanding apparatus 1).

  Next, the bit unit 11 will be described in detail with reference to FIGS. As described above, the bit portion 11 includes two (a pair of) cutting blade portions 21 for grinding the pilot hole H, and a cutting blade that holds the two cutting blade portions 21 in a slidable manner in the radial direction. Holding part 22. The cutting blade holding portion 22 is connected to the shank portion 12, and the cutting blade holding portion 22 and the two cutting blade portions 21 held thereby rotate as the shank portion 12 rotates. In addition, when the cutting blade holding portion 22 rotates, the two cutting blade portions 21 receive a centrifugal force and slide (translate) so as to expand outward in the radial direction. And when these two cutting blade parts 21 expand, the pilot hole H is ground and the enlarged diameter part Hb whose outline is a truncated cone shape is formed.

  The cutting blade holding portion 22 has a holding portion main body 31 that slidably holds the two cutting blade portions 21 and a holding portion receiver 32 on the shank portion 12 side to which the holding portion main body 31 is screwed. In this case, the bit part 11 is assembled by screwing the holding part main body 31 into the holding part receiver 32 after incorporating the two cutting blade parts 21 into the holding part main body 31. In addition, in this embodiment, although the holding | maintenance part main body 31 and the holding | maintenance part receiver 32 are made into screw joining, you may join this by welding etc. That is, the holding part main body 31 and the holding part receiver 32 may be in a detachable joining form or may be in a fixed joining form (fixed after the cutting blade part 21 is incorporated).

  The outer diameter of the holding portion receiver 32 is formed to be the same diameter as the tip ends of the two cutting blade portions 21 in the non-expanded state. Further, the outer diameter of the distal end flange portion 42 of the holding portion main body 31 described later is formed to be somewhat larger than the holding portion receiver 32 and the two cutting blade portions 21 having the same diameter. The holding portion receiver 32 may be formed integrally with the shank portion 12.

  The holding portion receiver 32 is integrally formed by a frustoconical shank connecting portion 34 connected to the shank portion 12 and a cylindrical main body connecting portion 35 connected to the shank connecting portion 34 and connected to the holding portion main body 31. Is formed. The shank connection portion 34 is formed with a first female screw portion 37 having a small diameter. The first female threaded portion 37 is screwed into the distal male threaded portion 15a of the shank portion 12, whereby the bit portion 11 is detachably attached to the shank portion 12. A second female threaded portion 38 is formed on the inner peripheral surface of the main body connecting portion 35 from the tip side. The base end side of the holding portion main body 31 is screwed into the second female screw portion 38, whereby the holding portion main body 31 is detachably incorporated in the holding portion receiver 32.

  The holding part main body 31 includes a cylindrical guide holding part 41 with which the cutting edge part 21 is slidably engaged, a flange-like tip flange part 42 (flange-like part) connected to the tip side of the guide holding part 41, and a tip. And a spire portion 43 provided on the distal end side of the flange portion 42. In this case, the guide holding part 41 and the tip flange part 42 are integrally formed. The two cutting blade portions 21 are held along the outer peripheral surface of the holding portion main body 31.

  The front end flange portion 42 has a front end half portion formed in a tapered shape, and a spire portion 43 is attached to an axial center portion of this portion. The spire portion 43 is made of, for example, a super steel alloy (super steel material), and is formed integrally with a tip cone portion 43a and a columnar portion 43b continuous therewith. In addition, the cone angle of the tapered portion of the tip flange portion 42 and the cone angle of the tip cone portion 43a are formed at the same angle, and the tip cone portion 43a is positioned on the extension of the tapered portion of the tip flange portion 42. It has become.

  The front flange portion 42 is formed to have a diameter (thickness) somewhat larger than the holding portion receiver 32 and the two cutting blade portions 21 having the same diameter. That is, the tip flange portion 42 is formed to have the largest diameter in the bit portion 11, and the diameter thereof is slightly smaller than the diameter of the pilot hole H (about 0.5 mm). The diameter-expanding drill bit 10 according to the embodiment rotates the spire portion 43 in a state of abutting against the hole bottom Ha of the pilot hole H, and forms a diameter-expanded portion Hb in the deep part of the pilot hole H. That is, when forming the enlarged diameter portion Hb, the enlarged diameter drill bit 10 is rotated in a state where the tip conical portion 43a is abutted against the center of the hole bottom Ha.

