Patent Publication Number: US-2016243633-A1

Title: Cutting tool

Description:
TECHNICAL FIELD 
     The present invention relates to a cutting tool, and particularly to a cutting tool that cuts a workpiece by reciprocating a blade. 
     BACKGROUND ART 
     A cutting tool such as a jigsaw known in the art performs cutting operations by converting the rotary motion of a motor serving as the drive source to reciprocal motion of a blade. One such cutting tool cuts the workpiece with a reciprocating blade as the main body of the tool is moved while a base attached to the main body remains in contact with the workpiece (for example, refer to Patent Literature 1 shown below). 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     Japanese Patent No. 4525532 
       FIG. 19  is a side elevation view showing the external appearance of a conventional jigsaw. The jigsaw  400  in  FIG. 19  includes a motor (not shown) built into a housing  401 . The jigsaw  400  converts the rotary motion of the motor to reciprocal motion of a blade  402 . A handle  403  is formed in the upper portion of the jigsaw  400 , and a trigger  404  is provided on the bottom of the handle  403  for switching the motor on and off. A base  405  is mounted on the bottom of the housing  401 . The operator grips the handle  403  and, with the bottom surface of the base  405  contacting the workpiece, pushes the body of the jigsaw  400  in a cutting direction. At this time, the base  405  slides over the workpiece in the cutting direction while the blade  402 , which is reciprocating up and down, cuts through the workpiece. 
     Although the jigsaw  400  can be used to cut a workpiece from its edge inward, in some cases the jigsaw  400  is needed to perform an interior cut. To perform an interior cut, the operator first forms a starter hole by executing a plunge cut to cut into the workpiece from above. Then, with the blade  402  inserted in the starter hole, the operator can cut a desired shape out of the interior of the workpiece.  FIG. 20  is an explanatory diagram illustrating a plunge cut performed with a conventional jigsaw. In this operation, the operator grips the handle  403 , tilts the top of the housing  401  forward, and places the tip of the cutting edge formed along the front of the blade  402  in contact with the starting point of the cut on a workpiece  500 . Next, the operator squeezes the trigger  404  to begin reciprocating the blade  402  so as to cut into the workpiece  500  and form a hole. 
     SUMMARY OF INVENTION 
     Technical Problem 
     When the jigsaw  400  described above is used to cut a flexible workpiece such as wood veneer, the weight of the body of the jigsaw  400  is transferred through the base  405  to cut sections of the workpiece to the rear of the blade  402 , deflecting the cut sections of the workpiece. When the jigsaw  400  makes a straight cut to cut the workpiece along a straight line, for example, the weight of the jigsaw  400  is received nearly equally on left and right cut sections, producing the same amount of deflection in each section. However, when the jigsaw  400  performs a curved cut to cut the workpiece along a curved line, the left and right cut sections receive differing amounts of weight, causing one side to deflect more than the other side and, thus, producing a level difference between the two cut sections along the cutting line. 
       FIG. 21  is a cross-sectional view of the base of the conventional jigsaw and the workpiece, and more specifically shows a cross section of the rear portion of the base  405 . Since the base  405  is placed on a left cut section  500 A of the workpiece in  FIG. 21 , the weight of the body of the jigsaw  400  is applied only to the left cut section  500 A through the base  405 . Consequently, a level difference δ 1  is produced along the cutting line  500 C in the workpiece between the left cut section  500 A and the right cut section  500 B. When the jigsaw  400  is performing a curved cut for cutting the workpiece along a line that curves further counterclockwise in this state, the operator directs the front of the jigsaw  400  leftward toward the cutting direction. When the front of the jigsaw  400  is moved leftward, the rear of the jigsaw  400  swings to the right, but the rear portion of the base  405  runs into and gets impeded by the right cut section  500 B due to the level difference δ 1  at the cutting line  500 C. Consequently, the operator must lift the rear of the jigsaw  400  over the right cut section  500 B. 
     Further, when beginning a plunge cut to initiate an interior cut as described above, the operator presses the front edge of the base  405  against the workpiece  500  in order to anchor the jigsaw  400  in position, as shown in  FIG. 20 . However, since the base  405  can slide over the workpiece  500 , the position of the body of the jigsaw  400  is not stable, making it difficult to form a starter hole. 
     In view of the foregoing, it is an object of the present invention to provide a cutting tool that can perform cutting operations smoothly, even when a level difference between cut sections is produced along the cutting line when executing a curved cut in a flexible workpiece. It is another object of the present invention to provide a cutting tool that can properly anchor the main body of the tool in the correct position when initiating a plunge cut. 
     Solution to Problem 
     In order to attain above and other object, the present invention provides a cutting tool that includes a housing; a motor; a plunger; a base; and a plate. The motor is accommodated in the housing. The plunger has an end portion to which a blade is attachable. The plunger is configured to be reciprocated by the motor. The base is attached to the housing. The base is configured to slidingly move along with the housing over a workpiece. The base has a base surface at a side opposite to the housing. The plate is detachably mounted on the base at a position on the base surface for facilitating a curved cut. The plate is formed of a resin. The plate has a length shorter than a length of the base surface in a cutting direction. The plate has a pawl for engagement with the base. 
