JP2008093748A - Hammer drill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lightweight hammer drill devised to simplify a manufacturing process. <P>SOLUTION: This hammer drill is furnished with a motor 21 furnished with a driving shaft part 22, a casing with the motor 21 built in it, a roughly cylindrical cylinder 44 provided in the casing 2, a central axis of which is regulated and which is driven to rotate around the central axis by the driving shaft part 22, a supporting member 31 connected to the casing 2, a bearing part 34 provided coaxially with the cylinder 44 on the supporting member 31 and to rotatably support the cylinder 44 and an energizing mechanism making contact with the bearing part 34 and to energize the bearing part 34 in the axial direction of the central axis and toward the supporting member 31. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hammer drill.

  Conventionally, a hammer drill that rotates a drill bit and applies a striking force is known. In order to generate a striking force, this hammer drill has a motor, a cylinder, a piston disposed in the cylinder, a motion conversion mechanism for converting the rotational force of the motor into a reciprocating motion of the piston, and a striking drive driven by the piston. (For example, refer patent document 1). The above-described cylinder is supported in the hammer drill by a support member connected to a casing portion that is an outer shell of the hammer drill. In addition, a bearing portion such as a metal bearing or a ball bearing is press-fitted to a portion of the support member that supports the cylinder, and the cylinder is rotatably supported.

The hammer drill is configured to have high rigidity as a whole because vibration associated with impact is generated. Accordingly, the bearing portion is pressed into the support member at a high pressure so as not to be detached from the support member due to vibration or the like.
Japanese Patent Laid-Open No. 2005-040880

  However, in order to press-fit the bearing portion at a high pressure, a device capable of generating a high pressure, such as a hydraulic device, is required, and the work may be complicated. Also in the support member, it is necessary to use a high-strength and high-strength material in order to withstand the press-fitting of the bearing portion, which tends to increase the weight of the hammer drill.

  Therefore, an object of the present invention is to provide a hammer drill that can simplify the manufacturing process and reduce the weight.

  In order to solve the above problems, the present invention provides a motor having a drive shaft portion, a casing portion containing at least the motor, a center axis provided in the casing portion, and a center axis defined by the drive shaft portion. A substantially cylindrical cylinder portion that is driven to rotate, a support member connected to the casing portion, a bearing portion provided coaxially with the cylinder on the support member to rotatably support the cylinder, and the bearing And a biasing mechanism for biasing the bearing portion toward the support member in the axial direction of the central axis.

  In the hammer drill configured as described above, the bearing portion has a first side surface and a second side surface which are end surfaces orthogonal to the central axis direction, the first side surface abuts on the support member, and the second side surface is It is preferable to contact the urging mechanism.

  According to such a configuration, since the bearing portion is always urged by the urging mechanism to the support member, it is possible to suppress the bearing portion from being dropped or displaced from the support member due to vibration or the like. Since it is not necessary to press-fit at a high pressure, it is not necessary to use a device that generates a high pressure related to press-fitting at the time of manufacture. Moreover, high strength is not required for the support member, a lighter support member can be used, and the weight of the hammer drill can be reduced.

  The urging mechanism includes a sleeve that abuts on the bearing portion, a spring that urges the sleeve toward the bearing portion, and a restricting portion that restricts the movement of the spring toward the non-bearing portion. It is preferable that it is comprised.

  According to such a configuration, the spring that generates the urging force and the bearing portion are connected via the sleeve. Therefore, sliding can be generated between the sleeve and the bearing portion.

  A shut-off mechanism capable of interrupting transmission of driving force between the cylinder portion and the drive shaft portion is provided between the cylinder portion and the drive shaft portion. In contact with the abutting portion rotating with an axis that is coaxial or parallel with the cylinder portion and rotating with an axis that is coaxial or parallel with the driving shaft portion in conjunction with the drive shaft portion. An abutting portion that contacts, and an urging portion that urges the corresponding contacting portion toward the abutted portion, the abutted portion including the restricting portion, and the urging portion from the spring Preferably, it is configured.

  According to such a configuration, it is possible to protect the drive shaft portion and the conduction motor connected thereto from abnormal rotation of the cylinder portion. In addition, since the parts constituting the urging mechanism and the blocking mechanism can be partly composed of common parts, the number of constituent parts can be reduced, and the weight of the hammer drill can be reduced.

