JP2013146842A - Screwdriver tool for removing screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screwdriver tool for removing a screw in which the tip of an operation part can be prevented from being broken when the operation part is driven in a cone-shaped damaged concave part, and furthermore, by making an operation edge bitten into the damaged concave part by weaker power, the loosening operation of the screw can be surely performed.SOLUTION: A valley groove 14 comprising a first valley surface 15, a second valley surface 16 and a bottom surface 17 is formed at an operation part 3 to be extended from the peripheral wall surface 22 of the operation part to the tip surface 23 of the operation part. Each rib-shaped projection 13 comprises: the first valley surface 15 and the second valley surface 16 of the valley groove 14 which are opposed to each other while interposing the rib-shaped projection 13 therebetween; and a rib peripheral surface 18. A tip sloping surface 19 is formed at the tip surface 23-side end of the rib peripheral surface 18. The operation edge 20 bitten into the damaged concave part 9 is formed at a ridge line where the second valley surface 16 and the rib peripheral surface 18 are made to cross each other. A biting edge 21 is formed at another ridge line where the rib peripheral surface 18 and the tip sloping surface 19 are made to cross each other. A first sloping surface 24 extended over the tip sloping surface 19, the tip surface 23, the first valley surface 15 and the bottom surface 17 is formed to form the tip sloping surface 19 to be an inverted trapezoid shape.

Description

  The present invention relates to a screwdriver such as a manual screwdriver or an electric screwdriver, and more particularly to a screwdriver for screw removal suitable for removing a screw whose operation groove of a screw operation head is broken into a mortar shape. .

  When loosening a rusted screw or a screw stuck to the fastening surface with a screwdriver such as a manual screwdriver or electric screwdriver, if the tool pressing force against the screw is small, the fan-shaped wall of the operation groove will be cross-shaped with a screwdriver. There is a case that the operation groove is broken by scraping with a blade. When loosening and removing a screw with such an operation groove broken, if the screw head protrudes from the fastening surface, such as a pan screw or truss screw, grip the screw head with a gripping tool such as a pliers. It can be removed by loosening the screw. However, in the case of a screw provided in a narrow space where a gripping tool cannot enter, or a screw whose screw head is buried in the fastening surface, such as a countersunk screw, the screw head is gripped with a tool. It cannot be gripped and it is difficult to loosen and operate the screw.

  The present applicant has previously proposed Patent Documents 1 to 3 as screwdrivers for removing screws that are difficult to loosen with the gripping tool as described above. In the driver bit of Patent Document 1, four rib-like protrusions and four valley grooves are alternately formed at the tip of the driver shaft, and the rib-like protrusions are tapered toward the tip. It is comprised by the rib surrounding surface which inclines, and the surrounding surface of the trough groove which pinches | interposes a rib surrounding surface in between. An operation edge for loosening a screw is provided on one ridge line portion of the rib-like projection. The rib peripheral surface that continues to the operation edge is a flank surface of the edge, and is formed in a state that it is orthogonal to the projection central axis of the rib-like projection and is inclined inward from a virtual plane that passes through the operation edge. According to this driver bit, in the state where the four rib-like projections are engaged with the broken operation groove (hereinafter simply referred to as a damaged recess), the operation edge is engaged with the base end corner of the sector wall. You can loosen the screw. Further, the operating edge can be reliably engaged with the base end corner of the fan-shaped wall, avoiding the flank (rib peripheral surface) from contacting the outer end surface of the operating groove.

  In the driver bit of Patent Document 2, a tightening / loosening operation portion is provided at the lower end of the bit body for driving into the inclined concave surface of the damaged concave portion to establish a fixed state with the screw. The tightening operation portion includes five or more rib-like protrusions and a trough formed between adjacent rib-like protrusions, and bites the corner portion of the lower outer edge of each rib-like protrusion. The part is formed. By driving this bite into the inclined concave surface of the damaged recess and rotating the screwdriver bit in the loosening direction with the screw firmly attached to the screw, it is possible to loosen and remove even a screw with a broken operation groove. it can.

