JPH0617918Y2 - Drilling rig - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to excavating equipment such as shield machine and tunnel excavators.

2. Description of the Related Art In a typical prior art (Japanese Patent Publication No. 55-38478, etc.), a disk-shaped roller cutter 3 has an elongated support shaft 4 in an opening 2 of a cutter disk 1, as shown in FIG. The rotation axes of these knives 3 are indicated by the reference numeral 5 and are individually supported for rotation above. The cutter disk 1 is rotationally driven about an axis of rotation 6 perpendicular to the plane of FIG.

In such a prior art, as clearly shown in the sectional view perpendicular to the axis of FIG. 6, the gap 7 between the inner peripheral surface of the opening 2 which is the earth and sand swallowing mouth and the outer peripheral surface of the cutter 3 is small, Therefore, the sediment adheres in the gap 7 to cause clogging, and the sediment consolidates there. Therefore, rotation resistance of the cutter 3 is generated. Especially when the cutting face 8 is a soft layer, the cutter 3
The cutting edge 3a of 3 is fitted into the ground and causes rotation resistance of the cutter 3. When the cutter 3 does not rotate, uneven wear of the cutter 3 occurs.

Another prior art is shown in FIG. Roller cutters 10 and 11 having a substantially conical shape are fixed to the cutter disk 9 by mounting seats 13 and 14 facing the opening 12 thereof. The rotation axes of the knives 10 and 11 are indicated by
16, the axis of rotation 17 of the cutter disk 9 is
It is perpendicular to the plane of the figure.

In such a prior art, the axis 17 of the cutter disk 9 is
As shown in FIG. 8, a cross section taken along is narrowed at the opening 12 at the portion 18 of the cutter disk 9 to which the mounting seats 13 and 14 are mounted. Therefore, the earth and sand of the cutting face 19 is the small earth and sand drinking port 18
Then, the cutters 10 and 11 are prevented from rotating smoothly.

Furthermore, in the prior art shown in FIGS. 7 and 8, the cutters 10 and 11 cannot be exchanged on the chamber side (that is, on the right side of FIG. 8, the excavator side). The exchanging work of the cutters 10 and 11 must be performed from the cutting face 19 side by retracting the cutting disc 9 in the excavating direction.
Replacing 0 and 11 is more difficult.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to provide a cutter capable of exchanging the cutter from the side of the chamber without the rotation of the cutter being blocked by adhesion and solidification of earth and sand. A drilling rig is provided.