     With this configuration, a plate is mounted on the base prior to performing a cutting operation in order to produce a gap equivalent to the thickness of the plate between the workpiece and the base surface. Therefore, even when a level difference is produced along the cutting line when performing a curved cut on a flexible workpiece, the base of the tool can turn along with the tool body in the direction of the curved cut without contacting the cut section on the outside of the curve that is raised higher than the cut section on the inside of the curve. This configuration improves the ease of operating the cutting tool since the operator need not perform annoying actions such as lifting the back of the tool body in order to turn the tool in the direction of cutting. 
     Preferably, the plate has a rear edge portion in the cutting direction. The rear edge portion is disposed below a gravitational center of a tool body assuming that the cutting tool is postured such that the base is disposed below the housing. 
     Since the weight of the tool body can be applied to the workpiece through the plate positioned beneath the gravitational center of the tool body in this configuration, the orientation of the tool can be stabilized when performing cutting operations with the plate mounted on the base, enabling accurate positioning without sacrificing ease of operations. 
     Preferably, the plate has a pawl for engaging with the base. 
     This configuration enables the plate to be fixed in position relative to the base and simplifies the operations for attaching the plate to and detaching the plate from the base. Accordingly, the plate can easily be attached or detached depending on the type of workpiece and the operation being performed, making the tool more user-friendly. 
     Preferably, the base has a front edge portion in the cutting direction. The plate has a front edge portion in the cutting direction at which the pawl is provided to engage with the front edge portion of the base so as to detachably fix the plate to the base. 
     With this construction, the position of the plate is reliably fixed relative to the base, and the pawl on the plate does not contact the workpiece when the plate is being moved over the workpiece during a cutting operation. Accordingly, the tool body can be moved smoothly, enabling a trouble-free cutting operation. 
     Preferably, the base has a side surface. The plate has a rear edge portion in the cutting direction at which the pawl is provided to engage with the side surface of the base so as to detachably fix the plate to the base. 
     With this construction, the position of the plate is reliably fixed relative to the base, and the pawl on the plate do not contact the workpiece when the plate is being moved over the workpiece during a cutting operation. Accordingly, the tool body can be moved smoothly, enabling a trouble-free cutting operation. 
     Preferably, the side surface of the base is formed with a groove for engagement with the pawl. 
     With this configuration, the pawl does not protrude outward from the side surface of the base. Accordingly, the pawl does not contact the workpiece when the plate is being moved over the workpiece during a cutting operation, enabling smooth moving over the workpiece. 
     Preferably, the plate is fixed to the base with a screw. 
     With this configuration, the plate can be reliably fixed relative to the base without providing any pawls on the plate. 
     Preferably, the base has a front portion in the cutting direction formed with an insertion space for allowing passage of the blade. The insertion space is generally U-shaped opened at the front edge portion. The plate is formed in generally U-shape for covering the front edge portion of the base surface. 
     This configuration can stabilize the orientation of the tool body without interfering with the reciprocating blade. 
     Preferably, the plate includes a plate body, and a pair of protruding parts. The pair of protruding parts is extendible rearward from the plate body in the cutting direction and retractable into the plate body. 
     With this configuration, the protruding parts can be extended outward when performing a straight cut to stabilize the orientation of the tool body, and can be retracted when performing a curved cut to prevent the rear of the base from contacting the workpiece. Accordingly, the plate can be left mounted on the base while changing the state of the protruding parts between their extended state or retracted state according to the type of workpiece and operation being performed. Thus, this configuration improves the ease and effectiveness of operations. 
     Preferably, the base is formed of a steel material. 
     This configuration stabilizes the orientation of the tool body and suppresses friction generated between the workpiece. Accordingly, this configuration enables a trouble-free cutting operation. 
     Preferably, the plate is formed of a resin. 
     This configuration prevents the surface of the workpiece from being scratched or damaged when the plate is being moved over the workpiece. Accordingly, this configuration makes the tool more user-friendly. 
     Preferably, the plate has a contact surface configured to contact the workpiece. The contact surface is coated with a friction-reducing agent. 
     This configuration suppresses friction generated between the workpiece, enabling a trouble-free cutting operation. 
     Preferably, the cutting tool further includes an antislip part. The antislip part is provided on a front edge portion of the plate. 
     With this configuration, the antislip part can be placed in contact with the workpiece when initiating a plunge cut in order to reliably position and anchor the tool body. Accordingly, the tool can form a starting hole with great precision, thereby further improving the ease and effectiveness of operations. 
     According to another aspect, another aspect provides a cutting tool that includes: a housing; a motor; a plunger; a base; and an antislip part. The motor is accommodated in the housing. The plunger has an end portion to which a blade is attachable. The plunger is configured to be reciprocated by the motor. The base is attached to the housing. The base has a base surface in an opposite side from the housing and a front edge portion in a cutting direction. The base is configured to slide over a workpiece. The antislip part is provided on the front edge portion of the base. 
     With this configuration, the antislip part can be placed in contact with the workpiece when initiating a plunge cut in order to reliably position and anchor the tool body. Accordingly, the tool can form a starting hole with great precision, thereby improving the ease of operations. 
     Preferably, the antislip part has a slope portion. The slope portion protrudes from the front edge portion of the base toward the housing and slopes rearward in the cutting direction. 
