JP2001146886A - Excavating tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excavating tool capable of excavating holes with different inner diameters even with one tool body for erecting casing pipes with different outer diameters. SOLUTION: This excavating tool has diameter-enlarged bits 26 fitted to the tip part outer periphery of the tool body 11 rotated around an axis O, so as to be rotatable around center axes X parallel with the axis O and decentered onto the outer peripheral side. Following the rotation of the tool body 11 during excavation, the diameter-enlarged bits 26 are rotated in such a manner as to enlarge the outer diameter from the axis O. In such an excavating tool, the tool body 11 can be fitted with plural kinds of diameter-enlarged bits 80 different in outer diameter from the axis O when enlarged in diameter during excavation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excavating tool having a diameter-enlarging bit whose outer diameter increases with the rotation of the tool body during excavation.

[0002]

2. Description of the Related Art As such a drilling tool, the inventors of the present invention have proposed the one shown in FIGS. 6 and 7 in Japanese Patent Application No. 9-235246. In the excavating tool shown in these figures, the axis of the tool body 1 is located at the center of the tip of a substantially multi-stage cylindrical tool body (device) 1 whose diameter gradually increases toward the tip side (left side in FIG. 6). A mounting hole 2 is formed along O, and a number of chips 4 made of a hard material such as cemented carbide are implanted in the mounting hole 2 at the tip of a disc-shaped bit body 3A, and a cutting edge is provided. The pilot bit 3 is mounted by screwing a mounting shaft 3B protruding from the rear end surface of the bit main body 3A. A plurality of recesses 5 are formed on the outer periphery of the distal end portion of the tool body 1, and a support hole having a center axis X eccentric to the outer circumference with respect to the axis O is formed on the bottom surface of these recesses 5. 5A are respectively formed, and in this support hole 5A,
A tip 7 is also implanted at the tip of the bit body 6A, and an enlarged bit 6 provided with a cutting edge is provided.
A shaft portion 6B protruding from the rear end surface of A is fitted and rotatably mounted around the central axis X.

[0003] The excavating tool thus constructed is provided with a hammer (not shown) attached to a shank portion 1A on the rear end side of the tool body 1 to be rotated about an axis O in a tool rotation direction T and to have a tip end in the axis O direction. Receiving the impact force on the side, the enlarged diameter bit 6 is rotated to the rear side in the tool rotation direction T around the central axis X, and is positioned in a state in which the outer diameter from the axis O is enlarged, and the diameter is increased. The cutting edge 7 of the bit 6
A hole is formed in the ground or the like by the cutting edge 4 of the pilot bit 3 and the casing pipe 8 is inserted into the hole through a casing top 8A that engages with the tool body 1 toward the tip end in the direction of the axis O. Build in. After the end of the excavation, by rotating the tool body 1 in the opposite direction to the tool rotation direction T, the diameter-enlarging bit 6 rotates in the opposite direction, and the bit body 6A is housed in the recess 5 and the axis line is removed. Since the positioning is performed in a state where the outer diameter from O is reduced, the drilling tool can be pulled out by leaving the tool body 1 as it is, leaving only the casing top 8A and the casing pipe 8 in the drilled holes.

[0004]

By the way, the inner diameter of a drilled hole drilled by such a drilling tool varies depending on the conditions of the drilling operation, and accordingly, the casing pipe 8 also has various inner and outer diameters. used. However, in this case, when the inner diameter of the casing pipe 8 is different, by changing the casing top 8A to have a different wall thickness, even if the tool main body 1 of the same excavating tool has the axis O
The casing pipe 8 can be engaged with the front end in the direction and can be built into the drilled hole.