  Further, it is preferable that the urging mechanism is installed in the cylinder part, and the cylinder part is provided with a drop-off preventing member that prevents the urging mechanism from dropping from the cylinder part in a non-biased state. .

  According to such a configuration, the urging mechanism is prevented from dropping from the cylinder portion when the bearing portion is not urged by the urging mechanism. Therefore, at the time of assembling the hammer drill, the cylinder portion incorporating the urging mechanism can be easily assembled to the support member.

  The bearing portion includes an outer ring that comes into contact with the support member, and an inner ring that is rotatably supported by the outer ring and rotates about the central axis, and supports the cylinder portion. It is preferable to urge the inner ring.

  According to such a configuration, the urging mechanism does not come into contact with the outer ring, so that no sliding portion is generated between the urging mechanism and the bearing portion, and the rotation of the cylinder portion is not suppressed.

  Moreover, it is preferable that this support member is comprised from resin. According to such a configuration, the support member can be reduced in weight, and thus the hammer drill can be reduced in weight.

  According to the hammer drill of the present invention, the manufacturing process can be simplified and the weight can be reduced.

  A first embodiment in which the power tool of the present invention is applied to a hammer drill will be described with reference to FIGS. 1 and 2. The hammer drill 1 is configured using a casing portion 2 including a handle portion 10 and a motor casing 20 and a gear casing 30 connected to each other as an outer shell.

  The handle portion 10 is provided in the motor casing 20 so as to extend from the side surface of the motor casing 20 at the position opposite to the gear casing 30. A power cable 11 is attached to the handle portion 10 and a switch mechanism 12 is built therein. A trigger 13 that can be operated by a user is mechanically connected to the switch mechanism 12. The power cable 11 connects the switch mechanism 12 to an external power source (not shown) and operates the trigger 13 to switch between connection and disconnection of the switch mechanism 12 and the power source. In the hammer drill 1, the side where the handle portion 10 is provided in the longitudinal direction of the casing portion 2 is defined as the rear side, and the opposite side in the longitudinal direction is defined as the front side. This front-rear direction is the same as the direction of the central axis of rotation of a cylinder 44 described later. Further, a direction extending from the casing portion 2 of the handle portion 10 and substantially perpendicular to the front-rear direction is defined as a lower side, and an opposite lower side is defined as an upper side.

  The motor casing 20 is a resin molded product and is integrally formed with the handle portion 10. An electric motor 21 is accommodated in the motor casing 20. The electric motor 21 includes an output shaft portion 22 that is a drive shaft, and outputs a rotational driving force. The output shaft portion 22 is pivotally supported by a bearing 31 </ b> A which will be described later, and its front end is located in the gear casing 30. A first gear 22 </ b> B is provided at the front end portion of the output shaft portion 22 located in the gear casing 30.

  The gear casing 30 is provided on the side opposite to the handle portion 10 of the motor casing 20. A support member 31 is provided inside the gear casing 30. The support member 31 is made of a resin called engineering plastic such as nylon, PPS (polyphenylene sulfide), polyurethane, or the like as a base material, and a base portion 32 connected to the motor casing 20 and extends from the base portion 32 toward the front side. And a cylinder support 33.

  The base portion 32 is configured in a plate shape orthogonal to the front-rear direction, and a hole 32a through which the output shaft portion 22 is inserted is formed in a substantially central portion so as to penetrate in the front-rear direction. A hole (not shown) through which a screw (not shown) to be connected is passed is formed. Further, as shown in FIG. 1, the surface of the base portion 32 connected to the motor casing 20 is formed with a hole in which a bearing 31 </ b> A that supports the output shaft portion 22 is disposed, and the surface on the gear casing 30 side is formed. Is formed with a perforation in which a bearing 41B for supporting an intermediate shaft portion 41 described later is disposed.

  As shown in FIGS. 1 and 2, the cylinder portion support portion 33 defines a space in which a later-described motion conversion member 52 and a piston 54 are inserted, and has an annular shape at the distal end portion in the extending direction. The metal bearing 34 is provided. As shown in FIG. 2, a first side surface 34A is defined at an end surface orthogonal to the front-rear direction of the metal bearing 34 and in contact with the support member 31, and a sleeve described later is provided on the opposite side of the first side surface 34A. A second side surface 34B that contacts 44E is defined. Further, in the metal bearing 34, when the cylinder support portion 33 and the metal bearing 34 are cut in a cross section passing through the central axis of the metal bearing 34 and parallel to the front-rear direction, the inner surface of the metal bearing 34 is the inner surface of the cylinder support portion 33. It is configured to protrude closer to the central axis.

