JP2013146830A - Screwdriver tool for removing screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screwdriver tool for removing a screw by which the screw can be removed precisely while capturing a remainder wall remaining in an operation groove of the screw by a biting edge and a drive plane.SOLUTION: Four rib-shaped projections 5 and four valley grooves 6 are formed alternately on an operation shaft 4 at equal intervals. The rib-shaped projection 5 has a tapered rib peripheral surface 7 and a biting edge 10 at a ridge line where a drive plane 8 and the rib peripheral surface 7 are made to cross each other. An edge angle E held between the drive plane 8 and the rib peripheral surface 7 is set to be an acute angle. A tilt angle F of the biting edge 10 with respect to a driver center axis P is set within 25°30' to 26°30' and made coincident with a tilt angle G of a blade bottom wall 26 constituting an operation groove 22 of the screw 21. The drive plane 8 is formed in parallel with a vertical plane R passing through both a projection center axis Q of the rib-shaped projection 5 and the driver center axis P. When the screw 21 is unscrewed, the lower part side of the biting edge 10 is bitten into a remainder wall 30 ahead of the upper part side of the biting edge 10.

Description

  The present invention relates to a screwdriver tool applied to a manual screwdriver, an electric screwdriver, or the like, and more particularly to a screwdriver tool suitable for removing a screw in which a cross-shaped operation groove provided on a screw head is crushed.

  The present applicant has previously proposed this type of screwdriver (Patent Document 1). In this case, four rib-shaped protrusions and four valley grooves are alternately arranged at the tip of the driver shaft to form an operation shaft portion having a cross-shaped cross section. The rib-shaped protrusion is composed of a rib circumferential surface inclined in a tapered manner toward the tip of the driver shaft, and a circumferential surface of the valley groove that sandwiches the rib circumferential surface. A biting edge for loosening the screw is provided at one ridge line portion where the rib peripheral surface and the rib peripheral surface are adjacent to each other. In the case of this screwdriver, the circumferential surface of one trough groove including the biting edge is a drive surface that transmits torque to the screw operation groove, and the drive surface is slightly in relation to the center axis of the driver shaft. It is tilted. The rib peripheral surface is formed as a flat surface inclined with respect to the drive surface, and therefore, the angle between the drive surface and the rib peripheral surface is an acute angle.

  In the screwdriver of Patent Document 2, the portion corresponding to the drive surface is formed as a concave surface, and the biting function of the biting edge is strengthened, whereby the screw can be tightened firmly.

  In the screwdriver tool according to the present invention, when loosening a screw whose crisscross-shaped operation groove is crushed, a bite edge is bitten into a damaged recess cut by a screwdriver. 3 is known. There, four biting blades having a wedge-shaped cross section, which are pointed toward the outer edge, are provided on the driver shaft, and the screws are loosened by biting the biting blade into the opening edge of a mortar-shaped damaged recess.

  In the screwdriver tool according to the present invention, the biting edge is formed in parallel with the central axis of the driver shaft. This type of screwdriver tool is disclosed in Patent Document 4, for example. There, a vertical wall parallel to the longitudinal axis of the blade is provided at the tip of the driver blade, and this vertical wall is used as a drive surface. The opposite surface of the blade is inclined with respect to the vertical wall. The screw that is tightened with a screwdriver in Patent Document 4 is used as a medical screw, and its operation groove is H-shaped or Z-specified by JIS frequently used in Japan. It has a special shape that is different from the cross hole. Therefore, a normal screwdriver corresponding to a screw conforming to the JIS standard cannot be inserted into and engaged with the screw operation groove of Patent Document 4.

International Publication No. 2007/20681 (paragraph number 0038, FIG. 1, FIG. 4) Japanese Patent Publication No. 36-4449 (page 3, lines 2-5, FIG. 6) Japanese Utility Model Publication No. 43-15438 (first page, right column, lines 19 to 24, FIG. 3) Japanese translation of PCT publication No. 2002-513331 (page 8, lines 18-20, FIG. 2)

  According to the screwdriver of Patent Document 1, as shown in FIG. 8, even if the cross-shaped operation groove is crushed, the biting edge and the driving surface are engaged with the remaining wall of the damaged recess, Most screws can be loosened. However, the shape of the damaged recess cut by the screwdriver is not necessarily constant, so depending on the remaining position or the remaining shape of the remaining wall, it is difficult to engage the biting edge with the remaining wall and the screw cannot be loosened. is there. For example, when the remaining wall is formed near the bottom of the operation groove, it is difficult to engage the biting edge and the driving surface with the remaining wall.