However, when the outer diameter of the casing pipe 8 is different, the inner diameter of the drilled hole, that is, the outer diameter from the axis O of the expanded bit 6 in the expanded state is larger than the outer diameter of the casing pipe 8. If the diameter is too small, a large resistance acts when the casing pipe 8 is erected in the drilled hole, and in some cases, the casing pipe 8 cannot be erected. If the diameter is too large than the outer diameter of the casing pipe 8, the clearance between the drilled hole and the casing pipe 8 will be too large, resulting in impaired stability of the built-in casing pipe 8. For this reason, conventionally, in order to lay a plurality of types of casing pipes 8 having different outer diameters, a plurality of enlarged diameter bits 6 are attached to the tool body 1 so that the outer diameters at the time of expanding are different accordingly. A variety of drilling tools had to be provided, which was extremely inefficient and uneconomical.

The present invention has been made in view of such circumstances, and a drilling tool capable of excavating a bore having a different inner diameter with a single tool body in order to build casing pipes having different outer diameters. It is intended to provide.

[0007]

In order to solve the above-mentioned problems and to achieve such an object, the present invention provides an outer peripheral portion of a tool main body which is rotated around an axis and which is parallel to and parallel to the axis. A diameter-enlarging bit is attached so as to be rotatable about a central axis that is eccentric to the side, and as the tool body rotates during excavation, the diameter-expanding bit expands its outer diameter from the axis. In the excavating tool rotated in the above-mentioned manner, a plurality of types of diameter-enlarging bits having different outer diameters from the axis when the diameter is enlarged during excavation can be attached to the tool body. Therefore, according to such an excavating tool, the plurality of types of expanding bits having different outer diameters at the time of expanding can be attached to the tool main body. By mounting an expanding bit that matches the inner diameter of the hole, it is possible to drill a hole having a different inner diameter with one tool body.

Here, in order to enable a plurality of kinds of diameter-enlarging bits to be attached to the tool body, one support hole centering on the center axis is formed on the tool body side. A support shaft inserted into the support hole may be provided in the diameter-enlarging bit, and the outer diameter of the support shaft may be made equal between the plurality of types of diameter-enlarging bits. The diameter of the pitch circle formed by the center axis about the axis is the outer diameter D of the tool body.
Is preferably set in the range of 0.65 to 0.75 × D, and if the diameter of the pitch circle is larger than this range, the thickness between the outer circumference of the tool body and the outer diameter is ensured. The inner diameter of the support hole must be limited, and the mounting rigidity of the enlarged diameter bit may be impaired.On the other hand, if the diameter of the pitch circle is smaller than the above range, the diameter becomes the center of rotation of the enlarged diameter bit. Even if the center axis is too close to the axis which is the center of rotation of the tool body, even if the diameter expansion bit is rotated by the rotation of the tool body during excavation, the outer diameter from the axis can be sufficiently enlarged. It may not be possible.

[0009]

FIG. 1 to FIG. 5 show an embodiment of the present invention. In the present embodiment, the tool body 11 has a substantially multi-stage cylindrical shape having an outer diameter that is increased by one step on the front end side (left side in FIG. 1) with respect to the rear end side, and the reduced rear end portion is a shank portion 12. When a hammer (not shown) is attached to the shank portion 12, the shank portion 12 is rotated around the axis O in the tool rotation direction indicated by the symbol T in the figure during excavation, and the striking force is directed toward the tip of the axis O direction. Receiving is used for excavation of the ground. In the tool body 11, a supply hole 13 for compressed air or the like is formed along the axis O from the rear end of the shank portion 12 toward the front end side. A bifurcated hole 13A is formed which is branched in three directions at equal intervals in the circumferential direction and extends obliquely toward the outer periphery of the tip, and is further branched from the bifurcated hole 13A on the way to the axis O.
A small-diameter branch hole 13B extending toward the front end side and a branch hole 13C extending obliquely toward the rear end outer peripheral side of the tool body 11 are formed. Further, the supply hole 13 extending along the axis O is increased in diameter by one step at the tip of the tool main body 11, and a female screw portion is formed on the inner periphery thereof, thereby forming a mounting hole 15 for the pilot bit 14.