  A speed reduction chamber 40 a that houses a rotation transmission mechanism, which will be described later, is defined in a lower portion of the support member 31 in the gear casing 30. An intermediate shaft portion 41 is disposed in the deceleration chamber 40a. The intermediate shaft portion 41 is parallel to the output shaft portion 22 and is supported by the gear casing 30 and the support member 31 via a bearing 41B and the like so as to be rotatable about its axis. Further, a side handle 16 is provided in the vicinity of the tool holding portion 15 described later of the gear casing 30.

  A second gear 41 </ b> A that meshes with the first gear 22 </ b> B is coaxially fixed to the intermediate shaft portion 41 at the end portion on the electric motor 21 side that is the rear side of the intermediate shaft portion 41. On the front side of the intermediate shaft portion 41, a clutch 42 that rotates together with the intermediate shaft portion 41 and is slidable in the axial direction of the intermediate shaft portion 41 is disposed. Further, on the front side of the clutch 42, a third gear 43A that can mesh with a later-described fourth gear 44A is provided.

  A cylinder 44 is provided in the gear casing 30 at a position on the other end side of the intermediate shaft portion 41 and in the vicinity of the upper side. The cylinder 44 extends parallel to the intermediate shaft portion 41 and is rotatably supported by the metal bearing 34 of the cylinder portion support portion 33 on the support member 31 and the bearing 40D on the gear casing 30. A fourth gear 44A is fixed to the outer periphery of the cylinder 44 and in the vicinity of the third gear 43A so as to be rotatable coaxially with the cylinder 44. By engaging the third gear 43A and the fourth gear 44A, the cylinder 44 is configured to be rotatable with respect to the gear casing 30 about its axis.

  A blocking mechanism is interposed between the fourth gear 44 </ b> A and the cylinder 44. The shut-off mechanism is provided on the opposite side of the flange portion 44B across the fourth gear 44 with the flange portion 44B being a contacted portion provided in the vicinity of the fourth gear 44A of the cylinder 44, and the fourth gear 44A. A spring 44C for urging the flange portion 44B and a contact surface 44D which is a side surface of the fourth gear 44A and contacts the flange portion 44B. During normal rotation, the spring 44C biases the contact surface 44D of the fourth gear 44A toward the flange portion 44B to generate a frictional resistance between the contact surface 44D and the flange portion 44B, and the fourth gear 44A and the cylinder And 44 are rotated together. When there is a sudden change in rotation such as a tip tool (not shown) biting into the work material, the frictional resistance generated by the biasing force of the spring 44C is resisted between the contact surface 44D and the flange portion 44B. As a result of slippage, the cylinder 44 idles with respect to the fourth gear 44 </ b> A to interrupt the transmission of a sudden change in rotation, and the mechanism that transmits the driving force connected to the electric motor 21 and the output shaft 22 can be protected. .

  Further, in the cylinder 44, an urging mechanism is disposed in the vicinity of the metal bearing 34. The urging mechanism includes the above-described spring 44C, the above-described flange portion 44B that is a restricting portion that restricts the movement of the spring 44C to the front side, and a sleeve 44E positioned between the spring 44C and the metal bearing 34. Some of the parts also serve as parts constituting the shut-off mechanism. Thereby, the number of parts which comprise hammer drill 1 can be reduced, and the weight of hammer drill 1 can be reduced.

  The sleeve 44 </ b> E is formed in a substantially cylindrical shape and is mounted on the outer peripheral portion of the cylinder 44, and the material thereof is made of a material that can slide with the metal bearing 34. A recess 44e having an inner periphery that is recessed over the entire inner periphery of the cylinder is formed on the end surface portion of the sleeve 44E that faces the metal bearing 34.

