Patent Publication Number: US-11642769-B2

Title: Power tool having a hammer mechanism

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to a power tool configured to linearly reciprocally drive a tool accessory. 
     BACKGROUND 
     A rotary hammer (hammer drill) is configured to linearly reciprocally drive a tool accessory coupled to a tool holder along a driving axis (i.e. perform a hammering operation) and to rotationally drive the tool accessory around the driving axis (i.e. perform a drilling operation). In typical rotary hammers, a motion converting mechanism for converting rotation of an intermediate shaft into linear motion is employed to perform the hammering operation, and a rotation-transmitting mechanism for transmitting rotation to the tool holder via the intermediate shaft is employed to perform the drilling operation. Such a rotary hammer is subjected to a reaction force from a workpiece against the striking force of the tool accessory during the hammering operation. The reaction force generates vibration in an extension direction of the driving axis (hereinafter also referred to as an axial direction). Vibration thus generated is transmitted to the housing of the rotary hammer and to its user. 
     Japanese Patent No. 6325360 discloses a structure for absorbing such vibration. Specifically, a driving mechanism for performing a hammering operation is held by a holding member configured to be slidably movable relative to the housing along a guide shaft. The holding member is biased forward (i.e. in a direction in which a striking force is applied to the workpiece) by a biasing member. When a tool accessory is subjected to a reaction force during the hammering operation, the force causes the driving mechanism and the holding member to move rearward together with the tool accessory relative to the housing. At this time, the biasing member elastically deforms and partially cushions the reaction force. This cushioning effect serves to reduce vibration to be transmitted to the housing due to the reaction force. 
     In typical rotary hammers including the one disclosed in the Japanese Patent No. 6325360, plastic is used to form its constituent members when possible in order to reduce the weight. For example, plastic is commonly used to form a housing defining an outer shell of a rotary hammer. Plastic is also commonly used to form a member supporting a bearing for an intermediate shaft. 
     SUMMARY 
     A power tool is disclosed in this specification. The power tool may include a final output shaft, a motor, a driving mechanism, a housing, a movable support, a biasing member, a first guide shaft, at least one intermediate shaft, at least one bearing, and a single (integral) support made of metal (hereinafter referred to as a metal support). 
     The final output shaft may be configured to removably hold a tool accessory. The final output shaft may also define a driving axis of the tool accessory. The motor may have a motor shaft. The driving mechanism may be configured to perform at least a hammering operation of linearly reciprocally driving the tool accessory along the driving axis by using power from the motor. The housing may accommodate the motor and the driving mechanism. The movable support may at least partially support the final output shaft and the driving mechanism. The movable support may also be configured to be integrally movable relative to the housing in an axial direction of the driving axis. When one side in the axial direction in which the final output shaft is disposed is defined as a front side and an opposite side in the axial direction in which the motor is disposed is defined as a rear side, the biasing member may bias the movable support toward the front side in the axial direction. The first guide shaft may extend in the axial direction and may be configured to slidably guide movement of the movable support in the axial direction. The at least one intermediate shaft may extend in the axial direction. The at least one intermediate shaft may also be configured to rotate in response to rotation of the motor shaft and transmit the power of the motor to the driving mechanism. The at least one bearing may support an end portion of the at least one intermediate shaft, that is located in the front side in the axial direction (hereinafter referred to as a front end portion). The single metal support may be disposed to be immovable relative to the housing and may support the at least one bearing. The single metal support may also have a first hole for partially receiving the first guide shaft. 
     The first guide shaft may also be configured to move together with the movable support in the axial direction. In this case, the first guide shaft may be received in the first hole of the metal support so as to be slidable within the first hole when the movable support moves in the axial direction. Alternatively, the first guide shaft may be immovably received in the first hole of the metal support. In this case, the first guide shaft held by the metal support may be slidably received in a hole formed in the movable support. 
     According to the above-described power tool, the at least one bearing for supporting the front end portion of the at least one intermediate shaft is supported by the metal support. This provides stronger support strength compared to the case in which a support made of plastic (hereinafter simply referred to as a plastic support) is used to support the at least one bearing. Therefore, even if high power operation of the power tool results in increased vibration generated due to a reaction force against the striking force, the positional accuracy for the at least one intermediate shaft can be maintained at the required level. Further, according to the power tool of this aspect, the first guide shaft is partially received in the first hole of the metal support. Therefore, even if high power operation of the power tool results in an increased amount of heat produced when the first guide shaft slidably guides movement of the movable support in the axial direction, the support can have reduced thermal expansion compared to the case in which a plastic support is used to receive the first guide shaft. Therefore, the positional accuracy for the first guide shaft partially received in the first hole of the metal support can be maintained at the required level. This in turn provides satisfactory sliding property related to the first guide shaft and also allows for satisfactory isolation of vibration. As such, the power tool of the present aspect can achieve both high power operation and reduced vibration. Moreover, the use of the single metal support for supporting the at least one bearing and also for receiving the first guide shaft enables simplified tool structure as well as reduced man-hours related to manufacturing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a sectional view of a rotary hammer according to one embodiment of the present disclosure. 
         FIG.  2    is a sectional view taken along line II-II in  FIG.  1   . 
         FIG.  3    is a sectional view taken along line III-III in  FIG.  2   . 
         FIG.  4    is a sectional view taken along line IV-IV in  FIG.  2   . 
         FIG.  5    is a sectional view taken along line V-V in  FIG.  2   . 
         FIG.  6    is a sectional view taken along line VI-VI in  FIG.  2   . 
         FIG.  7    is a sectional view taken along line VII-VII in  FIG.  2   , wherein the movable support is located in its foremost position. 
         FIG.  8    is a sectional view taken along line VII-VII in  FIG.  2   , wherein the movable support is located in its rearmost position. 
         FIG.  9    is a sectional view taken along line IX-IX in  FIG.  2   , wherein the movable support is located in its foremost position. 
         FIG.  10    is a sectional view taken along line IX-IX in  FIG.  2   , wherein the movable support is located in its rearmost position. 
         FIG.  11    is a perspective view of a first support. 
         FIG.  12    is a perspective view of the movable support. 
         FIG.  13    is a perspective view of a second support. 
         FIG.  14    is a perspective view of the second support. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In one or more of embodiments, the housing may be made of plastic. The metal support may be fixed to the housing. According to the present embodiment, the power tool can achieve both high power operation and reduced vibration while successfully having a reduced weight. 
     In one or more embodiments, the metal support may include a first positioning part in the front side. The first positioning part is disposed so as to circumferentially surround the final output shaft. The housing may include a second positioning support also disposed so as to circumferentially surround the final output shaft. The first positioning part and the second positioning part may be shaped to be fitted with each other in the axial direction. According to the present embodiment, the first and second positioning parts can be aligned and fitted with each other in the process of assembling the power tool. This enables easy positioning of the metal support relative to the housing in a direction orthogonal to the axial direction. 
     In one or more embodiments, the metal support may include an attachment surface in the front side. The attachment surface spreads in form of a single plane at a position radially outward of the first positioning part. The attachment surface may abut on the housing in the axial direction. According to the present embodiment, the attachment surface can be abutted on the housing in the axial direction in the process of assembling the power tool. This enables easy positioning of the metal support relative to the housing in the axial direction. 
     In one or more embodiments, the first guide shaft may be disposed so as to be at least partially in the front side of the movable support. The power tool may further include a second guide shaft that is disposed so as to be at least partially in the rear side of the movable support and coaxial with the first guide shaft. According to the present embodiment, the distance over which the guide shafts extend as a whole can be shortened compared to a case in which a single guide shaft extends from where the first guide shaft is to where the second guide shaft is. The rotary hammer can thus have a reduced weight. Moreover, since the guide shafts are respectively placed on both sides of the movable support in the axial direction, the movable support can be guided satisfactorily irrespective of the reduced weight. 
     In one or more embodiments, the first guide shaft may extend frontward from the movable support. The first guide shaft may be configured to move together with the movable support in the axial direction. According to the present embodiment, the sliding property related to the first guide shaft can be maintained satisfactory. 
     In one or more embodiments, the metal support may include a first sleeve within the first hole. The first sleeve is made of iron-based metal. The first guide shaft may be configured to slide on an inner peripheral surface of the first sleeve while the movable support moves in the axial direction. The metal support may be made of aluminum-based metal except for the first sleeve. Examples of the iron-based metal include iron and any alloy that contains iron as its main component. Examples of the aluminum-based metal include aluminum and any alloy that contains aluminum as its main component. According to the present embodiment, the metal support can have sufficient strength to withstand sliding movement relative to the guide shaft and can also have a reduced weight as a whole. 
     In one or more embodiments, the movable support may include a second hole for partially receiving the second guide shaft, and a second sleeve disposed within the second hole. The second guide shaft may be disposed so as to be immovable relative to the housing. An inner peripheral surface of the second sleeve may be configured to slide on the second guide shaft while the movable support moves in the axial direction. The biasing member may be disposed around the second guide shaft in the rear side of the movable support in the axial direction, and may be configured to bias the movable support including the second sleeve integrally frontward. According to the present embodiment, only the second sleeve, among all the parts constituting the movable support, slides on the second guide shaft. Therefore, making the second sleeve from a selected material of sufficient strength can lead to smooth sliding property. Also, since the second sleeve is biased frontward by the biasing member, the sleeve can be prevented from being left behind and off the second hole while the movable support moves frontward. 
