Patent Publication Number: US-2023133010-A1

Title: Pair of blades and working machine comprising the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-179363, filed on Nov. 2, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The technique disclosed herein is related to a pair of blades and a working machine comprising the same. 
     BACKGROUND 
     Japanese Patent Application Publication No. 2010-98972 describes a working machine including a pair of blades and a prime mover that reciprocates the pair of blades relative to each other. Each of the pair of blades includes a plurality of edge portions disposed along a reciprocating direction. Each of the plurality of edge portions of one of the pair of blades includes: a slide surface which slides with respect to the plurality of edge portions of the other of the pair of blades as the pair of blades reciprocates relative to each other; and an edge surface connected to the slide surface via a connecting line and disposed at a first angle with respect to the slide surface. The connecting line is inclined with respect to the reciprocating direction. 
     SUMMARY 
     In a working machine as described in Japanese Patent Publication Application No. 2010-98972, which cuts an object to be cut such as grass and plants by reciprocating a pair of blades including a plurality of edge portions relative to each other, when the object is cut, the edge portions of the pair of blades cut into the object using their cutting edges and tear and open the object in a direction orthogonal to a cutting direction using their portions that are separated away from the cutting edges. Therefore, when the object is cut, very high load is applied to the cutting edges of the edge portions of the pair of blades. On the other hand, sharpness of the edge portions of the pair of blades depends on resistance received in the cutting direction when the edge portions tear and open the object using the portions separated away from the cutting edges. In addition to the sharpness, durability is also required for such edge portions of the pair of blades as described above, especially when they are designed to operate under a high voltage and high torque. The working machine of Japanese Patent Application Publication No. 2010-98972 only has one edge surface disposed at an angle with respect to the slide surface at each of the edge portions of the pair of blades. Consequently, when an angle between the slide surface and the edge surface is decreased, the sharpness is increased due to decrease in the resistance received in the cutting direction, however, the durability against the load applied upon cutting is adversely decreased. On the other hand, when the angle between the slide surface and the edge surface is increased, the durability against the load applied upon cutting is increased, however, the sharpness is adversely decreased due to increase in the resistance received in the cutting direction. In other words, the sharpness and the durability cannot be achieved simultaneously by the edge portions of the pair of blades of the working machine of Japanese Patent Application Publication No. 2010-98972. The present disclosure provides a technique capable of achieving both sharpness and durability in edge portions of a pair of blades included in a working machine. 
     A working machine disclosed herein may comprise: a pair of blades; and a prime mover configured to reciprocate the pair of blades relative to each other. Each of the pair of blades may comprise a plurality of edge portions disposed along a reciprocating direction. Each of the plurality of edge portions of one of the pair of blades may comprise: a slide surface configured to slide with respect to the plurality of edge portions of the other of the pair of blades as the pair of blades reciprocates relative to each other; a first edge surface connected to the slide surface via a first connecting line and disposed at a first angle with respect to the slide surface, the first connecting line being inclined with respect to the reciprocating direction; and a second edge surface connected to the first edge surface via a second connecting line and disposed at a second angle with respect to the slide surface, the second connecting line being inclined with respect to the reciprocating direction. The first angle may be greater than the second angle. 
     A pair of blades disclosed herein may be configured to be attached to a working machine comprising a prime mover and reciprocated relative to each other by the prime mover. Each of the pair of blades may comprise a plurality of edge portions disposed along a reciprocating direction. Each of the plurality of edge portions of one of the pair of blades may comprise: a slide surface configured to slide with respect to the plurality of edge portions of the other of the pair of blades as the pair of blades reciprocates relative to each other; a first edge surface connected to the slide surface via a first connecting line and disposed at a first angle with respect to the slide surface, the first connecting line being inclined with respect to the reciprocating direction; and a second edge surface connected to the first edge surface via a second connecting line and disposed at a second angle with respect to the slide surface, the second connecting line being inclined with respect to the reciprocating direction. The first angle may be greater than the second angle. 
