Patent Abstract:
A working tool includes a housing ( 10 ) and a lever ( 3 ) having a gap defined therein for accommodating a rotatable switch lock ( 1 ). The switch lock has a first engagement portion ( 1   a ) defined on a first side and a stopper portion ( 1   b ) defined on a second side, and the lever has a support portion ( 3   a ) proximal to the first engagement portion. A handle portion of the housing has a left push button ( 8 ) and a right push button ( 5 ) inserted therein, a first groove ( 8   a ) and a second groove ( 8   b ) of the left push button ( 8 ) and right push button ( 5 ) each having a second engagement portion formed on a groove wall thereof, each of a first extension section ( 3   a - 2 ) and second extension sections ( 3   a - 1 ) being provided with, at a side facing a corresponding second engagement portion, a third engagement portion engageable with the corresponding second engagement portion. The working tool is capable of reducing operation mistakes as much as possible, preventing inadvertent shutdown of the motor, and allowing any operator, no matter left-handed or right-handed, to operate it conveniently.

Full Description:
TECHNICAL FIELD 
     The present invention relates to a portable electric angle grinder for use in grinding or polishing a workpiece. 
     BACKGROUND 
     An ordinary electric angle grinder typically includes: a housing; a working mechanism disposed on a head portion of the housing and configured to grind or polish a workpiece; a motor disposed within the housing and configured to drive the working mechanism; a switch disposed within a handle portion of the housing and configured to activate or deactivate the motor; and a lever disposed right under the switch and configured to allow an operator to operate the switch in the housing through manipulating the lever. Once the motor is switched on, a grinding wheel of the working mechanism starts to rotate at a very high speed, during which, if the operator improperly operates the tool or is unfamiliar with the tool, the grinding wheel rotating at a very high speed might lead to body injury. For this reason, the grinder generally further includes a lock means disposed in proximity of the lever in order to prevent operation mistakes as much as possible. 
     Examples in this regard include a working tool as disclosed in PCT App. No. PCT/JP2009/065259, entitled “Working Tool”. In one embodiment, the working tool is an electric angle grinder including: a motor for driving a grinding wheel to grind or polish a workpiece; a motor housing for housing the motor, the motor housing having a portion defining a handle; a wheel guard coupled to a rear portion of the motor housing, at a location opposite to where the grinding wheel is mounted; a lever adapted to be operated by an operator by hand, the lever having a strip shape and being disposed above both the motor housing and wheel guard; and a switch disposed within the wheel guard and connected to the lever via an opening. The motor can be activated or deactivated by a manipulation to the lever by the operator. 
     In order to prevent operation mistakes, the electric angle grinder further includes a lock means disposed on the lever. The lock means includes a rotating shaft, an engagement portion and a manipulation portion. The principle of the lock means is that when the lock means is in a locked state, the engagement portion engages with a protrusion of the lever with the aid of an elastic force exerted by a spring, and the operator, thus, cannot operate the lever any more. To activate the motor to initiate the grinding or polishing operation of the grinding wheel, the operator needs to operate, with one hand, the manipulation portion with a force exceeding the elastic force of the spring so as to cause the lock means to rotate and the engagement portion to gradually detach from the protrusion of the lever. After the engagement portion becomes disengaged from the protrusion portion, the operator further needs to push the lever upwards, with the other hand, to switch on the switch. Moreover, in order to prevent a restoring force of the switch from causing the engagement portion of the lock means to re-engage with the protrusion of the lever and thus shutting down the motor, the operator further needs to always press the lever throughout the whole process of the grinding or polishing operation. 
     As indicated in the foregoing description, although this lock means facilitates mistaken operation prevention, it leads to disadvantages such as increase of the operator&#39;s physical workload, reduction of operational efficiency, and possible occurrence of undesirable motor shutdown. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an objective of the present invention to provide an electric angle grinder capable of reducing the operator&#39;s physical workload and improving operational efficiency and suitable for use by both left-hand and right-hand operators. 