     In one or more embodiments, the driving mechanism may further be configured to perform a drilling operation of rotationally driving the tool accessory around the driving axis by using power from the motor. The at least one intermediate shaft may include a first intermediate shaft configured to transmit power for the hammering operation to the driving mechanism, and a second intermediate shaft configured to transmit power for the drilling operation to the driving mechanism. The at least one bearing may include a first bearing for supporting the first intermediate shaft, and a second bearing for supporting the second intermediate shaft. The first intermediate shaft may be configured to transmit power for the hammering operation but not for the drilling operation; whereas the second intermediate shaft may be configured to transmit power for the drilling operation but not for the hammering operation. According to the present embodiment, the first intermediate shaft and the second intermediate shaft can be made shorter compared to the case in which one common intermediate shaft is used for both the hammering operation and the drilling operation. Thus, the overall length of the rotary hammer can be reduced in the driving-axis direction. Further, the first intermediate shaft and the second intermediate shaft are respectively dedicated for power transmission for the hammering operation and power transmission for the drilling operation. This optimizes power transmission via the first intermediate shaft and power transmission via the second intermediate shaft to the final output shaft, respectively. 
     In one or more embodiments, the first bearing and the second bearing may be disposed at positions different from each other in the axial direction. According to the present embodiment, the positions of the first and second bearings may be set without any constraints from the metal support. Therefore, the positions of the first and second bearings can be set so as not to damage the effect of having shorter first and second intermediate shafts. In other words, increase in length of the rotary hammer due to the use of the metal support is reduced or eliminated. 
     The embodiment of the present disclosure is now described in more detail with reference to the drawings. 
     In this embodiment, a rotary hammer (hammer drill)  101  is described as an example of a power tool according to the present teachings. The rotary hammer  101  is a hand-held power tool that may be used for processing operations such as chipping and drilling. The rotary hammer  101  is configured to be capable of performing the operation (hereinafter referred to as a hammering operation) of linearly reciprocally driving a tool accessory  91  along a driving axis A 1  and of performing the operation (hereinafter referred to as a drilling operation) of rotationally driving the tool accessory  91  around the driving axis A 1 . 
     First, the general structure of the rotary hammer  101  is described with reference to  FIG.  1   . As shown in  FIG.  1   , an outer shell of the rotary hammer  101  is mainly formed by a body housing  10  and a handle  17  connected to the body housing  10 . 
     The body housing  10  is a hollow body which may also be referred to as a tool body or an outer shell housing. The body housing  10  houses parts such as a spindle  31 , a motor  2 , a driving mechanism  5 , and the like. The spindle  31  is an elongate member having a hollow circular cylindrical shape. At its end portion in the axial direction, the spindle  31  has a tool holder  32  configured to removably hold the tool accessory  91 . A longitudinal axis of the spindle  31  defines a driving axis A 1  of the tool accessory  91 . The body housing  10  extends along the driving axis A 1 . The tool holder  32  is disposed within one end portion of the body housing  10  in an extension direction of the driving axis A 1  (hereinafter simply referred to as a driving-axis direction). 
     The handle  17  is an elongate hollow body configured to be held by a user. One axial end portion of the handle  17  is connected to the other end portion (an end portion located on the side opposite to the side in which the tool holder  32  is located) of the body housing  10  in the driving-axis direction. The handle  17  protrudes from the other end portion of the body housing  10  and extends in a direction crossing (more specifically, generally orthogonal to) the driving axis A 1 . Further, in this embodiment, the body housing  10  and the handle  17  are integrally formed by a plurality of components connected together with screws or the like. A power cable  179  extends from the protruding end of the handle  17  and can be connected to an external alternate current (AC) power source. The handle  17  has a trigger  171  to be depressed (pulled) by a user, and a switch  172  configured to be turned ON in response to a depressing operation of the trigger  171 . 
     In the rotary hammer  101 , when the switch  172  is turned ON, the motor  2  is energized and the driving mechanism  5  is driven so that the hammering operation and/or the drilling operation is performed. 
     The detailed structure of the rotary hammer  101  is now described. In the following description, for convenience sake, the extension direction of the driving axis A 1  (the longitudinal direction of the body housing  10 ) is defined as a front-rear direction of the rotary hammer  101 . The side of one end of the rotary hammer  101  in the front-rear direction in which the tool holder  32  is disposed is defined as a front side of the rotary hammer  101 ; whereas the opposite side (the side in which the motor  2  is disposed) is defined as a rear side of the rotary hammer  101 . The direction that is orthogonal to the driving axis A 1  and corresponds to an axial direction of the handle  17  is defined as an up-down direction of the rotary hammer  101 . In the up-down direction, the side of one end of the handle  17  that is connected to the body housing  10  is defined as an upper side and the side of the protruding end of the handle  17  is defined as a lower side. Further, the direction that is orthogonal to both the front-rear direction and the up-down direction is defined as a left-right direction of the rotary hammer  101 . In the left-right direction, the side to the right when viewed from the rear side to the front side is defined as a right side of the rotary hammer  101  and the opposite side is defined as a left side of the rotary hammer  101 . 
     First, the structure of the body housing  10  is described. As shown in  FIG.  1   , the body housing  10  has a front end portion of a hollow circular cylindrical shape. The portion is referred to as a barrel part  131 . The remaining portion of the body housing  10  other than the barrel part  131  has a generally rectangular box-like shape. An auxiliary handle  132  is removably attachable to the barrel part  131 . 
     The internal space of the body housing  10  is partitioned into two volumes by a first support  15  that is disposed within the body housing  10 . The first support  15  is arranged to cross the driving axis A 1 , is fitted into an inner periphery of the body housing  10 , and is fixedly held by the body housing  10  (so as to be immovable relative to the body housing  10 ). The volume in the rear of the first support  15  is a volume (space) for mainly housing the motor  2 . The volume in front of the bearing support  15  is a volume (space) for mainly housing the spindle  31  and the driving mechanism  5 . In the following description, the portion of the body housing  10  that corresponds to the region for housing the motor  2  is referred to as a rear housing  11 , and the portion (including the barrel part  131 ) of the body housing  10  that corresponds to the region for housing the spindle  31  and the driving mechanism  5  is referred to as a front housing  13 . 
     The rear housing  11  and the front housing  13  are both formed of plastic. The rotary hammer  101  can thus have a reduced weight. The rear housing  11  and the front housing  13 , however, may at least partially be formed of a freely-selected material (e.g., metal). Each of the rear housing  11  and the front housing  13  is a single tubular member. 
     The first support  15  is a member for supporting bearings of various shafts. Details of the first support  15  will be described later. To provide a required level of positional accuracy for the bearings, the first support  15  is formed of metal. In this embodiment, the first support  15  is formed of aluminum-based metal. The rotary hammer  101  can thus have a reduced weight. As shown in  FIG.  1   , the first support  15  is fitted into a rear end portion of the front housing  13  so that an outer peripheral surface of the first support  15  comes into contact with an inner peripheral surface of the front housing  13 . 
     As shown in  FIG.  1   , an annular groove  152  is formed on the outer peripheral surface of the first support  15  that is in contact with the inner peripheral surface of the body housing  11 . A rubber O-ring  151  is fitted in this groove  152 . The O-ring  151  serves as a seal member for sealing a gap between the body housing  10  and the first support  15 , and prevents lubricant used within the front housing  13  from leaking into the rear housing  11 . 
     The internal structures of the body housing  10  are now described. First, the motor  2  is described. In this embodiment, an AC motor, which may be powered by an external AC power source, is employed as the motor  2 . As shown in  FIG.  1   , the motor  2  is fixed to the rear housing  11 . The motor  2  has a body  20  including a stator and a rotor, and a motor shaft  25  configured to rotate together with the rotor. In this embodiment, a rotation axis A 2  of the motor shaft  25  extends below the driving axis A 1  and in parallel to the driving axis A 1 . 
     The motor shaft  25  is supported via two bearings  251  and  252  so as to be rotatable around the rotation axis A 2  relative to the body housing  10 . The front bearing  251  is held on a rear surface side of the first support  15 , and the rear bearing  252  is held by the rear housing  11 . 
     A cooling fan  27  for cooling the motor  2  is fixed to a portion of the motor shaft  25  between the body  20  and the front bearing  251 . The cooling fan  27  is a centrifugal fan and is configured to suck air in the axial direction and discharge the air radially outward. Rotation of the motor shaft  25  and thus of the fooling fan  17  produces a flow of air inside the rotary hammer  101 . The air flows from outside the rotary hammer  101  through an inlet opening  28  into the rotary hammer  101 , goes through the motor  2  (more specifically, between the rotor and the stator) in the axial direction, and then is directed radially outward by the cooling fan  27  and discharged outside through a discharge opening  29 . The passage for the thus produced flow of air is shown by an arrow  26  in  FIG.  1   . 