  In the screwdriver of Patent Document 3, a plurality of rib-shaped protrusions and a V-shaped valley groove are alternately formed at the tip of the driver shaft, and each rib-shaped protrusion is formed in a trapezoidal cross section. ing. An operation edge that cuts into the damaged recess is formed at the ridge line where the first trough surface of the rib-shaped projection intersects the rib peripheral surface, and this operation edge is inclined by the biting angle with respect to the central axis of the driver shaft. It is. The biting angle is inclined so that the biting start end of the operation edge is looser than the terminal end of the operation edge and is located on the upper side in the rotational direction. As a result, the operation edge and the starting edge of the bite can be bitten diagonally toward the screw shaft and spirally with respect to the inclined concave surface of the damaged recess, and the operation edge can be securely fixed to the screw. The screw can be loosened and operated. Further, by providing a biting angle, it is possible to prevent a cam-out phenomenon in which the driver shaft receives an operation reaction force and lifts away from the inclined surface, and the screw loosening operation can be performed accurately.

International Publication No. 2007/20681 (paragraph number 0019, FIG. 1, FIG. 4) Japanese Patent No. 4647710 (paragraph number 0013, FIGS. 1 and 4) Japanese Patent No. 4787377 (paragraph number 0018, FIG. 1, FIG. 6)

  When the base end portion of the fan-shaped wall is left in the operation groove, the driver bit of Patent Document 1 can loosen the screw by engaging the operation edge with the base end corner of the fan-shaped wall. However, if the fan-shaped wall is completely scraped and the damaged recess has a mortar shape, the operating edge cannot be engaged and it is extremely difficult to loosen the screw.

  In that respect, the bite portion is driven into the inclined concave surface of the damaged concave portion in the driver bit of Patent Document 2, so even if it is a dent-like damaged concave portion, the screw is rotated in the loosening direction and removed. be able to. Also in the screwdriver of Patent Document 3, the operating edge is bitten into the inclined concave surface of the damaged concave portion, and the screw can be similarly rotated in the loosening direction. However, in the driver bit of Patent Document 2, since the biting portion is formed at an acute angle in order to facilitate the biting of the damaged concave portion into the inclined concave surface, the biting portion is missing due to the impact of the hitting when driving. And damage such as deformation is likely to occur. Further, since the biting portion is likely to bite into the inclined concave surface, when an excessive tapping force is applied, the screw head itself may be damaged.

  In the screwdriver of Patent Document 3, the upper surface of the grip is struck to bite the operation edge. However, as the biting edge bites into the damaged recess, the biting resistance derived from the tip slope increases. Further, as the biting depth is increased, biting resistance due to an increase in the contact area between the screw operating head and the operating portion is also added. Therefore, a large tapping force is required to deeply bite the biting edge into the inclined concave surface. When the structural strength of the screw fastening target is low, the fastening target itself is damaged when the operating edge is bitten deeply. There is a risk. Incidentally, in the screwdriver of Patent Document 3, the tip slope at the lower end of the rib-like protrusion is formed in a trapezoidal shape with the lower side longer than the upper side in front view, and the upper side portion of the tip slope is a biting edge. Therefore, as the biting edge bites into the inclined concave surface, the length of the contact tip between the tip inclined surface and the inclined concave surface gradually increases, which is a factor that increases the biting resistance derived from the tip inclined surface. .

  The object of the present invention is to prevent the tip of the operation unit from being damaged when the operation unit is driven into a mortar-shaped damaged recess, and further, the operation edge is bitten into the damaged recess without applying a large tapping force. An object of the present invention is to provide a screwdriver for screw removal that can be reliably removed by loosening a rusted screw or a screw stuck to a fastening surface. An object of the present invention is to provide a screwdriver for removing a screw that can be removed by performing a loosening operation of a screw by reliably applying an operating torque at the time of loosening operation from the bitten operation edge to the screw. There is.

