KR101851160B1 - Hand drill coupled extended core bit - Google Patents

Abstract

The present invention relates to a hand drill coupling type expanding core bit capable of expanding a bottom part of a hole as a drilling bit is ejected and retracted when being operated by being mounted on a hand drill in a state of being inserted into a hole drilled on concrete by the hand drill, thereby providing user convenience simply attaching/detaching the expanding core bit to/from the hand drill, and providing operation safety selectively providing a pressing force of the drilling bit mechanically or by hydraulic pressure, and smoothly performing ejecting and retracting operation of the drilling bit. According to the present invention, the expanding core bit comprises: a main body having a hand drill coupling type upper part formed in a closed pipe shape and having a bottom closed by a cover; a plurality of bit ejecting and retracting holes formed on the main body in a circumferential direction to be placed on an upper side of the cover; a bit assembly including the drilling bit ejected and retracted through the bit ejecting and retracting holes; and a pressing means disposed on an upper side of the bit assembly, pressing the bit assembly to allow the drilling bit to be ejected through the bit ejecting and retracting hole in a pressing state, and retracting the drilling bit to the inside of the bit ejecting and retracting hole in a non-pressing state. When forming the expanding core bit, the expanding core bit includes a polygonal shaft support part formed in a center of a top of the main body to be engaged with and fixated in a chuck of the hand drill.

Description

[0001] The present invention relates to a hand drill coupled extended core bit

The present invention relates to a hand drill-coupled extended core bit which can be enlarged at the lower end of a hole while engaging with a hand drill in a state of being inserted into a hole drilled in a concrete using a hand drill, More specifically, it is intended to provide ease of use in which the expanded core bit can be easily detached and used in a hand drill, and the pressing force of the excavating bit is selectively made by mechanical or fluid pressure, To provide an operating safety to the hand drill.

An anchor bolt is inserted into the hole in a state where a hole is drilled in the concrete using a hand drill, or an anchor bolt is inserted together with a repair material such as a cement mortar or the like.

In addition, the bollard which is installed at the wharf to fix the ships, or the fixing ring which is installed to fix the fenders to prevent the collision of the side of the ship against the wharf, will be repaired and replaced after a certain period of time.

In general, as a method of repairing a bollard or a fixing ring, a bollard is separated from an anchor bolt, an anchor bolt or a ring exposed on a concrete surface is cut, and a hole is drilled around the anchor bolt After removing the core by a method of separating the core, an anchor bolt is inserted into the hole together with a repair material such as a cement mortar, and the repair material is cured.

This method is generally used because it can repair the fixing ring for bollard or fenders at low cost.

However, in the above-mentioned method, there is a problem that the repair material filled in the hole together with the anchor bolt is not firmly fused with the existing concrete, and is separated from the hole due to external impact.

On the other hand, a method of increasing the coupling strength between concrete and a repair material by forming an extension in the hole formed by the core bit may be proposed. However, in the case of the core bit used in the past, Korean Patent Publication No. 10-2014-0022287 (2014.02.24 A core bit for a core drill is proposed which has a coupling portion to be coupled to a core drill, a shank integrally provided with the coupling portion, a shank having a predetermined diameter, a plurality of holes provided on an outer peripheral surface of the shank, A plurality of grooves having an inclination angle of 30-80 degrees from the upper end toward the lower end with respect to the rotation direction are formed at regular intervals in the inner and outer circumferential surfaces of the tip, .

Another example is a separable core drill of the Korean Registered Utility Model (Y1) 20-0381846 (Apr. 26, 2005), which is composed of a cylindrical separable core drill mounted on a drill and perforating stone, asphalt, A coupling including a first coupling groove formed with a plurality of concave grooves on the lower outer peripheral portion, a drill mounting portion mounted with a drill on an inner circumferential surface of the upper surface, and a first insertion portion formed with a concave end on a lower outer peripheral portion, ; A second fastening groove having a plurality of "a" -shaped concave grooves formed on a lower outer circumferential portion thereof, and a second fastening groove having a plurality of " A tube having a first seating portion formed with a receiving end and a second insertion portion formed with a receiving end at a lower outer periphery, A plurality of second fastening portions protruding to be mounted on the second fastening groove on the upper inner circumference, a second seating portion formed with a concave / convex shape to receive the second inserting portion, A bit made of a machining tip to which a diamond is attached; As shown in FIG.