According to the present invention, a single first opening 23 is formed to include the rotation axis 32 of a cutter disk 21 which is driven to rotate about a rotation axis 32 extending in the lateral direction, and a first opening 23 is formed. A second opening 34a and a third opening 34b are formed in this order from the first opening 23 outward in the radial direction, and the chamber 31 is located rearward of the cutter disk 21 in the excavation direction.
In the excavation device for discharging the excavated earth and sand in the first opening 23, first and second hat-shaped cutters having first and second axes 37 and 46 in a plane including the rotation axis 32 are provided in the first opening 23. 24 and 25 are Chamamba 3
The first and second shafts 36, 47 arranged so as to be inclined so as to expand outward from the first opening 23 as the position becomes closer to the first side.
The first cutter 24 has an outwardly convex outer peripheral surface that is tapered toward the rotation axis 32 and is hollow at the base end portion 65.
On the outer peripheral surface of the cutter body 24a and the first cutter body 24a, the first projecting outwardly and sequentially formed from the distal end portion 64 to the proximal end portion 65 at intervals along the first axis 37, Second and third blade 6
1, 62, 63, and the first blade 61 has the first cutter body 2 along the first axis 37.
The second and third blades 62, 63 extend in a direction closer to the rotation axis 32 than the tip portion 64 of the 4a, and are formed in an annular shape. The first, second, and third blades 6 centering on the first axis 37
The radii r61, r62, r63 of 1, 62, 63 are set larger in this order, and moreover, a virtual plane 65a which is perpendicular to the rotation axis 32 and which is in contact with the outer peripheral end 62a of the second blade 62 in front of the cutter disk 21. The first blade 61 is located rearward with a gap δ1, the first cutter 24 covers the tip end portion 36a of the first shaft 36, and the base end portion 36b of the first shaft 36 is attached to the cutter disk 21. To
It is fitted into the first fitting recess 39 of the first mounting seat 38 that is fixed so as to face the first opening 23, and the bottom end 38 a of the first mounting seat 38 has a base end portion 3 of the first shaft 36.
The end face of 6b abuts, and the bottom 38a of the first mounting seat 38 is formed with a first detent hole 41 having an axis 41a at a position deviated from the first axis 37. In the first detent hole 41, Base end portion 36b of the first shaft 36
The projection 40 formed on the first mounting seat 38 is fitted to prevent mutual rotation of the first shaft 36 and the first mounting seat 38, and faces the first fitting recess 39 on the side of the first mounting seat 38. The first bolt insertion hole 42 is formed, and the shaft portion 43 a of the first bolt 43 that is inserted through the first bolt insertion hole 42 is formed in the screw hole 4 formed on the side portion of the first shaft 36.
4, the bolt head 45 of the first bolt 43 is inserted into the first bolt head recess 66 formed in the first mounting seat 38, and the second cutter 25 approaches the rotation axis 32. A second hollow member having a tapered outer peripheral surface, which is open at the base end portion 75
On the outer peripheral surface of the cutter body 25a and the second cutter body 25a, a fourth projecting outwardly and sequentially from the distal end portion 74 to the proximal end portion 75 at intervals along the second axis 46, Fifth and sixth blade 7
1, 72, 73, and the fourth blade 71 is arranged along the second axis 46 along the second cutter body 2
The fifth and sixth blades 72, 73 extend toward the rotation axis 32 side with respect to the tip portion 74 of 5a, and are formed in an annular shape. The fourth, fifth, and sixth blades 7 centering on the second axis 46
The radii r71, r72, r73 of 1, 72, 73 are formed in this order to be large, and moreover, a virtual plane 65b which is perpendicular to the rotation axis 32 and which is in contact with the outer peripheral end 72a of the fifth blade 72 in front of the cutter disk 21. The fourth blade 71 is located rearward with a gap δ2, the second cutter 25 covers the tip of the second shaft 47, and the base end 47b of the second shaft 47 is attached to the cutter disk 21. ,
It is fitted into the second fitting recess 79 of the second mounting seat 48 that is fixed so as to face the first opening 23, and the bottom end 48 a of the second mounting seat 48 has the base end portion 4 of the second shaft 47.
The end face of 7b abuts, and the bottom 48a of the second mounting seat 48 is formed with a second detent hole 81 having an axis 81a at a position deviated from the second axis 46. In the second detent hole 81, Base end portion 47b of the second shaft 47
The second shaft 47 and the second mounting seat 48 are prevented from rotating with each other by fitting the projection 80 formed on the second mounting seat 48, and the second fitting recess 79 is formed on the side of the second mounting seat 48. A second bolt insertion hole is formed, and the shaft portion of the second bolt that is inserted through the second bolt insertion hole is
The bolt head of the second bolt is screwed into the screw hole formed in the side portion of the second shaft 47, and the bolt head of the second bolt is inserted into the second bolt head recess formed in the second mounting seat 48. In the third openings 34a, 34b, the third and fourth cutters 33a, 33b having the third and fourth axes in the plane including the rotation axis 32 are arranged in the first and second positions as the chamber 31 side is approached. The angle θ33a formed by the axis 71 of the third cutter 33a and the rotation axis 32 is arranged so as to extend outward from the openings 34a, 34b, and the angle θ33a formed by the axis 72 of the fourth cutter 33b is the same as the rotation axis 32. The excavator is characterized in that it is selected to be larger than the formed angle θ33b.

Operation According to the present invention, the first and second cutters 24 and 25 are
The first and second cutters 24, 2 are rotatably supported in a single cantilever manner within a single first opening 23 including the rotation axis 32 of the cutter disk 21.
Since No. 5 is supported by the first and second shafts 36 and 47 that are arranged to be inclined so as to expand outward from the first opening 23 as it approaches the chamber 31, it is generated by excavation of the face. The earth and sand do not adhere and solidify at the first opening 23. Therefore, the first and second cutters 2
The 4,25 rotation is not blocked by the earth and sand.

When the first and second cutters 24 and 25 are replaced, the replacement work can be performed from the chamber 31 side, ensuring safety and improving workability.

Embodiment FIG. 1 is a sectional view of an embodiment of the present invention. The cut disk 21 of the tunnel excavator is formed with an opening 23 which is a mouth of the earth and sand generated by the excavation of the face 22, and the opening 23 has one or more rotatable cutters 24, 25 are provided.

