JPWO2018180832A1 - Compressed air driven chisel - Google Patents

Abstract

  Provided is a compressed air-driven chisel that enables a needle holder to be reduced in diameter. A reverse drive annular recess (22a) is provided on the outer peripheral surface of the needle holder (22) which is provided movably in the axial direction in the cylinder, and when the needle holder (22) is advanced, the reverse drive annular recess (22a). Compressed air was supplied to the reverse drive chamber (26) via

Description

  The present invention relates to a compressed air-driven chisel driven by compressed air.

  The compressed air drive type chisel is a piston, anvil, and needle holder that are sequentially attached to the cylindrical member from the rear to the front in the axial direction of the cylindrical member and are slidable with respect to the cylindrical member. The needle holder holds a needle (needle chisel) extending forward. When compressed air is supplied to the forward drive chamber formed in the rear part of the piston, the piston is driven forward to strike the rear part of the anvil, the anvil is driven forward, and the needle holder is driven forward by being pushed by the anvil. The Further, when the needle holder is driven forward, the compressed air in the forward drive chamber is discharged to the outside, and the compressed air is supplied to the reverse drive chamber formed on the front end side of the needle holder, and the needle The holder, anvil, and piston are returned to the rear. When the needle holder is driven forward, the tip of the needle strikes the work site and performs a desired operation such as crawl.

  The needle holder of such a compressed air type chisel consists of a large-diameter holder main body that is hermetically engaged with the inner peripheral surface of the cylindrical member and slidable in the axial direction, and is coaxial with the holder main body. A small-diameter cylindrical extension that extends forward and is hermetically engaged with the inner peripheral surface of the front end opening of the cylindrical member and is slidable in the axial direction. The holder body has an annular front end surface formed around the rear end of the cylindrical extension at the front end, and the reverse drive chamber has an inner peripheral surface and a front end of a cylindrical member housing the needle holder. It is demarcated by the rear side surface of the opening, the outer peripheral surface of the cylindrical extension, and the annular front end surface of the holder body.

  In such a conventional compressed air drive type chisel, a plurality of needle holding holes for passing a plurality of needles through the holder body in the front-rear direction are provided around the center in the radial direction of the holder body, and near the outer peripheral surface of the holder body. Is provided with a plurality of axial passages that extend in parallel to the needle holding hole and open to the annular front end surface of the holder body to supply compressed air to the reverse drive chamber. (See Patent Documents 1 and 2)

JP 2006-289607 A Shoko Sho 16-16295

  In the compressed air drive type chisel as disclosed in the above-mentioned patent document, the axial direction hole for supplying compressed air to the reverse drive chamber opens near the outer peripheral surface of the holder main body so as to open to the annular front end surface of the holder main body as described above. To be provided. The needle holder is repeatedly reciprocated by striking with the piston as described above. Therefore, the thickness from the axial hole to the outer peripheral surface of the holder body is sufficient to withstand such a reciprocating motion. This has been a limiting factor when trying to reduce the outer diameter of the needle holder in order to reduce the size of the compressed air driven chisel.

  In view of the above, the present invention has an object to provide a compressed air-driven chisel that allows the outer diameter of a needle holder to be smaller than that of a conventional needle holder.