  The sleeve 44E abuts against the second side surface 34B by a reaction force that urges the fourth gear 44A of the spring 44C, and urges the metal bearing 34 coaxially with the central axis of the cylinder 44 toward the rear side. . As a result, the metal bearing 34 is urged to the cylinder portion support portion 33 by the first side surface 34A, and the metal bearing 34 is prevented from falling off from the cylinder portion support portion 33. Therefore, it is not necessary to press-fit the metal bearing 34 into the cylinder portion support portion 33 at a high pressure, and the metal bearing 34 is at least as long as the metal bearing 34 does not fall off the cylinder portion support portion 33 when the hammer drill 1 is assembled. It is only necessary to be held at 33.

  Since the sleeve 44E is interposed between the spring 44C and the metal bearing 34, it is possible to generate frictional sliding between the sleeve 44E and the metal bearing 34 when the cylinder 44 rotates. In this case, the sleeve can be suitably rotated without suppressing the rotation of the cylinder 44 by forming the sleeve from a low friction material. Further, since the sleeve 44E biases the metal bearing 34 to the rear side on the same axis as the center axis of the cylinder 44, a force acting on the metal bearing 34 in a direction intersecting the center axis direction is not generated. Therefore, even when the metal bearing 34 is urged by the sleeve 44E, the metal bearing 34 can support the cylinder 44 suitably.

  A space 44 a is defined inside the cylinder 44, and the space 44 a opens at the front side and the rear side of the cylinder 44, respectively. A piston 54 is slidably arranged in the space 44a from the opening at the rear end of the cylinder 44 so as to be slidable in the reciprocating direction and the circumferential direction. On the front side of the cylinder 44, a tool holding portion 15 serving as a mounting position of a tip tool (not shown) is provided. In the tool holding portion 15, a tip tool (not shown) can be inserted into the space 44a from the opening on the front side of the cylinder 44, and the tip tool inserted into the space 44a can be fixed.

  A groove is formed in the circumferential portion in the portion that is inserted in the metal bearing 34 of the cylinder 44 and is mounted on the cylinder support portion 33, and in the vicinity of the metal bearing 34. 44F is provided. The ring 44F is disposed on the rear side of the cylinder 44 in a state where the sleeve 44E is mounted on the cylinder 44. When the sleeve 44E is urged by the spring 44C and moves to the rear side, the ring 44F enters the recess 44e. 44E is restricted from moving beyond the ring 44F to the rear side. Due to the presence of the ring 44F, the sleeve 44E is disengaged from the cylinder 44 by the urging force of the spring 44C even if the sleeve 44E is not particularly pressed when the cylinder 44 with the sleeve 44E assembled is mounted on the cylinder support 33. There is nothing. Therefore, workability at the time of assembly can be improved.

  In addition, after the cylinder 44 is assembled to the cylinder support 33, the rear end surface of the sleeve 44E and the second side surface 34B of the metal bearing 34 come into contact with each other, and the sleeve 44E moves forward against the urging force of the spring 44C. Moving. As a result, the ring 44F and the sleeve 44E are separated from each other, thereby preventing the ring 44F from preventing the sleeve 44E from urging the metal bearing 34.

  As shown in FIG. 1, the piston 54 is configured integrally with a cylindrical portion 54A and a connecting portion 54B. The cylindrical portion 54A is configured in a substantially cylindrical shape that is open on the front side and closed on the rear side, and an air chamber 54a is defined therein. A plurality of air holes 54b (FIG. 2) are formed in a side wall portion of the piston 54 that defines the air chamber 54a. Further, the outer diameter of the cylindrical portion 54A is configured to be substantially the same as the inner diameter on the rear end side of the space 44a. The connecting portion 54B is provided on the rear end side of the cylindrical portion 54A and is connected to an arm portion 52A described later.

  A striking element 56 is disposed in the air chamber 54a of the piston 54 so as to be slidable back and forth. When the piston 54 moves from the rear side to the front side, the striker 56 is configured to be moved to the front side by the pressure of the compressed air in the air chamber 54a. Further, in the space 44 a of the cylinder 44, an intermediate element 57 that can come into contact with an impact tool 56 and a tip tool (not shown) held by the tool holding part 15 is provided between the piston 54 and the tool holding part 15. It is slidably arranged. Therefore, when the striker 56 strikes the intermediate element 57, the impact force is applied to the tip tool (not shown) via the intermediate element 57.