The pilot bit 14 is formed by integrally forming a mounting shaft portion 14B at the rear end of a disk-shaped bit body 14A along the center line of the bit body 14A. On the outer periphery of the mounting hole 15B, a male screw portion to be screwed with the female screw portion of the mounting hole 15 is formed.
, The center line is aligned with the axis O and attached to the tip of the tool main body 11. Also,
An annular groove 14C is formed on the rear end side of the mounting shaft portion 14B with respect to the male screw portion, while the annular groove 14C is formed in the tool body 11 with the pilot bit 14 attached.
And a pin mounting hole 16 extending along a plane perpendicular to the axis O and opening so as to be in contact with the inner periphery of the mounting hole 15. By inserting the pin 17 into the annular groove 14C and engaging it with the annular groove 14C, the pilot bit 1
4 are retained.

Further, the pilot bits 14 include:
A supply hole 18 communicating with the supply hole 13 is formed along the axis O from the rear end to the front end side of the mounting shaft portion 14B. The supply hole 18 extends along the axis O at the bit body 14A. 2 toward the outer circumference side opposite to each other
The bit body 14A is opened in the tip end surface of the bit body 14A. The tip end surface of the bit main body 14A is formed in a mortar shape with a central portion recessed with respect to the outer peripheral portion, and a pair of diametrical directions with respect to the axis O extends from the concave central portion to the outer periphery of the bit main body 14A. The exhaust holes 19 are formed, and the supply hole 1 is branched in two directions.
Numeral 8 is opened at the bottom of these exhaust grooves 19, 19, respectively.

Further, on the outer periphery of the bit body 14A, a plurality of strips (6 in this embodiment) extending parallel to the axis O are provided.
) Are formed at equal intervals in the circumferential direction, and the outer circumferential ends of the exhaust grooves 19 are opposite to each other across the axis O of the discharge grooves 20. It is arranged so that it may communicate with the tip of a pair of discharge slots 20 and 20 located. A large number of chips 21 made of a hard material such as cemented carbide are implanted on the distal end surface of the bit body 14A and the distal end side of the outer peripheral surface so as to avoid the exhaust grooves 19, 19 and the exhaust grooves 20. Thus, the cutting edge of the pilot bit 14 is configured.

On the other hand, a plurality of (three in the present embodiment) openings on the outer peripheral side of the mounting hole 15 at the distal end surface and the outer peripheral surface of the tool main body 11 at the enlarged distal end portion of the tool main body 11.
Are formed at equal intervals in the circumferential direction. The concave portion 22 is formed so as to retreat one step from the distal end surface of the tool main body 11 and faces the distal end side, and extends from the bottom surface 22A to the distal end side parallel to the axis O to extend the tool main body 1.
1 is defined by a wall surface 22B reaching the tip end surface, and a circular section in the center of a central axis X parallel to the axis O and eccentric to the outer peripheral side behind the bottom surface 22A in the tool rotation direction T. The support holes 23 are formed, and the support holes 2 are formed.
On the tool rotation direction T side than 3, a recess 24 is formed to be recessed so as to be inclined toward the rear end side toward the outer peripheral side. Further, on the outer periphery of the enlarged diameter tip portion of the tool main body 11, a 3 to 6 strip of excavating waste 2 extending parallel to the axis O is provided.
Are formed at equal intervals in the circumferential direction for each pair, and the pair of discharge grooves 25,
The branch hole 1 which is opened to the tool rotation direction T side and the rear side in the tool rotation direction T, and is branched from the supply hole 13.
3A and 13B are opened in the recess 24, and the branch hole 13C is opened in the discharge groove 25, respectively.