The compressed air drive type chisel according to the present invention is
A cylinder having a rear end closing member provided at the rear end, and a front end cylindrical member provided at the front end and defining a front end opening;
A needle holder that is slidable in an axial direction of the cylinder in the cylinder and holds a plurality of needles so as to extend forward from the front end opening, and a piston disposed at a rear position of the needle holder; A movable element, wherein the piston is driven forward by introducing compressed air into a forward drive chamber formed in the rear part of the piston in the cylinder, and a striking force from the rear to the front of the needle holder. The needle holder has a large-diameter holder body that is hermetically engaged with the inner peripheral surface of the cylinder and is slidable in the axial direction, and extends forward from the holder body. A small-diameter cylindrical portion that is hermetically engaged with the inner peripheral surface of the front-end cylindrical member and is slidable in the axial direction, and the holder main body has a rear end at the front end of the cylindrical portion. Formed around the edge An annular front end surface and a needle holding hole penetrating in the axial direction for accommodating the needle so as to extend in the front-rear direction inside the cylindrical portion, and the needle holder is driven by the striking force of the piston. Driven forward, the annular front end surface is displaceable to a front end position where it abuts against the rear end portion of the front end tubular member, and the inner peripheral surface of the cylinder is located from the position of the rear end of the front end tubular member. A movable element extending rearward in the axial direction and having a chamber defining recess having a diameter larger than the outer peripheral surface of the holder body and defining a reverse drive chamber with the outer peripheral surface of the needle holder;
A forward drive passage for supplying compressed air to the forward drive chamber and a reverse drive passage for supplying the forward drive chamber to the forward drive chamber, and the compressed air is forwarded through the forward drive passage and the reverse drive passage. A compressed air supply passage for alternately supplying the drive chamber and the reverse drive chamber, wherein the reverse drive passage passes through the cylinder and is slidably engaged with the outer peripheral surface of the holder body. The reverse drive cylinder passage that opens to the inner peripheral surface and the outer peripheral surface of the holder main body and the inner peripheral surface of the cylinder that slidingly engages with the outer peripheral surface are provided to extend in the axial direction. A reverse drive communication recess communicated with the drive cylinder passage, and when the needle holder is at the front end position, the reverse drive communication recess communicates with the reverse drive chamber to transmit the compressed air. Configured to supply to the reverse drive chamber A compressed air supply passage being,
Have

  In this compressed air drive type chisel according to the present invention, when the needle holder is brought to the front end position, a passage for communicating the opening of the reverse drive cylinder passage to the reverse drive chamber is provided as described above. It is not provided as an axial hole near the outer peripheral surface of the needle holder as in the case of the one, but extends in the axial direction on at least one of the outer peripheral surface of the holder body and the inner peripheral surface of the cylinder that is slidably engaged with the outer peripheral surface. It is a provided recess (reverse drive communication recess). For this reason, when the axial hole is provided, there is no need to increase the thickness from the axial hole to the outer surface of the holder body in order to maintain the strength of the needle holder, and for supplying compressed air. The required channel cross section can be obtained with a recess having an extremely small depth compared to the diameter dimension of the axial hole when the required axial section passing through the needle holder is provided. . For this reason, in this compressed air drive type chisel of the present invention, the diameter of the needle holder can be greatly reduced as compared with the conventional one.

  A specific example of the reverse drive communication recess is formed on the outer peripheral surface of the holder body, and a portion between the front end of the outer periphery of the holder main body and the axial front end of the reverse drive communication recess is In a state where the cylinder is sealingly engaged with the inner peripheral surface, the reverse drive communication recess can be prevented from communicating with the reverse drive chamber.

  More specifically, the communication recess for reverse drive can be an annular recess extending in the circumferential direction of the outer peripheral surface of the holder body.

  The reverse drive communication recess is formed on the inner peripheral surface of the cylinder, instead of or in addition to the one provided on the outer peripheral surface of the holder body, and the opening of the reverse drive cylinder passage and the And the outer peripheral surface of the holder body is hermetically engaged with the reverse drive communication recess, and the reverse drive is forward of the reverse drive cylinder passage in front of the opening. The drive communication recess has a sealing projection that is slidable, and the seal projection moves forward from the reverse drive communication recess when the needle holder is in the front end position, and the reverse drive. The reverse drive cylinder passage can be communicated with the chamber defining recess through the communication recess.

Each of the needle holding holes has a needle head receiving portion that gradually increases in diameter from the vicinity of the rear end of the needle holding hole toward the rear end surface of the holder body, and the needle head receiving portion is inserted into the needle holding hole. And a head provided at the rear end of the needle held by the needle is received so that the rear end of the head protrudes backward from the needle head receiving portion. An annular protrusion that protrudes rearward from the head of the protruding needle along the peripheral edge can be provided. This makes it easy to narrow the interval between the needles.
In this case, the head of the needle may have a side surface that gradually expands backward corresponding to the needle head receiving portion.

In particular,
A cylindrical housing for accommodating the cylinder coaxially;
A compressed air supply passage is formed between the outer peripheral surface of the cylinder and the inner peripheral surface of the housing so as to extend in the axial direction, and allows compressed air introduced into the housing to pass along the outer peripheral surface of the cylinder. The reverse drive cylinder passage may pass through the cylinder in the radial direction and communicate with the compressed air supply passage.

  The compressed air supply passage may be a cylindrical passage formed between the cylinder and the housing.