     With this constraction, the upper part of the antislip part is placed in contact with the workpiece, thereby enabling the blade to be placed in contact with a cutting start position on the workpiece and reliably positioning the tool body. Accordingly, the cutting tool with this construction can form a starting hole with great precision. 
     Preferably, the antislip part is formed of an elastically deformable material. 
     With this construction, the antislip part on the plate can be pressed against the workpiece regardless of the type and shape of the workpiece in order to reliably anchor the tool body in position. Thus, this construction enhances the versatility of the cutting tool and improves its ease of operations. 
     Preferably, the antislip part has a higher coefficient of friction than the base surface. 
     With this configuration, the antislip part can be reliably fixed without slipping over the workpiece. Accordingly, the cutting tool with this configuration can be reliably anchored, thereby enabling the cutting tool to form a starting hole with great precision. 
     Preferably, the cutting tool further includes a plate. The plate is detachably mounted on the base in a position on the base surface and having a front edge portion in the cutting direction. The antislip part is provided on the front edge portion of the plate. 
     By mounting the plate on the base prior to performing cutting operations with the cutting tool having this configuration, the tool can be slid over the workpiece without scratching or damaging the surface of the workpiece, thereby improving convenience. Further, the tool body can be fixed in position by placing the antislip parts in contact with the workpiece, thereby reliably positioning the tool body for a plunge cut while the plate remains mounted on the base. Accordingly, the cutting tool with this configuration can form a starting hole with great precision, further improving the effectiveness of operations. 
     Preferably, the plate has a plate surface at a side opposite to the housing. The antislip part provides a coefficient of friction higher than that of the plate surface. 
     With this configuration, the antislip part can be reliably fixed without slipping over the workpiece. Accordingly, the cutting tool with this configuration can be reliably anchored, thereby enabling the cutting tool to form a starting hole with great precision. 
     Advantageous Effects of Invention 
     With the cutting tool according to the present invention, a cutting operation can be performed smoothly even when executing a curved cut on a flexible workpiece. Further, with the cutting tool according to the present invention, the tool body can be reliably anchored when initiating a plunge cut, thereby enabling a cutting operation with great precision. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side elevation view showing an external appearance of a jigsaw according to a first embodiment of the present invention; 
         FIG. 2  is a center cross-sectional view showing an internal structure of the jigsaw according to the first embodiment of the present invention; 
         FIG. 3  is a bottom view of a base when a plate is mounted on the base used in the jigsaw according to the first embodiment of the present invention; 
         FIG. 4  is a top view of the plate in the jigsaw according to the first embodiment of the present invention; 
         FIG. 5  is a side view of the plate in the jigsaw according to the first embodiment of the present invention; 
         FIG. 6  is a rear view of the plate in the jigsaw according to the first embodiment of the present invention; 
         FIG. 7  is a side elevation view of the jigsaw according to the first embodiment of the present invention when sliding parts are extended; 
         FIG. 8  is a bottom view of the base in the jigsaw according to the first embodiment of the present invention when the sliding parts are extended; 
         FIG. 9  is a cross-sectional view along a line A-A in  FIG. 7 ; 
         FIG. 10  is an explanatory diagram illustrating a curved cut performed by the jigsaw according to embodiments of the present invention on a workpiece; 
         FIG. 11  is a cross-sectional view along a line B-B in  FIG. 10 ; 
         FIG. 12  is an explanatory diagram illustrating a plunge cut performed by the jigsaw according to the first embodiment of the present invention; 
         FIG. 13  is an explanatory diagram illustrating the plunge cut performed by the jigsaw according to the first embodiment of the present invention; 
         FIG. 14  is an explanatory diagram illustrating the plunge cut performed by the jigsaw according to the first embodiment of the present invention; 
         FIG. 15  is a bottom view of a base used in a jigsaw according to a second embodiment of the present invention; 
         FIG. 16  is a side elevation view showing an external appearance of a jigsaw according to a third embodiment of the present invention; 
         FIG. 17  is a bottom view of a base when a plate is mounted on the base used in the jigsaw according to the third embodiment of the present invention; 
         FIG. 18  is a side elevation view showing an external appearance of a jigsaw according to a fourth embodiment; 
         FIG. 19  is a side elevation view showing an external appearance of a conventional jigsaw; 
         FIG. 20  is an explanatory diagram illustrating a plunge cut performed with a conventional jigsaw; and 
         FIG. 21  is a cross-sectional view of a base of a conventional jigsaw and a workpiece. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, embodiments of the present invention will be described while referring to the accompanying drawings. In the examples described below, the present invention is applied to a jigsaw. 
     First, a jigsaw  1  according to a first embodiment of the present invention will be described with reference to  FIGS. 1 through 14 .  FIG. 1  is a side elevation view showing the external appearance of the jigsaw  1 .  FIG. 2  is a center cross-sectional view showing the internal structure of the jigsaw  1 . The jigsaw  1  is primarily configured of a housing  2 , a motor  3 , a gear cover  4 , a motion-converting mechanism  5 , and a blade  6 . The jigsaw  1  is a cutting tool that cuts a workpiece (not shown) with the blade  6 . In the following description, the direction in which the motion-converting mechanism  5  is disposed relative to the motor  3  will be defined as the forward direction, while the opposite direction will be defined as the rearward direction. Further, the direction in which the blade  6  extends from a base  41  described later will be defined as the downward direction, while the opposite direction will be defined as the upward direction. A cutting edge  6 A is formed on the front of the blade  6  for cutting workpieces. Thus, the forward direction will be called the cutting direction. 