     In order to achieve the foregoing objective, one aspect of the present invention provides a working tool which includes: a housing; a working mechanism disposed on a working portion of the housing and configured to grind or polish a workpiece, the working mechanism driven to work by a motor disposed within the housing; a switch disposed within a handle portion of the housing and configured to activate or deactivate the motor; and a lever disposed under the switch and having a first end connected to the housing, wherein the lever has a gap formed therein for accommodating a switch lock, the switch lock having a rotating shaft inserted therethrough, the rotating shaft having two ends both connected to the lever and surrounded by a torsion spring, the switch lock including a first portion extending out of the lever and a second portion hiding in the housing, wherein the second portion of the switch lock has a first engagement portion defined on a first side and a stopper portion defined on a second side thereof, the lever having a support portion proximal to and engageable with the first engagement portion, wherein the handle portion of the housing has a left push button and a right push button partially inserted therein from a left side and a right side, respectively, the left push button and the right push button each having a first end horizontally protruding out of the housing to act as a manipulation portion and a main body and a second end hiding in the housing, the second end of the left push button slidably fitting in the second end of the right push button to allow the left push button to move horizontally towards the right push button and the right push button to move horizontally towards the left push button, the second ends of the left push button and right push button having a reset mechanism interconnected therebetween, wherein the main bodies of the left push button and the right push button in the housing are formed with a first groove and a second groove, respectively, the lever having a first extension section and a second extension section formed at a second end thereof in correspondence with the positions of the first groove and the second groove, respectively, the first extension section and the second extension section extending in the first groove and the second groove, respectively, each of the first groove and the second groove having a second engagement portion formed on a groove wall thereof, each of the first extension section and the second extension section being provided with, at a side facing a corresponding second engagement portion, a third engagement portion engageable with the corresponding second engagement portion, wherein when the working tool is in a locked state, the first engagement portion engages with the support portion, the stopper portion being pushed against a fixation member disposed in the housing, each second engagement portion being disengaged from the corresponding third engagement portion, and wherein when the working tool is in an unlocked state, the first engagement portion is disengaged from the support portion, the stopper portion being apart from the fixation member, the second engagement portion on the first groove engaging with the third engagement portion on the first extension portion or the second engagement portion on the second groove engaging with the third engagement portion on the second extension portion. 
     Preferably, the second end of the left push button may define third extension sections each formed with a first sliding groove, and the second end of the right push button may define fourth extension sections each formed with a second sliding groove, wherein each of the third extension sections has an end portion horizontally slidably disposed in a corresponding second sliding groove, and each of the fourth extension sections has an end portion horizontally slidably disposed in a corresponding first sliding groove, wherein the end portions of the third extension sections and the end portions of the fourth extension sections are hooked up when the working tool is in a locked state, and the reset mechanism is disposed in a space defined by the third extension sections and the fourth extension sections. 
     Preferably, the reset mechanism may include a reset spring and a protrusion extending from a central area of the second end of the left push button towards the right push button, wherein the reset spring surrounds the protrusion. 
     Preferably, the working mechanism may include a grinding wheel and a guard securing means disposed spacedly around the grinding wheel; the grinding wheel may be driven to rotate by the motor, wherein the guard securing means may include a guard disposed around the grinding wheel and a front cover coupled to the housing; the guard may be provided a snap ring axially extending from a surface thereof opposite to the grinding wheel in a direction departing from the grinding wheel; the snap ring may be formed with one or more protrusions on the inner surface, and a top portion of the front cover defines one or more recesses, a number of which is equal to a number of the one or more protrusions; the front cover may define an outer circumstantial surface formed with an annular groove, and the one or more protrusions of the snap ring may fit in the annular groove with an aid of the one or more recesses of the front cover; the snap ring and the front cover may sandwich a portion of a wrench and leave a hanging tongue of the wrench outside; the snap ring may be formed with stop notches, and the portion of the wrench sandwiched between the snap ring and the front cover may be formed with a stop cog engaging with one of the stop notches. 