  Like the screwdriver tool of Patent Document 2, when the portion corresponding to the drive surface is formed as a concave surface and the biting function of the biting edge is strengthened, the biting edge is bitten into the proximal end portion of the remaining wall, and the screw side The remaining wall can be captured more reliably by the operation shaft. However, in each of the screwdrivers of Patent Document 1 and Patent Document 2, the biting edge and the drive surface are slightly inclined with respect to the center axis of the driver shaft in the same manner as a normal driver. Therefore, when the screw is loosened and operated, the driving surface including the biting edge is subject to an operating reaction force and tends to float away from the inner surface of the operating groove, so that the biting edge and the driving surface are slightly removed from the remaining remaining wall. You may not be able to loosen the operation.

  In the screwdriver of Patent Document 3, for example, the grip end of the screwdriver is struck with a hammer to bite the biting blade into the opening edge of the conical recess. It is difficult to eat evenly. Therefore, the rotational torque of the screwdriver tool cannot be transmitted accurately to the screw head. In most cases, the result is often that the opening edge of the conical recess is scraped with a biting blade, and the opening edge only widens.

  When the operation groove 22 is crushed, the portion cut by the driver of the electric tool is a fan-shaped wall 24, and the fan-shaped wall 24 is cut to form a conical recess as shown in FIG. At this time, it is the triangular blade side wall 27 (see FIG. 7) located on the loose side that first receives the torque (shearing force) of the driver. The upper surface of the meat wall 24 is sheared. At this time, the closer to the upper opening edge of the blade groove 23 in the blade side wall 27, the smaller the shear resistance, the easier it is to be cut by a driver, and the closer to the blade bottom wall 26, the higher the shear resistance, the less difficult it is to cut by a screwdriver. Become. This means that the closer to the blade bottom wall 26 and the closer to the groove bottom wall 25, the easier the remaining wall 30 remains.

  The remaining wall 30 is inclined obliquely because it is a part of the blade side wall 27 originally formed in a tapered shape having a downward slope. Therefore, in a situation where a rotational moment in the loosening direction acts on the remaining wall 30, a reaction force that pushes up the driving surface acts on the driving surface that is in close contact with the remaining wall 30, and the driving surface moves from the remaining wall 30. It becomes easy to come off. In particular, when the biting edge and the drive surface are inclined along the inclination of the blade side wall 27 as seen in the screwdrivers of Patent Document 1 and Patent Document 2, the reaction force increases. For this reason, the drive surface is easily detached from the remaining wall 30. Based on the above knowledge, the present inventor has reexamined the structure of the screwdriver tool, studied what should be done to more accurately perform the screw removal work, and proposed the present invention.

  The object of the present invention is to remove the screw more accurately than the conventional screwdriver tool by accurately capturing the remaining wall remaining in the operation groove of the screw with the biting edge and the driving surface. It is to provide a screwdriver tool.

  In the screw removal tool for screw removal according to the present invention, four rib-like projections 5 and valley grooves 6 are alternately formed at equal intervals on the operation shaft portion 4 at the tip of the driver shaft 2. The rib-shaped protrusion 5 is formed by a rib peripheral surface 7 that is tapered toward the tip of the operation shaft portion 4 and a peripheral surface of a pair of valley grooves 6 that sandwich the rib peripheral surface 7 therebetween. is there. A biting edge 10 is formed at the ridge line where the rib peripheral surface 7 and the drive surface 8 provided on one side thereof intersect. As shown in FIG. 5, the rib peripheral surface 7 is inclined with respect to the drive surface 8, and the edge angle E between the drive surface 8 and the rib peripheral surface 7 is set to an acute angle. Further, as shown in FIG. 1, the inclination angle F of the biting edge 10 with respect to the driver central axis P is set so as to be within a range of 25 degrees 30 minutes to 26 degrees 30 minutes. The drive surface 8 is formed in parallel with a vertical plane R passing through the projection center axis Q of the rib-like projection 5 and the driver center axis P. In a state where the screw 21 is loosened, the lower side of the biting edge 10 bites into the remaining wall 30 preceding the upper side of the biting edge 10.