  In the intermediate shaft portion 41, a cam portion 51 is provided between the second gear 41 </ b> A and the clutch 42. The cam portion 51 has a substantially hemispherical shape and is normally disconnected from the intermediate shaft portion 41. Therefore, the cam portion 51 does not rotate with the intermediate shaft portion 41 unless the clutch 42 is connected.

  The cam portion 51 has a groove 51a formed on the entire surface of the spherical outer periphery in a direction intersecting the axis of the intermediate shaft portion 41. The cam portion 51 is provided with a motion conversion member 52. The motion converting member 52 is configured in a substantially annular shape, and includes a plurality of balls 52B inside the annular shape. The balls 52B are attached to the cam portion 51 by engaging with the grooves 51a. An arm portion 52A extends from an annular side surface located above the motion conversion member 52, is inserted into the cylinder portion support portion 33, and is connected to the rear end portion of the piston 54. The cam portion 51, the motion conversion member 52, and the ball 52B constitute a motion conversion mechanism.

  A change lever 45 is provided at a position below the gear casing 30 and in the vicinity of the clutch 42. The change lever 45 is operated by the user to slide the clutch 42 forward and backward, and the clutch 42 and the cam portion 51 are controlled to be connected / disconnected.

  When the user works on the hammer drill 1 having the above-described configuration, first, the change lever 45 is used to select whether to rotate the tip tool or to rotate / blow it.

  When the tip tool is rotated and hit, the clutch 42 and the cam portion 51 are connected. Then, by pulling the trigger 13 and supplying electric power to the electric motor 21, the cylinder 44 rotates, and a tip tool (not shown) attached to the tip of the cylinder 44 rotates together with the cylinder 44. In addition, the cam portion 51 converts the rotational motion into a reciprocating motion, whereby the piston 54 reciprocates back and forth, and a striking force is applied to a tip tool (not shown).

  Since the support member 31 is made of resin, the weight of the hammer drill 1 is reduced as a whole, and the burden on the operator is reduced even in long-time work, and workability is improved. Further, since the metal bearing 34 provided in the cylinder portion support portion 33 of the support member 31 does not need to be press-fitted at a high pressure, the cylinder portion support portion 33 may be configured to have a strength enough to hold the metal bearing 34. There is no need to adopt a configuration that can withstand high-pressure press-fitting, such as making the periphery of the metal bearing 34 thick. Therefore, it is possible to further reduce the weight of the support member 31 and further reduce the burden on the operator.

  The hammer drill of the present invention is not limited to the embodiment described above, and various modifications and improvements can be made within the scope described in the claims. For example, in the above-described embodiment, a metal bearing is used as the bearing portion. However, the present invention is not limited to this, and a needle bearing 134 may be used as the bearing portion as shown in FIGS. As shown in FIG. 4, the needle bearing 134 includes an outer ring portion 134 </ b> C having a first side surface 134 </ b> A and a second side surface 134 </ b> B that constitutes an outer shell of the needle bearing 134 and that are both end surfaces orthogonal to the front-rear direction. The needle portion 134D is rotatably supported by the 134C. While the outer ring portion 134C abuts on the cylinder portion support portion 33 and the needle portion 134D abuts on and supports the cylinder 44, the cylinder portion support portion 33 can rotatably support the cylinder 44. .

  In such a configuration, if the needle bearing 134 is press-fitted into the support member 31 at a high pressure, the outer ring portion 134C may be deformed and the performance thereof may be reduced, so that high-pressure press-fitting cannot be performed. However, since the needle bearing 134 is urged to the support member 31 by the urging mechanism, the needle bearing 134 is favorably supported without dropping off at the cylinder portion support portion 33 without performing high-pressure press-fitting.

  Moreover, in a bearing part, you may use the bearing comprised from the ball | bowl which interposes not only the above-mentioned thing but an outer ring and an inner ring, and an outer ring and an inner ring, for example. In this case, the outer ring contacts the support member, and the inner ring contacts the cylinder part, so that the cylinder part can be rotatably supported with respect to the support member. In this configuration, the sleeve constituting the urging mechanism is brought into contact with only the inner ring to prevent the bearing from falling off the support member. According to such a configuration, since the sleeve does not come into contact with the outer ring, no sliding portion is generated between the sleeve and the bearing, and the rotation of the cylinder portion is not suppressed.