  As a result, the tip cone portion 43a (spire portion 43) makes point contact with the center of the hole bottom Ha, and the friction with the hole bottom Ha can be minimized as it rotates. Moreover, since the spire part 43 is comprised with the super steel alloy, wear of the spire part 43 can be suppressed as much as possible. Furthermore, the rotation blur of the bit part 11 (cutting edge part 21) can be suppressed by the spire part 43 and the large-diameter tip flange part 42. Therefore, the enlarged diameter portion Hb can always be formed at a predetermined position from the hole bottom Ha of the pilot hole H. In addition, although the spire part 43 is attached to the front-end | tip flange part 42 by welding, shrink fitting, etc., you may attach rotatably.

  The guide holding part 41 is formed in a cylindrical shape and integrally with the tip flange part 42. The guide holding portion 41 includes a cylindrical guide portion 45 extending from the front end flange portion 42, a cylindrical screw portion 46 that is connected to the cylindrical guide portion 45 and has the same diameter as the cylindrical guide portion 45, and the cylindrical guide portion 45 and the cylindrical screw portion. 46 and two guide slits 47 formed in 46 (see FIG. 4). A male screw is formed on the outer peripheral surface of the cylindrical screw portion 46. The male screw is screwed into the second female screw portion 38 of the holding portion receiver 32, and the holding portion main body 31 is detachably attached to the holding portion receiver 32.

Each guide slit 47 extends to the cylindrical guide portion 45 in the axial direction so as to be cut from the end of the cylindrical screw portion 46, and the slit width is freely slidable on a rib-like support portion 52 of the cutting blade portion 21 described later. It corresponds to the plate thickness of the rib-like support portion 52 so as to be engaged with each other. Further, the two guide slits 47 are formed at 180 ° point symmetrical positions in the circumferential direction of the cylindrical guide portion 45 and the cylindrical screw portion 46. Accordingly, the two cutting edge portions 21 are held at 180 ° point symmetrical positions by the guide holding portion 41. In this case, the two cutting blade portions 21 are incorporated into the guide holding portion 41 so as to slide from the end of the cylindrical screw portion 46, that is, from the small edge.

  As described above, the two cutting edge portions 21 are disposed at 180 ° point symmetrical positions around the axis, and the outer diameter in the non-expanded state is formed to be somewhat smaller than the diameter of the pilot hole H. . Thereby, when inserting the bit part 11 in the pilot hole H, the cutting blade part 21 is not caught in the pilot hole H, and the two cutting blade parts 21 are expanded so as to be translated in a balanced manner. .

  Each cutting blade portion 21 is provided at the end of a cutting blade body 51 having an outer peripheral portion having an arc-shaped cross section, a plate-like rib-like support portion 52 that supports the cutting blade body 51 from the inside, and the rib-like support portion 52. And a retaining portion 53. In this case, the cutting blade main body 51 is arranged so as to be along the outer peripheral surface of the holding portion main body 31 in a state where the base end portion is in contact with the holding portion main body 31. The rib-like support portion 52 is slidably engaged with the guide slit 47 of the holding portion main body 31 while supporting the cutting blade main body 51. The retaining portion 53 abuts on the inner side of the holding portion main body 31 and regulates the outer moving end position of the cutting blade main body 51.

  The cutting blade main body 51 is formed in a shape in which the tip side cuts into the pilot hole H prior to other portions. Specifically, the cutting blade body 51 is connected to the first grinding portion 55 on the distal end side facing the pilot hole H in the axial direction and the proximal end side of the first grinding portion 55, and the pilot hole H in the axial direction. And a second grinding portion 56 on the base end side that is inclined to face each other. That is, the cutting blade body 51 integrally connects the first grinding part 55 having a shape obtained by cutting a part of a cylinder and the second grinding part 56 having a shape obtained by cutting a part of a truncated cone in the axial direction. Is formed. As a result, the contour shape when the cutting blade body 51 rotates (strictly speaking, circular motion) becomes a shape obtained by adding a partial cylinder to the lower part of the truncated cone.

  Each of the first grinding part 55 and the second grinding part 56 is composed of a diamond cutting blade in which diamond is applied to the outer peripheral surface of a metal base. Thereby, when the cutting blade part 21 rotates by centrifugal force, the cutting blade main body 51 (the 1st grinding part 55 and the 2nd grinding part 56) contacts the inner peripheral surface of the pilot hole H, and this is ground. In this case, when the cutting edge portion 21 starts to rotate, first, the entire region of the first grinding portion 55 on the distal end side comes into contact with the pilot hole H and starts grinding. On the other hand, the second grinding part 56 starts contact with the pilot hole H from the front end side simultaneously with the first grinding part 55, and gradually increases the contact area toward the base end side. Then, at the final stage of grinding, the entire area of the first grinding portion 55 and the second grinding portion 56 comes into contact with the pilot hole H and is ground.