  A round surface portion 13 having a partial arc shape in cross section is formed at the protruding corner portion between the flat end surface 12 of the operation shaft portion 4 and the rib peripheral surface 7, and the lower portion of the biting edge 10 is rounded.

  In a state where the operation shaft portion 4 is engaged with the operation groove 22 of the screw 21, the formation position of the end surface 12 is positioned above the lower end of the blade bottom wall 26 (see FIG. 6).

  The width dimension J of the rib-like protrusion 5 at an arbitrary position in the vertical direction of the rib peripheral surface 7 is set to be smaller than the groove width dimension K of the operation groove 22 (see FIG. 9A).

  The cross section of the corner 14 between the drive surface 8 and the flank 9 is rounded into a partial arc.

  In the present invention, in the screwdriver for screw removal, in which four rib-like projections 5 and valley grooves 6 are alternately formed at equal intervals on the operation shaft portion 4, the drive surface 8 and the rib peripheral surface 7 are provided. The edge angle E sandwiched between and was set to an acute angle. Further, the inclination angle F of the biting edge 10 was set to fall within the range of 25 degrees 30 minutes to 26 degrees 30 minutes. Further, when the drive surface 8 is formed in parallel with the vertical plane R passing through the projection central axis Q of the rib-like projection 5 and the driver central axis P, and the screw 21 is loosened, the lower side of the biting edge 10 is the biting edge 10. The remaining wall 30 was eaten ahead of the upper side of the.

  As described above, when the operation groove 22 is crushed into a conical concave shape, the opening edge side of the operation groove 22 is easily scraped, and is closer to the blade bottom wall 26 or closer to the groove bottom wall 25. The remaining wall 30 is easily formed. Therefore, as described above, according to the screwdriver of the present invention in which the lower side of the biting edge 10 bites in front of the upper side, the biting edge 10 and the driving surface 8 are bitten into the remaining wall 30 and the screw 21 The screw 21 can be loosened in a state in which the screw 21 is properly captured, and the screw 21 can be removed more reliably than a conventional screwdriver of this type. Further, since the drive surface 8 is formed in parallel with the vertical plane R passing through the projection center axis Q of the rib-like projection 5 and the driver center axis P, the drive surface 8 including the biting edge 10 when the screw 21 is loosened. Can be prevented from being lifted off from the blade bottom wall 26 due to the operation reaction force, and the screw 21 can be further loosened and operated.

  When the round surface portion 13 is formed at the protruding corner portion between the flat end surface 12 and the rib peripheral surface 7 and the lower portion of the biting edge 10 is rounded, the rib peripheral surface 7, the drive surface 8, and the end surface 12 are adjacent to each other. The mechanical strength of the corner portion to be improved can be improved. Accordingly, the corner portion where the rib peripheral surface 7, the drive surface 8, and the end surface 12 are adjacent to each other can be prevented from being damaged and missing, and the durability of the screwdriver tool can be improved.

  In a state where the operation shaft portion 4 is engaged with the operation groove 22 of the screw 21, if the position where the end surface 12 is formed is positioned above the lower end of the blade bottom wall 26, the end surface 12 is grooved prior to other parts. By preventing contact with the bottom wall 25, the biting edge 10 and the drive surface 8 can be in close contact with the remaining wall 30. In addition, since a gap is secured between the end surface 12 and the groove bottom wall 25, even when a foreign object enters the groove bottom wall 25, the end surface 12 hits the foreign object and the biting edge 10 becomes the base end of the remaining wall 30. It can be prevented from floating away from the corner. Therefore, the rotational torque in the loosening direction of the operation shaft portion 4 can be reliably transmitted to the screw 21 and removed.