The movable element has an anvil that is displaceable in the axial direction between the piston and the needle holder, and the anvil is struck from the rear by a piston driven forward and driven forward. It is designed to transmit the striking force from the piston to the needle holder,
The needle holder has an exhaust passage penetrating the diametrical center in the axial direction, and the exhaust passage communicates with the forward drive chamber when the needle holder is at the front end position, and the compressed air in the forward drive chamber is compressed. Can be discharged outside the front of the needle holder.

  Each of the needle holding holes further displaceably held in the axial direction and further extending forward from the needle holder in the axial direction and extending forward from the front end opening of the cylinder; The needle head receiving portion may have a side surface that protrudes rearward from the rear end and gradually decreases in diameter toward the front side, and the side surface abuts on the surface of the needle head receiving portion.

  Hereinafter, an embodiment of a compressed air drive type chisel according to the present invention will be described with reference to the accompanying drawings.

It is a perspective view of the compressed air drive type chisel concerning one embodiment of the present invention. It is a longitudinal cross-sectional view in the state where the compressed air drive type chisel of FIG. 1 is not driven. It is a figure which expands and shows a part in the longitudinal cross-sectional view of FIG. FIG. 3 is a view similar to FIG. 2, but showing a state in which compressed air is introduced into the forward drive chamber and the piston advances to strike the anvil. It is a figure which expands and shows a part in the longitudinal cross-sectional view of FIG. FIG. 3 is a view similar to FIG. 2, but shows a state when the needle holder reaches the front end position. It is a figure which expands and shows a part in the longitudinal cross-sectional view of FIG.

  As shown in FIG. 1, a compressed air driven chisel 10 according to the present invention includes a plurality (six needles in the figure) of needles (needle chisel) 12, and an air introduction hole at the rear end of the compressed air driven chisel 10. The needle 12 is driven back and forth as a whole by compressed air introduced through a compressed air supply pipe (not shown) connected to 11 (FIG. 2), and the work site is struck by hitting the work site with its tip. Is to do.

  As shown in FIG. 2, the compressed air drive type chisel 10 includes a cylindrical housing 14 and a cylinder 16 that is coaxially mounted in the housing 14. The compressed air drive type chisel 10 further includes a piston 18, an anvil 20, and a needle holder 22 that are sequentially attached from the rear to the front in the axial direction in the cylinder 16. The needle holder 22 holds each needle 12 so as to extend forward from the front end opening 17 of the needle holder 22. In the illustrated example, the housing 14 includes a housing rear portion 14a and a housing front portion 14b coupled to the housing rear portion 14a. The cylinder 16 has a cylindrical cylinder body 16a, a rear end closing member 16b that is attached to the rear end of the cylinder body 16a and closes the rear end, and is attached to the front end of the cylinder body 16a and extends forward. The front end cylindrical member 16c is defined.

  In the cylinder 16, there is a forward drive chamber 24 (FIGS. 2, 4 and 6) between the piston 18 and the rear end closing member 16b, and a reverse drive chamber 26 between the needle holder 22 and the front end cylindrical member 16c. A cylindrical compressed air supply passage that extends between the inner peripheral surface of the housing 14 and the outer peripheral surface of the cylinder 16 through the valve 28 provided in the rear portion 14a of the housing. The compressed air is alternately supplied to the forward drive chamber 24 and the reverse drive chamber 26 through 30.