  The screw removal tool for screw removal according to the present invention has a plurality of rib-like protrusions 13 and valley grooves 14 alternately formed at the tip of the operation portion 3 formed at one end of the driver shaft 2. The shaft 2 is struck in the direction of its central axis, and the operation edge 20 provided on the rib-shaped protrusion 13 is bitten into the damaged recess 9 of the screw operation head 7. The trough groove 14 includes a first trough surface 15, a second trough surface 16, and an arc-shaped bottom surface 17 that connects both trough surfaces 15 and 16, and extends from the peripheral wall surface 22 to the distal end surface 23 of the operation unit 3. Form. Each rib-like protrusion 13 has a rib peripheral face 18 that connects the first valley face 15 and the second valley face 16 of the valley groove 14 facing each other with the rib-like protrusion 13 in between and the outer peripheral edges of both valley faces 15 and 16. And consist of A tip slope 19 is formed at the end of the rib peripheral surface 18 on the tip surface 23 side. An operation edge 20 that bites into the damaged recess 9 is formed at the ridgeline where the second valley surface 16 and the rib peripheral surface 18 intersect. A biting edge 21 is formed at the ridge line where the rib peripheral surface 18 and the tip slope 19 intersect. And the 1st inclined surface 24 is formed over the front end slope 19, the front end surface 23, the 1st trough surface 15, and the bottom face 17, and the front end slope 19 is formed in an inverted trapezoid shape. The inverted trapezoidal shape herein refers to a trapezoid whose ridgeline portion where the tip slope 19 and the tip surface 23 intersect is shorter than the biting edge 21 which is the ridgeline portion where the tip slope 19 and the rib peripheral surface 18 intersect.

  A second inclined surface 25 is formed between the second valley surface 16 of each valley groove 14 and the tip surface 23 of the operation unit 3.

  Four rib-shaped protrusions 13 and valley grooves 14 are alternately formed at the same angle interval at the tip of the operation unit 3.

  The second valley surface 16 constituting the operation edge 20 is formed on a surface perpendicular to a plane orthogonal to the central axis of the driver shaft 2.

  The driver shaft 2 is formed in a hexagonal cross section, and the operation portion 3 is formed in a circular cross section. And the operation part 3 is formed in the inverted truncated cone shape which narrows as it goes to a front-end | tip.

  In the screwdriver of the present invention, the tip slope 19 is formed at the tip of each rib-shaped protrusion 13 formed in a rectangular cross section, and the biting edge 21 is formed at the ridge line where the rib peripheral surface 18 and the tip slope 19 intersect. did. Further, a first inclined surface 24 is formed across the tip slope 19, the first valley surface 15 and bottom surface 17 of each valley groove 14, and the tip surface 23 of the operation unit 3, and the tip slope 19 is inverted trapezoidal. Formed. In this way, when the tip slope 19 is formed in an inverted trapezoidal shape whose lower side is shorter than the upper side, the biting resistance derived from the tip slope can be reduced. Specifically, when the tip slope 19 has an inverted trapezoidal shape, when the biting edge 21 and the operation edge 20 bite into the inclined concave surface 10, the length of the contact tip between the tip slope 19 and the inclined concave surface 10 depends on the progress of biting. Accordingly, the biting resistance at the contact tip gradually decreases. Therefore, unlike the prior art, since the biting resistance does not increase due to the tip slope, it is not necessary to apply a large tapping force, and the operation edge 20 can be deeply bitten. Further, when the first inclined surface 24 is formed, it becomes the same as a state in which chamfering is performed on a ridge line portion where the first valley surface 15 and the bottom surface 17 intersect with the distal end surface 23 of the operation unit 3. Therefore, the angle of the ridge line portion where the first inclined surface 24, the first valley surface 15, the bottom surface 17, and the front end surface 23 of the operation unit 3 intersect can be made an obtuse angle, and the ridge line portion chipped due to the impact of tapping, etc. Can be prevented from being damaged.