  In this embodiment, diamond is applied to the entire outer peripheral surface of the base, but it may be applied to a part of the circumferential direction. In addition, after grinding, the illustrated upper end portion of the cutting blade body 51 may be chamfered or tapered in order to facilitate drawing from the prepared hole H of the cutting blade portion 21.

  The rib-like support portion 52 is preferably formed in a plate shape so as to have the same height as the cutting blade body 51, and the cutting blade body 51 is welded to the end surface at an intermediate position in the circumferential direction. The rib-like support portion 52 is slidably engaged with the guide slit 47 (see FIG. 4) of the holding portion main body 31. That is, the rib-shaped support portion 52 connects the cutting blade body 51 positioned outside the holding portion body 31 and the retaining portion 53 positioned inside, and reduces the cutting resistance acting on the cutting blade body 51 to the guide slit. It has a function of escaping to the holding part main body 31 via 47.

  The retaining portion 53 is formed on the rib-like support portion 52 side in a circular arc shape along the inner peripheral surface of the holding portion main body 31 (guide holding portion 41). Then, when the retaining portion 53 comes into contact with the inner peripheral surface of the guide holding portion 41, the position of the outer moving end of the cutting blade portion 21 is regulated. That is, the initial position of the cutting blade body 51 along the outer peripheral surface of the guide holding portion 41 is the inner rotation end position (non-expanded state) of the cutting blade portion 21, and the retaining portion 53 is the inner periphery of the guide holding portion 41. The position in contact with the surface is the outer rotation end position (expanded state) of the cutting blade portion 21. In addition, it is preferable that the cutting depth to the pilot hole H regulated by the retaining portion 53, that is, the diameter expansion (radius) dimension of the diameter expansion portion Hb is about 3 to 5 mm on the distal end side.

  Next, with reference to FIG. 3, 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 previously formed 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.

  In the diameter expansion operation, first, the diameter expansion drill bit 10 attached to the diameter expansion device 1 is inserted into the pilot hole H, and the spire portion 43 of the bit part 11 is abutted against the hole bottom Ha of the pilot hole H. When the bit portion 11 is abutted against the hole bottom Ha, the supply of the cooling liquid is started. If supply of a cooling fluid is confirmed, the electric drill 2 will be driven and the drill bit 10 for diameter expansion will be rotated. When the diameter-expanding drill bit 10 rotates, centrifugal force acts on the two cutting blade portions 21, and the two cutting blade portions 21 expand.

  Thereby, the 1st grinding part 55 and the 2nd grinding part 56 of the rotating cutting-blade main body 51 grind the inner surface of the pilot hole H, gradually increasing a contact area. As a result, an enlarged-diameter portion Hb that follows the contour of the cutting blade body 51 (expands in a skirt shape) is formed in the inner portion of the prepared hole H. On the other hand, the coolant supplied from the in-shank channel 18 is supplied to the cutting blade body 51 from the inside of the holding portion body 31 through the guide slit 47 to cool the cutting blade body 51. According to the experiment, the rotational speed of the bit part 11 is preferably 10,000 rpm or more, and the enlarged diameter part Hb is cut in about 10 to 20 seconds.

  In this way, when the enlarged-diameter portion Hb having a predetermined shape is formed, the retaining portion 53 of the cutting blade portion 21 comes into contact with the inner peripheral surface of the guide holding portion 41, and the cutting blade portion 21 is moved by centrifugal force. Be regulated. Due to the movement restriction of the cutting blade portion 21, the rotational load of the electric drill 2 is rapidly reduced, and the formation of the enlarged diameter portion Hb is confirmed. Here, the operator stops the driving of the electric drill 2 and pulls out the diameter-expanding drill bit 10 from the pilot hole H (cooling liquid supply stop).

  As described above, according to the diameter expanding drill bit 10 of the present embodiment, the contour when the first grinding part 55 and the second grinding part 56 constituting the cutting blade body 51 rotate (circular movement around the axis). The shape is a shape obtained by adding a part of a cylinder to the lower part of the truncated cone. For this reason, when the cutting edge portion 21 starts to rotate, the entire area of the first grinding portion 55 on the front end side contacts the prepared hole H, while the second grinding portion 56 is connected to the first grinding portion 55 with respect to the prepared hole H. At the same time, contact is started from the distal end side, and the contact area is gradually increased toward the proximal end side.

  As a result, when the electric drill 2 starts to rotate, a large cutting resistance does not occur instantaneously around the bit portion 11, and this operates even if an overcurrent breaker is incorporated in the motor control circuit of the electric drill 2. There is nothing. Therefore, the problem that the motor does not start even when the electric drill 2 is driven can be solved. Note that the first grinding part 55 may be formed in a shape that is reversely inclined (reverse taper) to the second grinding part 56.