     In the example shown in  FIG.  1   , the inlet opening  28  is formed on a side surface of the handle  17 , and the discharge opening  29  is formed on a bottom surface of the rear housing  11 . The inlet opening  28  and the discharge opening  29  may, however, be formed in freely-selected locations. For example, the inlet opening  28  may be formed on an upper surface of the handle  17  in addition to or instead of the side surface of the handle  17 . Also, the discharge opening  29  may be formed on one or both side surfaces or on an upper surface of the rear housing  11  in addition to or instead of the bottom surface of the rear housing  11 . The flow of air thus generated serves to cool the motor  2 . 
     The first support  15  is disposed adjacent to the cooling fan  27  in the front-rear direction. The space in the rear of the first support  15  is in communication with a space in which the cooling fan  27  is disposed. Moreover, in this embodiment, the first support  15  is formed of metal. Therefore, the flow of air going through the passage  26  also serves to cool the first support  15 . In other words, the first support  15  is arranged such that heat generated in the front side of the first support  15  and transmitted to the first support  15  can be dissipated. Details of this function will be described later. 
     A front end portion of the motor shaft  25  extends through a through hole  153  of the first support  15  and protrudes into the front housing  13 . A pinion gear  255  is fixed to this end portion of the motor shaft  25  that protrudes into the front housing  13 . 
     Next, power-transmission paths from the motor shaft  25  to the driving mechanism  5  are described. As shown in  FIGS.  2  and  3   , in this embodiment, the rotary hammer  101  includes two intermediate shafts (i.e. a first intermediate shaft  41  and a second intermediate shaft  42 ). The driving mechanism  5  is configured to perform the hammering operation using power transmitted from (via) the first intermediate shaft  41  and perform the drilling operation using power transmitted from (via) the second intermediate shaft  42 . In other words, the first intermediate shaft  41  is a shaft provided exclusively for (dedicated to) power transmission for hammering operations, and the second intermediate shaft  42  is a shaft provided exclusively for (dedicated to) power transmission for drilling operations. 
     Both the first intermediate shaft  41  and the second intermediate shaft  42  extend within the front housing  13  in parallel to the driving axis A 1  and the rotation axis A 2 . As shown in  FIG.  3   , the first intermediate shaft  41  is supported via two bearings  411  and  412  so as to be rotatable around a rotation axis A 3  relative to the body housing  10 . Similarly, the second intermediate shaft  42  is supported via two bearings  421  and  422  so as to be rotatable around a rotation axis A 4  relative to the body housing  10 . 
     The bearing  411  that supports the first intermediate shaft  41  in the front side and the bearing  421  that supports the second intermediate shaft  42  in the front side are supported by a second support  16 . More specifically, the bearing  411  is supported by a portion of the second support  16 , namely a bearing-support part  164 , that is formed into an generally hollow circular cylindrical shape, and the bearing  421  is supported by another portion of the second support  16 , namely a bearing-support part  165 , that is formed into an generally hollow circular cylindrical shape (see  FIGS.  3 ,  13 , and  14   ). The bearing  412  that supports the first intermediate shaft  41  in the rear side and the bearing  422  that supports the second intermediate shaft  42  in the rear side are supported by the first support  15 . More specifically, the bearing  412  is supported by a portion of the first support  15 , namely a bearing-support part  154 , that is formed into a hollow circular cylindrical shape, and the bearing  422  is supported by another portion of the first support  15 , namely a bearing-support part  155 , that is formed into a hollow circular cylindrical shape (see  FIGS.  3  and  11   ). 
     As shown in  FIG.  3   , the bearing  411  for supporting the first intermediate shaft  41  in the front side and the bearing  421  for supporting the second intermediate shaft  42  in the front side are disposed at positions different from each other in the front-rear direction. This is because the bearings  411  and  421  are arranged at positions that allow the first intermediate shaft  41  and the second intermediate shaft  42  to have minimum lengths, respectively. That is, even though the bearings  411  and  421  are supported by a single (integral) member, namely the second support  16 , the positions of the bearings  411  and  421  in the front-rear direction are not constrained by the second support  16 . Therefore, the rotary hammer  101  can be prevented from getting longer due to the use of a single member to support both the bearings  411  and  421 . 
     As shown in  FIGS.  1  and  3   , the second support  16  is fixed inside the front housing  13 . More specifically, as shown in  FIGS.  13  and  14   , the second support  16  includes a first positioning part  163 , an attachment surface  168 , and two through holes  162 . The first positioning part  163  is a portion having a hollow circular cylindrical shape protruding frontwards. As shown in  FIGS.  7  and  8   , this first positioning part  163  is disposed so as to circumferentially surround the spindle  31  (in other words, so that the spindle  31  extends through the first positioning part  163  in the front-rear direction). As shown in  FIGS.  13  and  14   , the attachment surface  168  spreads, at a position radially outward of the first positioning part  163 , in the form of a single plane orthogonal to the front-rear direction. The two through holes  162  extend through the second support  16  in the front-rear direction, respectively. 
     On the other hand, the front housing  13  to which the second support  16  is fixed includes a second positioning part  133  and an attachment surface  135 , as shown in  FIGS.  7  and  8   . The second positioning part  133  is a portion of the inside of the front housing  13  protruding rearward. The second positioning part  133  has a concave portion formed on its radially inward side and is disposed so as to circumferentially surround the spindle  31 . A rear end surface of the second positioning part  133  forms the attachment surface  135  orthogonal to the front-rear direction. 
     As shown in  FIGS.  7  and  8   , the second support  16  is attached to the front housing  13  so that the first positioning part  163  is fitted with the concave portion of the second positioning part  133  in the front-rear direction. The fitting structure between the concave and convex shapes enables precise and easy positioning of the second support  16  relative to the front housing  13  in a direction orthogonal to the front-rear direction in the process of assembling the rotary hammer  101 . In an alternative embodiment, the first positioning part  163  and the second positioning part  133  may have reversed shapes. That is, the first positioning part  163  may be a concave portion formed in the second support  16 ; whereas the second positioning part  133  may be a convex portion protruding from the front housing  13  and may be fitted with the concave portion of the second support  16 . 
     As shown in  FIGS.  7  and  8   , the attachment surface  168  of the second support  16  abuts the attachment surface  135  of the front housing  13  in the front-rear direction when the first positioning part  163  is fitted with the second positioning part  133  in the front-rear direction. Each of the attachment surfaces  168  and  135  is a plane orthogonal to the front-rear direction. This enables precise and easy positioning of the second support  16  relative to the front housing  13  in the front-rear direction in the process of assembling the rotary hammer  101 . 
     The second support  16  thus positioned relative to the front housing  13  is then fixed to the front housing  13  by screws  161  respectively inserted into the through holes  162  of the second support  16 , as shown in  FIG.  4   . 
     To provide a required level of positional accuracy for the bearings  411  and  421 , the second support  16  of such a structure is formed of metal. In this embodiment, the second support  16  is formed of aluminum-based metal. The rotary hammer  101  can thus have a reduced weight. 
     As shown in  FIG.  3   , a first driven gear  414  is fixed to a rear end portion of the first intermediate shaft  41  adjacent to and in front of the bearing  412 . The first driven gear  414  meshes with a pinion gear  255 . 
     A gear member  423  having a second driven gear  424  is disposed adjacent to and in front of the bearing  422  on a rear end portion of the second intermediate shaft  42 . The second driven gear  424  meshes with the pinion gear  255 . The gear member  423  has a hollow circular cylindrical shape and is disposed on an outer peripheral side of the second intermediate shaft  42  (specifically, of a drive-side member  74  which will be described later). A spline part  425  is provided on an outer periphery of a hollow circular cylindrical front end portion of the gear member  423 . The spline part  425  includes a plurality of splines (external teeth) extending in a direction of the rotation axis A 4  (i.e. front-rear direction). Rotation of the second driven gear  424  (the gear member  423 ) is transmitted to the second intermediate shaft  42  via a second transmitting member  72  and a torque limiter  73 . Details of the mechanism will be described in detail later. 
     As described above, in this embodiment, two power-transmission paths branch from the motor shaft  25  and respectively serve as a power-transmission path dedicated to hammering operations and another power-transmission path dedicated to drilling operations. 
     The spindle  31  is now described. The spindle  31  is a final output shaft of the rotary hammer  101 . As shown in  FIG.  1   , the spindle  31  is arranged within the front housing  13  along the driving axis A 1  and is supported to be rotatable around the driving axis A 1  relative to the body housing  10 . The spindle  31  is configured as an elongate, stepped hollow circular cylindrical member. 
     A front half of the spindle  31  forms the tool holder  32  to or in which the tool accessory  91  can be removably attached. The tool accessory  91  is inserted into a bit-insertion hole  330  formed in a front end portion of the tool holder  32  such that a longitudinal axis of the tool accessory  91  coincides with the driving axis A 1 . The tool accessory  91  is held in the insertion hole  330  so as to be movable relative to the tool holder  32  in the axial direction while its rotation around the axis is restricted (blocked). A rear half of the spindle  31  forms a cylinder  33  configured to slidably hold a piston  65  described below. The spindle  31  is supported by a bearing  316  held within the barrel part  131  and a bearing  317  held by a movable support  18  described below. 