In the case of the core drills described above, the core drill is configured to improve the workability and to improve the usability of the core drill by separating the lower end coupled with the bit to improve the usability of the core drill. However, These technologies are not being used.

The inventors of the present invention have proposed the above-described problems in an expanded core bit for core drilling in Korean Patent Laid-Open Publication No. 10-2016-0149582 (Dec. 28, 2016) ; A main body in which a fastening screw portion screwed to the drive shaft of the core drill is formed at the upper end and is inserted into a hole formed by the core bit and the lower end is sealed by the cover; A plurality of bit projections formed circumferentially in the body so as to be positioned above the cover; A bit assembly including excavation bits which are exposed to and from the plurality of bit projection and extraction holes; A pressing means for pressing the excavating bit toward the bit projecting and retracting hole when the drive shaft is engaged with the clamping screw portion and allowing the excavating bit to be pulled into the bit projecting and recessing hole when the driving shaft is separated from the fastening screw portion, .

However, the above-described configuration has a problem in that it is difficult to create a hand drill carried by a worker, and the configuration of the bit assembly is complicated and the preparation of the bit assembly is deteriorated.

KR 1020140022287 A 2014.02.24. KR 200381846 Y1 2005.04.06. KR 1020160149582 A 2016.12.28.

The anchor bolts are separated from the concrete by an external force in the state where the anchor bolts are installed in the state where the holes are drilled in the conventional concrete, and the present invention was researched and developed.

That is, according to the present invention, a shaft portion is formed at the upper end of the main body so that it can be easily attached to the chuck of the hand drill so that the attachment and detachment can be performed easily. To be provided with a mechanical pressure by a compressed air or oil supplied through a mechanical or a swivel installed to freely rotate in the main body, thereby providing an operational safety for allowing the expansion bit to move smoothly. The present invention has been accomplished on the basis of the technical object of the present invention.

According to an aspect of the present invention, there is provided a hand drill comprising: a main body having a closed upper pipe structure and a lower end closed by a cover; A plurality of bit projections formed circumferentially in the body so as to be positioned above the cover; A bit assembly including excavation bits which are exposed to and from the plurality of bit projection and extraction holes; And an urging means for urging the bit assembly when the pressing assembly is in a pressurized state to push the excavating bit into the bit projecting and retracting hole, ; And a polygonal shank portion formed at the upper center of the body so as to be held by the chuck of the hand drill; The pressing means includes a rod having a lower end coupled to the bit assembly, a spring holding plate provided at an upper end of the rod, an upper spring disposed above the spring holding plate, a spring pressing plate positioned above the upper spring, A lower spring disposed on the plate lower rod; a spring support ring fixed to the body in a state that a rod hole through which the rod passes is formed at the center to support the lower spring; And a pressing nut which is coupled to the spring pressing plate and which is drawn out to the outside through an operation slot formed in the body in the axial direction and a pressing nut which presses the pressing pin in a state of being assembled to the thread portion formed in the main body.

The second hand drill-coupled upper portion is a closed pipe configuration and the lower end is sealed by the cover; A plurality of bit projections formed circumferentially in the body so as to be positioned above the cover; A bit assembly including excavation bits which are exposed to and from the plurality of bit projection and extraction holes; And an urging means for urging the bit assembly when the pressing assembly is in a pressurized state to push the excavating bit into the bit projecting and retracting hole, ; And a polygonal shank portion formed at the upper center of the body so as to be held by the chuck of the hand drill; The pressing means includes a rod having a lower end coupled to the bit assembly, a spring holding plate provided at an upper end of the rod, an upper spring disposed at an upper side of the spring holding plate, A lower spring located on the lower side of the spring seat plate and a rod hole through which the lower spring is supported and a rod through which the rod passes, A spring support ring fixed to the body; A fluid inlet hole and a fluid outlet hole formed in the main body so as to supply and discharge the fluid to and from the fluid inlet space, a fluid inlet hole communicating with the body so as to freely rotate to supply fluid to the fluid inlet hole, And a swivel to be used as a swivel.

Thirdly, the bit assembly is constituted of two upper and lower parts in the main body.

Fourth, the bit assembly includes a plurality of excavation bits protruding and retracted by the bit protruding and detaching holes formed in the body, and a pair of links each having one end fixed to the upper and lower ends of the excavating bit and the other end fixed to the rod.