     Another aspect of the present invention provides a working tool, which includes: a working mechanism disposed on a working portion of the housing and configured to grind or polish a workpiece, the working mechanism driven to work by a motor disposed within the housing; a switch disposed within a handle portion of the housing and configured to activate or deactivate the motor; and a lever disposed under the switch and having a first end connected to the housing, wherein the lever has a gap formed therein for accommodating a switch lock, the switch lock having a resilient shaft inserted therethrough, the resilient shaft having two ends both connected to the lever and surrounded by a torsion spring, the switch lock including a first portion extending out of the lever and a second portion hiding in the housing, wherein the second portion of the switch lock has a first engagement portion defined thereon, and the lever has a support portion proximal to and engageable with the first engagement portion, wherein the handle portion of the housing has a left push button and a right push button partially inserted therein from a left side and a right side, respectively, the left push button and the right push button each having a first end horizontally protruding out of the housing to act as a manipulation portion and a main body and a second end hiding in the housing, the second end of the left push button slidably fitting in the second end of the right push button to allow the left push button to move horizontally towards the right push button and the right push button to move horizontally towards the left push button, the second ends of the left push button and right push button having a reset mechanism interconnected therebetween, wherein the left push button has a first extension portion extending towards the lever and the right push button has a second extension portion extending towards the lever, the first extension portion having an end portion defining a fourth engagement portion and the second extension portion having an end portion defining a fifth engagement portion, the fourth engagement portion and the fifth engagement portion spacedly disposed opposing each other to form an engagement gap between the first extension portion and the second extension portion, the lever having a fifth extension section extending towards and partially inserted in the engagement gap, the fifth extension section having a sixth engagement portion in the engagement gap and engageable with the fourth engagement portion or the fifth engagement portion, wherein when the working tool is in a locked state, the first engagement portion engages with the support portion, and the sixth engagement portion is disengaged from both of the fourth engagement portion and the fifth engagement portion, and wherein when the working tool is in an unlocked state, the first engagement portion is disengaged from the support portion, and the sixth engagement portion engages with the fourth engagement portion or the fifth engagement portion. 
     Preferably, the housing and the lever may have a handle reinforcement plate formed therebetween and the handle reinforcement plate may be fixedly coupled to the lever. 
     Advantageously, the working tool of the present invention entails an electric angle grinder that can be locked to reduce operation mistakes as much as possible by employing a simple structure. Also advantageously, the electric angle grinder can be maintained in an unlocked state throughout an operation process without needing an operator to always press the lever, thereby reducing the operator&#39;s physical workload, improving operational efficiency, and preventing inadvertent shutdown of the motor. Still also advantageously, the design of the left and right push buttons allows any operator, no matter left-handed or right-handed, to operate the tool conveniently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a partial schematic cross-sectional view illustrating a working tool in a locked state in accordance with Embodiment 1 of the present invention. 
         FIG. 1B  is an enlarged view of part of  FIG. 1A . 
         FIG. 2  is a cross-sectional view taken along line B-B of  FIG. 1A . 
         FIG. 3  is a cross-sectional view taken along line A-A of  FIG. 2 . 
         FIG. 4  depicts a partial schematic cross-sectional view illustrating a working tool of Embodiment 1 after a switch lock is turned counterclockwise. 
         FIG. 5  depicts a partial schematic cross-sectional view illustrating a working tool of Embodiment 1 after a lever is pressed down. 
         FIG. 6  is a cross-sectional view taken along line B-B of  FIG. 5 . 
         FIG. 7  is a transverse cross-sectional view of  FIG. 6 . 
         FIG. 8  depicts  FIG. 6  after a right push button is pressed down; 
         FIG. 9  is a transverse cross-sectional view of  FIG. 8 . 
         FIG. 10  is a cross-sectional view of a right push button of the working tool of Embodiment 1 in an unlocked state. 
         FIG. 11  is a cross-sectional view taken along line A-A of  FIG. 10 . 
         FIG. 12A  is an exploded view of a guard securing means in accordance with the present invention. 
         FIG. 12B  is a diagram illustrating the guard securing means in accordance with the present invention after it is assembled. 
         FIG. 13A  schematically illustrates how the guard securing means in accordance with the present invention is assembled. 
         FIG. 13B  depicts a guard having a snap ring formed thereon in accordance with the present invention. 
         FIG. 13C  depicts a front cover of the guard securing means in accordance with the present invention. 
         FIG. 14A  depicts the guard securing means in a secured state in accordance with the present invention. 