  If the width dimension J of the rib-like protrusion 5 is set to be smaller than the groove width dimension K of the operation groove 22, coupled with the fact that the edge angle E is set to an acute angle, the operation shaft portion 4 is moved to the operation groove. In the state engaged with 22, only the biting edge 10 can be brought into contact with the blade bottom wall 26. Accordingly, when the operation shaft portion 4 is rotated in the loosening direction, the biting edge 10 is brought into contact with the proximal end corner portion of the remaining wall 30 and the driving surface 8 is brought into contact with the meat wall of the fan-shaped meat portion 24 including the remaining wall 30. The contact area can be expanded by encroaching, and the screw 21 can be further loosened and operated.

  When the cross section of the corner 14 between the drive surface 8 and the flank 9 is rounded in a partial arc shape, the mechanical strength of the protruding base of the rib-like protrusion 5 is improved and the durability of the screwdriver tool is improved. Can be further improved.

It is a front view which shows the cross section of the screwdriver tool which concerns on this invention, and the screw of removal object. It is a front view of the screwdriver tool concerning the present invention. It is a bottom view of the operation shaft part concerning the present invention. It is the sectional view on the AA line in FIG. It is the BB sectional view taken on the line in FIG. It is a vertical front view of the state which engaged the operation shaft part with the operation groove of the screw. It is a top view which shows the detailed structure of the operation groove | channel of a screw. It is a top view of the screw in the state where the operation groove was crushed. It is explanatory drawing which shows the biting operation | movement of a biting edge and a drive surface.

(Embodiment 1) FIGS. 1 to 9 show an embodiment in which the screwdriver according to the present invention is applied to a manual driver. In FIG. 2, reference numeral 1 denotes a driver grip, and 2 denotes a replaceable driver shaft. The driver shaft 2 can be extracted from the grip 1 by pushing the chuck 3 provided at the mounting base end of the grip 1 against the spring. An operation shaft portion 4 is formed at the tip of the driver shaft 2 formed of a hexagonal shaft.

  The operation shaft portion 4 is formed in a cross-shaped cross section by alternately forming four rib-like protrusions 5 and four trough grooves 6 on the round shaft portion. 3 and 4, each rib-like protrusion 5 is arranged in a state in which the protrusion center axis Q is positioned around the operation shaft portion 4 at equal intervals, and is inclined in a tapered shape toward the tip. The rib peripheral surface 7 and the peripheral surfaces of the pair of valley grooves 6 sandwiching the rib peripheral surface 7 therebetween. One of the pair of peripheral surfaces of the trough 6 is the drive surface 8 and the other is the flank 9. A biting edge 10 is formed at the ridge line where the rib peripheral surface 7 and the drive surface 8 intersect.

  As shown in FIG. 5, the rib peripheral surface 7 is formed as a flat surface inclined with respect to the drive surface 8, and the edge angle E sandwiched between the drive surface 8 and the rib peripheral surface 7 is set to an acute angle (75 degrees). ing. Further, by inclining the rib peripheral surface 7 in a tapered shape toward the tip of the operation shaft portion 4, the inclination angle F of the biting edge 10 with respect to the driver center axis P is set to the operation groove of the countersunk screw 21. 22 is made to coincide with the inclination angle G of the blade bottom wall 26 constituting 22 (see FIG. 1). The shape of the operation groove 22 of the countersunk screw 21 matches the shape of the H-shaped cross hole defined in JISB-1012, and the inclination angle G of the blade bottom wall 26 is 26 degrees 30 minutes. Further, the allowable intersection of the inclination angle G is +15 minutes and −0. Therefore, if the inclination angle G of the blade bottom wall 26 is within the range of 26 degrees 30 minutes to 26 degrees 45 minutes, it conforms to the JIS standard.