     The driving mechanism  5  is now described. As shown in  FIGS.  3 ,  5 , and  6   , in this embodiment, the driving mechanism  5  includes a striking mechanism  6  and a rotation-transmitting mechanism  7 . The striking mechanism  6  is a mechanism for performing hammering operations, and is configured to convert rotation of the first intermediate shaft  41  into linear motion and linearly reciprocally drive the tool accessory  91  along the driving axis A 1 . The rotation-transmitting mechanism  7  is a mechanism for performing drilling operations, and is configured to transmit rotation of the second intermediate shaft  42  to the spindle  31  and rotationally drive the tool accessory  91  around the driving axis A 1 . The structures of the striking mechanism  6  and the rotation-transmitting mechanism  7  are now described in detail in this order. 
     In this embodiment, as shown in  FIGS.  3  and  5   , the striking mechanism  6  includes a motion-converting member  61 , a piston  65 , a striker  67 , and an impact bolt  68 . 
     The motion-converting member  61  is disposed around the first intermediate shaft  41 , and is configured to convert rotation of the first intermediate shaft  41  into linear reciprocating motion and transmit it to the piston  65 . More specifically, the motion-converting member  61  includes a rotary body  611  and an oscillating member  616 . The rotary body  611  is supported by a bearing  614  so as to be rotatable around the rotation axis A 3  relative to the body housing  10 . The oscillating member  616  is rotatably mounted on an outer periphery of the rotary body  611 , and is configured to oscillate (pivot or rock back and forth) in an extension direction of the rotation axis A 3  (i.e. front-rear direction) while the rotary body  611  is rotating. The oscillating member  616  has an arm  617  extending upward away from the rotary body  611 . 
     The piston  65  is a bottomed hollow circular cylindrical member, and is disposed within the cylinder  33  of the spindle  31  so as to be slidable along the driving axis A 1 . The piston  65  is connected to the arm  617  of the oscillating member  616  via a connecting pin and reciprocally moves in the front-rear direction while the oscillating member  616  is oscillating (pivoting or rocking back-and-forth in the front-rear direction). 
     The striker  67  is a striking element for applying a striking force to the tool accessory  91 . The striker  67  is disposed within the piston  65  so as to be slidable along the driving axis A 1 . An internal space of the piston  65  in the rear of the striker  67  is defined as an air chamber that serves as an air spring. The impact bolt  68  is an intermediate element for transmitting kinetic energy of the striker  67  to the tool accessory  91 . The impact bolt  68  is disposed within the tool holder  32  in front of the striker  67  so as to be movable along the driving axis A 1 . 
     When the piston  65  is moved in the front-rear direction along with oscillating movement of the oscillating member  616 , the air pressure within the air chamber fluctuates and the striker  67  slides in the front-rear direction within the piston  65  by the action of the air spring. More specifically, when the piston  65  is moved forward, the air within the air chamber is compressed and its internal pressure increases. Thus, the striker  67  is pushed forward at high speed by the action of the air spring and strikes the impact bolt  68 . The impact bolt  68  transmits the kinetic energy of the striker  67  to the tool accessory  91 . Thus, the tool accessory  91  is linearly driven along the driving axis A 1 . On the other hand, when the piston  65  is moved rearward, the air within the air chamber expands and its internal pressure decreases so that the striker  67  is retracted (moved) rearward. The tool accessory  91  moves rearward along with the impact bolt  68  by being pressed against a workpiece. In this manner, the striking mechanism  6  repetitively performs the hammering operation. 
     In this embodiment, rotation of the first intermediate shaft  41  is transmitted to the motion-converting member  61  (specifically, the rotary body  611 ) via a first transmitting member  64  and an intervening member  63 . The intervening member  63  and the first transmitting member  64  are now described in this order. 
     As shown in  FIG.  5   , the intervening member  63  is a hollow circular cylindrical member coaxially disposed around the first intermediate shaft  41 , between the first intermediate shaft  41  and the motion-converting member  61  (specifically, the rotary body  611 ). The intervening member  63  is immovable in the front-rear direction relative to the first intermediate shaft  41  while being rotatable around the rotation axis A 3  relative to the first intermediate shaft  41 . 
     More specifically, a front end portion (a portion adjacent to the rear side of the front bearing  411 ) of the first intermediate shaft  41  is configured as a maximum-diameter part having a maximum outer diameter. A spline part  416  is provided on an outer periphery of the maximum-diameter part. The spline part  416  includes a plurality of splines (external teeth) extending in the rotation axis A 3  direction (i.e. front-rear direction). The intervening member  63  is held to be immovable in the front-rear direction between the spline part  416  and the first driven gear  414  fixed to the rear end portion of the first intermediate shaft  41 . 
     A spline part  631  is provided on an outer periphery of the intervening member  63  and extends generally over the entire length of the intervening member  63 . The spline part  631  includes a plurality of splines (external teeth) extending in the rotation axis A 3  direction (i.e. front-rear direction). 
     On the other hand, a spline part  612  is formed on an inner periphery of the rotary body  611 . The spline part  612  includes splines (internal teeth) to be engaged (meshed) with the spline part  631 . The intervening member  63  is always spline-engaged with the rotary body  611 , and is held by the rotary body  611 . Such a structure allows the rotary body  611  to be movable in the rotation axis A 3  direction (i.e. front-rear direction) relative to the intervening member  63  and the first intermediate shaft  41  as well as to be rotatable together with the intervening member  63 . 
     The first transmitting member  64  is disposed on the first intermediate shaft  41 , and is configured to be rotatable together with the first intermediate shaft  41  as well as to be movable in the rotation axis A 3  direction (i.e. front-rear direction) relative to the first intermediate shaft  41  and the intervening member  63 . 
     More specifically, the first transmitting member  64  is a generally hollow circular cylindrical member disposed around the first intermediate shaft  41 . A first spline part  641  and a second spline part  642  are provided on an inner periphery of the first transmitting member  64 . 
     The first spline part  641  is provided on a rear end portion of the first transmitting member  64 . The first spline part  641  includes a plurality of splines (internal teeth) configured to be engaged (meshed) with the spline part  631  of the intervening member  63 . As described above, the spline part  631  of the intervening member  63  is also engaged (meshed) with the spline part  612  of the rotary body  611 . The second spline part  642  is provided on a front half of the first transmitting member  64 . The second spline part  642  includes a plurality of splines (internal teeth) configured to be always engaged (meshed) with the spline part  416  of the first intermediate shaft  41 . 
     With such a structure, when the first spline part  641  of the first transmitting member  64  that is movable in the front-rear direction is placed in a position (hereinafter referred to as an engagement position) to be engaged with the spline part  631  of the intervening member  63 , as shown in  FIG.  5   , the first transmitting member  64  is rotatable together with the intervening member  63 , that is, first transmitting member  64  is capable of transmitting power (rotational force) from the first intermediate shaft  41  to the intervening member  63 . 
     On the other hand, when the first spline part  641  of the first transmitting member  64  moveable in the front-rear direction is placed in a position (not shown, hereinafter referred to as a spaced apart position) to be spaced apart from (incapable of being engaged with) the spline part  631 , the first transmitting member  64  disables (interrupts, disconnects) power transmission from the first intermediate shaft  41  to the intervening member  63 . 
     As shown in  FIG.  6   , in this embodiment, the rotation-transmitting mechanism  7  includes a driving gear  78  and a driven gear  79 . The driving gear  78  is fixed to a front end portion (a portion adjacent to the rear side of the front bearing  421 ) of the second intermediate shaft  42 . The driven gear  79  is fixed to an outer periphery of the cylinder  33  of the spindle  31  and meshes with the driving gear  78 . The driving gear  78  and the driven gear  79  form a speed-reducing (torque-increasing) gear mechanism. The spindle  31  is rotated together with the driven gear  79  in response to rotation of the driving gear  78  together with the second intermediate shaft  42 . The drilling operation is thus performed in which the tool accessory  91  held by the tool holder  32  is rotationally driven around the driving axis A 1 . 
     As described above, in this embodiment, rotation of the second driven gear  42  caused by rotation of the motor shaft  25  is transmitted to the second intermediate shaft  42  via the second transmitting member  72  and the torque limiter  73 . The torque limiter  73  and the second transmitting member  72  are now described in this order. 
     As shown in  FIG.  6   , the torque limiter  73  includes a drive-side member  74 , a driven-side member  75 , and a biasing spring  77 . The drive-side member  74  is a hollow circular cylindrical member and is supported by a rear half of the second intermediate shaft  42  so as to be rotatable relative to the second intermediate shaft  42 . The driven-side member  75  is a hollow circular cylindrical member and is disposed around the second intermediate shaft  42  in the front side of the drive-side member  74 . The driven-side member  75  is configured to be rotatable together with the second intermediate shaft  42  as well as to be movable in the rotation axis A 4  direction (i.e. front-rear direction) relative to the second intermediate shaft  42 . The biasing spring  77  always biases the driven-side member  75  in a direction toward the drive-side member  74 . Therefore, in normal times, a front end portion of the drive-side member  74  and a rear end portion of the driven-side member  75  are engaged with each other. This allows torque to be transmitted from the drive-side member  74  to the driven-side member  75  and in turn enables rotation of the second intermediate shaft  42 . 