     The housing  2  is constructed of a frame formed of resin or the like. A handle  21  is provided on the top of the housing  2  and is the member that is gripped by the operator. An opening is formed in the front of the housing  2 , and a cover is provided over the opening. The motor  3  is accommodated in the housing  2  beneath the handle  21 . The gear cover  4  is also accommodated in the housing  2  at a position in proximity to the motor  3 . A power cable  26  is provided in the rear portion of the housing  2  so as to extend rearward therefrom. A trigger switch  22  is provided on the front portion of the handle  21 . The trigger switch  22  has a trigger  22 A that the operator operates to control the supply of power to the motor  3 . 
     The motor  3  is primarily provided with an output shaft  31  extending in the front-rear direction, and a fan  32 . A pinion gear  31 A is provided on the distal end (front end) of the output shaft  31 . The fan  32  is provided to the rear of the pinion gear  31 A and is coaxially fixed on the output shaft  31 . The fan  32  draws cooling air into the housing  2  through an air intake (not shown) formed in the housing  2  in order to cool the motor  3 , motion-converting mechanism  5 , and the like. 
     A base  41  is attached to the bottom portion of the gear cover  4 . The base  41  has a base material of aluminum, steel or the like, and is formed in a general rectangular shape. The gear cover  4  accommodates the motion-converting mechanism  5 . The gear cover  4  is provided with an orbital mechanism  9  that implements what is known as orbital action for swiveling the blade  6  in association with rotation of the motor  3 . 
     The base  41  is fixed to the bottom-surface side of the housing  2  by a bolt  42 , with the longitudinal dimension of the base  41  aligned in the cutting direction. The bottom surface of the base  41  opposite the housing  2  is defined as a base surface  41 A that confronts the workpiece. A plate  7  is provided beneath the front side of the base  41 . The plate  7  is formed of a thermoplastic such as polyacetal (POM). The plate  7  is detachably mounted on the base  41  in a position on the base surface  41 A of the base  41 . Antislip parts  8  are provided on the front edge of the plate  7 . The antislip parts  8  are formed of an elastically deformable material and have a higher coefficient of friction than the base  41  and plate  7 . 
     Here, the shapes of the base  41 , plate  7 , and antislip parts  8  will be described in greater detail with reference to  FIGS. 2 through 9 .  FIG. 3  shows the base surface  41 A when the plate  7  is mounted on the base  41 . An insertion space  41 B is formed in the front side of the base  41  and has a general U-shape that is open on the front side for allowing passage of the blade  6 . The blade  6  extends downward through the insertion space  41 B. As shown in  FIGS. 2 and 9 , the base  41  also has a center portion  41 C that is shaped like a hollow semicircular column. The base  41  is fixed to the housing  2  at the center portion  41 C by the bolt  42 . As shown in  FIG. 2 , guide holes  41 F are respectively formed in the pair of front-end portions of the base  41  that extend forward on either side of the insertion space  41 B. The guide holes  41 F penetrate the respective front-end portions from their side surfaces to the insertion space  41 B and function to receive guide members (not shown) in a direction orthogonal to the cutting direction. 
     The plate  7  has a plate body  7 A formed in a plate shape with a thickness S.  FIGS. 4, 5, and 6  respectively show top, side, and rear views of the plate  7 . The plate body  7 A is formed in a general U-shape for covering the front end of the base  41  and is shorter than the base  41  in the longitudinal direction. Thus, an insertion space is formed in the front section of the plate  7  for allowing passage of the blade  6 . As shown in  FIG. 2 , the rear edge of the plate body  7 A reaches a position approximately below the center of gravity G of the jigsaw  1 . 
     The plate  7  also has front pawls  7 B and  7 C respectively provided on the two front ends of the plate body  7 A that extend forward, and rear pawls  7 D and  7 E provided on both side surfaces of the plate body  7 A at the rear edge of the same. The front pawls  7 B and  7 C protrude upward from the front edge of the plate body  7 A, and then slope further upward toward the rear. The front pawls  7 B and  7 C are provided with small protrusions  7   b  and  7   c  that protrude toward the base  41  (rearward). When the plate  7  is mounted on the base  41 , the small protrusions  7   b  and  7   c  are inserted into recessed parts formed in the front edge of the base  41 . The rear pawls  7 D and  7 E protrude upward from the side surfaces of the plate  7  at the rear edge of the same. The rear pawls  7 D and  7 E are provided with small protrusions  7   d  and  7   e  that protrude toward the interior of the base  41 . The plate  7  is mounted on the base  41  so that the plate body  7 A is positioned on the base surface  41 A, by engaging the front pawls  7 B and  7 C with the pair of front-end portions of the base  41  that extend forward and by engaging the rear pawls  7 D and  7 E with the side surfaces of the base  41 . A step is formed in the top surface of the base  41  at the position corresponding to the rear pawls  7 D and  7 E so that the front portion of the base  41  is higher than the rear portion. When the plate  7  is mounted on the base  41 , the small protrusions  7   d  and  7   e  of the corresponding rear pawls  7 D and  7 E abut the step, preventing the plate  7  from being pulled forward off the base  41 . In other words, the plate  7  holds the base  41  in the longitudinal direction by gripping the base  41  with the front pawls  7 B and  7 C and the small protrusions  7   d  and  7   e . The plate  7  also holds the base  41  in the lateral direction orthogonal to the longitudinal direction by gripping the base  41  with the rear pawls  7 D and  7 E and the small protrusions  7   b  and  7   c . When the plate  7  is mounted on the base  41 , the bottom surface of the plate  7  becomes the surface that contacts the workpiece. In order to reduce friction generated between the plate  7  and the workpiece, the bottom surface of the plate  7  is coated with a friction-reducing agent. 