  Specifically, the compressed air supply passage 30 is connected to a forward drive cylinder passage 16d provided so as to penetrate in the radial direction toward the rear of the cylinder 16, and forward from the rear passage 30a. And a forward passage portion 30b communicating with the reverse drive cylinder passage 16e provided so as to penetrate in the radial direction toward the front of the cylinder 16. The piston 18 has, on its outer peripheral surface, a small diameter portion 18a provided so as to extend from a position closer to the rear to the front end, and a large diameter portion 18b on the rear side of the small diameter portion 18a. The diameter portion 18b is hermetically engaged with a corresponding diameter portion of the inner peripheral surface of the cylinder 16 and is slidable. The small-diameter portion 18 a is provided with a forward drive radial passage 18 d that penetrates in the diametrical direction. The forward drive axial direction extends from the forward drive radial passage 18 d to the rear end surface of the piston 18 and communicates with the forward drive chamber 24. A passage 18c is provided. The compressed air passed through the forward drive cylinder passage 16d is a space 32 formed between the inner peripheral surface of the cylinder 16 and the small diameter portion 18a when the cylinder 16 is at the rear end position shown in FIG. The forward drive chamber 24 is supplied through the drive diameter direction passage 18d and the forward drive axial passage 18c. When the needle holder 22 is driven forward, the reverse drive cylinder passage 16e sends the compressed air to the reverse drive chamber 26 via the reverse drive annular recess 22a (FIG. 7) provided on the outer peripheral surface of the needle holder 22. It can be supplied. Specifically, the needle holder 22 has a large-diameter holder main body 22b that is slidably engaged with and slidable with respect to the inner peripheral surface of the cylinder 16, and a front end cylindrical member 16c that extends forward from the holder main body 22b. A small-diameter cylindrical portion 22c that is hermetically engaged with and slidable with respect to the inner peripheral surface of the cylindrical portion 22c. The holder body 22b has an annular front end surface 22d formed around the rear end of the cylindrical portion 22c at the front end thereof. When the needle holder 22 is driven forward by the anvil 20, the annular front end surface 22d. Is displaceable to a front end position that abuts against a rear end portion of the front end cylindrical member 16c. The reverse drive annular recess 22a is provided on the outer peripheral surface of the holder body 22b at an intermediate position away from the front end and the rear end. The inner peripheral surface of the cylinder 16 extends rearward in the axial direction from the position of the rear end of the front end cylindrical member 16c and has a larger diameter than the outer peripheral surface of the holder main body 22b. A chamber defining recess 16f is defined. When the needle holder 22 is driven forward (FIGS. 6 and 7), the reverse drive annular recess 22a communicates with the reverse drive chamber 26, and compressed air is supplied to the reverse drive chamber 26. ing.

  The needle holder 22 has a needle holding hole 22e that passes through the holder main body 22b in the front-rear direction and holds the needle 12, and an exhaust passage 22f that passes through the center of the cross section of the holder main body 22b in the front-rear direction. . The needle holding hole 22e has a needle head receiving portion 22g having an inclined surface 22h that gradually increases in diameter from near the rear end toward the rear end surface of the holder main body 22b, and the needle 12 has an inclined surface 22h of the needle head receiving portion 22g. A needle head portion 12b having a side surface 12a corresponding to. In a state where the needle head portion 12b is received by the needle head receiving portion 22g, the side surface 12a of the needle head receiving portion 12b abuts on the inclined surface 22h of the needle head receiving portion 22g, and the rear end of the needle head 12b is the needle head. It protrudes backward from the part receiving part 22g. The rear end surface of the needle holder 22 has an annular protrusion 22j protruding further rearward than the needle head 12b protruding rearward from the needle head receiving portion 22g along the periphery thereof. A forward driving force to the needle holder 22 is transmitted via the annular protrusion 22j. The needle 12 is aligned with the needle holding hole 22e when the needle head 12b is received by the needle head receiving portion 22g as described above, so that the needle 12 is not easily shaken.

  When the compressed air drive type chisel 10 is in an inoperative state where the compressed air shown in FIG. 2 is not introduced, when the valve 34 is opened by lowering the lever 34 pivotally attached to the housing rear portion 14a, the compressed air is compressed as described above. The air is supplied to the forward drive chamber 24 via the rear passage portion 30a of the air supply passage 30, the forward drive cylinder passage 16d, the forward drive diameter passage 18d, and the forward drive axial passage 18c. As a result, the piston 18 is driven forward, and the anvil 20 is hit from behind by the hitting protrusion 18e provided at the front end thereof (FIGS. 4 and 5). In this state, the forward drive radial passage 18d extending from the forward drive chamber 24 is in communication with a space 35 formed on the rear side of the anvil 20, and the compressed air in the forward drive chamber 24 that has driven the piston 18 forward is provided. Is passed through a space 36 between the front end surface of the anvil 20 and the rear end surface of the needle holder 22 through an axial hole 20a provided in the anvil 20, and is exhausted to the outside through an exhaust passage 22f of the needle holder 22. Become so. At this time, the reverse drive annular recess 22a of the outer peripheral surface of the holder body 22b is not yet communicated with the reverse drive chamber 26, and compressed air is not supplied to the reverse drive chamber 26. When the needle holder 22 is driven forward, the volume of the reverse drive chamber 26 is reduced, but the air in the reverse drive chamber 26 has a radius provided in the cylindrical portion 22 c of the needle holder 22. The needle holder 22 is discharged to the outside through the direction exhaust hole 22i so that the needle holder 22 can move forward substantially without receiving resistance due to air pressure in the reverse drive chamber 26.