FIG. 2 is a sectional view of a part of a tunnel machine equipped with such cutters 24 and 25. Cutlet Disk 2
1 is driven by the power of the drive motor 26, and the pinion 27,
It is rotationally driven via the ring gear 28 and the cutter disk support 29, and the face 22 is excavated thereby.
The earth and sand is discharged from the chamber 31 side by the soil discharging device 30.

FIG. 3 is a front view of the cutter disk 21. The cutters 24 and 25 shown in FIG. 1 are arranged in the vicinity of the rotation axis 32 of the cutter disk 21, and further other rotatable cutters 33 are mounted on the cutter disk 21. A scraper 35 and the like are attached to the earth and sand swallowing opening 34, and the cut disk 21 is configured so that the entire face can be uniformly excavated.

FIG. 4 is a front view around the cutters 24 and 25. The outer shape of the cutter 24 is substantially conical as shown in FIG. 1, and one end of the cutter 24 in the axial direction is rotatably supported by a shaft 36 by a bearing 55. The axis 37 of the cutter 24 coincides with the axis of the shaft 36. The shaft 36 is fitted in the fitting recess 39 of the mounting seat 38. A protrusion 40 is formed on the shaft 36 at a position deviated from the axis, and the protrusion 40 fits into a rotation-stop hole 41 formed in the mounting seat 38, whereby the shaft 36 and the mounting seat 38 are separated from each other. Mutual rotation is blocked. A bolt insertion hole 42 is formed in the mounting seat 38. The bolt 43 inserted through the bolt insertion hole 42 is screwed into a screw hole 44 formed in the shaft 36. In this way, the shaft 36 and the mounting seat 38 are integrally fixed. The bolt head 45 of the bolt 43 is inserted into the mounting seat 38.

The other cutter 25 has the same structure as the cutter 24, and a shaft 47 having an axis on the same straight line as the axis 46 of the cutter 25 is fixed to the mounting seat 48. The mounting seats 38 and 48 are fixed to the cutter disk 21.

The axis line 37 of the cutter 24 and the shaft 36 is inclined so as to expand outward from the opening 23 toward the chamber 31 side, and the same applies to the other cutter 25. The cutters 24 and 25 are arranged at positions displaced in the radial direction with respect to the rotation axis 32 of the cutter disk 21, and therefore, the rotation of the cutter disk 21 allows the face 22 to be uniformly excavated.

In this way, the axes 37 and 46 of the cutters 24 and 25, and thus the axes 36 and 47, are inclined so as to spread outward from the opening 23 as they approach the chamber 31 side.
The earth and sand generated by excavation of the face 22 are prevented from adhering and solidifying in the opening 23. Therefore, the cutlet 2
The rotation of the knives 24 and 25 is not blocked by the earth and sand, and the knives 24 and 25 can smoothly rotate.

Moreover, when replacing the cutter 24, the bolt 43
Then, the cutter 24 and the shaft 36 can be removed from the mounting seat 38, and the replacement work can be performed in the chamber 31.
Therefore, it is not necessary for the worker to come out to the face 22 and the safety is ensured, and the work of exchanging the cutter 24 can be performed efficiently. This is another Katsu 2
The same applies to 5.

The configuration will be further described. A single opening 23 is formed to include the rotation axis 32 of the cutter disk 21 which is rotationally driven about a rotation axis 32 extending in the lateral direction, and
An opening 34a and an opening 34b are formed in this order radially outward from the opening 23. Cutlet Disk 21
The excavated earth and sand is discharged by the chamber 31 which is located rearward of the excavation direction.

In the opening 23, a hat-shaped cutter 24 having axes 37 and 46 in a plane including the rotation axis 32,
The shafts 36 and 47 are arranged so as to be inclined so that 25 spreads outward from the opening 23 as the position becomes closer to the chamber 31.
Are supported and arranged.

The cutter 24 has an outwardly convex outer peripheral surface that is tapered toward the rotation axis 32, and has a hollow cutter main body 24a open at the base end portion 65 and an outer peripheral surface of the cutter main body 24a. It has blades 61, 62, 63 that project inwardly and are formed sequentially from the distal end portion 64 to the proximal end portion 65 at intervals along the axis 37. The blade 61 extends along the axis 37 more than the tip 64 of the cutter body 24a, rather than the rotation axis 32.
Extend to the side. The blades 62 and 63 are formed in a ring shape. Radius r61, r of the blades 61, 62, 63 centering on the axis 37
62 and r63 are set larger in this order. Moreover, the blade 61 is behind the imaginary plane 65a that is perpendicular to the rotation axis 32 and is in front of the cutter disk 21 and in contact with the outer peripheral end 62a of the blade 62 with a gap δ1. Vine 24
Covers the tip portion 36 a of the shaft 36.