     The plate  7  also includes a pair of sliding parts  7 F and  7 G that can be extended rearward from the rear edge of the plate body  7 A and can be retracted into the plate body  7 A.  FIG. 7  shows a side elevation view of the jigsaw  1  when the sliding parts  7 F and  7 G are extended.  FIG. 8  shows the base surface  41 A of the base  41 .  FIG. 9  is a cross-sectional view along a line A-A in  FIG. 7 . The sliding parts  7 F and  7 G are shaped like strips and are accommodated in the plate body  7 A, as shown in  FIG. 3 . Grooves  7 H and  7 I are respectively formed in the rear ends of the corresponding sliding parts  7 F and  7 G. The operator can grip the grooves  7 H and  7 I with fingers to pull the sliding parts  7 F and  7 G rearward from the plate body  7 A. When the plate  7  is mounted on the base  41  and the sliding parts  7 F and  7 G are protruding from the plate body  7 A, the rear ends of the sliding parts  7 F and  7 G are positioned slightly forward of the rear edge of the base  41 , as shown in  FIG. 8 . When the jigsaw  1  is operated while the sliding parts  7 F and  7 G are extended, the surfaces of the sliding parts  7 F and  7 G opposite the housing  2  side contact the workpiece. In order to reduce friction generated between the sliding parts  7 F and  7 G and the workpiece, the surfaces of the sliding parts  7 F and  7 G on the opposite side from the housing  2  are coated with a friction-reducing agent. 
     The antislip parts  8  are provided on the top of the front pawls  7 B and  7 C, respectively. The bottom edges of the antislip parts  8  are positioned higher than the bottom surface of the plate body  7 A. The antislip parts  8  are shaped so as to protrude first upward and then slope upward toward the rear, and have a higher coefficient of friction than that of the base surface  41 A of the base  41  and the plate  7 . 
     Returning to  FIG. 2 , the motion-converting mechanism  5  is primarily configured of a gear  51 , a weight  52 , an engaging pin  53 , and a plunger  54 . The gear  51  is engaged with the pinion gear  31 A and is rotatably supported in the gear cover  4  by a support shaft  50  extending forward from the gear cover  4 . The weight  52  is disposed in front of the gear  51  and is supported on the support shaft  50 . The weight  52  functions as a counterweight to the plunger  54  by moving in the direction opposite the plunger  54  in order to reduce vibrations during operations of the jigsaw  1 . 
     The engaging pin  53  is provided forward of the weight  52  and rotates about the support shaft  50  together with the gear  51 . The engaging pin  53  protrudes forward so as to be parallel to but not aligned with the output shaft  31 . 
     The plunger  54  has a general columnar shape and extends in a direction orthogonal to the output shaft  31  (vertical direction). The plunger  54  is supported in the housing  2  so as to be rotatable and vertically reciprocal. Specifically, the plunger  54  can rotate about a shaft oriented in the left-right direction (a rotational shaft  44  described later). The plunger  54  is provided with a pin receiving part  54 A, and a blade retaining part  54 B. 
     The pin receiving part  54 A is provided in the approximate vertical center of the plunger  54 . The pin receiving part  54 A has a general U-shape in a side view, with the opening of the “U” facing rearward. The pin receiving part  54 A is elongated in the left-right direction. The engaging pin  53  is inserted into a groove formed in the pin receiving part  54 A. The engaging pin  53  is permitted to move in the left and right directions within the groove of the pin receiving part  54 A, but is restricted from moving vertically. Accordingly, the pin receiving part  54 A moves only vertically in response to vertical movement of the engaging pin  53 . In this way, the motion-converting mechanism  5  can convert rotary motion outputted from the output shaft  31  to up-down linear motion. As will be described later, the pin receiving part  54 A is formed with sufficient depth to be able to retain the engaging pin  53  as the plunger  54  rotates about a rotational shaft  44 . 
     The blade retaining part  54 B is provided on the bottom end of the plunger  54 . The blade retaining part  54 B holds the blade  6  that is detachably mounted therein. In a plan view, the center of the plunger  54  is substantially aligned with the center position of the blade  6 . 