  For the operation groove 22 configured as described above, the inclination angle F of the biting edge 10 is a standard value of 26 degrees 30 minutes, which is the same as the inclination angle G of the blade bottom wall 26, but the allowable intersection is +0, In the state where the operation shaft portion 4 is engaged with the operation groove 22 of the screw 21, the lower side of the biting edge 10 bites into the remaining wall 30 ahead of the upper side of the biting edge 10. That is, the inclination angle F of the biting edge 10 is set to an angle within the range of 25 degrees 30 minutes to 26 degrees 30 minutes. If the inclination angle F of the biting edge 10 is smaller than 25 degrees 30 minutes, it becomes difficult to bite the upper side of the biting edge 10 into the remaining wall 30, and in particular, the inclination angle G of the blade bottom wall 26 varies. The tendency becomes remarkable when it is biased toward the + side. Further, when the inclination angle F of the biting edge 10 is larger than 26 degrees 30 minutes, the upper side of the biting edge 10 comes in contact with the opening edge of the conical concave portion shaved with a screwdriver, and the lower side of the biting edge 10 is left as the rest. It becomes difficult to bite into the wall 30.

  The drive surface 8 is provided on the peripheral surface of the trough groove 6 on the side that contacts the remaining wall 30 of the operation groove 22 of the countersunk screw 21 when the countersunk screw 21 is loosened and operated by the operation shaft portion 4. Specifically, as shown in FIG. 4, when the countersunk screw 21 made of a right-hand screw is loosened in the direction of arrow D, the side that contacts the blade side wall 27 located on the upper side in the loosening rotation direction is the drive surface 8. In order to accurately capture the remaining wall 30 remaining in the operation groove 22 by the biting edge 10 and the driving surface 8, the driving surface 8 is perpendicular to the protrusion central axis Q of the rib-shaped protrusion 5 and the driver central axis P. (See FIG. 5).

  As shown in FIG. 1, the flank 9 is slightly inclined with respect to the projection central axis Q, so that the outer shape of the rib peripheral surface 7 in a state of facing the bottom can be made to be a narrow shape. The inclination angle H of the flank 9 is 4 degrees. The width dimension J of the rib-like protrusion 5 at an arbitrary position in the vertical direction of the rib peripheral surface 7 is set to be smaller than the groove width dimension K of the operation groove 22 (see FIG. 9). Further, as described above, the rib peripheral surface 7 is inclined with respect to the drive surface 8 by the edge angle E. Therefore, in the state where the rib-shaped protrusion 5 is engaged with the operation groove 22, only the biting edge 10 can be brought into contact with the blade bottom wall 26 as shown in FIGS. Can be brought into contact with the base end corner of the remaining wall 30.

  The end surface 12 at the tip of the operation shaft portion 4 is a flat surface orthogonal to the driver center axis P. A round surface portion 13 having a partial arc shape in cross section is formed at the protruding corner portion between the end surface 12 and the rib peripheral surface 7, and thereby the lower portion of the biting edge 10 is rounded. By rounding the lower part of the biting edge 10, the mechanical strength of the corner portion where the rib peripheral surface 7, the drive surface 8 and the end surface 12 are adjacent can be improved, and the corner portion can be well prevented from being damaged and missing. Similarly, the cross section of the corner portion 14 between the continuous drive surface 8 and the flank 9 in the trough 6 can be rounded into a partial arc so that the mechanical strength of the protruding base portion of the rib-like protrusion 5 can be improved. I have to.

  In a state where the operation shaft portion 4 is engaged with the operation groove 22 of the countersunk screw 21, in order to avoid the end surface 12 from coming into contact with the groove bottom wall 25, the formation position of the end surface 12 is set from the inclined lower end of the blade bottom wall 26. It is located above. Incidentally, the inclination angle of the blade bottom wall 26 and the inclination angle of the groove bottom wall 25 are constant irrespective of the difference in the screw size, and the total depth of the blade bottom wall 26 is different in the screw size and the shape of the operation head. Only depending on the. Accordingly, the radial facing distance of the lower end portion of the blade bottom wall 26 is always constant, and the facing distance of the outer edges of the pair of biting edges 10 on the end face 12 is larger than the facing distance of the lower end portion of the blade bottom wall 26. If the position where the end face 12 is formed is set to the end face 12, it can be avoided that the end face 12 contacts the groove bottom wall 25. In addition, as shown in FIG. 6, even when a foreign object enters the groove bottom wall 25 by securing a gap between the end surface 12 and the groove bottom wall 25, the end surface 12 hits the foreign object and the biting edge 10 becomes It is possible to prevent floating from the blade bottom wall 26. In addition, the opposing space | interval of the outer edge of a pair of biting edge 10 in the end surface 12 is the biting state of the sharp state in the state before the round surface part 13 is formed in the protrusion corner part between the end surface 12 and the rib surrounding surface 7. This is the distance between the outer edges of the edge 10.