Fifth, the bit assembly includes a plurality of excavating bits having a pressing piece formed to protrude and retract into a main body of the main body, and a bit spring interposed between the main body inner wall and the pressing piece to press the excavating bit to the inside of the main body, And a guide protrusion formed on the pressing piece is formed in an inclined shape below the rod so that when the rod moves downward, the excavating bit is pressed and the excavating bit is pulled out by the bit projecting and retracting hole, And an excavation bit is introduced into the excavator.

In the case of using the hand drill-coupled extended core bit provided in the present invention, it is possible to form an annular extension portion at the lower end of the hole by inserting the expanded core bit into the hole while drilling a hole in the building using a hand drill or the like will be.

Therefore, when the anchor bolt or the like installed in the hole is inserted and installed together with the repairing material, the repairing material flowing into the inside of the expanding part serves as an anchor in the cured state, so that a more rigid anchor bolt fixing state can be provided.

In addition, the hand drill-coupled extended core bit provided in the present invention has a polygonal shaft portion on the upper portion of the main body, and can be easily used by being chucked on the chuck of the hand drill. The excavation bit provided in the bit assembly can be taken out by the operation of the pressurizing means for supplying and discharging the excavation bit.

1 is an external perspective view showing a first preferred embodiment of a hand drill-coupled extended core bit provided by the present invention;
Fig. 2 is an exploded perspective view of Fig.
Figure 3 is a cross-
FIG. 4 is a cross-sectional view showing a configuration in which a bit assembly is installed in two stages in a hand drill-coupled extended core bit provided in the present invention
5 is an external perspective view showing a second preferred embodiment of the hand drill-coupled extended core bit provided by the present invention.
Fig. 6 is an exploded perspective view of Fig. 5
Figure 7 is a cross-
FIG. 8 is an exploded perspective view showing another example of a bit assembly that can be used in the present invention.
Figure 9 is a cross-
10 is a cross-sectional view
11 is a flowchart showing an operation sequence of forming an enlarged portion in a hole using the present invention

Preferred embodiments of the hand drill-coupled extended core bit provided in the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an external perspective view showing a first preferred embodiment of a hand drill-coupled extended core bit provided in the present invention, FIG. 2 is an exploded perspective view of FIG. 1, and FIG. 3 is a sectional view of FIG. 1 .

The hand drill-attached extended core bit 1 provided in the present invention is provided with a polygonal shank 3 at the upper end of the main body 2 for use in connection with the chuck 110 of the hand drill 100 . In the present invention, a hexagonal shaft portion 3 is shown.

The main body 2 has a pipe structure and its lower end is sealed by a cover 4. [ In the present invention, only the lower end portion 2a in which the bit assembly 10 is built is expanded so that the frictional resistance can be minimized in the state where the main body 2 is inserted into the hole 200 drilled by the drill, A plurality of bit projecting / recessing holes 5 are formed in the circumferential direction so as to pass through the inside and outside. This configuration minimizes the area of friction between the hole 200 and the main body 2 and simplifies the insertion of the main body 2 and allows the bit assembly 10 to be easily inserted into the bit assembly 10 when the main body 2 is rotated. And the frictional resistance can be increased.

The plurality of bit projecting and retracting holes 5 are formed to be narrow in width and longer in the axial direction and the excavating bit 11 coupled to the bit projecting and retracting hole 5 is tightly fitted in the width direction, And is provided so as to be capable of providing a sufficient clearance for vertically moving up and down in the longitudinal direction.

The excavation bit 11 is included in the bit assembly 10 and the bit assembly 10 comprises a excavation bit 11 and a link 11 having one end rotatably connected to the upper and lower ends of the excavation bit 11, (12), and a rod (13) rotatably coupled to the other end of the link (12) by a pin. A bit 11a such as a carbide or diamond is coupled to the excavation bit 11 so as to be able to crush concrete.

The bit assembly 10 is pressed by a pressing means 20 installed inside the main body 2.

The pushing means 20 presses the bit assembly 10 to pull the excavating bit 11 out of the bit projecting hole 5 or release the pressing force to pull the excavating bit 11 into the bit projecting / The spring assembly plate 21 is integrally formed on the upper end of the rod 13 constituting the bit assembly 10. The upper spring 22 ). And a lower spring 24 is disposed on the lower rod 13 of the spring holding plate 21. The lower spring 24 is disposed on the lower side of the spring holding plate 21,

The lower spring 24 is supported by a spring support ring 25 fixed to the main body 2 with a rod hole 25a through which the rod 13 passes.