Further, the wall surface 22A of the concave portion 22 is located rearward of the concave portion 22 in the tool rotation direction T, and is inclined rearward in the tool rotation direction T from the outer periphery of the tool body 11 to the inner peripheral side. Wall surface portion 22a facing the tool rotation direction T side
A wall portion 22b which has a concave arc shape having a larger radius than the support hole 23 centered on the center axis X and which smoothly contacts the wall portion 22a; Wall surface 22c extending in the tool rotation direction T side while facing, and a step-shaped wall portion 22d crossing toward the inner peripheral side while intersecting the wall surface portion 22c at an obtuse angle while projecting and bending.
And a wall portion 22e that crosses the wall surface portion 22d while forming an obtuse angle at an obtuse angle and that is bent toward the outer peripheral side.
At an obtuse angle, intersect while being concavely bent toward the outer peripheral side, and the tool body 1 is located on the tool rotation direction T side of the concave portion 22.
1 and a wall surface portion 22f reaching the rear side in the tool rotation direction T that reaches the outer peripheral surface of the outer peripheral surface 1. The three recesses 22 formed in this manner are formed so as to be rotationally symmetric with respect to each other by 120 ° around the axis O. Therefore, the center axis X of the support hole 23 of each recess 22 is centered on the axis O. It is located on one pitch circle C. In the present embodiment, the diameter d of the pitch circle C is equal to the tool body 1.
0.65 to 0.7 with respect to the outer diameter D of the enlarged tip portion of 1.
The range is set to 5 × D.

Each of the recesses 22 thus formed is provided with an enlarged bit 26. In the case of the excavating tool shown in FIGS. 1 to 3 of the present embodiment, the diameter-enlarging bit 26 is a block-shaped bit main body 2 having a blade shape when viewed from the tip side of the tool main body 11 in a state of being attached to the concave portion 22.
6A and columnar support shafts 26B and 26C formed coaxially and integrally on the front and rear end surfaces of the blade-shaped root portion formed by the bit main body 26A, and the rear end support shaft 26C is supported by the support shaft 26C. The outer diameter that can be inserted into the hole 23 is slightly longer than the depth of the support hole 23, and the support shaft 26B on the front end side has an outer diameter smaller than the support shaft 26C on the rear end side.
The length of the support shaft 26 at the rear end side is reduced.
C is inserted into the support hole 23 so as to be rotatable around the central axis X.

The bit main body 26A has a root portion formed in a convex arcuate surface coaxial with the support shafts 26B and 26C, and in the mounting state, the bit wall portion 22b of the concave portion 22 is formed.
And a pair of side surfaces 26b and 26c, which are gradually in contact with the side surface 26a and gradually widen as the bit body 26A moves toward the blade tip side of the blade. ing. Then, when the diameter-enlarging bit 26 rotates rearward in the tool rotation direction T around the central axis X with the rotation of the tool body 11 during excavation, the side surface 26b is formed on the wall surface of the recess 22 as shown in FIG. 2
2a, the bit body 26A is positioned in an expanded state, and when the bit body 26A is rotated around the central axis X in the tool rotation direction T, the side surface 26c contacts the wall surface portion 22c and the bit body 26A is reduced in diameter. It is designed to be positioned in a state where it is set.

In the excavating tool shown in FIGS. 1 to 3, the blade tip side portion of the bit body 26A, which forms a blade, has a stepped side surface 26d which intersects the side surface 26c while forming an obtuse angle and concavely bending. A side surface 26e that intersects with the side surface 26d while forming an obtuse angle at an obtuse angle and that is one step convex in parallel with the side surface 26c, and a side surface 26f that intersects with the side surface 26b while forming an obtuse angle at an obtuse angle. , Side 26
e and a side surface 26g of a convex arc surface extending between the side surfaces 26f
The side surfaces 26d and 26e are attached to the wall portions 22d and
22a, the side surface 26g forms an arc surface centered on the axis O when the diameter-expanding bit 26 is expanded. The tip surface and the side surfaces 26e, 26f of the blade tip side portion of the bit main body 26A.
A large number of chips 27 made of a hard material such as a cemented carbide are implanted on the tip end side of the tip, and a cutting edge of the enlarged bit 26 is formed.