The base end portion 36 b of the shaft 36 is fitted into the fitting recess 39 of the mounting seat 38 which is fixed to the cutter disk 21 so as to face the opening 23. An end surface of the base end portion 36b of the shaft 36 contacts the bottom 38a of the mounting seat 38. The bottom 38a of the mounting seat 38 is formed with a detent hole 41 having an axis 41a at a position displaced from the axis 37. The protrusion 40 formed on the base end portion 36b of the shaft 36 is fitted into the rotation preventing hole 41 to prevent mutual rotation of the shaft 36 and the mounting seat 38. A bolt insertion hole 42 facing the fitting recess 39 is formed on a side portion of the mounting seat 38. The shaft portion 43a of the bolt 43 which is inserted through the bolt insertion hole 42 is screwed into the screw hole 44 formed in the side portion of the shaft 36. The bolt head 45 of the bolt 43 enters into the bolt head recess 66 formed in the mounting seat 38.

The cutter 25 has an outwardly convex outer peripheral surface that is tapered toward the rotation axis 32, and has a hollow cutter main body 25a open at the base end portion 75 and an outer peripheral surface of the cutter main body 25a. The blades 71, 72, 73 are formed in this order from the distal end portion 74 to the proximal end portion 75 so as to project toward one another and at intervals along the axis 46. The blade 71 extends along the axis 46 more than the tip portion 74 of the cutter body 25a and rotates 32.
Extend to the side. The blades 72, 73 are formed in a ring shape. Radius r71, r of the blades 71, 72, 73 centering on the axis 46
72 and r73 are formed large in this order. Moreover, the blade 71 is behind the imaginary plane 65b that is perpendicular to the rotation axis 32 and is in contact with the outer peripheral end 72a of the blade 72 in front of the cutter disk 21 and at a distance δ2. Cutlet 25
Covers the tip of the shaft 47.

The base end portion 47b of the shaft 47 is fitted into the fitting recess 79 of the mounting seat 48 fixed to the cutter disk 21 so as to face the opening 23. An end surface of a base end portion 47b of the shaft 47 contacts the bottom 48a of the mounting seat 48. The bottom 48a of the mounting seat 48 is formed with a detent hole 81 having an axis 81a at a position displaced from the axis 46. The shaft 4 is inserted into the rotation stopping hole 81.
The projection 80 formed on the base end portion 47b of
7 and the mounting seat 48 are prevented from rotating with each other. Mounting seat 4
A bolt insertion hole that faces the fitting recess 79 is formed on the side portion of 8. The shaft of the bolt that goes through this bolt insertion hole
It is screwed into a screw hole formed on the side portion of the shaft 47. The bolt head of this bolt enters into the bolt head recess formed in the mounting seat 48.

In the openings 34a, 34b, the cutters 33a, 33b having an axis in the plane including the rotation axis 32 are arranged so as to be inclined so as to spread outward from the openings 34a, 34b toward the chamber 31 side. To be done. Cutlet 3
The angle θ33a formed by the axis 71 of 3a and the rotation axis 32.
Is selected to be larger than the angle θ33b formed by the axis 72 of the cutter 33b and the rotation axis 32.

The present invention can be widely implemented in connection with excavation equipment such as shield machines and tunnel excavators.

Effects of the Invention As described above, according to the present invention, it is possible to prevent adhesion and solidification of earth and sand to the opening formed in the cutlet disk, and therefore, the rotation of the cutler is not blocked,
As a result, the cutter can rotate smoothly for excavation, uneven wear of the cutter can be prevented, and excavation work can be performed for a long period of time. Further, such a cutter can be exchanged on the side of the chamber, so that the safety can be secured and the exchanging work of the cutter can be smoothly performed.

Particularly according to the present invention, the first and second cutters 24, 25
Has a hat shape, covers the tip portions of the first and second shafts 36 and 47, and is rotatable by the bearing 35. Therefore, the first and second cutters 24 and 25 are, so to speak, pieces. It is configured to be supported in a holding manner, and accordingly, the tip end portions 6 of the first and second cutter main bodies 24a and 25a.
Since no bearings are provided in 4,74, there is no problem of damage to such bearings.