     According to the above configuration, each of the edge portions of the pair of blades has two edge surfaces. The first edge surface positioned at the cutting edge of each of the edge portions of the pair of blades is disposed at the first angle with respect to the slide surface, and the second edge surface positioned away from the cutting edge is disposed at the second angle, which is smaller than the first angle, with respect to the slide surface. Therefore, sharpness is increased by decreasing resistance received in a cutting direction when the edge portions tear and open the object to be cut, and durability against load applied upon cutting is also increased. In other words, according to the above configuration, both the sharpness and the durability can be achieved in the edge portions of the pair of blades. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    illustrates a perspective view of a hedge trimmer  100  of an embodiment viewed from the front right upper side. 
         FIG.  2    illustrates a side cross-sectional of an internal structure of the hedge trimmer  100  of the embodiment viewed from the right side. 
         FIG.  3    illustrates a perspective view of a pair of blades  12  included in the hedge trimmer  100  of the embodiment viewed from the front right lower side. 
         FIG.  4    illustrates the pair of blades  12  included in the hedge trimmer  100  of the embodiment viewed from above. 
         FIG.  5    illustrates an enlarged view of an edge portion  120  of the pair of blades  12  included in the hedge trimmer  100  of the embodiment viewed from above. 
         FIG.  6    illustrates a cross-sectional view of the edge portion  120  of the pair of blades  12  included in the hedge trimmer  100  of the embodiment, taken along a D-D cross section of  FIG.  5   . 
         FIG.  7    illustrates a cross-sectional view of the edge portion  120  of the pair of blades  12  included in the hedge trimmer  100  of the embodiment, taken along a E-E cross section of  FIG.  5   . 
         FIG.  8    illustrates a cross-sectional view of the edge portion  120  of the pair of blades  12  included in the hedge trimmer  100  of the embodiment, taken along a F-F cross section of  FIG.  5   . 
         FIG.  9 A  illustrates how a lower blade  12   c  reciprocates relative to the upper blade  12   b  in the hedge trimmer  100  of the embodiment when the pair of blades  12  is actuated. 
         FIG.  9 B  illustrates how the lower blade  12   c  reciprocates relative to the upper blade  12   b  in the hedge trimmer  100  of the embodiment when the pair of blades  12  is actuated. 
         FIG.  9 C  illustrates how the lower blade  12   c  reciprocates relative to the upper blade  12   b  in the hedge trimmer  100  of the embodiment when the pair of blades  12  is actuated. 
         FIG.  9 D  illustrates how the lower blade  12   c  reciprocates relative to the upper blade  12   b  in the hedge trimmer  100  of the embodiment when the pair of blades  12  is actuated. 
         FIG.  10 A  illustrates a cross-sectional schematic diagram of cutting operation of edge portions  120   b ,  120   c  of the pair of blades  12  in the state of  FIG.  9 A  in the hedge trimmer  100  of the embodiment viewed from the left side. 
         FIG.  10 B  illustrates a cross-sectional schematic diagram of the cutting operation of the edge portions  120   b ,  120   c  of the pair of blades  12  in the state of  FIG.  9 B  in the hedge trimmer  100  of the embodiment viewed from the left side. 
         FIG.  10 C  illustrates a cross-sectional schematic diagram of the cutting operation of the edge portions  120   b ,  120   c  of the pair of blades  12  in the state of  FIG.  9 C  in the hedge trimmer  100  of the embodiment viewed from the left side. 
         FIG.  10 D  illustrates a cross-sectional schematic diagram of the cutting operation of the edge portions  120   b ,  120   c  of the pair of blades  12  in the state of  FIG.  9 D  in the hedge trimmer  100  of the embodiment viewed from the left side. 
         FIG.  11    illustrates a schematic view of an edge portion  120  of a pair of blades  12  included in a hedge trimmer  100  of a variant viewed from the left side. 
     
    
    
     DETAILED DESCRIPTION 
     Representative, non-limiting examples of the present disclosure will now be described in further detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing aspects of the present teachings and is not intended to limit the scope of the present disclosure. Furthermore, each of the additional features and teachings disclosed below may be utilized separately or in conjunction with other features and teachings to provide improved working machines and pairs of blades as well as methods for using and manufacturing the same. 