Furthermore, a spacer 28 is interposed between the tip end of the tool body 11 to which the enlarged diameter bits 26 are attached and the bit body 14A of the pilot bit 14. As shown in FIGS. 1 and 4, the spacer 28 has a hole 28 </ b> A into which the mounting shaft portion 14 </ b> B of the pilot bit 14 is inserted and formed in the center, and the outer periphery of the hole 28 </ b> A extends to the tool body 11. Is formed in a plate-like shape in which extending portions 28B extending rearward in the tool rotation direction T of the concave portions 22 are formed when viewed from the front end side, and the rear ends of the extending portions 28B in the above-mentioned attached state are formed. A support hole 28C having a circular cross section into which a support shaft 26B on the distal end side of the enlarged diameter bit 26 can be inserted is provided on a surface facing the side.
It is formed so as to be coaxial with the central axis X in the attached state. The spacer 28 is provided in the hole 1
4A, the mounting shaft portion 14B of the pilot bit 14 is inserted and the mounting shaft portion 14B is screwed into the mounting hole 15 so that the supporting shaft 2 is inserted into the supporting hole 28C as described above.
6B is inserted so that each of the enlarged bits 26 is rotatably supported on the distal end side as well, so as to be sandwiched between the distal end surface of the tool main body 11 and the rear end surface of the bit main body 14A of the pilot bit 14. It is mounted and attached.

The excavating tool having the above-mentioned construction is constructed such that the casing pipes 29 with the diameter-expanding bits 26.
When the tip of the tool body 11 protrudes from the tip of the casing pipe 29, the tool is rotated in the tool rotation direction T by applying a rotary impact force from the hammer to rotate the tool body 11 in the tool rotation direction T. The enlarged diameter bits 26 are expanded by the resistance and positioned as described above, and the ground and the like are excavated by the cutting edge of the pilot bit 14 and the cutting edge of the enlarged diameter bits 26 to form a hole. The casing pipe 29 is erected in the hole. After the excavation is completed, the diameter of the enlarged bits 26 is reduced by rotating the tool body 11 in the direction opposite to the tool rotation direction T during the excavation, so that the pilot pipe is left with the casing pipe 29 left in the borehole. The tool body 11 can be pulled out of the casing pipe 29 together with the bit 14 and the enlarged bits 26.

In the above-structured excavating tool, when the casing pipe 29 is changed to one having a different outer diameter due to digging conditions or the like, the larger-diameter bit is fitted to the outer diameter of the casing pipe. By exchanging the bit 26, it becomes possible to dig a hole having an inner diameter suitable for the changed casing pipe, and to reliably build the casing pipe into the hole. For example, when the casing pipe 29 is changed to one having a smaller outer diameter than that shown in FIG. 1, as shown in FIG.
6 is an enlarged bit 3 whose outer diameter from the axis O of the bit main body 30A is smaller than the enlarged bit 26 when the diameter is enlarged.
It may be replaced with 0.

The diameter-enlarging bit 30 is formed so that the peripheral edge of the blade-shaped tip portion formed by the bit body 26A of the diameter-enlarging bit 26 is cut out in a substantially L-shape as viewed from the front end. That is, as shown in FIG. 5, the bit main body 30A has side surfaces 30a to 30c of the same shape as the side surfaces 26a to 26c of the bit main body 26A at its root portion as shown in FIG. On the other side of the blade tip side, a side surface 30d that intersects with a side surface 30c that contacts the wall surface portion 22c of the concave portion 22 at an obtuse angle at the time of diameter reduction while intersecting with the side surface 30d at the time of diameter expansion. A side surface 30e extending in a convex arc shape is provided between the side surface 30b and the side surface 30b abutting on the wall surface portion 22a. Align Te are disposed on a circular arc surface shape centered on the small axis O of the diameter than the arcuate surface which the side surface 26g of the enlarged bit 26 forms.