The spring pressing plate 23 is provided with a pressing pin 27 that is pulled out to the outside through an operation slot 26 formed in the axial direction of the main body 2 and the pressing pin 27 is engaged with the threaded portion 28) of the pressing nut (29).

When the pressing nut 20 is configured as described above, when the pressing nut 29 is locked to the bit assembly 10 side, when the pressing nut 29 presses the pressing pin 27 coupled to the spring pressing plate 23, The upper spring 23 is pressed down. The upper spring 22 presses the spring seat plate 21 integrally formed on the upper end of the rod 13 and the lower spring 24 located between the spring seat plate 21 and the spring support ring 25 Compressed.

At this time, the excavating bit 11 of the bit assembly 10 coupled to the lower side of the rod 13 is pulled out from the bit projecting and recessing hole 5 formed in the main body 2 and positioned outside the main body 2, When the hand drill 100 is driven, the drilling bit 11 forms an annular extension 210 at the lower end of the hole 200. At this time, the excavation bit 11 is gradually drawn out as the extending portion 210 is formed.

When the pressing nut 29 is released to the opposite side of the bit assembly 10, the pressing force is removed from the pressing pin 27 which is coupled to the spring pressing plate 23 by the pressing nut 29. At this time, The spring holding plate 21 and the spring pressing plate 23, which are integrally formed with the rod 13, are pushed upward and restored to their original shape while the lower spring 24 and the lower spring 24 expand.

FIG. 4 is a cross-sectional view illustrating a configuration in which a bit assembly is installed in two stages in a hand drill-coupled extended core bit provided in the present invention.

As shown in FIG. 4, the bit assembly 10 is provided at the lower end of the main body 2 in two stages.

That is, as in the first embodiment of the present invention, the bit assembly 10 is mounted to the lower end of the rod 13, and the spring support ring 25 (not shown) supporting the lower bit assembly 10 and the lower spring 24 The bit assembly 10 is further configured to be positioned between the bit assembly 10 and the bit assembly 10.

The bit assembly 10 has the same configuration as that of the first embodiment, and it is of course possible to apply the bit assembly 10 as shown in FIGS. 8 to 10, which will be described later, although not separately shown.

FIG. 5 is an external perspective view showing a second preferred embodiment of the hand drill-coupled extended core bit provided by the present invention, FIG. 6 is an exploded perspective view of FIG. 5, and FIG. 7 is a sectional view of FIG. 5 will be.

The second embodiment of the hand drill-coupled extended core bit 1 of the present invention differs from the construction of the pressing means 20 in construction.

In the first embodiment, a configuration is proposed in which the pressure can be applied by using the pressure nut 29. However, in the second embodiment, the configuration is made possible by the fluid pressure.

The pushing means 20 includes a spring seat plate 21 integrally formed at the upper end of the rod 13 constituting the bit assembly 10, And the upper spring 22 is placed on the upper side of the main body 21. And a lower spring 24 is disposed on the lower rod 13 of the spring holding plate 21. The lower spring 24 is disposed on the lower side of the spring holding plate 21,

The lower spring 24 is supported by a spring support ring 25 fixed to the main body 2 with a rod hole 25a through which the rod 13 passes.

At this time, the spring-biasing plate 23 positioned above the upper spring 22 is assembled so as to ascend and descend from the inner surface of the main body 2 in a watertight state, and the fluid inflow space 30 is formed in the main body 2 on the upper side.

A fluid inflow hole 31 and a fluid discharge hole 32 are formed in the main body 2 to supply and discharge the fluid to and from the fluid inflow space 30, And a swivel 33 that freely rotates in a state of being freely rotatable and supplies fluid to the fluid inflow hole 31 and discharges the fluid to the fluid discharge hole 32. The swivel 33 is provided with fluid supply means So that the fluid can be supplied and discharged. In addition, the swivel (33) is equipped with a seal for maintaining watertightness with the main body (2) and a bearing for free rotation.

The fluid may be either compressed air or oil having pressure.

FIG. 8 is a perspective view showing another embodiment of a bit assembly that can be applied to the present invention, FIG. 9 is a front elevational view of the assembled state of FIG. 8, and FIG. 10 is a top sectional view of FIG.

This is another example of the bit assembly 10 that can be applied to the present invention and is composed of a pushing piece 11b formed to protrude into and retract into the bit projection and ejection hole 5 formed in the main body 2 and to be positioned inside the main body 2 The excavating bit 11 is pressed between the inner wall of the main body 2 and the pressing piece 11b via the bit spring 14 to press the inside of the main body 2 .