     Moreover, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the present disclosure in the broadest sense, and are instead taught merely to particularly describe representative examples of the present disclosure. Furthermore, various features of the above-described and below-described representative examples, as well as the various independent and dependent claims, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings. 
     All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter. 
     In one or more embodiments, a working machine may comprise: a pair of blades; and a prime mover configured to reciprocate the pair of blades relative to each other. Each of the pair of blades may comprise a plurality of edge portions disposed along a reciprocating direction. Each of the plurality of edge portions of one of the pair of blades may comprise: a slide surface configured to slide with respect to the plurality of edge portions of the other of the pair of blades as the pair of blades reciprocates relative to each other; a first edge surface connected to the slide surface via a first connecting line and disposed at a first angle with respect to the slide surface, the first connecting line being inclined with respect to the reciprocating direction; and a second edge surface connected to the first edge surface via a second connecting line and disposed at a second angle with respect to the slide surface, the second connecting line being inclined with respect to the reciprocating direction. The first angle may be greater than the second angle. 
     In one or more embodiments, a pair of blades may be configured to be attached to a working machine comprising a prime mover and reciprocated relative to each other by the prime mover. Each of the pair of blades may comprise a plurality of edge portions disposed along a reciprocating direction. Each of the plurality of edge portions of one of the pair of blades may comprise: a slide surface configured to slide with respect to the plurality of edge portions of the other of the pair of blades as the pair of blades reciprocates relative to each other; a first edge surface connected to the slide surface via a first connecting line and disposed at a first angle with respect to the slide surface, the first connecting line being inclined with respect to the reciprocating direction; and a second edge surface connected to the first edge surface via a second connecting line and disposed at a second angle with respect to the slide surface, the second connecting line inclined with respect to the reciprocating direction. The first angle may be greater than the second angle. 
     According to the above configuration, each of the edge portions of the pair of blades has two edge surfaces. The first edge surface positioned at the cutting edge of each of the edge portions of the pair of blades is disposed at the first angle with respect to the slide surface, and the second edge surface positioned away from the cutting edge is disposed at the second angle, which is smaller than the first angle, with respect to the slide surface. Therefore, sharpness is increased by reducing resistance received in the cutting direction when the edge portions tear and open an object to be cut, and durability against load applied upon cutting is also increased. In other words, according to the above configuration, both sharpness and durability can be achieved in the edge portions  120  of the pair of blades. 
     In one or more embodiments, the first edge surface may have a first width in a direction orthogonal to the first connecting line, as viewed in a direction orthogonal to the slide surface. The second edge surface may have a second width in a direction orthogonal to the second connecting line, as viewed in the direction orthogonal to the slide surface. A ratio of the first width to the second width may be 1:4. 
     If the ratio of the first width of the first edge surface cutting into an object to the second width of the second edge surface tearing and opening the object is too small, the sharpness upon cutting is adversely decreased. Contrary to this, if the ratio of the first width of the first edge surface to the second width of the second edge surface is too large, the durability against the load applied upon cutting is adversely decreased. According to the above configuration, both the sharpness and durability can more suitably be achieved in each of the edge portions of the pair of blades. 
     In one or more embodiments, the first width may be within a range from 0.28 mm to 0.8 mm. 
     When the first width of the first edge surface is too small, it is difficult to achieve an effect of improving the durability. On the other hand, when the first width of the first edge surface is too large, this may cause a substantial decrease in the sharpness. According to the above configuration, in the edge portions of the pair of blades, the effect of improving the durability can sufficiently be obtained without causing a substantial decrease in the sharpness. 
     In one or more embodiments, the second width may be within a range from 1.12 mm to 3.2 mm. 
     When the second width of the second edge surface is too small, it is difficult to achieve an effect of improving sharpness. On the other hand, when the second width of the second edge surface is too large, this may cause a substantial decrease in durability. According to the above configuration, in the edge portions of the pair of blades, the effect of improving the sharpness can sufficiently be obtained without causing a substantial decrease in the durability. 
     In one or more embodiments, a ratio of the first angle to the second angle may be 3:2. 