Further, on the front and rear end surfaces of the root portion of the bit body 30A, support shafts 30B and 30C having the same diameter and the same length as the support shafts 26B and 26C of the enlarged diameter bit 26 are coaxial with each other. And a bit body 30 having a convex arc shape that is in sliding contact with the wall surface portion 22a of the concave portion 22
A is formed so as to be coaxial with the center of the side surface 30a of A, and these support shafts 30B and 30C are
The enlarged diameter bit 30 is inserted into the support hole 26C of the tool body 11 and the support hole 23 of the tool body 11 so that the enlarged diameter bit 30 is rotatable about the central axis X similarly to the enlarged diameter bit 26. It can be attached. Further, the tip surface and the side surfaces 30d, 30d of the blade tip side portion of the bit main body 30A.
A tip 31 is implanted in e, and a cutting edge of the enlarged bit 30 is formed.

Therefore, according to the excavating tool having the above-described configuration, a plurality of types of the enlarged bits 26 and 30 having different outer diameters from the axis O at the time of the enlarged diameter can be attached to one tool body 11. Therefore, even when installing casing pipes having different outer diameters, it is possible to drill a bore having an inner diameter corresponding to the outer diameter of the casing pipe with one tool body 11, and the clearance between the casing pipe and the bore is reduced. It is possible to prevent such a situation that the friction is too large when the casing pipe is erected and the casing pipe is too small and the clearance is too large to make the erected casing pipe unstable. On the other hand,
Even when these casing pipes having different outer diameters are erected, only one tool body 11 is used. Therefore, it is not necessary to prepare different excavation tools for each tool body according to the casing pipe, and this is economical. A single hammer or the like for applying a rotary impact force to the tool body 11 may be used, which is also efficient.

By the way, when the casing pipe is changed to have a different outer diameter, the inner diameter of the casing pipe is often changed accordingly. Therefore, when the inner diameter of the casing pipe is smaller than the outer diameter D of the tool body 11, the excavating tool is inserted into the casing pipe and protruded from the tip thereof for excavation. On the other hand, if the inner diameter of the casing pipe becomes significantly larger than the outer diameter D of the tool body 11, it becomes difficult to match the axis O of the tool body 11 with the center line of the casing pipe. There is a possibility that the straightness of the drilling may be impaired. Therefore, in such a case, the outer diameter D of the tool main body 11 is set according to the smaller inner diameter of the casing pipes having different inner diameters. A casing top having an inside diameter into which the tool body 11 can be inserted may be attached to the tip of the casing.

On the other hand, in the excavating tool of the present embodiment, as described above, a plurality of types of enlarged bits 26 and 30 having different outer diameters from the axis O at the time of diameter enlargement can be attached to one tool body 11. , The tip of the tool body 11 and the spacer 28
The supporting holes 23 and 28C having the center axis X as the center are formed at the same time, and the enlarged diameter bits 26 and 30 have the same diameter supporting shafts 26 that can be inserted into the supporting holes 23 and 28C.
B, 26C and the support shafts 30B, 30C, that is, at least these support shafts 26B, 26C,
Since the enlarged bits 26 and 30 having different outer diameters can be rotatably attached to one tool body 11 by sharing the common 30B and 30C, these plural kinds of enlarged bits according to the dimensions of the casing pipe are provided. 26,30 designs,
It has the advantage of being relatively easy to manufacture. Moreover,
In the present embodiment, in addition to this, these enlarged bits 2
The base portions of the bit bodies 26A, 30A of 6, 6 also have the side surfaces 26a to 26c and the side surfaces 30a to 30c of the same size and shape, and are commonly used. Since the rotation angle at the time of diameter and the posture in the positioning state are also constant, for example, the size of the other enlarged bit 30 relative to the one enlarged bit 26 serving as a reference,
What is necessary is just to set a shape, and more easy design and manufacture can be aimed at.