     When the second intermediate shaft  42  is rotating and a load exceeding the threshold is applied to the second intermediate shaft  42  via the tool holder  32  (the spindle  31 ), the driven-side member  75  moves in a direction away from the drive-side member  74  (i.e. forward) against the biasing force of the biasing spring  77  and thus becomes disengaged from the drive-side member  74 . This disconnects transmission of torque from the drive-side member  74  to the driven-side member  75  and interrupts rotation of the second intermediate shaft  42 . 
     The drive-side member  74  includes a spline part  743 . The spline part  743  is provided on an outer periphery of the drive-side member  74  and includes a plurality of splines (external teeth) extending in the rotation axis A 4  direction (i.e. front-rear direction). 
     As shown in  FIG.  6   , the second transmitting member  72  is disposed around the second intermediate shaft  42 , and is configured to be rotatable together with the drive-side member  74  of the torque limiter  73  as well as to be movable in the rotation axis A 4  direction (i.e. front-rear direction) relative to the drive-side member  74  and the gear member  423 . 
     More specifically, the second transmitting member  72  is a generally hollow circular cylindrical member disposed around the drive-side member  74 . A first spline part  721  and a second spline part  722  are provided on an inner periphery of the second transmitting member  72 . The first spline part  721  is provided on a front half of the second transmitting member  72 . The first spline part  721  includes a plurality of splines (internal teeth) that are always engaged (meshed) with the spline part  743  of the drive-side member  74 . The second spline part  722  is provided on a rear end portion of the second transmitting member  72  and has a larger inner diameter than the first spline part  721 . The second spline part  722  includes a plurality of splines (internal teeth) configured to be engaged (meshed) with the spline part  425  of the gear member  423 . 
     With such a structure, when the second spline part  722  of the second transmitting member  72  movable in the front-rear direction is placed in a position (hereinafter referred to as an engagement position) to be engaged with the spline part  425  of the gear member  423  in the front-rear direction, as shown in  FIG.  6   , the second transmitting member  72  is rotatable together with the gear member  423 . This allows the drive-side member  74 , which is spline-engaged with the second transmitting member  72 , and thus the second intermediate member  42 , to which torque is transmitted via the driven-side member  75 , also to be rotatable together with the gear member  423 . 
     On the other hand, when the second spline part  722  movable in the front-rear direction is placed in a position (not shown, hereinafter referred to as a spaced apart position) to be spaced apart (separated) from (incapable of being engaged with) the spline part  425 , the second transmitting member  72  disables (interrupts, disconnects) power transmission from the gear member  423  to the drive-side member  74  and thus to the second intermediate shaft  42 . 
     As described above, in this embodiment, the first transmitting member  64  and the intervening member  63  function as a first clutch mechanism that transmits power for the hammering operation or interrupts this power transmission; whereas the second transmitting member  72  and the gear member  423  function as a second clutch mechanism that transmits power for the drilling operation (tool holder rotation) or interrupts this power transmission. Each of the first clutch mechanism and the second clutch mechanism is switched between a power-transmission state and a power-interruption state in response to user manipulation of a mode-changing dial  800  (see  FIG.  1   ). More specifically, an intermediate member (not shown) configured to operate in response to the mode-changing dial  800  changes the position of the first transmitting member  64  and/or the position of the second transmitting member  72  according to the dial position of the mode-changing dial  800  and thereby achieves mode-switching of the first clutch mechanism and the second clutch mechanism. 
     In this embodiment, the rotary hammer  101  is switched between three action modes, namely a hammer-drill mode (rotation with hammering), a hammer mode (hammering only), and a drill mode (rotation only), in response to the manipulation of the mode-changing dial  800 . The hammer-drill mode is a mode in which the striking mechanism  6  and the rotation-transmitting mechanism  7  are both driven, so that the hammering operation and the drilling operation are both performed, i.e. the tool accessory  91  is simultaneously rotated and axially hammered. The hammer mode is a mode in which power transmission for the drilling operation is interrupted by the second clutch mechanism and only the striking mechanism  6  is driven, so that only the hammering operation is performed, i.e. the tool accessory  91  is only hammered (without rotation). The drill mode is a mode in which power transmission for the hammering operation is interrupted by the first clutch mechanism and only the rotation-transmitting mechanism  7  is driven, so that only the drilling operation is performed, i.e. the tool accessory  91  is only rotated (without hammering). 
     As described above, the rotary hammer  101  of this embodiment includes two separate (discrete) intermediate shafts (i.e. the first intermediate shaft  41  and the second intermediate shaft  42 ) that are configured to extend in parallel to the driving axis A 1  and transmit power for the hammering operation and the drilling operation, respectively. Therefore, the first intermediate shaft  41  and the second intermediate shaft  42  can be made shorter compared to a case in which one common intermediate shaft is used for power transmission for both the hammering operation and the drilling operation. Thus, the overall length of the rotary hammer  101  can be reduced in the driving-axis direction. 
     Further, the first intermediate shaft  41  and the second intermediate shaft  42  are respectively dedicated to power transmission for the hammering operation and power transmission for the drilling operation. This optimizes power transmission via the first intermediate shaft  41  and power transmission via the second intermediate shaft  42 , respectively. 
     In this embodiment, the rotary hammer  101  is configured to reduces vibration (in particular, vibration in the front-rear direction) to be transmitted to the body housing  10  and the handle  17  due to driving of the driving mechanism  5 . The vibration-isolating structure of the rotary hammer  101  is now described. 
     In this embodiment, as shown in  FIG.  1   , the spindle  31  and the striking mechanism  6  (specifically, the motion-converting member  61 , the piston  65 , the striker  67 , and the impact bolt  68 ) are disposed within the body housing  10  so as to be movable in the driving-axis direction (i.e. front-rear direction) relative to the body housing  10 . More specifically, a movable support  18  is disposed within the body housing  10  in a state in which the movable support  18  is biased forward relative to the body housing  10 , and is movable in the front-rear direction relative to the body housing  10 . The spindle  31  and the striking mechanism  6  are supported by the movable support  18  and are thus movable together with the movable support  18  relative to the body housing  10 . 
     As shown in  FIGS.  5 ,  6 , and  12   , the movable support  18  includes a spindle-support part  185  and a rotary-body-support part  187 . In this embodiment, the movable support  18  is formed as a single (integral) metal member. 
     The spindle-support part  185  has a generally circular cylindrical shape and is configured as a part for supporting the spindle  31 . As shown in  FIGS.  5  and  6   , the bearing  317  is held inside the spindle-support part  185 . The spindle-support part  185  supports a rear portion of the cylinder  33  via the bearing  317  so that the cylinder  33  is rotatable around the driving axis A 1 . As described above, the spindle  31  is supported by the two bearings  316  and  317  so as to be rotatable around the driving axis A 1  relative to the body housing  10 . The other bearing  316  is held within the barrel part  131  and supports a rear portion of the tool holder  32  so that the tool holder  32  is rotatable around the driving axis A 1  and movable in the front-rear direction. 
     The rotary-body-support part  187  is a generally hollow circular cylindrical portion and is located in the lower right side of the spindle-support part  185 . As shown in  FIG.  5   , the bearing  614  is fixed to the rotary-body-support part  187  by screws. The rotary-body-support part  187  supports the rotary body  611  via the bearing  614  so that the rotary body  611  is rotatable around the rotation axis A 3 . 
     As described above, the spindle  31  and the rotary body  611  are supported by the movable support  18 . Therefore, the oscillating member  616 , which is mounted on the rotary body  611 , and the piston  65 , the striker  67 , and the impact bolt  68 , which are disposed within the spindle  31 , are also supported by the movable support  18 . Thus, the movable support  18 , the spindle  31 , and the striking mechanism  6  form a movable unit  180  as an assembly that is integrally movable relative to the body housing  10  (or in other words, the motor  2 ) in the front-rear direction. 
     Movement of the movable unit  180  including the movable support  18  in the front-rear direction is slidably guided by a pair of first guide shafts  191  and a pair of second guide shafts  192 . As shown in  FIGS.  7  and  8   , the pair of first guide shafts  191  and the pair of second guide shafts  192  coaxially extend in the axial direction (i.e. front-rear direction). 
     More specifically, as shown in  FIGS.  7 ,  8 , and  12   , the movable support  18  includes a pair of hollow circular cylindrical parts  181  radially outward of the spindle-support part  185  (only one hollow circular cylindrical part  18  is visible in  FIG.  12   ). As shown in  FIGS.  7  and  8   , the pair of hollow circular cylindrical part  181  are arranged to be bilaterally symmetrical. In other words, the hollow circular cylindrical parts  181  are symmetrically arranged respectively on the right and left sides of an imaginary plane P 1  (see  FIG.  2   ) including the driving axis A 1  and the rotation axis A 2 . A hole  183  is formed through each hollow circular cylindrical part  181  in the front-rear direction. Approximately a rear half of each first guide shaft  191  is press fitted into the corresponding hole  183 , while approximately a front half of each first guide shaft  191  extends frontward from the movable support  18 . Therefore, the first guide shafts  191  are fixed to the movable support  18  and are configured to move in the front-rear direction together with the movable support  18 . 