Next, with reference to FIG. 5, about the diameter-expansion drill bit 10 which concerns on 2nd Embodiment, a different part from 1st Embodiment is mainly demonstrated.
As shown in the figure, in this diameter-expanding drill bit 10, the cylindrical guide portion 45 of the holding portion main body 31 is formed in a tapered shape, that is, a truncated cone shape. The cutting blade body 51 is composed of a diamond cutting blade having a shape along the outer peripheral surface of the cylindrical guide portion 45. That is, the cutting blade body 51 is formed in a shape obtained by cutting a part of the truncated cone. The retaining portion 53 is also inclined following the tapered shape of the cylindrical guide portion 45.

  Also in the drill bit 10 for diameter expansion of the second embodiment configured as described above, the cutting blade body 51 starts contact with the pilot hole H from the distal end side, and gradually contacts the proximal end side. Will increase. Therefore, when the electric drill 2 starts to rotate, a large cutting resistance does not occur instantaneously around the bit portion 11, and even if an overcurrent breaker is incorporated in the motor control circuit of the electric drill 2, it operates. There is no.

  Note that the cutting blade body 51 of the present invention only needs to be formed in a shape in which a part in the axial direction is cut into the pilot hole H prior to the other part. For example, the cutting blade body of both embodiments The shape which turned 51 upside down in the axial direction may be sufficient. Further, the contour shape of the cutting blade body 51 when rotated may be a bell shape, a drum shape with a thick middle portion in the axial direction, a drum shape with a thin middle portion in the axial direction, or the like. On the other hand, the guide holding part 41 and the holding part receiver 32 may be integrally formed, and the tip flange part 42 may be screwed (joined) to the guide holding part 41. Moreover, the cutting blade part 21 may be three or more.

  DESCRIPTION OF SYMBOLS 1: Drilling device, 2: Electric drill, 3: Coolant attachment, 10: Drill bit for diameter expansion, 11: Bit part, 12: Shank part, 18: Shank flow path, 21: Cutting blade part, 22: Cutting Blade holding part, 31: Holding part body, 32: Holding part receiver, 41: Guide holding part, 42: Tip flange part, 43: Spire part, 45: Cylindrical guide part, 47: Guide slit, 51: Cutting blade body, 52: rib-shaped support part, 53: retaining part, 55: first grinding part, 56: second grinding part, A: concrete frame, H: pilot hole, Ha: hole bottom, Hb: diameter-enlarged part

Claims (8)

A drill bit for expanding a diameter, which is inserted into a prepared hole drilled in a housing and expands a part of the prepared hole by grinding,
A plurality of cutting blade portions that slide outward in the radial direction by centrifugal force accompanying rotation and grind a part of the pilot hole, and a cutting blade holder that holds the plurality of cutting blade portions slidably in the radial direction. And a shank portion that supports the cutting blade holding portion,
Each cutting edge part is
A cutting blade body formed in a shape in which a part of the axial direction is cut in advance of the other part with respect to the pilot hole,
A drill bit for diameter expansion characterized by having a rib-like support part which supports said cutting-blade main body from the inside, and engages slidably with said cutting-blade holding part.   2. The diameter-expanded diameter according to claim 1, wherein the cutting blade main body is formed in a shape in which a tip side that is a part in the axial direction is cut in advance of the other part with respect to the pilot hole. Drill bit for. The cutting blade body is
A first grinding portion on the front end side facing in parallel to the pilot hole in the axial direction;
The diameter-expanding drill bit according to claim 2, further comprising: a second grinding part that is connected to the base end side of the first grinding part and that is inclined to face the pilot hole in the axial direction.   The drill bit for diameter expansion according to any one of claims 1 to 3, wherein the cutting blade body has an arc-shaped cross section orthogonal to the axial direction.   The cutting blade portion further includes a retaining portion that is continuous with the rib-shaped support portion and that abuts against the cutting blade holding portion and regulates a position of a moving end of the cutting blade main body radially outward. The drill bit for diameter expansion as described in any one of Claims 1 thru | or 4 characterized by the above-mentioned. The cutting blade holding part has a spire part located coaxially at the tip part,
6. The diameter-expanding drill bit according to claim 1, wherein the spire portion is made of a super steel material.   The said cutting blade holding | maintenance part has the flange-shaped part formed in the larger diameter rather than the said several cutting blade part of a non-expanded state while being inserted in the said pilot hole. The drill bit for diameter expansion as described in any one of 1 thru | or 6.   The diameter expansion according to any one of claims 1 to 7, wherein the plurality of cutting blade portions are constituted by two cutting blade portions disposed at a 180 ° point symmetrical position around the axis. Drill bit for.

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