A guide protrusion 11c is formed in the pressing piece 11b so as to be inserted into the guide groove 15 formed in the rod 13. [

The guide protrusion 11c is inclined so that the guide protrusion 11c coincides with the inclined surface 15a of the guide groove 15, Lt; / RTI >

In the case of the bit assembly 10 described above, when the rod 13 is pressed downward by the pressing means 20, the guide protrusion 11c which is in the state of being inserted into the guide groove 15 moves toward the bit spring 14 The bit for spring 14 is pressed and the excavating bit 11 is drawn out to the outside of the bit projecting and depressing hole 5. Conversely, when the pressing force of the pressing means 20 is released, The guide protrusion 11c is moved toward the center of the main body 2 by the restoring force of the bit spring 14. At this time, the excavation bit 11 is drawn into the bit projecting /

11 shows an operation flow chart for forming an enlarged portion in a hole by using the present invention.

An example of forming the extended portion 210 in the drilled hole 200 using the hand drilled combined core bit 1 of the present invention is as follows: (1) (2) pulling in the expanded core bit, (3) pushing the bit assembly, (4) forming the extension, (4) releasing the pressing of the bit assembly and pulling out the expanded core bit. Hereinafter, do.

(1) Expanded core bit on hand drill

In order to use the hand drill-coupled extended core bit 1 provided in the present invention, the shaft portion 3 provided on the upper side of the main body 2 is first fixed to the chuck 110 of the hand drill 100.

(2) Extension core bit input

In this state, the hand drill-attached extended core bit 1 of the present invention is inserted into the hole 200 which is drilled using the drill while the shank portion 3 is fixed to the chuck 110.

At this time, the excavating bit 11 is positioned in the bit projecting / recessing hole 5 formed in the main body 2, so that the expanded core bit 1 is naturally drawn into the hole 200.

(3) Pressurization of the bit assembly

In a state in which the expanded core bit 1 is inserted into the hole 200, the bit assembly 10 is first pressed using the pressing means 20.

The pressing means 20 in the first embodiment can be achieved by rotating the pressing nut 29 or by rotating the hand drill 100 in the normal direction while holding the pressing nut 29 by hand , The pressing means 20 in the second embodiment supplies fluid to the fluid inflow space 30 to press the bit assembly 10. [

(4) Expansion part formation

When the bit assembly 10 is pressed using the pressing means 20 as described above, the excavating bit 11 of the bit assembly 10 is guided to the main body 2 through the bit projecting / When the hand drill 100 is driven in this state, the excavating bit 11 is gradually drawn outwardly to form the extended portion 210. In this case,

(5) Unpressing the bit assembly and withdrawing the expanded core bit

Since the extended core bit is drawn out from the hole 200 in the state where the extended portion 210 is formed in the hole 200 as described above is not possible by the excavating bit 11, The excavating bit 11 may be pulled into the main body 2 by removing the pressing force provided to the main body 10 and drawing the extended core bit.

The pressing means 20 in the first embodiment can be achieved by rotating the pressing nut 29 or by rotating the hand drill 100 in the reverse direction while holding the pressing nut 29 by hand , The pressing means 20 in the second embodiment may remove the pressing force for pressing the bit assembly 10 by discharging the fluid to the outside in the fluid inflow space 30. [

Although the present invention is described for the purpose of forming the enlarged portion 210 in the hole 200 drilled in the structure in the building, it is possible to prevent the hull of the ship from colliding with the bollard or the pier installed in the wharf It is obvious that the present invention can be variously applied to a repair work of a similar structure as well as an application for repairing a fixing ring or the like which is provided to fix a fendtable device to be prevented.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. Therefore, the scope of protection of the present invention should not be limited to the described embodiment, but should be determined by the equivalents as well as the claims that follow.