In the present embodiment, the center axis X, which is the center of rotation of the enlarged bits 26 and 30, is defined by the tool body 1.
1, the diameter d is located on a pitch circle C whose diameter d is in the range of 0.65 to 0.75 × D, and this center axis X is arranged. If the diameter d of the pitch circle C is larger than the above range, that is, if the difference between the diameter d and the outer diameter D of the tool main body 11 becomes too small, the support hole formed on the tool main body 11 side particularly as in the present embodiment. 2
When the support shafts 26B, 26C, 30B, and 30C are inserted into the support shafts 3 and 28C and the enlarged diameter bits 26 and 30 are rotatably attached, the inner diameters of the support holes 23 and 28C and the support shaft 26 are used.
This is because the outer diameters of B, 26C, 30B, and 30C cannot be increased, and it may not be possible to sufficiently secure the mounting rigidity of the enlarged bits 26, 30. On the other hand, if the diameter d is smaller than the above range, that is, if the center axis X and the axis O of the tool body 11 are too close,
Since the diameter expansion amount due to the rotation of the diameter expansion bits 26 and 30 becomes small, there is a possibility that the outer diameter of the diameter expansion bits 26 and 30 at the time of diameter expansion cannot be adjusted to a casing pipe having a wide range of outer diameter. , The diameter d is desirably set within the above range.

[0027]

As described above, according to the present invention,
By enabling a plurality of types of expanding bits having different outer diameters at the time of expanding to be rotatably attachable to the tool body, it becomes possible to excavate holes of different inner diameters with one tool body.
Even when casing pipes having different outer diameters are erected in the borehole, there is no need to prepare a plurality of types of excavating tools, and efficient excavating work can be performed.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention.

FIG. 2 shows the embodiment shown in FIG.
6 is a front view from the front end side showing a state where the diameter is enlarged.

FIG. 3 shows an enlarged diameter bit 2 in the embodiment shown in FIG.
6 is a front view from the front end side showing a state in which the diameter is reduced.

FIG. 4 is a plan view of the spacer 28 of the embodiment shown in FIG.

FIG. 5 is a front view of the embodiment shown in FIG. 1, showing a state where different diameter-enlarging bits 30 are mounted, as viewed from the distal end side. (However, the pilot bit 14 and the spacer 28 are not shown for the sake of explanation.)

FIG. 6 is a side sectional view showing a conventional excavation tool.

FIG. 7 is a front view of the excavating tool shown in FIG. 6 as viewed from a tip end side.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Tool main body 14 Pilot bit 22 Recess 23, 28C Support hole 26, 30 Diameter expansion bit 26B, 26C, 30B, 30C Support shaft 28 Spacer 29 Casing pipe O Axis line of tool main body 11 X Center axis of rotation of diameter expansion bit 14 T Tool rotation direction during excavation D Outer diameter of tool body 11 C Pitch circle formed by center axis X about axis O d Diameter of pitch circle C

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuyoshi Yoshida 1528 Nakashinden, Yokoi, Kobe-cho, Anpachi-gun, Gifu F-term in Mitsubishi Materials Corporation Gifu Works (reference) 2D029 EB04 PA06 PC02

Claims (3)

[Claims] 1. An enlarged diameter bit is attached to an outer periphery of a tip end portion of a tool main body that is rotated around an axis so as to be rotatable around a central axis parallel to the axis and eccentric to the outer periphery side. With the rotation of the tool body, in the excavating tool, the diameter expanding bit is rotated so that the outer diameter from the axis increases, the tool body includes, from the axis when the diameter is expanded during excavation. An excavating tool wherein a plurality of types of enlarged bits having different outer diameters can be attached. 2. A support hole centering on the center axis is formed on the tool body side, and a support shaft inserted into the support hole is provided on the enlarged diameter bit. The excavating tool according to claim 1, wherein the outer diameter of the support shaft is made equal between the kinds of enlarged bits. 3. The diameter of a pitch circle formed by the central axis with the axis as a center is set at 0. 0 to the outer diameter D of the tool body.
The excavating tool according to claim 1, wherein the excavating tool is set within a range of 65 to 0.75 × D.