  FIG. 7 shows a detailed structure of the operation groove 22 formed in the operation head of the countersunk screw 21. The operation groove 22 matches the shape of the H-shaped cross hole defined in JIS B-1012, and has four blade grooves 23 arranged in a cross shape and four blade grooves 23 positioned between the blade grooves 23. The fan-shaped meat portion 24 and a groove bottom wall 25 formed at the intersection of each blade groove 23 are configured. In more detail, the blade groove 23 is composed of an isosceles trapezoidal blade bottom wall 26 and a triangular blade sidewall 27 continuous with the oblique side portion of the blade bottom wall 26. The pair of blade side walls 27 facing each other with the blade bottom wall 26 therebetween is formed in a tapered shape that is tapered downward when viewed from the center axis side of the screw. The fan-shaped wall 24 is surrounded by two blade side walls 27 of the blade grooves 23 adjacent to each other in the circumferential direction and a square-shaped refracting wall 28 provided between the blade side walls 27.

  FIG. 8 shows a plan view of the operation groove 22 crushed by, for example, a power tool driver. In this case, most of the fan-shaped meat portion 24 is scraped off to the extent that the original shape cannot be stopped with a screwdriver to form a conical recess. Thus, when the fan-shaped meat portion 24 is cut into a conical recess shape, a portion having a smaller shear resistance than other portions, specifically, a ridge line where the blade side wall 27 and the upper surface of the fan-shaped meat portion 24 are adjacent to each other. The portion, the ridge line portion where the upper surface of the square-shaped refracting wall 28 and the fan-shaped meat portion 24 are adjacent are shaved in advance of other portions. Further, since the shear resistance increases toward the side closer to the blade bottom wall 26 and further toward the groove bottom wall 25, the remaining wall 30 tends to remain.

  As shown in FIG. 9A, when the operating shaft portion 4 is engaged with the operating groove 22 of the countersunk screw 21 and rotated in the loosening direction, the lower end of the biting edge 10 is the remaining wall 30 and the blade bottom wall. 26, the lower part of the driving surface 8 contacts the remaining wall 30. When the driver shaft 2 is further rotated in the loosening direction in this state, the biting edge 10 and the driving surface 8 bite into the fan-shaped meat portion 24 including the remaining remaining wall 30 as shown in FIG. 9B. The contact area between the drive surface 8 and the countersunk screw 21 is increased. Therefore, it is possible to perform the loosening operation while reliably transmitting the rotational torque in the loosening direction of the driver shaft 2 to the countersunk screw 21. At this time, since the drive surface 8 is formed in parallel with the vertical plane R passing through the projection center axis Q of the rib-like projection 5 and the driver center axis P, the drive surface 8 including the biting edge 10 receives an operation reaction force. Thus, it is possible to prevent the blade bottom wall 26 from being lifted off.

  Therefore, according to the screwdriver according to this embodiment, the rotational torque in the loosening direction of the driver shaft 2 can be accurately transmitted to the countersunk screw 21, and the countersunk screw 21 can be further loosened. Further, since the countersunk screw 21 is loosened with the remaining remaining wall 30 as an engagement target, even the countersunk screw 21 that cannot be grasped by the pliers can be removed without any problem. As can be understood from the above description, in the state in which the countersunk screw 22 is loosened, the lower side of the biting edge 10 bites into the remaining wall 30 of the operation groove 22 prior to the upper side of the biting edge 10.

  The edge angle E can be selected within a range of 50 degrees or more and less than 90 degrees, and is preferably selected within a range of 70 degrees or more and less than 90 degrees. When the edge angle E is less than 50 degrees, the structural strength of the biting edge 10 is lowered, and defects are easily generated. On the other hand, when the edge angle E is 90 degrees or more, the rib peripheral surface 7 comes into contact with the blade bottom surface 26 first, so that the biting edge 10 cannot be brought into contact with the base end corner portion of the remaining wall 30. More preferably, the edge angle E is set to 75 degrees or more and less than 85 degrees.