     A plunger guide  43  supports the plunger  54  at its approximate vertical center region so that the plunger  54  can slide vertically. The top of the plunger guide  43  is rotatably supported in the gear cover  4  so that the plunger guide  43  can revolve about the rotational shaft  44  oriented in the left-right direction. When the plunger guide  43  revolves about the rotational shaft  44 , the plunger  54  and blade  6  also revolve about the rotational shaft  44 . In this way, the plunger  54  and blade  6  can follow the orbital motion of the orbital mechanism  9 . 
     The orbital mechanism  9  is primarily provided with a roller holder  91 , a roller  92 , and a switching part  93 . As shown in  FIG. 2 , the roller holder  91  has a general L-shape in a side view and is rotatably supported on the gear cover  4  about a support part  94 . The roller  92  is positioned in the front end of the roller holder  91  and is rotatably supported therein. The roller  92  has a groove formed around its entire circumferential surface that is recessed radially inward. The roller  92  contacts the rear surface of the blade  6  with the blade  6  positioned in the groove. The degree of orbital motion performed by the orbital mechanism  9  can be adjusted with the switching part  93 . 
     Next, the operations of the jigsaw  1  will be described. The power cable  26  is connected to a commercial power supply (not shown). The motor  3  rotates when the operator pulls the trigger  22 A. The motion-converting mechanism  5  converts the rotation of the motor  3  from rotary motion to reciprocal motion and transfers this motion to the plunger  54  and blade  6 , causing the blade  6  to move up and down. At the same time, the roller holder  91  rotates about the support part  94 . The roller  92  presses against the blade  6 , causing the blade  6  to pivot about the rotational shaft  44 . Through the up-down movement of the blade  6  and rotation of the roller holder  91 , the distal end of the blade  6 , i.e., the cutting edge  6 A, moves along a substantially elliptical path (orbital motion). The jigsaw  1  halts when the operator releases the trigger  22 A. 
     When the jigsaw  1  having the configuration described above is operated to perform a straight cut in a workpiece beginning from the peripheral edge of the workpiece and when the workpiece is formed of a material that cuts easily and smoothly or when smoothness is not critical, the cutting operation is preferably performed without the plate  7  being mounted on the base  41 . The operator grips the handle  21  of the jigsaw  1  and places the front-end portion of the base surface  41 A on the workpiece, with the cutting edge  6 A of the blade  6  in contact with a cutting start position on the peripheral edge of the workpiece. Next, the operator squeezes the trigger  22 A and pushes the body of the jigsaw  1  in the cutting direction so that the workpiece is cut by the reciprocating blade  6 . At this time, the base surface  41 A slides over the workpiece in the cutting direction. Since the jigsaw  1  is operated while the entire base surface  41 A is pressed against the workpiece, the orientation of the tool body is stable and can slide smoothly over the workpiece with little friction. Accordingly, a precise cut can be made in the workpiece. 
     In order to perform a straight cut without damaging the workpiece, it is preferable to first mount the plate  7  on the base  41  and to perform the cutting operation after extending the sliding parts  7 F and  7 G from the plate body  7 A. In this case, the plate body  7 A and the sliding parts  7 F and  7 G slide over the workpiece. Accordingly, the orientation of the tool body is stabilized, enabling the jigsaw  1  to cut the workpiece with good precision. Further, since the bottom surface of the plate body  7 A and the surfaces of the sliding parts  7 F and  7 G that contact the workpiece have been precoated with a friction-reducing agent, the jigsaw  1  can slide more smoothly over the workpiece, cutting smoothly through the workpiece without leaving a rough cut. 
     On the other hand, when performing a curved cut in a workpiece, and particularly on a flexible workpiece such as wood veneer, it is preferable to mount the plate  7  on the base  41  and to execute the cutting operation with the sliding parts  7 F and  7 G withdrawn into the plate body  7 A. Curved cuts performed using the jigsaw  1  will be described next with reference to  FIGS. 10 and 11 .  FIG. 10  is an explanatory diagram illustrating a curved cut performed by the jigsaw  1  on a workpiece  100 .  FIG. 11  is a cross-sectional view along a line B-B in  FIG. 10 . 
     Prior to performing the cutting operation, the operator mounts the plate  7  on the base  41  of the jigsaw  1 . To mount the plate  7 , the operator first places the front pawls  7 B and  7 C against the front edge of the base  41 , with the small protrusions  7   b  and  7   c  inserted into the recessed parts formed in the front edge of the base  41 , and subsequently rotates the plate  7  so that the rear pawls  7 D and  7 E move toward the base  41 . When the small protrusions  7   d  and  7   e  of the rear pawls  7 D and  7 E contact the bottom surface of the base  41 , the rear pawls  7 D and  7 E elastically deform by expanding outward so that the small protrusions  7   d  and  7   e  slide up along the side surfaces of the base  41 . Once the small protrusions  7   d  and  7   e  pass the top edge of the base  41  next to the step formed in the top edge, the rear pawls  7 D and  7 E return to their original shapes, with the small protrusions  7   d  and  7   e  contacting the step. At this time, the plate  7  is fully mounted. Note, for this operation it is preferable that the sliding parts  7 F and  7 G are not extended from the plate body  7 A but are retracted therein. 