1: (Hand drill combined type) Extension core Bit 2: Body
2a: lower end portion 3:
4: cover 5: bit of immigration
10: bit assembly 11: excavation bit
11a: bit 11b:
11c: guide projection 11d:
12: Link 13: Load
14: spring for bit 15: guide groove
15a: inclined surface 20: pressing means
21: spring holding plate 22: upper spring
23: spring pressure plate 24: lower spring
25: spring support ring 25a: rod hole
26: working elongated hole 27: pressing pin
28: threaded portion 29: pressing nut
30: fluid inflow space 31: fluid inflow hole
32: fluid discharge hole 33: swivel
100: hand drill 110: chuck
200: hole 210: extension part

Claims (5)

A hand drill (100), comprising: a main body (2) in which a mating upper part is a closed pipe structure and a lower end is sealed by a cover (4); A plurality of bit projecting and depressing holes 5 formed in the main body 2 in the circumferential direction so as to be positioned above the cover 4; A bit assembly (10) including excavation bits (11) protruding and retracting into and out of said plurality of bit projecting and recessing holes (5); When the bit assembly 10 is positioned on the upper side of the bit assembly 10 and presses the bit assembly 10 so that the excavating bit 11 is pulled out to the bit projecting hole 5 and the excavating bit 11, (20) for pulling the bit core into the bit projecting / depressing hole (5);
And a polygonal shading portion (3) formed at the upper center of the main body (2) so as to be held by the chuck (110) of the hand drill (100);
The pressing means 20 includes a rod 13 coupled to the bit assembly 10 at the lower end thereof, a spring holding plate 21 provided at the upper end of the rod 13, A lower spring 24 positioned on the lower side rod 13 of the spring seat plate 21 and a lower spring 24 positioned on the upper side of the upper spring 22. The upper spring 22, A spring support ring 25 which is fixed to the main body 2 with a rod hole 25a through which the rod 13 passes; A pressing pin 27 which is coupled to the spring pressing plate 23 and drawn out to the outside through an operating slot 26 formed in the main body 2 in the axial direction and a screw 28 formed in the main body 2 And a pressing nut (29) for pressing the pressing pin (27).
A hand drill (100), comprising: a main body (2) in which a mating upper part is a closed pipe structure and a lower end is sealed by a cover (4); A plurality of bit projecting and depressing holes 5 formed in the main body 2 in the circumferential direction so as to be positioned above the cover 4; A bit assembly (10) including excavation bits (11) protruding and retracting into and out of said plurality of bit projecting and recessing holes (5); When the bit assembly 10 is positioned on the upper side of the bit assembly 10 and presses the bit assembly 10 so that the excavating bit 11 is pulled out to the bit projecting hole 5 and the excavating bit 11, (20) for pulling the bit core into the bit projecting / depressing hole (5);
And a polygonal shading portion (3) formed at the center of the upper end of the main body (2) so as to be held by the chuck (110) of the hand drill (100);
The pressing means 20 includes a rod 13 coupled to the bit assembly 10 at the lower end thereof, a spring holding plate 21 provided at the upper end of the rod 13, A spring 22 which is located on the upper side of the upper spring 22 and is assembled so as to ascend and descend from the inner surface of the main body 2 in a watertight state and in which the fluid inflow space 30 is formed in the main body 2, A lower spring 24 positioned on the lower rod 13 of the spring seat plate 21 and a rod hole 25a through which the rod 13 passes, A spring support ring (25) fixed to the main body (2) in a state in which the main body (2) is formed; A fluid inlet hole 31 and a fluid outlet hole 32 formed in the main body 2 to supply and discharge the fluid to and from the fluid inlet space 30; , And a swivel (33) connected to the fluid supply means and connected to the fluid supply means, the swivel (33) being connected to the fluid supply means.
The method according to claim 1 or 2,
Wherein the bit assembly (10) is formed on the body (2) at two upper and lower portions.
The method according to claim 1 or 2,
The bit assembly 10 includes a plurality of excavating bits 11 which protrude and retract into a bit projecting and recessing hole 5 formed in the main body 2,
And a pair of links (12) one end of which is fixed to the upper and lower ends of the excavating bit (11) and the other end is fixed to the rod (13).
The method according to claim 1 or 2,
The bit assembly 10 includes a plurality of excavating bits 11 having a pressing piece 11b formed in the main body 2 to protrude and retract into the bit projecting and recessing hole 5 formed in the main body 2, A bit spring 14 interposed between the inner wall and the pressing piece 11b for pressing the excavating bit 11 to the inside of the main body 2 and a guide protrusion 11c formed on the pressing piece 11b, So that when the rod 13 moves downward, the excavating bit 11 is pressed to draw the excavating bit 11 into the bit projecting and depressing hole 5, and when the excavating bit 11 is pulled out, 11) is released to allow the excavating bit (11) to enter into the bit projecting / retracting hole (5).

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