Moreover, according to the present invention, the first and second cutters 24, 2
The first and fourth blades 61 and 71 of No. 5 are the first and second cutter bodies 24 along the first and second axes 37 and 46.
Since the reference numerals ΔL1 and ΔL2 in FIG. 1 project and extend toward the rotation axis 32 side from the tip portions 64 and 74 of a and 25a, it is possible to avoid contact of the face with these tip portions 64 and 74. First and second cutters 24, 25 of
It is possible to smoothly rotate.

Further in accordance with the present invention, the first and second cutters 24,2
5, the first and fourth blades 61, 71 are perpendicular to the rotation axis 32 and in front of the cutter disk 21 (left in FIG. 1), the outer peripheral ends 6 of the second and fifth blades 62, 72.
2a, 72a in contact with the virtual plane 65a, 65b,
It is behind (to the right in FIG. 1) with a space of δ1 and δ2,
Therefore, when the second and fifth blades 62, 72 come into contact with the face to rotate the cutter disk 21, the face is not
Also, the fifth blades 62, 72 come into contact with each other and can rotate smoothly.

Further, the end faces of the base end portions 36b of the first and second shafts 36, 47 are provided with bottoms 38a, 4 of the first and second mounting seats 38, 48.
8a, and thus the first and second cutters 24,
The effect that the forces acting in the axial direction of the axes 37 and 46 of the first shaft 36 and the second shaft 47 of 25 are received and the strength is improved is also achieved.

Further according to the present invention, the first and second detent holes 4
1, 81 to the base end portion 36 of the first and second shafts 36 and 47.
By fitting the protrusions 40 and 80 formed on b and 47b, mutual rotation of the first and second shafts 36 and 47 and the first and second mounting seats 38 and 48 is prevented, Detent is reliably achieved.

Furthermore, the retaining of the first shaft 36 is achieved by means of the first bolt 43, which is also the case for the other second shaft 47, by using such first and second bolts. As a result, the first and second shafts 36, 47 can be easily attached and detached, and the maintenance becomes easy.

Further, according to the present invention, when excavating a large-diameter drill hole, the third and fourth cutters 33a and 33b are provided, and the angle θ33a of the axis 71 of the third cutter 33a on the radially inner side is the radial direction. It is selected to be larger than the angle θ33b of the axis 72 of the fourth cutter 33b on the outer side, which facilitates rotation of the third and fourth cutters 33a and 33b during excavation of a large diameter tunnel or the like.

Since the first and second cutter bodies 24a and 25a have outer peripheral surfaces that are convex outward, there is no risk of soil clogging.

[Brief description of drawings]

1 is a sectional view of an embodiment of the present invention, FIG. 2 is a sectional view of a tunnel excavator equipped with the cutters 24 and 25 shown in FIG. 1, FIG. 3 is a front view of a cutter disk 21, and FIG. FIG. 4 is a front view around the cutters 24 and 25, FIG. 5 is a front view of the prior art, FIG. 6 is a sectional view perpendicular to the axis of the disk cutter 3 of the prior art shown in FIG. 5, and FIG. Another prior art front view, FIG. 8 is a sectional view of the prior art shown in FIG. 21 ... cut disk, 22 ... face, 23 ... opening, 24,25 ... cut, 55 ... bearing, 36,47
…… Shaft, 38, 48 …… Mounting seat

Claims (1)