     When the ratio of the first angle between the first edge surface and the slide surface to the second angle between the second edge surface and the slide surface is too small, sharpness upon cutting is adversely decreased. On the other hand, when the ratio of the first angle with respect to the second angle is too large, durability against the load applied upon cutting is adversely decreased. According to the above configuration, both the sharpness and durability can more suitably be achieved in the edge portions of the pair of blades. 
     In one or more embodiments, the first angle may be within a range from 45 degrees to 70 degrees. 
     When the first angle is too small, it is difficult to achieve effect of improving durability. On the other hand, when the first angle is too large, this may cause a substantial decrease in sharpness. According to the above configuration, in the edge portions of the pair of blades, the effect of improving the durability can sufficiently be obtained without causing a substantial decrease in the sharpness. 
     In one or more embodiments, the second angle may be within a range from 20 degrees to 45 degrees. 
     When the second angle is too small, this may cause a substantial decrease in the durability. On the other hand, when the second angle is too large, it is difficult to achieve an effect of improving the sharpness. According to the above configuration, in the edge portions of the pair of blades, the effect of improving the sharpness can sufficiently be obtained without causing a substantial decrease in the durability. 
     In one or more embodiments, the first edge surface and the second edge surface may be formed by die forging. 
     When the first edge surface and the second edge surface are formed on each of the edge portions, it is contemplated to perform polishing. In that case, however, the polishing needs to be separately performed on each of the plurality of edge portions, which makes mass production of the pair of blades difficult. According to the above configuration, the first edge surface and the second edge surface can be formed in one processing, thus the mass production of the pair of blades is facilitated. 
     Embodiment 
     With reference to drawings, a hedge trimmer  100  will be described below as an example of a working machine comprising a pair of blades  12 . The hedge trimmer  100  is a gardening tool used mainly in trimming hedges and plants. As illustrated in  FIG.  1   , the hedge trimmer  100  includes the pair of blades  12 , a housing  14  supporting the pair of blades  12 , a front handle  16  and a rear handle  18  which a user can grip, and a power cable  20  for supplying external power. 
     The pair of blades  12  linearly extends forward from the housing  14  and includes a plurality of edge portions  120  disposed along the longitudinal direction. The pair of blades  12  is configured to trim hedges and plants using the plurality of edge portions  120  by reciprocating relative to each other in the longitudinal direction. In the hedge trimmer  100  of the present embodiment, each of the pair of blades  12  is configured to reciprocate relative to the housing  14 . 
     Here, in the present embodiment, the longitudinal direction of the pair of blades  12  is defined as a front-rear direction, a direction extending from the housing  14  to the pair of blades  12  is defined as a frontward direction, and a direction extending from the pair of blades  12  to the housing  14  is defined as a rearward direction. Further, a direction orthogonal to the front-rear direction and parallel to the plane where the plurality of edge portions  120  of the pair of blades  12  is positioned is defined as a left-right direction. A direction orthogonal to the front-rear direction and the left-right direction is defined as an up-down direction. 
     As illustrated in  FIG.  2   , the front handle  16  and the rear handle  18  are attached to the housing  14 . The front handle  16  is positioned on the front upper side of the housing  14 . The rear handle  18  is positioned on the rear side of the housing  14 . The hedge trimmer  100  is a hand-held electric tool and a user usually operates the hedge trimmer  100  by gripping the front handle  16  with his/her one hand and gripping the rear handle  18  with the other hand. The front handle  16  extends along a plane angled relative to the front-rear direction. The rear handle  18  extends along the plane parallel to the front-rear direction and the up-down direction (i.e., the plane orthogonal to the left-right direction). 
     A first drive switch  21  is disposed on the front handle  16 , and a second drive switch  22  is disposed on the rear handle  18 . A lock switch  24  is disposed on the rear handle  18 . The hedge trimmer  100  is configured to actuate the pair of blades  12  only when the first drive switch  21  and the second drive switch  22  are concurrently operated. The second drive switch  22  is usually mechanically locked by the lock switch  24 , and its operation is permitted only when the lock switch  24  is operated. The first drive switch  21 , the second drive switch  22  and the lock switch  24  are operated by the user gripping the front handle  16  and the rear handle  18 . Therefore, the hedge trimmer  100  is configured such that actuation of the pair of blades  12  is prohibited unless the user grips both the front handle  16  and the rear handle  18 . 