         FIG. 14B  is a top view of  FIG. 14A  in accordance with the present invention. 
         FIG. 14C  schematically illustrates how the orientation of the guard of the guard securing means is adjusted. 
         FIG. 14D  is a top view of  FIG. 14C . 
         FIG. 15  depicts how the guard securing means in accordance with the present invention is disassembled. 
         FIG. 16  is a partial schematic cross-sectional view illustrating a working tool in a locked state in accordance with Embodiment 2 of the present invention. 
         FIG. 17  is a cross-sectional view taken along line B-B of  FIG. 16 . 
         FIG. 18  is a cross-sectional view taken along line A-A of  FIG. 17 . 
         FIG. 19  depicts  FIG. 17  and  FIG. 18  after a lever moves upwards. 
         FIG. 20  is a cross-sectional view taken along line A-A of  FIG. 19 . 
         FIG. 21  is an enlarged view of part I of  FIG. 20 . 
         FIG. 22  depicts  FIG. 17  and  FIG. 18  after a right push button is pushed inwardly. 
         FIG. 23  is a cross-sectional view taken along line A-A of  FIG. 22 . 
         FIG. 24  is an enlarged view of part II of  FIG. 23 . 
         FIG. 25  depicts  FIG. 17  and  FIG. 18  after the engagement between engagement portions. 
         FIG. 26  is a cross-sectional view taken along line A-A of  FIG. 25 . 
         FIG. 27  is an enlarged view of part III of  FIG. 26 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will become more readily apparent and better understood as the following detailed description of preferred embodiments of the invention is considered in connection with the accompanying drawings. 
     Embodiment 1 
     Referring now to  FIGS. 1A and 1B , the present embodiment discloses a working tool including a housing  10 . A working mechanism  11  is disposed on a working portion of the housing  10  and configured to grind or polish a workpiece. In this embodiment, the working portion is located at the left end of the housing  10 . The working mechanism  11  is driven to work by a motor disposed within the housing  10 . A switch  9  is disposed within a handle portion of the housing  10 . In this embodiment, the handle portion is located at the right end of the housing  10 . The switch  9  is configured to activate or deactivate the motor. When the motor is activated, the working mechanism  11  is driven to grind or polish; or when the motor is deactivated, the working mechanism  11  stops its operation. A lever  3  is disposed under the switch  9  and has its left end connected to the housing  10 . When an operator presses down the lever  3 , the motor is activated. The lever  3  has a gap formed therein for accommodating a switch lock  1 , and the switch lock is disposed in this gap. The switch lock  1  has a rotating shaft inserted through a middle portion thereof and the rotating shaft has its two ends both connected to the lever  3 , thereby allowing the switch lock  1  to rotate about the rotating shaft. The rotating shaft is surrounded by a torsion spring  2 . The switch lock  1  includes a first portion extending out of the lever  3  and a second portion hiding in the housing  10 . The second portion of the switch lock  1  has a first engagement portion  1   a  extending outwardly on a right side thereof and a stopper portion  1   b  extending upwardly on a left side thereof. The lever  3  has a support portion  3   a  proximal to and engageable with the first engagement portion  1   a . With further reference to  FIG. 2 , the handle portion of the housing  10  is provided with a left push button  8  and a right push button  5  partially inserted therein from the left and right sides, respectively. The left push button  8  and the right push button  5  each has a first end horizontally protruding out of the housing  10  to act as a manipulation portion and a rest portion including a main body and a second end hiding in the housing  10 . The second end of the left push button  8  slidably fits in the second end of the right push button  5 , thereby allowing the left push button  8  to move horizontally towards the right push button  5  and the right push button  5  to move horizontally towards the left push button  8 . 
     In the present embodiment, the fitting between the second ends of the left and right push buttons may be accomplished by the following design. The second end of the left push button  8  defines third extension sections  8   b  each extending towards the right push button  5  and has a first sliding groove formed thereon. Similarly, the second end of the right push button  5  defines fourth extension sections  5   b  each extending towards the left push button  8  and has a second sliding groove formed thereon. Each of the third extension sections  8   b  has an end portion horizontally slidably disposed in a corresponding first sliding groove, and each of the fourth extension sections  5   b  has an end portion horizontally slidably disposed in a corresponding second sliding groove. The end portions of the third and fourth extension sections  8   b ,  5   b  can be hooked up when the working tool is in a locked state. 