[Scope of utility model registration request] 1. A single first opening 23 is formed to include the rotation axis 32 of a cutter disk 21 which is driven to rotate about a rotation axis 32 extending in the lateral direction, and a first opening 23 is formed.
A second opening 34a and a third opening 34b are formed radially outward from the opening 23 in this order, and the chamber 31 located rearward of the cutter disk 21 in the excavation direction.
In the excavation device for discharging the excavated earth and sand in the first opening 23, first and second hat-shaped cutters having first and second axes 37 and 46 in a plane including the rotation axis 32 are provided in the first opening 23. 24 and 25 are Chamamba 3
The first and second shafts 36, 47 arranged so as to be inclined so as to expand outward from the first opening 23 as the position becomes closer to the first side.
The first cutter 24 has an outwardly convex outer peripheral surface that is tapered toward the rotation axis 32 and is hollow at the base end portion 65.
On the outer peripheral surface of the cutter body 24a and the first cutter body 24a, the first projecting outwardly and sequentially formed from the distal end portion 64 to the proximal end portion 65 at intervals along the first axis 37, Second and third blade 6
1, 62, 63, and the first blade 61 has the first cutter body 2 along the first axis 37.
The second and third blades 62, 63 extend in a direction closer to the rotation axis 32 than the tip portion 64 of the 4a, and are formed in an annular shape. The first, second, and third blades 6 centering on the first axis 37
The radii r61, r62, r63 of 1, 62, 63 are set larger in this order, and moreover, a virtual plane 65a which is perpendicular to the rotation axis 32 and which is in contact with the outer peripheral end 62a of the second blade 62 in front of the cutter disk 21. The first blade 61 is located rearward with a gap δ1, the first cutter 24 covers the tip end portion 36a of the first shaft 36, and the base end portion 36b of the first shaft 36 is attached to the cutter disk 21. To
It is fitted into the first fitting recess 39 of the first mounting seat 38 that is fixed so as to face the first opening 23, and the bottom end 38 a of the first mounting seat 38 has a base end portion 3 of the first shaft 36.
The end face of 6b abuts, and the bottom 38a of the first mounting seat 38 is formed with a first detent hole 41 having an axis 41a at a position deviated from the first axis 37. In the first detent hole 41, Base end portion 36b of the first shaft 36
The projection 40 formed on the first mounting seat 38 is fitted to prevent mutual rotation of the first shaft 36 and the first mounting seat 38, and faces the first fitting recess 39 on the side of the first mounting seat 38. The first bolt insertion hole 42 is formed, and the shaft portion 43 a of the first bolt 43 that is inserted through the first bolt insertion hole 42 is formed in the screw hole 4 formed on the side portion of the first shaft 36.
4, the bolt head 45 of the first bolt 43 is inserted into the first bolt head recess 66 formed in the first mounting seat 38, and the second cutter 25 approaches the rotation axis 32. A second hollow member having a tapered outer peripheral surface, which is open at the base end portion 75
On the outer peripheral surface of the cutter body 25a and the second cutter body 25a, a fourth projecting outwardly and sequentially from the distal end portion 74 to the proximal end portion 75 at intervals along the second axis 46, Fifth and sixth blade 7
1, 72, 73, and the fourth blade 71 is arranged along the second axis 46 along the second cutter body 2
The fifth and sixth blades 72, 73 extend toward the rotation axis 32 side with respect to the tip portion 74 of 5a, and are formed in an annular shape. The fourth, fifth, and sixth blades 7 centering on the second axis 46
The radii r71, r72, r73 of 1, 72, 73 are formed in this order to be large, and moreover, a virtual plane 65b which is perpendicular to the rotation axis 32 and which is in contact with the outer peripheral end 72a of the fifth blade 72 in front of the cutter disk 21. The fourth blade 71 is located rearward with a gap δ2, the second cutter 25 covers the tip of the second shaft 47, and the base end 47b of the second shaft 47 is attached to the cutter disk 21. ,
It is fitted into the second fitting recess 79 of the second mounting seat 48 that is fixed so as to face the first opening 23, and the bottom end 48 a of the second mounting seat 48 has the base end portion 4 of the second shaft 47.
The end face of 7b abuts, and the bottom 48a of the second mounting seat 48 is formed with a second detent hole 81 having an axis 81a at a position deviated from the second axis 46. In the second detent hole 81, Base end portion 47b of the second shaft 47
The second shaft 47 and the second mounting seat 48 are prevented from rotating with each other by fitting the projection 80 formed on the second mounting seat 48, and the second fitting recess 79 is formed on the side of the second mounting seat 48. A second bolt insertion hole is formed, and the shaft portion of the second bolt that is inserted through the second bolt insertion hole is
The bolt head of the second bolt is screwed into the screw hole formed in the side portion of the second shaft 47, and the bolt head of the second bolt is inserted into the second bolt head recess formed in the second mounting seat 48. In the third openings 34a, 34b, the third and fourth cutters 33a, 33b having the third and fourth axes in the plane including the rotation axis 32 are arranged in the first and second positions as the chamber 31 side is approached. The angle θ33a formed by the axis 71 of the third cutter 33a and the rotation axis 32 is arranged so as to extend outward from the openings 34a, 34b, and the angle θ33a formed by the axis 72 of the fourth cutter 33b is the same as the rotation axis 32. An excavator characterized by being selected to be larger than the angle θ33b formed.