     The hedge trimmer  100  further includes a motor  26  as an example of a prime mover. The motor  26  is housed in the housing  14  and actuates the pair of blades  12 . With regard to this point, the motor  26  is connected to the pair of blades  12  via crank cams  28  and is configured to reciprocate each of the pair of blades  12  relative to the housing  14 . The motor  26  of the present embodiment is a brushless motor. The rotation axis of the motor  26  extends orthogonally to the longitudinal direction of the pair of blades  12  and in the up-down direction. 
     The hedge trimmer  100  further includes an electric circuit unit  30  housed at a front upper portion inside the housing  14 . The electric circuit unit  30  is electrically connected to the power cable  20  and is configured to adjust external power supplied via the power cable  20  and supply the same to the motor  26 . When the user operates the first drive switch  21  and the second drive switch  22 , the electric circuit unit  30  starts supplying power to the motor  26 . The electric circuit unit  30  stops supplying power to the motor  26  when operation on the first drive switch  21  and/or the second drive switch  22  is released. Therefore, the electric circuit unit  30  can switch the motor  26  on and off. The electric circuit unit  30  further can switch the main power of the hedge trimmer  100  on and off, change a rotation speed of the motor  26 , drive the motor  26  in a backward rotation direction, and the like, based on an operation status of the operation button  32  which the user operates. In the present embodiment, the motor  26  is a brushless motor, thus the electric circuit unit  30  further includes an inverter circuit  30   a . The inverter circuit  30   a  is electrically connected to the power cable  20  and also electrically connected to the motor  26 . The inverter circuit  30   a  converts direct current from the power cable  20  to alternating current and supplies the same to the motor  26 . 
     (Configuration of Pair of Blades  12 ) 
     As illustrated in  FIG.  3   , the pair of blades  12  includes a guide bar  12   a , a guide plate  12   d , an upper blade  12   b  and a lower blade  12   c . A plurality of slots  13   b  and a plurality of slots  13   c  are defined in the upper blade  12   b  and the lower blade  12   c . The upper blade  12   b  and the lower blade  12   c  are attached to the guide bar  12   a  and the guide plate  12   d  positioned on the upper blade  12   b  by guide members  13   a  inserted into the slots  13   b ,  13   c . A slide surface  129   b  is formed on the lower surface of the upper blade  12   b , and a slide surface  129   c  is formed on the upper surface of the lower blade  12   c . The upper blade  12   b  and the lower blade  12   c  can slide and reciprocate relative to each other in the front-rear direction at the slide surfaces  129   b ,  129   c.    
     As illustrated in  FIG.  4   , each of the upper blade  12   b  and the lower blade  12   c  includes a plurality of edge portions  120   b ,  120   c  along the front-rear direction on the both sides in the left-right direction. The slide surfaces  129   b ,  129   c  of the upper blade  12   b  and the lower blade  12   c  extend to the plurality of edge portions  120   b ,  120   c . The plurality of edge portions  120   b ,  120   c  are disposed at predetermined intervals in the front-rear direction. In the present embodiment, a position of each of the plurality of edge portions  120   b  on the left side of the upper blade  12   b  in the front-rear direction is offset from its corresponding one of the plurality of edge portions  120   b  on the right side of the upper blade  12   b  by half the interval. Similarly, a position of each of the plurality of edge portions  120   c  on the left side of the lower blade  12   c  in the front-rear direction is offset from its corresponding one of the plurality of edge portions  120   c  on the right side of the lower blade  12   c  by half the interval. In the present embodiment, the upper blade  12   b  and the lower blade  12   c  have the same shape. Each of the plurality of edge portions  120   b  has the same shape on the left side. Each of the plurality of edge portions  120   b  has the same shape on the left side. A shape of each of the plurality of edge portions  120   b  on the left side of the upper blade  12   b  is a mirror-image of a shape of each of the plurality of edge portions  120   b  on the right side of the upper blade  12   b . Similarly, each of the plurality of edge portions  120   c  has the same shape on the left side. Each of the plurality of edge portions  120   c  has the same shape on the right side. A shape of each of the plurality of edge portions  120   c  on the left side of the lower blade  12   c  is a mirror-image of a shape of the each of the plurality of edge portions  120   c  on the right side of the lower blade  12   c . In other words, each of the edge portions  120   b  on the left side of the upper blade  12   b  has the same shape as each of the edge portions  120   c  on the right side of the lower blade  12   c . Each of the edge portions  120   b  on the right side of the upper blade  12   b  has the same shape as each of the edge portions  120   c  on the left side of the lower blade  12   c . In the present embodiment, stainless steel is used for the upper blade  12   b  and the lower blade  12   c , and the upper blade  12   b  and the lower blade  12   c  are formed by die forging such as heat forging or cold forging. Thus, even when the upper blade  12   b  and the lower blade  12   c  have a plurality of edge portions  120  ( FIG.  5   ) each including a plurality of edge surfaces to be described, the blades are easily created and mass manufacturing of the blades is enabled. 