  The anvil 20 struck from behind by the piston 18 is driven forward to drive the needle holder 22 forward, and the needle holder 22 is in a front end position where it collides with the front end tubular member 16c (FIGS. 6 and 7). In this state, the reverse drive annular recess 22 a communicates with the reverse drive chamber 26, compressed air is supplied to the reverse drive chamber 26, and driving of the needle holder 22 to the rear is started. When the anvil 20 and the piston 18 are returned to the state shown in FIG. 2 by the needle holder 22, the piston 18 is again driven forward by the compressed air. In this manner, the reciprocating motion of the needle holder 22 is repeated, and the work of hitting the work site by the needle 12 is performed.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this. For example, in the above-described embodiment, the reverse drive annular recess 22a provided on the outer peripheral surface of the holder main body 22b to communicate the reverse drive cylinder passage 16e with the reverse drive chamber 26 when the needle holder 22 is driven forward. However, the reverse drive annular recess may be provided on the inner peripheral surface of the cylinder 16 so as to extend between the reverse drive cylinder passage 16e and the chamber defining recess 16f. In this case, a sealing protrusion is formed on the outer peripheral surface of the holder main body 22b so as to be slidably engaged with the reverse drive communication recess and to be slidable in the reverse drive communication recess in front of the reverse drive cylinder passage 16e. When the needle holder 22 is driven toward the front end position, the sealing convex portion is moved forward from the reverse drive communication recess, whereby the reverse drive cylinder passage 16e and the chamber defining recess 16f are communicated with each other. Can be. Further, although the cylinder main body, the rear end closing member, and the front end cylindrical member are shown as separate members, they can be integrally formed.

Compressed air driven chisel 10;
Air inlet 11;
Needle (needle chisel) 12;
Side surface 12a;
Head 12b;
Housing 14;
Housing rear 14a;
Housing front 14b;
Cylinder 16;
Cylinder body 16a;
Rear end closing member 16b;
Front end tubular member 16c;
Forward drive cylinder passage 16d;
Reverse drive cylinder passage 16e;
A chamber defining recess 16f;
Piston 18;
Small diameter portion 18a;
Large diameter portion 18b;
Forward drive axial passage 18c;
A forward drive radial passage 18d;
Striking protrusion 18e;
Anvil 20;
An axial hole 20a;
Needle holder 22;
Reverse drive annular recess 22a;
Holder body 22b;
Cylindrical portion 22c;
Annular front end face 22d;
Needle holding hole 22e
Exhaust passage 22f
Needle head receiving portion 22g;
Inclined surface 22h;
Radial exhaust holes 22i;
Annular projection 22j;
Forward drive chamber 24;
Reverse drive chamber 26;
Valve 28;
Compressed air supply passage 30;
Rear passage part 30a;
Forward passage portion 30b;
Space 32;
Lever 34;
Space 35, 36

Claims (9)