     A reset mechanism is interconnected between the second ends of the left push button  8  and the right push button  5 . As illustrated, the reset mechanism may be disposed in a space defined by the third extension sections  8   b  and fourth extension sections  5   b . In the present embodiment, the reset mechanism includes: a reset spring  6  and a protrusion  12  extending from a central area of the second end of the left push button  8  towards the right push button  5 , wherein the reset spring  6  surrounds the protrusion  12 . 
     The main bodies of the left push button  8  and the right push button  5  in the housing  10  are formed with a first groove  8   a  and a second groove  5   a , respectively. Correspondingly, the lever  3  has a first extension section  3   a - 2  and a second extension section  3   a - 1  formed at its right end in correspondence with the positions of the first and second grooves  8   a  and  5   a , respectively. The first extension section  3   a - 2  and the second extension section  3   a - 1  extend in the first groove  8   a  and the second groove  5   a , respectively. The first groove  8   a  has a second left engagement portion  8   c  formed on its groove wall and the second groove  5   a  has a second right engagement portion  5   c  formed on its groove wall. The first extension section  3   a - 2  is provided with, at a side facing the second left engagement portion  8   c , a third left engagement portion  3   b - 1  engageable with the second left engagement portion  8   c ; and the second extension section  3   a - 1  is provided with, at a side facing the second right engagement portion  5   c , a third right engagement portion  3   b - 2  engageable with the second right engagement portion  5   c.    
     The working mechanism  11  of the present embodiment may include a grinding wheel  14  and a guard securing means  13  disposed spacedly around the grinding wheel  14 . The grinding wheel  14  can be driven to rotate by the motor. 
     Referring now to  FIGS. 12A and 12B , the guard securing means  13  may include a guard  13 - 1  disposed around the grinding wheel  14  and a front cover  13 - 6  coupled to the housing  10 . The guard  13 - 1  is provided with a snap ring  13 - 2  axially extending from a surface of the guard  13 - 1  opposite to the grinding wheel  14  in a direction departing from the grinding wheel  14 . The snap ring  13 - 2  is formed with protrusions e 1 , e 2 , e 3 , e 4 , and e 5  on the inner surface. Correspondingly, a top portion of the front cover  13 - 6  defines recesses g 1 , g 2 , g 3 , g 4 , and g 5  for engaging with the respective protrusions. The front cover  13 - 6  defines an outer circumstantial surface formed with an annular groove  13 - f , and the annular groove  13 - f  is also engageable with the protrusions. The snap ring  13 - 2  and the front cover  13 - 6  sandwich and fix a portion of a wrench  13 - 5  using an upper fixation plate  13 - 3  and screws  13 - 4  and leave a hanging tongue of the wrench  13 - 5  outside. The snap ring  13 - 2  is formed with stop notches  13 - b , and the wrench  13 - 5  is formed with a stop cog  13 - a  for engaging with one of the stop notches  13 - b . A spring  13 - 7  is disposed between the wrench  13 - 5  and an outer circumstantial surface of the front cover  13 - 6 . The guard  13 - 1  and the snap ring  13 - 2  are integrated as a whole  13 - 8  by welding. 
     Referring to  FIGS. 13A to 13C , the assembly of the guard can be accomplished by following the steps of: pushing down the wrench  13 - 5 ; aligning the protrusions e 1 , e 2 , e 3 , e 4 , and e 5  of the snap ring  13 - 2  with the corresponding recesses g 1 , g 2 , g 3 , g 4 , and g 5  of the front cover  13 - 6  and fitting the guard to the front cover  13 - 6 ; rotating the guard until the protrusions of the snap ring  13 - 2  are received in the annular groove  13 - f  of the front cover  13 - 6 ; further rotating the guard to a desired position; and releasing the wrench  13 - 5  such that the stop cog  13 - a  of the wrench  13 - 5  is inserted into a corresponding stop notch  13 - b  of the snap ring  13 - 2 , thereby preventing further rotation of the guard and finishing the assembly of the guard of the grinding wheel. 