     (Configurations of Plurality of Edge Portions  120   b ,  120   c ) 
     Hereafter, the plurality of edge portions  120   b ,  120   c  included in each of the pair of blades  12  of the embodiment will be described in detail with reference to the drawings, taking one of the edge portions  120  as an example. In  FIG.  5    to  FIG.  8   , the edge portion  120  is illustrated such that it corresponds to one of the edge portions  120   b  on the left side of the upper blade  12   b  or one of the edge portions  120   c  of on the right side the lower blade  12   c.    
     As illustrated in  FIG.  5    and  FIG.  6   , the edge portion  120  includes a first edge surface  121  and a second edge surface  122  on its front side. As illustrated in  FIG.  5   , the first edge surface  121  is connected to the slide surface  129  via a first connecting line b 1  inclined with respect to the front-rear direction at a tilting angle α 1 . The tilting angle α 1  may be within a range from 70 degrees to 90 degrees, and is 70 degrees in the present embodiment. As illustrated in  FIG.  6   , the first edge surface  121  is disposed at a first angle θ 1  with respect to the slide surface  129 . The first angle θ 1  may be within a range from 45 degrees to 70 degrees, and is 45 degrees in the present embodiment. As illustrated in  FIG.  5   , the second edge surface  122  is connected to the first edge surface  121  via a second connecting line b 2  inclined with respect to the front-rear direction at a tilting angle α 2 . The tilting angle α 2  may be within a range from 70 degrees to 90 degrees, and is 70 degrees in the present embodiment. The second edge surface  122  is connected to a top surface  128  via a top surface connecting line b 81  inclined with respect to the front-rear direction at a tilting angle α 81 . The tilting angle α 81  may be within a range from 70 degrees to 90 degrees, and is 70 degrees in the present embodiment. In the present embodiment, the top surface  128  is a surface parallel to the slide surface  129 . As illustrated in  FIG.  6   , the second edge surface  122  is disposed at a second angle θ 2  with respect to the slide surface  129 . The second angle θ 2  may be within a range from 20 degrees to 45 degrees, and is 30 degrees in the present embodiment. The first angle θ 1  is larger than the second angle θ 2 . A ratio of the first angle θ 1  with respect to the second angle θ 2  may be within a range from 1:1 to 7:2, and is 3:2 in the present embodiment. 
     As illustrated in  FIG.  5   , the first edge surface  121  has a first width d 1  in a direction orthogonal to the first connecting line b 1  as viewed from above. The first width d 1  is a distance between the first connecting line b 1  and the second connecting line b 2 . The second edge surface  122  has a second width d 2  in a direction orthogonal to the second connecting line b 2  as viewed from above. The second width d 2  is a distance between the second connecting line b 2  and the top surface connecting line b 81 . A ratio of the first width d 1  to the second width d 2  may be within a range from 7:80 to 5:7, and is 1:4 in the present embodiment. The first width d 1  may be within a range from 0.28 mm to 0.8 mm, and the second width d 2  may be within a range from 1.12 mm to 3.2 mm. In the present embodiment, the first width d 1  is 0.4 mm and the second width d 2  is 1.6 mm. 