  When the second inclined surface 25 is formed between the second trough surface 16 of each trough 14 and the front end surface 23 of the operation unit 3, a ridge line where the second trough surface 16 and the front end surface 23 of the operation unit 3 intersect with each other. It becomes the same as the state which chamfered the part. Therefore, the angle of the ridge line portion where the second inclined surface 25, the second valley surface 16, and the front end surface 23 of the operation unit 3 intersect is made an obtuse angle to prevent damage such as chipping of the ridge line portion due to the impact of tapping. Can do.

  When the fan-shaped wall 8 is scraped off with a cross-shaped blade and the operation groove 11 is broken into a mortar shape, when the inclined concave surface 10 of the damaged concave portion 9 is divided into four at equal angular intervals in plan view, The shape of the shavings of each inclined concave surface 10 is a shaving having substantially the same shape. Therefore, when four rib-like protrusions 13 and valley grooves 14 are alternately formed at the front end of the operation portion 3 at equal angular intervals, the operation portion is simply set regardless of the difference in the phase position of the operation portion 3 with respect to the damaged recess 9. By simply applying 3 to the damaged recess 9, the biting edge 21 of each rib-like protrusion 13 can be brought into contact with the inclined concave surface 10 having substantially the same shape, so that the central axis of the screw and the central axis of the operating portion 3 can coincide with each other. . Therefore, the biting edge 21 and the operation edge 20 can be bitten into the damaged recess 9 in a state where the central axis of the screw and the central axis of the operation portion 3 coincide with each other. Thereby, the operating torque during the loosening operation can be applied to the screw without fail, and the screw can be reliably loosened and removed.

  Incidentally, when three rib-like projections 13 are provided at equiangular intervals, the center axis of the screw and the center axis of the operation unit 3 may be shifted when the operation unit 3 is applied to the damaged recess 9. For example, if one rib-like protrusion 13 is positioned on the inclined concave surface 10 where the operation groove 11 is formed, the other rib-shaped protrusion 13 is positioned on the inclined concave surface 10 where the sector-shaped wall 8 is scraped. Become. Therefore, since the contact state of each rib-like protrusion 13 with the inclined concave surface 10 is different, the biting edge 21 and the operation edge 20 cannot be bitten into the inclined concave surface 10 at the same time. In addition, since the operating portion 3 is displaced during biting and the central axis of the screw and the central axis of the operating portion 3 are shifted, the biting edge 21 and the operating edge 20 bite into the inclined concave surface 10, so that the operation during the loosening operation is performed. Torque cannot be applied to the screw with certainty. Even when five protrusions 13 are provided at equal angular intervals, the same problem is likely to occur.

  When the second valley surface 16 constituting the operation edge 20 is formed on a plane perpendicular to the plane orthogonal to the central axis of the driver shaft 2, the second valley surface 16 perpendicular to the rotation direction is operated to a screw. Since torque can be applied, it is possible to prevent the cam-out phenomenon during the loosening operation. Therefore, the operating torque during the loosening operation can be reliably applied to the screw, and the screw can be reliably loosened and removed.

  When the operation section 3 having a circular cross section formed at one end of the driver shaft 2 having a hexagonal cross section is formed in an inverted truncated cone shape that narrows toward the tip, the structural strength of the boundary portion between the driver shaft 2 and the operation section 3 is increased. Can be high. More specifically, the boundary portion between the hexagonal cross section of the driver shaft 2 and the circular cross section of the operation portion 3 is a joint portion having a different cross sectional shape, so that the structural strength is reduced. Since the operation portion 3 needs to have a diameter that can be inserted into the damaged recess 9, it is inevitable that the cross-sectional area becomes smaller than the portion of the driver shaft 2. However, by forming the operation unit 3 in an inverted frustoconical shape that narrows toward the tip, the tip of the operation unit 3 has a diameter that can be inserted into the damaged recess 9, while the boundary part side of the operation unit 3 is closer to the tip than the tip. Also, the cross-sectional area can be increased with a large diameter. Therefore, the change in the cross-sectional area at the boundary portion between the driver shaft 2 and the operation portion 3 can be reduced, and the structural strength of the joint portion between the two shafts 2 and 3 can be increased.