     Referring to  FIGS. 14A to 14D , the securing and orientation adjustment of the guard can be accomplished by following the steps of: pushing the wrench  13 - 5  to make it slide along a sliding channel formed by a counter groove  13 - c  of the front cover  13 - 6  and the upper fixation plate  13 - 3  (which is fixed to the front cover  13 - 6  using the screws  13 - 4 ), until the stop cog  13 - a  of the wrench  13 - 5  becomes disengaged from the corresponding stop notch  13 - b  of the snap ring  13 - 2  (refer to t 1  of  FIG. 14D ); rotating the guard  13 - 1  until it is oriented at a desired angle; and after the guard  13 - 1  is adjusted in place, releasing the wrench  13 - 5 , so that the spring  13 - 7  will exert an elastic force which pushes the stop cog  13 - a  into the corresponding stop notch  13 - b  (refer to t 2  of  FIG. 14B ), thereby positioning the guard  13 - 1  and preventing its further rotation. 
     Referring to  FIG. 15 , the guard can be detached by pressing down the wrench  13 - 5 , rotating the guard  13 - 1  to a position corresponding to the front cover  13 - 6 , taking the guard  13 - 1  out, and releasing the wrench  13 - 5 . 
     Referring back to  FIG. 1B , when the working tool is in a locked state, the first engagement portion  1   a  firmly engages with the support portion  3   a  with the aid of the torsion spring  2 , and the stopper portion  1   b  is pushed tightly against a fixation member  10   a  disposed in the housing  10 . As such, an operator is unable to operate the lever  3 . Moreover, with further reference to both  FIG. 2  and  FIG. 3 , the end portions of the third and fourth extension sections  5   b ,  8   b  are hooked up, with the second left engagement portion  8   c  being disengaged from the third left engagement portion  3   b - 1  and the second right engagement portion  5   c  being disengaged from the third right engagement portion  3   b - 2 . 
     When to unlock the working tool, an operator needs to first rotate the switch  1  in the counterclockwise direction (as indicated by the arrow in  FIG. 4 ) with one hand to disengage the first engagement portion  1   a  from the support portion  3   a , accompanied with the departure of the stopper portion  1   b  from the fixation member  10   a . Generally, the left hand is used for a right-handed operator, and the right hand is used for a left-handed operator. 
     Next, the operator further needs to press the lever  3  in the direction as indicated by the arrow in  FIG. 5  with the other hand. Generally, the right hand is used for the right-handed operator, and the left hand is used for the left-handed operator. As such, with further reference to both  FIG. 6  and  FIG. 7 , the first extension section  3   a - 1  and second extension section  3   a - 2  move upwards with the lever  3 , thus causing the third left engagement portion  3   b - 1  and the third right engagement portion  3   b - 2  to move and stay over the second left engagement portion  8   c  and the second right engagement portion  5   c , respectively. Then, after the left-handed operator pushes, with the thumb of the left hand, the right push button  5  towards the left push button  8  in the direction as indicated by the arrow in  FIG. 8 , with further reference to  FIG. 9 , the second right engagement portion  5   c  will move and stay right under the third right engagement portion  3   b - 2 . As such, after the operator releases the lever  3 , which is accompanied with the downward movement of the third right engagement portion  3   b - 2  and thereafter its engagement with the second right engagement portion  5   c  as shown in  FIG. 10  and  FIG. 11 , the working tool will maintain an unlocked state without needing the operator to continuously press the lever  3  to keep the working tool in an operational state. It is to be understood that the right-handed operator can also make the working tool maintained in the unlocked state by pushing the left push button  8  towards the right push button  5  with the thumb of the right hand and then following the same subsequent steps, the detailed description of which is omitted for the sake of simplicity. 