A cylinder having a rear end closing member provided at the rear end, and a front end cylindrical member provided at the front end and defining a front end opening;
A needle holder that is slidable in an axial direction of the cylinder in the cylinder and holds a plurality of needles so as to extend forward from the front end opening, and a piston disposed at a rear position of the needle holder; A movable element, wherein the piston is driven forward by introducing compressed air into a forward drive chamber formed in the rear part of the piston in the cylinder, and a striking force from the rear to the front of the needle holder. The needle holder has a large-diameter holder body that is hermetically engaged with the inner peripheral surface of the cylinder and is slidable in the axial direction, and extends forward from the holder body. A small-diameter cylindrical portion that is hermetically engaged with the inner peripheral surface of the front-end cylindrical member and is slidable in the axial direction, and the holder main body has a rear end at the front end of the cylindrical portion. Formed around the edge An annular front end surface and a needle holding hole penetrating in the axial direction for accommodating the needle so as to extend in the front-rear direction inside the cylindrical portion, and the needle holder is driven by the striking force of the piston. Driven forward, the annular front end surface is displaceable to a front end position where it abuts against the rear end portion of the front end tubular member, and the inner peripheral surface of the cylinder is located from the position of the rear end of the front end tubular member. A movable element extending rearward in the axial direction and having a chamber defining recess that is larger in diameter than the outer peripheral surface of the holder body and defines a reverse drive chamber between the outer peripheral surface of the needle holder;
A forward drive passage for supplying compressed air to the forward drive chamber and a reverse drive passage for supplying the forward drive chamber to the forward drive chamber, and the compressed air is forwarded through the forward drive passage and the reverse drive passage. A compressed air supply passage for alternately supplying the drive chamber and the reverse drive chamber, wherein the reverse drive passage passes through the cylinder and is slidably engaged with the outer peripheral surface of the holder body. The reverse drive cylinder passage that opens to the inner peripheral surface and the outer peripheral surface of the holder main body and the inner peripheral surface of the cylinder that slidingly engages with the outer peripheral surface are provided to extend in the axial direction. A reverse drive communication recess communicated with the drive cylinder passage, and when the needle holder is at the front end position, the reverse drive communication recess communicates with the reverse drive chamber to transmit the compressed air. Configured to supply to the reverse drive chamber A compressed air supply passage being,
Compressed air driven chisel.   The reverse drive communication recess is formed on the outer peripheral surface of the holder body, and the portion between the front end of the holder main body on the outer peripheral surface and the axial front end of the reverse drive communication recess is the inner periphery of the cylinder. 2. The compressed air drive type chisel according to claim 1, wherein the reverse drive communication recess is prevented from communicating with the reverse drive chamber in a state of being sealingly engaged with the surface.   The compressed air drive type chisel according to claim 2, wherein the reverse drive communication recess is an annular recess extending in the circumferential direction of the outer peripheral surface of the holder body.   The reverse drive communication recess is formed in the inner peripheral surface of the cylinder and extends between the opening of the reverse drive cylinder passage and the chamber defining recess, and the outer peripheral surface of the holder body is the reverse drive A sealing protrusion that is hermetically engaged with the driving communication recess and is slidable in the backward driving communication recess in front of the opening of the reverse drive cylinder passage; When the needle holder is moved to the front end position, the needle holder is moved forward from the reverse drive communication recess, and the reverse drive cylinder passage is communicated with the chamber defining recess via the reverse drive communication recess. Item 2. The compressed air driven chisel according to Item 1.   Each of the needle holding holes has a needle head receiving portion that gradually increases in diameter from the vicinity of the rear end of the needle holding hole toward the rear end surface of the holder body, and the needle head receiving portion is inserted into the needle holding hole. And a head provided at the rear end of the needle held by the needle so that the rear end of the head protrudes rearward from the needle head receiving portion. The compressed air drive type chisel as described in any one of Claims 1 thru | or 4 which has the cyclic | annular protrusion part which protruded back rather than the head of the needle which protruded along the periphery. A cylindrical housing for accommodating the cylinder coaxially;
A compressed air supply passage is formed between the outer peripheral surface of the cylinder and the inner peripheral surface of the housing so as to extend in the axial direction, and allows compressed air introduced into the housing to pass along the outer peripheral surface of the cylinder. The compressed air drive type chisel according to any one of claims 1 to 5, wherein the reverse drive cylinder passage passes through the cylinder in a radial direction and communicates with the compressed air supply passage.   The compressed air drive type chisel according to claim 6, wherein the compressed air supply passage is a cylindrical passage formed between the cylinder and the housing. The movable element has an anvil that is displaceable in the axial direction between the piston and the needle holder, and the anvil is struck from the rear by a piston driven forward and driven forward. It is designed to transmit the striking force from the piston to the needle holder,
The needle holder has an exhaust passage penetrating the diametrical center in the axial direction, and the exhaust passage communicates with the forward drive chamber when the needle holder is at the front end position, and the compressed air in the forward drive chamber is compressed. The compressed air drive type chisel as described in any one of Claims 1 thru | or 7 discharged | emitted from the front exterior of this needle holder. Each of the needle holding holes further displaceably held in the axial direction and further extending forward from the needle holder in the axial direction and extending forward from the front end opening of the cylinder; 6. A side surface gradually projecting forward from the rear end protruding rearward from the needle head receiving portion, and the side surface is in contact with a surface of the needle head receiving portion. Compressed air driven chisel described in 1.

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