     With the plate  7  in this state, the operator grips the handle  21  of the jigsaw  1  and places the front-end portion of the plate body  7 A, and specifically the surface of the plate body  7 A on the side opposite the housing  2  on the workpiece  100 , with the cutting edge  6 A of the blade  6  contacting a cutting start position  100 S on the peripheral edge of the workpiece  100 . Next, the operator pushes the body of the jigsaw  1  in the cutting direction so that the workpiece is cut by the vertically reciprocating blade  6 . At this time, the bottom surface of the plate body  7 A slides over the workpiece  100 . The rear edge of this bottom surface is positioned slightly rearward than the position directly beneath the center of gravity G of the body of the jigsaw  1  but approximately beneath the center of gravity G. Hence, the weight of the body is applied to the workpiece  100  through the bottom surface of the plate body  7 A. This arrangement not only stabilizes the orientation of the jigsaw  1  so that its body does not wobble, but also shortens the length of the bottom surface on the plate body  7 A relative to the base  41 . Further, the rear portion of the base surface  41 A on the base  41  is higher than the bottom surface on the plate body  7 A by the thickness δ of the plate body  7 A, as illustrated in  FIG. 1 . Consequently, the base surface  41 A of the base  41  does not contact the workpiece  100 , as a gap corresponding to the thickness δ of the plate body  7 A is formed between the two. 
     As the cutting operation progresses, deflection begins to appear in cut sections  100 A and  100 B of the workpiece  100 . When the cutting operation has proceeded to the point shown in  FIG. 10 , the cut section  100 A of the workpiece  100  is deflected by the weight of the body of the jigsaw  1  and the pressure applied by the operator via the plate body  7 A in contact with the cut section  100 A. On the other hand, very little weight and pressure is applied to the cut section  100 B. Thus, the deflection in the cut section  100 B is smaller than that produced in the cut section  100 A. As a result, a level difference δ 1  is produced along the cutting area  100 C between the cut sections  100 A and  100 B of the workpiece  100 , as illustrated in  FIG. 11 . 
     If the operator directs the front of the jigsaw  1  in this state leftward in  FIG. 10  in order to cut a curved line that curves further counterclockwise in the workpiece  100 , the rear end of the jigsaw  1  will swing to the right in  FIG. 10 . However, since a gap equivalent to the thickness δ of the plate body  7 A is formed between the rear portion of the base  41  and the workpiece  100  as described above, the rear end of the base  41  will not contact the cut section  100 B if the thickness δ is greater than the level difference δ 1  produced at the cutting area  100 C. Therefore, the jigsaw  1  can perform the cutting operation while smoothly adjusting the direction in which its body advances. 
     Thus, the jigsaw  1  can perform a smooth cutting operation for a curved cut in a workpiece, even when a level difference is generated at the cutting area. 
     Next, an example of performing a plunge cut in the workpiece  100  with the jigsaw  1  will be described with reference to  FIGS. 12 through 14 . A plunge cut in this description is an operation performed to begin cutting from an interior position of the workpiece, i.e., a position not on the peripheral edge of the workpiece. 
     Prior to performing a plunge cut, the operator mounts the plate  7  on the base  41  of the jigsaw  1 . Next, the operator grips the handle  21  and tilts the top of the tool body forward, as illustrated in  FIG. 12 . The operator then presses the antislip parts  8  provided on the front edge of the plate  7  against the workpiece  100  and places the tip of the cutting edge  6 A on the front of the blade  6  in contact with the cutting start position. As described above, the antislip parts  8  have a higher coefficient of friction than the base  41  and plate  7  and are formed of a material that is both elastically deformable and shaped to slope upward toward the rear. Accordingly, the material and configuration of the antislip parts  8  prevent the antislip parts  8  from sliding over the workpiece  100 , regardless the shape of the cutting start position. 
     With the antislip parts  8  pressed against the workpiece  100 , the operator squeezes the trigger  22 A, causing the blade  6  to reciprocate as the jigsaw  1  begins cutting into the workpiece  100 . As the blade  6  continues to reciprocate, the back end of the jigsaw  1  slowly lowers as the body of the jigsaw  1  rotates about the antislip parts  8 , forming a hole in the workpiece  100 , as illustrated in  FIG. 13 . 
     Once the starter hole has been formed, the operator grips the handle  21  and, with the bottom surface of the plate  7  in contact with the workpiece  100 , pushes the body of the jigsaw  1  in the cutting direction, thereby cutting the workpiece  100  with the reciprocating blade  6 , as illustrated in  FIG. 14 . Since the antislip parts  8  are positioned above the bottom surface of the plate  7 , the antislip parts  8  do not contact the workpiece  100  at this time, enabling the bottom surface of the plate  7  to slide over the workpiece  100 . Accordingly, the cutting operation performed on the workpiece can be continued after forming the starter hole, without having to remove the plate  7 . 
     Since the blade  6  of the jigsaw  1  can be accurately positioned during a plunge cut for forming a starter hole and the jigsaw  1  can continue cutting operations after the starter hole has been formed, as described above, the jigsaw  1  according to the embodiment can perform interior cutting operations smoothly and rapidly. 