     Furthermore, the operator can shut down the working tool, simply by pushing the lever  3  upwards to cause the third left engagement portion  3   b - 1  or the third right engagement portion  3   b - 2  to move upwards with the lever and thus become disengaged from the corresponding second left engagement portion  8   c  or second right engagement portion  5   c . After this occurs, affected by the reset spring  6 , the second left engagement portion  8   c  or the second right engagement portion  5   c  will be pushed and no longer stay right under the corresponding third left engagement portion  3   b - 1  or third right engagement portion  3   b - 2 . As such, after the operator releases the lever  3 , the lever  3  will return to the original position with the aid of the torsion spring  2 , the first engagement portions  1   a  will again engage with the support portion  3   a , and the stopper portion  1   b  will be pushed against the fixation member  10   a , thereby locking the working tool again. 
     Embodiment 2 
     As illustrated in  FIG. 16 , the present embodiment provides a working tool including a housing  10 . A working mechanism  11  is disposed on a working portion of the housing  10  and configured to grind or polish a workpiece. The working mechanism  11  is driven to work by a motor disposed within the housing  10 . A switch  9  for activating or deactivating the motor is disposed within a handle portion of the housing  10 . A lever  3  is disposed under the switch  9  and has one end connected to the housing  10 . The lever  3  has a gap formed therein for accommodating a switch lock  1 , and the switch lock is disposed in this gap. A resilient shaft is inserted through the switch lock  1  and has its two ends both connected to the lever  3 . The resilient shaft is surrounded by a torsion spring  2 . The switch lock  1  includes a first portion extending out of the lever  3  and a second portion hiding in the housing  10 . The second portion of the housing  10  has a first engagement portion defined thereon, and the lever  3  has a support portion  3   a  proximal to and engageable with the first engagement portion  1   a . With additional reference to  FIGS. 17 and 18 , the handle portion of the housing  10  is provided with a left push button  8  and a right push button  5  partially inserted therein from the left side and right side, respectively. The left push button  8  and the right push button  5  each has a first end horizontally protruding out of the housing  10  to act as a manipulation portion and a rest portion including a main body and a second end hiding in the housing  10 . The second end of the left push button  8  slidably fits in the second end of the right push button  5 , thereby allowing the left push button  8  to move horizontally towards the right push button  5  and the right push button  5  to move horizontally towards the left push button  8 . A reset mechanism is interconnected between the second ends of the left push button  8  and right push button  5 . The left push button  8  has a first extension portion  8   d  extending towards the lever  3  and the right push button  5  has a second extension portion  5   d  extending towards the lever  3 . The first extension portion  8   d  has an end portion defining a fourth engagement portion  8   d - 1 , and the second extension portion  5   d  has an end portion defining a fifth engagement portion  5   d - 1 . The fourth engagement portion  8   d - 1  and the fifth engagement portion  5   d - 1  are spacedly disposed opposing each other to form an engagement gap  15  between the first extension portion  8   d  and the second extension portion  5   d . The lever  3  has a fifth extension section  3   c  extending towards and partially inserted in the engagement gap  15 . The fifth extension section  3   c  has a sixth engagement portion  3   c - 1  in the engagement gap  15  and engageable with the fourth engagement portion  8   d - 1  or the fifth engagement portion  5   d - 1 . 
     Referring back to  FIG. 1 , when the working tool is in a locked state, the sixth engagement portion  3   c - 1  is disengaged from both of the fourth engagement portion  8   d - 1  and the fifth engagement portion  5   d - 1 . 
     As shown in  FIGS. 19 to 21 , when to unlock the working tool, an operator needs to first push the lever  3  upwards to cause the sixth engagement portion  3   c - 1  to move and stay over the fourth engagement portion  8   d - 1  and the fifth engagement portion  5   d - 1 . Next, with further reference to  FIGS. 22 to 24 , the operator further needs to inwardly push the right push button  5  or the left push button  8  to cause the fourth engagement portion  8   d - 1  or the fifth engagement portion  5   d - 1  to move towards and stop right under the sixth engagement portion  3   c - 1 . As such, with further reference to  FIGS. 25 to 27 , after the operator releases the lever  3 , the sixth engagement portion  3   c - 1  moves downwards and engages with the fourth engagement portion  8   d - 1  or the fifth engagement portion  5   d - 1 . 
     The rest of this embodiment has the same structure and works in the same way as that described in Embodiment 1.

Technology Classification (CPC): 1