It is a front view which shows the structure of the operation part which concerns on this invention. It is a front view of the manual screwdriver concerning the present invention. It is a perspective view of the operation part and damage crevice concerning the present invention. It is a bottom view of the driver shaft concerning the present invention. It is an expansion perspective view of the operation part tip concerning the present invention. It is sectional drawing which shows the state which made the operation part which concerns on this invention bite into a damage recessed part. It is the sectional view on the AA line in FIG. It is explanatory drawing which shows the process in which the operation part which concerns on this invention bites into a damage recessed part.

(Example) FIGS. 1-8 shows the Example which applied the screwdriver which concerns on this invention to the manual driver. In FIG. 2, the manual driver includes a grip 1 and a replaceable driver shaft 2. The driver shaft 2 is made of a bar having a hexagonal cross section made of tool steel, and an operation portion 3 having a circular cross section is provided at the tip. As shown in FIG. 2, a chuck 4 that holds the mounting state of the driver shaft 2 is provided at the lower end of the grip 1, and the chuck 4 is pushed upward against a spring (not shown). The driver shaft 2 can be extracted from the grip 1. A cored bar 5 is provided at the axial center of the grip 1, and the upper end of the cored bar 5 is exposed at the upper end of the grip 1. When the driver shaft 2 is attached to the grip 1, the upper end of the driver shaft 2 is in contact with the lower end surface of the core bar 5, and the core bar 5 exposed at the upper end of the grip 1 is hit with a hammer or the like. A force can be applied to the driver shaft 2.

  FIG. 3 shows a countersunk screw in which the fan-shaped wall 8 provided on the screw operating head 7 is scraped off without a trace and the damaged recess 9 is shaped like a mortar. On the inner surface of the mortar-shaped damaged recess 9, an inclined concave surface 10 formed of a streak-like uneven surface is formed. Since the inclined concave surface 10 is formed by scraping the fan-shaped wall 8 with a blade of a cross-shaped driver, when the inclined concave surface 10 is divided into four equal parts in a plan view, each is formed into an uneven surface having substantially the same shape. . The damaged recess 9 is often formed when the screw screw shaft is rusted and fixed, or when the screw operation head 7 is stuck to the fastening surface. In particular, when an electric screwdriver having a large driving torque is loosened by applying it to the cross-shaped operation groove 11, it is likely to be formed if the pressing force of the electric screwdriver against the screw is small.

  As shown in FIGS. 1 and 4, the operation unit 3 is formed in a truncated conical shape by turning the driver shaft 2, and a rib-like protrusion 13 and a valley groove 14 are formed at the tip (lower end) thereof. Four are alternately formed at equal angular intervals. The valley groove 14 includes a first valley surface 15, a second valley surface 16, and an arc-shaped bottom surface 17 that connects both valley surfaces 15, 16, and is formed from the peripheral wall surface 22 to the tip surface 23 of the operation unit 3. ing. The trough groove 14 is formed by cutting the tip of the operation unit 3 with a milling cutter. The second valley surface 16 is formed on a surface perpendicular to a plane orthogonal to the central axis of the driver shaft 2.

  As shown in FIGS. 1, 4, and 7, the rib-shaped protrusion 13 includes a first valley surface 15 and a second valley surface 16 of the valley groove 14 facing each other with the rib-shaped protrusion 13 therebetween, and both valley surfaces 15. -It is comprised with the rib peripheral surface 18 which connects 16 outer periphery. A tip slope 19 that slopes toward the tip of the operation unit 3 is formed at the tip (lower end) portion of the rib-like protrusion 13. The tip slope 19 is a tapered surface formed by chamfering the tip periphery of the operation unit 3 and is formed prior to the cutting of the trough groove 14. An operation edge 20 that bites into the damaged recess 9 is formed at the ridge line portion where the second valley surface 16 and the rib peripheral surface 18 intersect, and the operation edge 20 is damaged at the ridge line portion where the rib peripheral surface 18 and the tip slope 19 intersect. A biting edge 21 is formed as a biting start end when biting into the recess 9.