     The pair of first guide shafts  191  are respectively received in a pair of holes  166  (see  FIGS.  13  and  14   ) formed in the second support  16 . More specifically, as shown in  FIGS.  7  and  8   , each hole  166  extends through the second support  16  in the front-rear direction. The inner diameter of each hole  166  is larger in its front portion than in its rear portion. Therefore, the second support  16  has stepwise inner surfaces each forming the corresponding hole  166 . The second support  16  includes a sleeve  167  of a hollow circular cylindrical shape within each hole  166 . The sleeve  167  is press fitted into the front portion of the hole  166  having the larger-diameter so that a rear end of the sleeve  167  abuts the step on the inner surface of the hole  166 . Each first guide shaft  191  is always received within the corresponding sleeve  167  so that the first guide shaft  191  slides on an inner peripheral surface of the sleeve  167  while the movable support  18  is moving in the front-rear direction. Each first guide shaft  191  only slides on the corresponding sleeve  167  but not on the other parts of the second support  16 . In this embodiment, a front end portion of each sleeve  167  abuts the front housing  13 . Therefore, the sleeve  167  is prevented from coming out of the hole  166  even if the first guide shaft  191  slides on the inner peripheral surface of the sleeve  167 . In this embodiment, the sleeve  167  is formed of iron-based metal. Meanwhile, the remaining parts of the second support  16  are formed of aluminum-based metal, as described above. Therefore, the second support  16  including the sleeves  167  can have sufficient strength to withstand sliding movement relative to the first guide shafts  191  and can also have a reduced weight as a whole. 
     The pair of second guide shafts  192  are located more rearward than the pair of first guide shafts  191  and are held by the first support  15 . More specifically, as shown in  FIGS.  7 ,  8 , and  11   , the first support  15  includes a pair of shaft-support parts  156 . Each shaft-support part  156  has a hollow circular cylindrical shape and extends frontward from a plate-like base  150  that is orthogonal to the front-rear direction. Approximately a rear half of each second guide shaft  192  is press fitted into the corresponding shaft-support part  156 . Therefore, the pair of second guide shafts  192  are immovable relative to the first support  15  and thus to the body housing  10 . Approximately a front half of each second guide shaft  192  extends frontward from the first support  15 . 
     As shown in  FIGS.  7 ,  8 , and  12   , the movable support  18  includes a pair of hollow circular cylindrical parts  182  coaxially with the pair of cylindrical parts  181 . A hole  184  is formed through each hollow cylindrical part  182  in the front-rear direction. The inner diameter of each hole  184  is larger in its rear portion than in its front portion. Therefore, each hollow cylindrical part  182  has a stepwise inner surface forming the corresponding hole  184 . The movable support  18  includes a sleeve  186  of a hollow circular cylindrical shape within each hole  184 . The sleeve  186  is press fitted into the larger-diameter rear portion of the corresponding hole  184  so that a front end of the sleeve  186  abuts the step on the inner surface of the hole  184 . A front end portion of each second guide shaft  192  is always received within the corresponding sleeve  186  so that an inner peripheral surface of the sleeve  186  slides on the second guide shaft  192  while the movable support  18  is moving in the front-rear direction. Each second guide shaft  192  only slides on the corresponding sleeve  186  but not on the other parts of the movable support  18 . In this embodiment, each sleeve  186  is formed of iron-based metal. Meanwhile, the remaining parts of the movable support  18  are formed of aluminum-based metal, as described above. Therefore, the movable support  18  including the sleeves  186  can have sufficient strength to withstand sliding movement relative to the second guide shafts  192  and can also have a reduced weight as a whole. In this embodiment, both the first guide shafts  191  and the second guide shafts  192  are formed of iron-based metal. 
     The first guide shafts  191  and the second guide shafts  192 , which are spaced apart from each other in the front-rear direction, are used to guide movement of the movable support  18  in the front-rear direction. Therefore, the distance over which the guide shafts extend as a whole can be shortened compared to a case in which a single guide shaft extends from where the first guide shaft  191  is to where the second guide shaft  192  is. The rotary hammer  101  can thus have a reduced weight. Moreover, since the guide shafts are respectively placed on both sides of the movable support  18  in the front-rear direction, the movable support  18  can be guided satisfactorily irrespective of the reduced weight. 
     A pair of biasing springs  193  are disposed in the rear side of the movable support  18 . Each spring  193  is a compression coil spring and is disposed in a compressed state between the first support  15  and the movable support  18 . More specifically, each biasing spring  193  is disposed around the corresponding one of the pair of second guide shafts  192 . A rear end of each biasing spring  193  abuts a washer disposed on the base  150  of the first support  15 . Each biasing spring  193  is fitted around the shaft-support part  156 . The biasing spring  193  is thus restricted from moving on a plane orthogonal to the front-rear direction. A front end of the each biasing spring  193  abuts a washer  195  disposed between the biasing spring  193  and the movable support  18 . 
     The sleeve  186  disposed within the hole  184  of the hollow circular cylindrical part  182  is always biased forward by the biasing spring  193  via the washer  195 . This allows the sleeve  186  to move together with the movable support  18  whenever the movable support  18  moves frontward. That is, the sleeve  186  can be prevented from being left behind and off the hole  184  when the movable support  18  is moving frontward. 
     With such a structure, the pair of biasing springs  193  always bias the movable support  18  (the movable unit  180 ) frontward. Therefore, when no rearward external force is being applied to the movable support  18 , the movable support  18  is held in (biased to) its foremost position (initial position) where the movable support  18  abuts the second support  16 , as shown in  FIG.  7   . An elastic member may be attached on a rear surface of the second support  16  in order to prevent direct abutment (to dampen the force of collision) between the second support  16  and the movable support  18 . 
     On the other hand, when a rearward external force is being applied to the movable support  18 , the movable support  18  can move to its rearmost position shown in  FIG.  8   . Structures for defining this rearmost position are described below. 
     As shown in  FIGS.  9  to  11   , the first support  15  includes a pair of elastic-member-holding parts  158  each having a bottomed hollow circular cylindrical shape and extending frontward from the base  150 . The pair of elastic-member-holding parts  158  are arranged to be bilaterally symmetrical. A hole  159  is formed in each elastic-member-holding part  158 . As shown in  FIG.  11   , each elastic-member-holding part  158  extends more forward than the shaft-support part  156 . An elastic member  194  having a hollow circular cylindrical shape is disposed in the hole  159  of each elastic-member-holding part  158 . A rear end of the elastic member  194  abuts the base  150  while a front end of the elastic member  194  protrudes more frontward than a front end of the elastic-member-holding part  158 . The elastic member  194  is held in a state fitted within the elastic-member-holding part  158 . More specifically, an outer diameter of the elastic member  194  is slightly larger than an inner diameter of the elastic-member-holding part  158 . The elastic member  194  is thus slightly pressed radially inward within the elastic-member-holding part  158  and therefore held within the hole  159  by the restorative force from the pressing. With such a structure, the elastic member  194  can be removably attached with ease. This in turn enables easy manufacturing and also allows easy replacement of an elastic member  194  when it is deteriorated or worn out. 
     As shown in  FIGS.  9 ,  10 , and  12   , the movable support  18  includes a pair of projections  188  and an abutment part  189 . Each projection  188  has a solid circular cylindrical shape and extends more rearward than the hollow circular cylindrical part  182 . Each projection  188  is always received within the corresponding elastic member  194 . An outer diameter of the projection  188  is slightly larger than an inner diameter of the elastic member  194 . The elastic member  194  is thus slightly pressed radially outward, and therefore, the projection  188  and the elastic member  194  are always held in a state fitted with each other by the restorative force from the pressing. As the movable support  18  moves in the front-rear direction, the projection  188  slides on the inner surface of the elastic member  194  while being kept in the state fitted with the elastic member  194 . The abutment part  189  is formed into an arch-shaped plane orthogonal to the front-rear direction, and is connected with base portions of the projections  188  at both ends of the arch. 
     When the movable support  18  is located in its foremost position shown in  FIG.  7   , the abutment part  189  of the movable support  18  is spaced apart from the front end portion of the elastic member  194  in the front-rear direction, as shown in  FIG.  9   . On the other hand, when the movable support  18  is located in its rearmost position shown in  FIG.  8   , the abutment part  189  of the movable support  18  abuts the front end portion of the elastic member  194  in the front-rear direction, as shown in  FIG.  10   . That is, the elastic member  194  serves as a stopper for restricting further rearward movement of the movable support  18 . This structure thus defines the rearmost position of the movable support  18  shown in  FIG.  8   . 
     In the rotary hammer  101  described above, when the tool accessory  91  is pressed against a workpiece and the processing operation is performed in the hammer-drill mode and the hammer mode in which the hammering operation is performed, vibration is caused mainly in the front-rear direction in the striking mechanism  6  due to the force of the striking mechanism  6  driving the tool accessory  91  and a reaction force from the workpiece against the striking force of the tool accessory  91 . Owing to this vibration, the movable unit  180  may move relative to the body housing  10  in the front-rear direction while being slidably guided by the first and second guide shafts  191  and  192 . At this time, the biasing springs  193  expand and contract (elastically deform). This elastic deformation absorbs (attenuates) vibration from the movable unit  180  and thereby reduces the amount of vibration transmitted to the body housing  10  and the handle  17 . Once the movable unit  180  has moved to its rearmost position, the abutment part  189  of the movable support  18  collides with and elastically deforms the elastic members  194 . This elastic deformation also serves to absorb (attenuate) vibration from the movable unit  180 . 