  In the above embodiment, the case where the operation groove 22 of the screw 21 matches the shape of the H-shaped cross hole defined in JISB-1012 has been described. However, in the screwdriver of the present invention, the operation groove 22 has the JISB. It can be applied to the screw 21 that matches the shape of the Z-shaped cross hole specified by -1012 or the screw 21 that matches the shape of the S-shaped cross hole specified by JISB-1012. Further, the screw (small screw) 21 may be a screw having a different shape of the operation head, such as a round small screw, a pan small screw, a flat screw, a truss small screw, and a bind small screw.

  Instead of the round surface portion 13, the protruding corner portion between the end surface 12 and the rib peripheral surface 7 can be chamfered with a flat surface. In the above embodiment, the biting edge 10 and the driving surface 8 are bitten into the fan-shaped wall 24 including the remaining wall 30 to loosen the screw 21. However, if necessary, the biting edge 10 is shaped like a conical recess. The screw 21 can be loosened and manipulated in a state where it has been driven into and devoured into the shavings. The driver shaft 2 according to the present invention may be a driver shaft used by being mounted on a power transmission tool. The rib peripheral surface 7 can be formed of a concave arc surface. The screw 21 may be a left-hand thread, and the biting edge 10 in that case is formed on the side of the flank 9 in the above embodiment.

2 Driver shaft 4 Operation shaft portion 5 Rib-shaped protrusion 6 Valley groove 7 Rib peripheral surface 8 Drive surface 9 Relief surface 10 Biting edge 21 Countersunk screw
22 Operation groove 24 Fan-shaped wall part 26 Blade bottom wall 27 Blade side wall 30 Remaining wall E Edge angle F Inclination angle G of biting edge Inclination angle P of blade bottom wall Driver center axis Q Projection center axes RP and Q of rib-like projections Vertical plane through

Claims (5)

Screw removal tool for screw removal, in which four rib-shaped protrusions (5) and valley grooves (6) are alternately formed at equal intervals on the operating shaft (4) at the tip of the driver shaft (2) Because
The rib-shaped protrusion (5) has a rib peripheral surface (7) inclined in a tapered shape toward the tip of the operation shaft portion (4) and a pair of valley grooves (nearly sandwiching the rib peripheral surface (7)). 6) and the peripheral surface,
The biting edge (10) is formed on the ridge line where the rib peripheral surface (7) and the drive surface (8) provided on one side thereof intersect,
The rib peripheral surface (7) is inclined with respect to the drive surface (8), and the edge angle (E) between the drive surface (8) and the rib peripheral surface (7) is set to an acute angle,
The inclination angle (F) of the biting edge (10) with respect to the driver central axis (P) is set to fall within a range of 25 degrees 30 minutes to 26 degrees 30 minutes,
The drive surface (8) is formed in parallel with a vertical plane (R) passing through the projection center axis (Q) of the rib-like projection (5) and the driver center axis (P),
A screwdriver for screw removal, characterized in that the lower side of the biting edge (10) bites into the remaining wall (30) preceding the upper side of the biting edge (10) in a state in which the screw (21) is loosened and operated. tool.   A round surface portion (13) having a partially arcuate cross section is formed at the protruding corner portion between the flat end surface (12) of the operation shaft portion (4) and the rib peripheral surface (7), and the biting edge (10) The screwdriver for screw removal according to claim 1, wherein a lower portion of the screw is rounded.   The end surface (12) is formed at a position higher than the lower end of the blade bottom wall (26) in a state where the operation shaft portion (4) is engaged with the operation groove (22) of the screw (21). Or a screwdriver for screw removal according to 2.   The width dimension (J) of the rib-like projection (5) at an arbitrary position in the vertical direction of the rib peripheral surface (7) is set smaller than the groove width dimension (K) of the operation groove (22). The screwdriver for screw removal according to any one of 3 above.   The screwdriver for screw removal according to claim 4, wherein the cross section of the corner (14) between the drive surface (8) and the flank (9) is rounded into a partial arc.

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