  In the state where the operating portion 3 is applied to the damaged recess 8, the taper angle of the tip inclined surface 19 is inclined to the damaged recess 9 in order to bring the biting edge 21 into contact with the inclined concave surface 10 of the damaged recess 9 in advance of other parts. The taper angle of the concave surface 10 is set larger. The taper angle of the inclined concave surface 10 is approximately equal to the tip angle of the driver engaged with the screw operation groove 11 and is approximately 26 to 30 degrees. In this embodiment, the taper angle of the tip inclined surface 19 is set to be inclined 45 degrees from the central axis of the driver shaft 2.

  As shown in FIGS. 1, 4, and 5, the first inclined surface 24 extends across the tip slope 19, the first valley surface 15 and the bottom surface 17 of the valley groove 14, and the tip surface 23 of the operation unit 3. Is formed. Further, a second inclined surface 25 is formed between the second valley surface 16 of the valley groove 14 and the tip surface 23 of the operation unit 3. The first inclined surface 24 and the second inclined surface 25 are each formed by cutting with a milling cutter. By forming both the inclined surfaces 23 and 24, chamfering is performed on the ridge line portion where the valley groove 14 and the tip surface 23 of the operation portion 3 intersect. By forming the first inclined surface 24, the shape of the front inclined surface 19 in a front view is formed in an inverted trapezoidal shape in which the lower side is shorter than the upper side that is the biting edge 21. In this embodiment, in FIG. 1, the angle formed by the first inclined surface 24 and the central axis of the driver shaft 2 is set to 40 degrees.

  The screwdriver configured as described above removes the screw in which the operation groove 11 is broken into a mortar shape in the following manner. First, the tip of the operation unit 3 is applied to the inclined concave surface 10 of the damaged concave portion 9 (see FIG. 8A). At this time, the fan-shaped wall 8 is scraped off by the cross-shaped blade of the driver, and the operation groove 11 destroyed in a mortar shape is divided into four in the shape of a sector of the inclined concave surface 10 of the damaged concave portion 9 in plan view. When this is done, the shape of the trace of each inclined concave surface 10 is a substantially identical shape. Accordingly, the biting edges 21 of the four rib-like protrusions 13 formed at equal angular intervals contact the inclined concave surface 10 in substantially the same state. Therefore, the center axis of the operation unit 3 and the center axis of the screw can be matched by simply applying the operation unit 3 to the damaged recess 9.

  From this state, the metal core 5 exposed on the upper surface of the grip 1 is struck with a hammer, and the biting edge 21 and the operation edge 20 which are the biting start ends are bitten into the inclined concave surface 10 as shown in FIG. I will. When both edges 20 and 21 bite into the inclined concave surface 10, the tip slope 19 also bites at the same time. As the operation unit 3 bites in, the contact tip between the tip slope 19 and the inclined concave surface 10 moves below the tip slope 19 and finally the tip surface 23 of the operation unit 3 becomes the contact tip. At this time, the tip slope 19 is formed in an inverted trapezoidal shape with the lower side shorter than the upper side, so that the length of the contact tip gradually decreases as the operation unit 3 bites in. Therefore, the biting resistance at the contact tip gradually decreases, and it is not necessary to apply a large tapping force, and the operation edge 20 can be deeply bitten as shown in FIG. Further, since the chamfering process is applied to the ridge line portion where the trough groove 14 and the distal end surface 23 of the operation unit 3 intersect, damage such as chipping of the ridge line portion due to the impact of tapping can be prevented. Note that the biting resistance increases as the biting depth of the biting edge 21 and the operation edge 20 increases, which is the same as that of a conventional screwdriver tool.