     Since the plate  7  is detachably mounted on the base surface  41 A of the base  41 , as described above in the present embodiment, the jigsaw  1  can be moved smoothly over the workpiece during curved cuts, even when a level difference is produced between cut sections of the workpiece along the cutting area, by mounting the plate  7  on the base  41  before beginning the cutting operation so that the rear of the base  41  does not come into contact with a cut section of the workpiece. Therefore, the jigsaw  1  according to the embodiment improves the ease of operations. Further, since the plate  7  is fixed to the base  41  with pawls  7 B,  7 C,  7 D, and  7 E, the plate  7  can easily be mounted and removed according to the type of workpiece being cut and the type of cutting operation, without the need of a tool or the like, thereby improving user-friendliness. Further, the antislip parts  8  provided on the front edge of the plate  7  can hold the jigsaw  1  in a fixed position without slipping over the workpiece  100 , thereby precisely positioning the jigsaw  1  for a plunge cut when performing an interior cutting operation. Therefore, interior cutting operations can be performed smoothly and with good precision, further improving operational efficiency. 
     Next, a jigsaw according to a second embodiment of the present invention will be described with reference to  FIG. 15 . The second embodiment differs from the first embodiment in the shape of the base. The remaining structure of the jigsaw in the second embodiment is identical to that in the first embodiment, and like parts and components are designated with the same reference numerals to avoid duplicating description. 
       FIG. 15  shows the surface of a base  141  used in the jigsaw according to the second embodiment of the present invention. In the second embodiment, a pair of grooves  141 D and  141 E is formed in the front-rear center region of the base  141 , with one formed in each side edge at opposing positions. The grooves  141 D and  141 E are formed at positions corresponding to the rear pawls  7 D and  7 E provided on the side surfaces of the plate  7  at the rear edge thereof and are capable of engaging with the rear pawls  7 D and  7 E. 
     By forming the base  141  as described above, the rear pawls  7 D and  7 E can engage with the base  141  without protruding outward from the side surface of the same. This configuration prevents the rear pawls  7 D and  7 E from contacting the workpiece when performing a cutting operation with the plate  7  mounted on the base  141 . Therefore, the jigsaw according to the second embodiment can smoothly move over the workpiece and, hence, can smoothly cut the workpiece. 
     Next, a jigsaw according to a third embodiment of the present invention will be described with reference to  FIGS. 16 and 17 . The third embodiment differs from the embodiments described above in the shape of the plate. The remaining structure of the jigsaw according to the third embodiment is identical to the previous embodiments, and like parts and components are designated with the same reference numerals to avoid duplicating description. 
       FIG. 16  is a side elevation view showing the external appearance of a jigsaw  201  according to the third embodiment of the present invention, and  FIG. 17  shows the base surface  41 A in the jigsaw  201 . A plate  207  is fixed to the base  41  with screws  271 . In the third embodiment, the plate  207  has a pair of pawls  207 B and  207 C on its front edge, but is not provided with pawls on its side surfaces at the rear edge, unlike in the embodiments described above. 
     By securing the plate  207  to the base  41  with screws, as described above, the plate  207  can be fastened to the base  41  without requiring pawls on its side surface, thereby preventing the plate  207  from contacting the workpiece during a cutting operation performed with the plate  207  mounted on the base  41 . Accordingly, the jigsaw  201  according to the third embodiment can move smoothly over the workpiece and can cut the workpiece smoothly. 
     Note that while the pawls  207 B and  207 C are provided on the front end of the plate  207  in the third embodiment, a structure that omits the pawls  207 B and  207 C is also possible. In such a case, the antislip parts  8  should be provided on the front edge of the base  41 , as will be described in a fourth embodiment. 
     Next, a jigsaw according to the fourth embodiment of the present invention will be described with reference to  FIG. 18 . The fourth embodiment differs from the embodiments described above in that the antislip parts are provided on the base itself. The remaining structure of the jigsaw is identical to the embodiments described above, and like parts and components are designated with the same reference numerals to avoid duplicating description. 
       FIG. 18  is a side elevation view showing the external appearance of a jigsaw  301  according to the fourth embodiment of the present invention. As shown in  FIG. 18 , antislip parts  308  are directly fixed to the front edge of a base  341 . With this configuration, a plunge cut can be performed in a workpiece to form a starter hole, without having to mount a plate  7  provided with antislip parts  8  on the base  341 , enabling the operator to perform cutting operations more rapidly during interior cutting operations requiring only straight cuts in workpieces that are not easily damaged, for example. Further, by fastening a plate having no pawls to the surface of the base  341  using screws, the jigsaw  301  of the fourth embodiment can also perform operations that require a plate. 
     By configuring the antislip parts  8  not to protrude toward the workpiece side of the sliding surface (bottom surface of the base  41  or bottom surface of the plate  7 ) as described above, the antislip parts  8  can facilitate smooth, quick cutting operations during normal cuts and can function to prevent slipping during interior cuts. 
     REFERENCE SIGNS LIST 
     
         
           1  jigsaw 
           2  housing 
           3  motor 
           4  gear cover 
           6  blade 
           6 A cutting edge 
           7  plate 
           7 A plate body 
           7 B,  7 C front pawl 
           7 D,  7 E rear pawl 
           7 F,  7 G sliding part 
           7 H,  7 I groove 
           8  antislip part 
           21  handle 
           22 A trigger 
           41  base 
           41 A base surface 
           41 B insertion space