     According to the rotary hammer  101  described above, the bearings  411  and  421  for respectively supporting the front end portions of the first intermediate shaft  41  and the second intermediate shaft  42  are supported by the second support  16  formed of metal. This provides stronger support strength than in a case in which the bearings  411  and  421  are supported by a plastic support. Therefore, even if high power operation of the power tool results in increased vibration due to a reaction force produced against the striking force of the tool accessory  91 , the positional accuracy for the bearings  411  and  421  and thus for the first intermediate shaft  41  and the second intermediate shaft  42  can be maintained at the required level. The effects can be further reinforced by the use of the first support  15  formed of metal to support the bearings  412  and  422  for supporting the respective rear end portions of the first intermediate shaft  41  and the second intermediate shaft  42 . 
     Furthermore, according to the rotary hammer  101 , the first guide shafts  191  are respectively partially received within the holes  166  (more specifically, holes of the sleeves  167 ) of the second support  16  formed of metal. Therefore, even if high power operation of the rotary hammer  101  results in an increased amount of heat produced as the first guide shafts  191  slidably guide movement of the movable support  18  in the front-rear direction, the second support  16  can have reduced thermal expansion compared to a case in which a plastic support is used to receive the first guide shafts  191 . Therefore, the positional accuracy required for the first guide shafts  191  partially received in the holes  166  of the second support  16  can be maintained at the required level. This in turn provides satisfactory sliding property related to the first guide shafts  191  and also allows for satisfactory isolation of vibration. The effects can be further reinforced by having the second guide shafts  192  respectively partially received within the holes  184  (more specifically, holes of the sleeves  186 ) of the movable support  18  formed of metal. 
     As such, the rotary hammer  101  can achieve both high power operation and reduced vibration. Moreover, the use of the single member, namely the second support  16 , for both supporting the bearings  411  and  421  and also for receiving the first guide shafts  191  enables simplified tool structure as well as reduced man-hours related to manufacturing. 
     Furthermore, the use of the elastic members  194  each serving as a stopper in the rotary hammer  101  can improve dissipation of heat produced due to sliding movement of the movable support  18  in the front-rear direction. Structures therefor are now described. As described above with reference to  FIGS.  9  and  10   , each elastic member  194  is disposed so as to be always in contact with the movable support  18  (more specifically, the projection  188 ) and the first support  15  (more specifically, the elastic-member-holding part  158 ) irrespective of where the movable support  18  is located in the front-rear direction. 
     An elastic material conductive of heat (e.g. conductive rubber) is used for the elastic members  194 . Heat conductivity may be achieved by forming the elastic member  194  from a filler-containing elastic material. Examples of the filler include metal, carbon nanotube, and the like. Being “conductive of heat” may be defined as having a heat conductivity of not less than 1.0 W/m*K. 
     As described above, the first support  15  is formed of metal, and is disposed adjacent to the passage  16  for flow of air generated by rotation of the cooling fan  27 . Therefore, the heat produced due to sliding movement of the movable support  18  in the front-rear direction can be transmitted via the heat conductive elastic member  194  to the first support  15  and then be dissipated efficiently by the flow of air generated by rotation of the cooling fan  27 . 
     In this embodiment, the elastic member  194  and the corresponding projection  188  of the movable support  18  are always kept in a state fitted with each other. Therefore, the elastic member  194  and the movable support  18  can have a larger contact area compared to a case in which the members makes a plane contact with each other. This enables enhanced heat transmission from the movable support  18  to the elastic member  194  and thus provides further improved heat dissipation. Also, the elastic member  194  and the corresponding elastic-member-holding part  158  of the first support  15  are always kept in a state fitted with each other. Therefore, the elastic member  194  and the first support  15  can have a larger contact area compared to a case in which the members makes a planar contact with each other. This enables enhanced heat transmission from the elastic member  194  to the first support  15  and thus provides further improved heat dissipation. Moreover, the fitted states are implemented as a hollow circular cylindrical shape fitted with another hollow circular cylindrical shape or with a solid circular cylindrical shape. This enables easy manufacturing while achieving a larger contact area. 
     Furthermore, as shown in  FIG.  11   , the elastic members  194  are disposed adjacent to the second guide shafts  192 . Therefore, heat can be transmitted over a short distance from where heat is produced due to sliding movement, via the movable support  18 , and to the elastic member  194 . This enables further efficient heat dissipation. 
     Furthermore, as shown in  FIG.  11   , in an imaginary plane orthogonal to the driving axis A 1  (in other words, a surface where the base  150  spreads), the distance between one of the pair of second guide shafts  192  (the one on the right side) and one of the pair of elastic members  194  (the one on the right side) that is disposed adjacent to the second guide shaft  192  is equal to the distance between the other one of the pair of second guide shafts  192  (the one on the left side) and the other one of the pair of elastic member  194  (the one on the left side). Therefore, the length of heat transmission path from the one of the second guide shafts  192  to the one of the elastic members  194  is equal to the length of heat transmission path from the other one of the second guide shafts  192  to the other one of the elastic members  194  (such an arrangement is also referred to as an equidistant arrangement). This reduces or minimizes unevenness of temperature in the movable support  18  and thus enables uniform heat dissipation. 
       FIG.  11    shows an example of equidistant arrangement in which one elastic member  194  is provided for one second guide shaft  192 . However, in alternative embodiments, multiple elastic members  194  may be provided for one second guide shaft  192 . For example, in an embodiment in which two elastic members  194  are provided for one second guide shaft  192  (in this case, there are four elastic members  194  in total), the equidistant arrangement may be implemented such that each distance between one of the second guide shafts  192  and each one of its corresponding two elastic members  194  is equal to each distance between the other one of the second guide shafts  192  and each one of its corresponding two elastic members  194 . 
     Correspondences between the features of the above-described embodiment and the features of the claims are as follows. The features of the above-described embodiment are, however, merely exemplary and do not limit the features of the present invention. The rotary hammer  101  is an example of the “power tool”. The spindle  31  is an example of the “final output shaft”. The driving axis A 1  is an example of the “driving axis”. The motor  2  and the motor shaft  25  are examples of the “motor” and the “motor shaft”, respectively. The driving mechanism  5  is an example of the “driving mechanism”. The body housing  10  is an example of the “housing”. The movable support  18  is an example of the “movable support”. The biasing spring  193  is an example of the “biasing member”. The first guide shaft  191  and the second guide shaft  192  are examples of the “first guide shaft” and the “second guide shaft”, respectively. The first intermediate shaft  41  and the second intermediate shaft  42  are examples of the “first intermediate shaft” and the “second intermediate shaft”, respectively. The bearing  411  and the bearing  421  are examples of the “first bearing” and the “second bearing”, respectively. The second support  16  is an example of the “metal support”. The hole  166  and the hole  184  are examples of the “first hole” and the “second hole”, respectively. The first positioning part  163  and the second positioning part  133  are examples of the “first positioning part” and the “second positioning part”, respectively. The sleeve  167  and the sleeve  186  are examples of the “first sleeve” and the “second sleeve”, respectively. The attachment surface  168  is an example of the “attachment surface”. 
     The above-described embodiment is merely an exemplary embodiment of the present disclosure, and power tools, such as rotary hammers and hammer drills, according to the present disclosure are not limited to the rotary hammer  101  of the illustrated structure. For example, the following modifications may be made. One or more of these modifications may be employed in combination with the rotary hammer  101  of the above-described embodiment or any one of the claimed aspects. 
     Instead of the first intermediate shaft  41  and the second intermediate shaft  42 , a single intermediate shaft may be used for both power transmission for hammering operations and power transmission for drilling operations. Such a structure is disclosed in, for example, US Patent Application NO. 2017/106517, the disclosed contents of all of which are hereby fully incorporated herein by reference. 
     The first guide shaft  191  may be fixedly received within the hole  166  of the second support  16 , instead of being fixedly held to the movable support  18 . In this modification, the first guide shaft  191  held by the second support  16  may be slidably received within a hole formed in the movable support  18 . 
     The movable support  18 , the elastic member  194 , and the first support  15  may always be in contact with each other in an alternative manner. For example, the elastic-member-holding part  158  may have a solid circular cylindrical shape, the elastic member  194  may have a hollow circular cylindrical shape surrounding the elastic-member-holding part  158 , and the projection  188  may have a hollow circular cylindrical shape surrounding the elastic member  194 . Alternatively, the movable support  18 , the elastic member  194 , and the first support  15  may make a plane contact with each other. 
     The elastic member conductive of heat (the elastic member  194  in the above-described embodiment) may be disposed to be always in contact with the movable support  18  as well as a freely selected metal member disposed to be heat dissipative. In this modification, the metal member may extend from the front side of and through the first support  15  all the way until it reaches above the air flow passage  26 . Alternatively, the metal member may be a freely selected member disposed to be at least partially exposed to outside the rotary hammer  101 . For example, at least a portion of the body housing  10  exposed to the outside may be formed of metal, and this metal portion and the elastic member may be configured to be always in contact with each other. 