  After the operation edge 20 is bitten deep into the damaged recess 9, the grip 1 is rotated in the loosening direction of the screw, and an operation torque is applied to the screw, whereby the operation groove 11 is broken in a mortar shape. Even if it exists, it can be removed. At this time, the operation torque is applied to the screw by the operation edge 20 and the second valley surface 16, but the second valley surface 16 is formed on a surface perpendicular to the plane orthogonal to the central axis of the driver shaft 2. Therefore, the cam-out phenomenon can be prevented during the loosening operation, and the operating torque can be accurately applied to the screw. In addition, since the central axis of the operation unit 3 and the central axis of the screw coincide with each other, the operating torque during the loosening operation can be applied to the screw with certainty.

  In the above embodiment, the angle of the tip slope 19 is set to 45 degrees. However, this is not necessary, and when the operating portion 3 is applied to the damaged recess 9, the biting edge 21 first contacts the inclined recess 10. What is necessary is just to set an angle. Further, the angle of 16 of the second inclined surface is not limited to 40 degrees and can be appropriately changed. The operation unit 3 is formed in a truncated conical shape, but may be formed in a stepped round shaft shape. The present invention can be applied to driver bits for electric drivers in addition to manual drivers. In this case, after driving the driver bit into the inclined concave surface 10 and biting it in, the driver bit is attached to the electric screwdriver and the screw is loosened while maintaining the biting state.

2 Driver shaft 3 Operation part 7 Screw operation head 9 Damaged recess 13 Rib-shaped protrusion 14 Valley groove 15 First valley surface 16 Second valley surface 17 Bottom surface 18 Rib circumferential surface 19 Tip slope 20 Operation edge 21 Biting edge 22 Circumferential wall surface 23 End surface 24 First inclined surface 25 Second inclined surface

Claims (5)

A plurality of rib-shaped protrusions (13) and valley grooves (14) are alternately formed at the tip of the operation portion (3) formed at one end of the driver shaft (2), and the driver shaft (2) A screwdriver for screw removal that taps in the direction of the central axis and bites the operation edge (20) provided on the rib-like projection (13) into the damaged recess (9) of the screw operation head (7). There,
The trough (14) is composed of a first trough surface (15), a second trough surface (16), and an arc-shaped bottom surface (17) connecting both trough surfaces (15, 16). ) From the peripheral wall surface (22) to the tip surface (23),
Each rib-like protrusion (13) includes a first valley face (15) and a second valley face (16) of the valley groove (14) facing each other with the rib-like protrusion (13) in between, and both valley faces (15 · 16) and a rib peripheral surface (18) that connects the outer peripheral edges of each other,
A tip slope (19) is formed at the end of the rib peripheral surface (18) on the tip surface (23) side,
An operation edge (20) that digs into the damaged recess (9) is formed at the ridgeline where the second valley surface (16) and the rib peripheral surface (18) intersect,
The biting edge (21) is formed on the ridge line where the rib peripheral surface (18) and the tip slope (19) intersect,
A first inclined surface (24) is formed across the tip slope (19), the tip surface (23), the first valley surface (15) and the bottom surface (17), and the tip slope (19) is an inverted base. A screwdriver for screw removal, which is formed in a shape.   2. The second inclined surface (25) according to claim 1, wherein a second inclined surface (25) is formed between the second valley surface (16) of each valley groove (14) and the distal end surface (23) of the operation portion (3). Screwdriver for screw removal.   The screw driver for screw removal according to claim 1 or 2, wherein four rib-like protrusions (13) and trough grooves (14) are alternately formed at the tip of the operation portion (3) at equal angular intervals. tool.   The second valley surface (16) constituting the operation edge (20) is formed on a surface perpendicular to a plane perpendicular to the central axis of the driver shaft (2). Screw driver for screw removal as described.   The driver shaft (2) is formed in a hexagonal cross section, the operation part (3) is formed in a circular cross section, and the operation part (3) is formed in an inverted truncated cone shape that narrows as it goes to the tip. The screwdriver for screw removal according to any one of claims 1 to 4.

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