  Further, a mechanism for reducing friction, such as a bearing or a metal bearing, may be interposed between the sleeve and the bearing portion. Thereby, the frictional resistance between the sleeve and the bearing portion can be further reduced. Further, the support member 31 may be molded from a highly rigid material other than resin, such as metal, and even in this case, the bearing can be prevented from moving in a direction away from the electric motor 21. It is possible to prevent the bearing from falling off.

Side surface sectional drawing of the hammer drill which concerns on embodiment of this invention. The side surface fragmentary sectional view of the cylinder periphery of the hammer drill which concerns on embodiment of this invention. The side surface fragmentary sectional view of the cylinder periphery which concerns on the modification of the hammer drill which concerns on embodiment of this invention. Side surface partial sectional drawing of the bearing part periphery which concerns on the modification of the hammer drill which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hammer drill 2 ... Casing part 10 ... Handle part 11 ... Power cable 12 ... Switch mechanism 13 ... Trigger 15 ... Tool holding part 16 ... Side handle 20 ... Motor casing 21 ... Electric motor 22 ..Output shaft 22B..First gear 30..Gear casing 31..Support member 31A..Bearing 31a..Hole 32..Base 32a..Hole 33..Cylinder portion support 34..Metal bearing 34A・ ・ First side surface 34B ・ ・ Second side surface 41B ・ ・ Bearing 40D ・ ・ Bearing 40a ・ ・ Deceleration chamber 41 ・ ・ Intermediate shaft part 41A ・ ・ Second gear 42 ・ ・ Clutch 43A ・ ・ Third gear 44 ・ ・ Cylinder 44A ··· fourth gear 44B · · collar 44C · · spring 44D · · contact surface 44E · · sleeve 44F · · ring 44a · · space 4 e .. Recess 45. Change lever 51. Cam 51a. Groove 52. Motion conversion member 52A. Arm 52B. Ball 54. Piston 54A. Tube 54B. Connection 54a. Air chamber 54b..Air hole 56..Batter 57..Medium 134..Needle bearing 134D..Needle portion 134C..Outer ring portion 134A..First side surface 134B..Second side surface

Claims (7)

A motor with a drive shaft,
A casing part containing at least the motor;
A substantially cylindrical cylinder portion provided in the casing portion, the central axis of which is defined and rotated around the central axis by the drive shaft portion;
A support member connected to the casing portion;
A bearing portion provided coaxially with the cylinder portion on the support member and rotatably supporting the cylinder portion;
A hammer drill comprising: an urging mechanism that abuts against the bearing portion and urges the bearing portion toward the support member in the axial direction of the central axis. The bearing portion has a first side surface and a second side surface which are end surfaces orthogonal to the central axis direction,
The hammer drill according to claim 1, wherein the first side surface is in contact with the support member, and the second side surface is in contact with the biasing mechanism.   The urging mechanism includes a sleeve that abuts on the bearing portion, a spring that urges the sleeve toward the bearing portion, and a restricting portion that restricts the movement of the spring toward the non-bearing portion. The hammer drill according to claim 1, wherein the hammer drill is configured. Between the cylinder part and the drive shaft part, a shut-off mechanism capable of interrupting transmission of driving force between the cylinder part and the drive shaft part is provided,
The shut-off mechanism includes a contacted portion that rotates on an axis that is coaxial or parallel to the cylinder portion in conjunction with the cylinder portion, and an axis that is coaxial or parallel to the drive shaft portion in conjunction with the drive shaft portion. A contact portion that contacts the contacted portion, and a biasing portion that biases the contact portion toward the contacted portion,
The hammer drill according to claim 3, wherein the contacted portion is constituted by the restricting portion, and the biasing portion is constituted by the spring. The urging mechanism is installed in the cylinder part,
5. The drop-off prevention member for preventing the urging mechanism from dropping from the cylinder portion when the urging mechanism is not urged is provided in the cylinder portion. The hammer drill described in 1. The bearing portion includes an outer ring that contacts the support member, and an inner ring that is rotatably supported by the outer ring and rotates about the central axis and supports the cylinder portion.
The hammer drill according to any one of claims 1 to 5, wherein the biasing mechanism biases the inner ring.   The hammer drill according to claim 1, wherein the support member is made of resin.

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