     In the above-described embodiments, the rotary hammer  101  capable of performing hammering operations and drilling operations is illustrated as an example of a power tool. However, the power tool may alternatively be an electric hammer (scraper, demolition hammer) capable of performing hammering operations only. 
     Further, to enhance dissipation of heat produced due to between-parts sliding movement, the following aspects  1  to  10  can be provided. Any one of the following aspects  1  to  10  can be employed on its own or in combination with any one or more others of the following aspects  1  to  10 . Alternatively, at least one of the following aspects  1  to  10  may be employed in combination with the rotary hammer  101  of the above-described embodiment, its modifications described above, and the claimed features. 
     Aspect 1 
     A power tool comprising: 
     a final output shaft configured to removably hold a tool accessory and defining a driving axis of the tool accessory; 
     a motor including a motor shaft; 
     a driving mechanism configured to linearly reciprocally drive the tool accessory along the driving axis by using power from the motor; 
     a movable support at least partially supporting the final output shaft and the driving mechanism, the movable support being configured to be integrally movable relative to the motor in an axial direction of the driving axis; 
     a biasing member configured to bias the movable support toward a front side in the axial direction, the front side being defined as one side in the axial direction in which the final output shaft is disposed and a rear side being defined as an opposite side in the axial direction in which the motor is disposed; 
     at least one guide shaft extending in the axial direction and configured to slidably guide movement of the movable support in the axial direction; 
     a metal member disposed to be capable of dissipating heat; 
     at least one elastic member conductive of heat, the at least one elastic member being disposed to be always in contact with the movable support and the metal member irrespective of where the movable support is located in the axial direction. 
     According to the power tool of this Aspect, the at least one elastic member conductive of heat is always in contact with the movable support and also with the metal member disposed to be capable of dissipating heat. Therefore, heat produced due to sliding movement for guiding the movement of the movable support can be transmitted from the movable support to the metal member via the at least one elastic member and then be dissipated therefrom. This enhances dissipation of heat produced due to sliding movement for guiding the movement of the movable support. 
     Aspect 2 
     The power tool according to Aspect 1, wherein 
     the metal member is disposed to be at least partially exposed to outside of the power tool. 
     According to this Aspect, heat transmitted from the movable support to the metal member can be dissipated with a simple structure. In this Aspect, the metal member may be a portion of a housing that defines an outer shell of the power tool. 
     Aspect 3 
     The power tool according to Aspect 1 or 2, further comprising 
     a fan fixed to the motor shaft, 
     wherein the metal member is disposed on a passage for flow of air generated by rotation of the fan or is disposed adjacent to the passage. 
     According to this Aspect, heat transmitted from the movable support to the metal member can be dissipated efficiently by flow of air generated by rotation of the fan. 
     Aspect 4 
     The power tool according to any one of Aspects 1 to 3, wherein: 
     the at least one elastic member is held by the metal support; and 
     the movable support is configured to slide on the at least one elastic member while the movable support moves in the axial direction. 
     According to this Aspect, the at least one elastic member can always be in contact with the movable support and the metal support in an easily implemented manner. 
     Aspect 5 
     The power tool according to any one of Aspects 1 to 4, wherein 
     the at least one elastic member and the movable support are always kept in a state fitted with each other. 
     According to this Aspect, the at least one elastic member and the movable support can have a larger contact area compared to a case in which the at least one elastic member and the movable support makes a plane contact with each other. This enables enhanced heat transmission from the movable support to the at least one elastic member and thus provides further improved heat dissipation. 
     Aspect 6 
     The power tool according to Aspect 5, wherein 
     the at least one elastic member and the movable support are shaped such that the state in which the at least one elastic member and the movable support are fitted with each other is implemented as a hollow circular cylindrical shape fitted with another hollow circular cylindrical shape or a solid circular cylindrical shape. 
     This Aspect enables easy manufacturing while achieving a larger contact area between the at least one elastic member and the movable support. 
     Aspect 7 
     The power tool according to any one of Aspects 1 to 6, wherein 
     the at least one elastic member is disposed adjacent to the at least one guide shaft. 
     According to this Aspect, heat can be transmitted over a short distance from a portion of the movable support where heat is produced due to sliding movement to the at least one elastic member. This enables efficient heat dissipation. 
     Aspect 8 
     The power tool according to any one of Aspects 1 to 7, wherein 
     when the movable support moves rearwards in the axial direction, the at least one elastic member serves as a stopper by abutting the movable support in the axial direction and restricting further rearward movement of the movable support. 
     According to this Aspect, elastic deformation of the at least one elastic member when serving as a stopper functions to cushion a part of a reaction force from a workpiece due to the hammering operation of the tool accessory. This enhances isolation of vibration in the power tool. The tool can also achieve improved durability. 
     Aspect 9 
     The power tool according to any one of Aspects 1 to 8, wherein: 
     the at least one guide shaft includes a plurality of guide shafts; 
     the at least one elastic member includes a plurality of elastic members corresponding to the plurality of guide shafts; and 
     the at least one guide shaft and the at least one elastic member are arranged such that each one of the plurality of guide shafts and its corresponding elastic member (which may be one or more) are separated by an equal distance on an imaginary plane orthogonal to the driving axis. 
     According to this Aspect, each one of the plurality of guide shafts and its corresponding elastic member(s) are separated by an equal distance (i.e. heat is transmitted over a path of equal distance). This reduces or minimizes unevenness of temperature in the movable support and thus enables uniform heat dissipation. 
     Aspect 10 
     The power tool according to any one of Aspects 1 to 9, wherein: 
     the metal support includes at least one hole; and the at least one elastic member is held in a state fitted within the at least one hole. 
     According to this Aspect, the at least one elastic member and the metal support can have a larger contact area compared to a case in which the at least one elastic member and the metal support makes a plane contact with each other. This enables enhanced heat transmission from the at least one elastic member to the metal support and thus provides improved heat dissipation. Furthermore, the at least one elastic member can be removably attached to the metal member with ease. This enables easy manufacturing and also allows for easy replacement of the at least one elastic member when it is deteriorated or worn out. 
     Correspondences between the features of the above-described embodiment and the features of Aspects 1 to 10 are as follows. The features of the above-described embodiment are, however, merely exemplary and do not limit the features of the present invention. 
     The rotary hammer  101  is an example of the “power tool”. The spindle  31  is an example of the “final output shaft”. The driving axis A 1  is an example of the “driving axis”. The motor  2  and the motor shaft  25  are examples of the “motor” and the “motor shaft”, respectively. The driving mechanism  5  is an example of the “driving mechanism”. The movable support  18  is an example of the “movable support”. The biasing spring  193  is an example of the “biasing member”. The second guide shaft  192  (or the second guide shaft  192  and the first guide shaft  191 ) is an example of the “at least one guide shaft”. The first support  15  is an example of the “metal support”. The elastic member  194  is an example of the “at least one elastic member”. The cooling fan  27  is an example of the “fan”. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
       2 : motor,  5 : driving mechanism,  6 : striking mechanism,  7 : rotation-transmitting mechanism,  10 : body housing,  11 : rear housing,  13 : front housing,  15 : first support,  16 : second support,  17 : handle,  18 : movable support,  20 : body,  25 : motor shaft,  26 : passage for flow of air,  27 : cooling fan,  28 : inlet opening,  29 : discharge opening,  31 : spindle,  32 : tool holder,  33 : cylinder,  41 : first intermediate shaft,  42 : second intermediate shaft,  61 : motion-converting member,  63 : intervening member,  64 : first transmitting member,  65 : piston,  67 : striker,  68 : impact bolt,  72 : second transmitting member,  73 : torque limiter,  74 : drive-side member,  75 : driven-side member,  77 : biasing spring,  78 : driving gear,  79 : driven gear,  91 : tool accessory,  101 : rotary hammer,  131 : barrel part,  132 : auxiliary handle,  133 : second positioning part,  135 : attachment surface,  150 : base,  151 : O-ring,  152 : groove,  153 : through hole,  154 ,  155 : bearing-support part,  156 : shaft-support part,  158 : elastic-member-holding part,  159 : hole,  161 : screw,  162 : through hole,  163 : first positioning part,  164 ,  165 : bearing-support part,  166 : hole,  167 : sleeve,  168 : attachment surface,  171 : trigger,  172 : switch,  179 : power cable,  180 : movable unit,  181 ,  182 : hollow circular cylindrical part,  183 ,  184 : hole,  185 : spindle-support part,  186 : sleeve,  187 : rotary-body-support part,  188 : projection,  189 : abutment part,  191 : first guide shaft,  192 : second guide shaft,  193 : biasing spring,  194 : elastic member,  195 : washer,  251 ,  252 : bearing,  255 : pinion gear,  316 ,  317 : bearing,  330 : bit-insertion hole,  411 ,  412 : bearing,  414 : first driven gear,  416 : spline part,  421 ,  422 : bearing,  423 : gear member,  424 : second driven gear,  425 : spline part,  611 : rotary body,  612 : spline part,  614 : bearing,  616 : oscillating member,  617 : arm,  631 : spline part,  641 : first spline part,  642 : second spline part,  721 : first spline part,  722 : second spline part,  743 : spline part,  800 : mode-changing dial, A 1 : driving axis, A 2 , A 3 , A 4 : rotation axis, P 1 : imaginary plane.