     As illustrated in  FIG.  6   , the edge portion  120  has a thickness T in the up-down direction. The thickness T of the edge portion  120  in the up-down direction may be within a range from 1.6 mm to 4.0 mm, and the thickness T of the edge portion  120  in the up-down direction is 2.0 mm in the present embodiment. The edge portion  120  is formed such that a thickness t 1  of the first edge surface  121  in the up-down direction is 0.3 times or less the thickness T of the edge portion  120  in the up-down direction. 
     As illustrated in  FIG.  5    and  FIG.  7   , the edge portion  120  includes a third edge surface  123  and a fourth edge surface  124  on its rear side. As illustrated in  FIG.  5   , the third edge surface  123  is connected to the slide surface  129  via a third connecting line b 3  inclined with respect to the front-rear direction at a tilting angle α 3 . The tilting angle α 3  may be within a range from 70 degrees to 90 degrees, and is 80 degrees in the present embodiment. As illustrated in  FIG.  7   , the third edge surface  123  is disposed at a third angle θ 3  with respect to the slide surface  129 . The third angle θ 3  may be within a range from 45 degrees to 70 degrees, and is 45 degrees in the present embodiment. As illustrated in  FIG.  5   , the fourth edge surface  124  is connected to the third edge surface  123  via a fourth connecting line b 4  inclined with respect to the front-rear direction at a tilting angle α 4 . The tilting angle α 4  may be within a range from 70 degrees to 90 degrees, and is 80 degrees in the present embodiment. The fourth edge surface  124  is connected to a top surface  128  via a top surface connecting line b 82  inclined with respect to the front-rear direction at a tilting angle α 82 . The tilting angle α 82  may be within a range from 70 degrees to 90 degrees, and is 80 degrees in the present embodiment. As illustrated in  FIG.  7   , the fourth edge surface  124  is disposed at a fourth angle θ 4  with respect to the slide surface  129 . The fourth angle θ 4  may be within a range from 20 degrees to 45 degrees, and is 30 degrees in the present embodiment. The third angle θ 3  is larger than the fourth angle θ 4 . A ratio of the third angle θ 3  to the fourth angle θ 4  may be within a range from 1:1 to 7:2, and is 3:2 in the present embodiment. 
     As illustrated in  FIG.  5   , the third edge surface  123  has a third width d 3  in a direction orthogonal to the third connecting line b 3  as viewed from above. The third width d 3  is a distance between the third connecting line b 3  and the fourth connecting line b 4 . The fourth edge surface  124  has a fourth width d 4  in a direction orthogonal to the fourth connecting line b 4  as viewed from above. The fourth width d 4  is a distance between the fourth connecting line b 4  and the top surface connecting line b 82 . A ratio of the third width d 3  to the fourth width d 4  may be within a range from 7:80 to 5:7, and is 1:4 in the present embodiment. The third width d 3  may be within a range from 0.28 mm to 0.8 mm, and the fourth width d 4  may be within a range from 1.12 mm to 3.2 mm. In the present embodiment, the third width d 3  is 0.4 mm and the fourth width d 4  is 1.6 mm. 
     As illustrated in  FIG.  7   , the edge portion  120  is formed such that a thickness t 3  of the third edge surface  123  in the up-down direction is 0.3 times or less the thickness T of the edge portion  120  in the up-down direction. 
     As illustrated in  FIG.  5    and  FIG.  8   , the edge portion  120  includes a fifth edge surface  125  and a sixth edge surface  126  on its left side. As illustrated in  FIG.  5   , the fifth edge surface  125  is connected to the slide surface  129  via a fifth connecting line b 5  inclined with respect to the front-rear direction at a tilting angle α 5 . The tilting angle α 5  may be within a range from 0 degree to 30 degrees, and is 15 degrees in the present embodiment. As illustrated in  FIG.  8   , the fifth edge surface  125  is disposed at a fifth angle θ 5  with respect to the slide surface  129 . The fifth angle θ 5  may be within a range from 45 degrees to 70 degrees, and is 45 degrees in the present embodiment. As illustrated in  FIG.  5   , the sixth edge surface  126  is connected to the fifth edge surface  125  via a sixth connecting line b 6  inclined with respect to the front-rear direction at a tilting angle α 6 . The tilting angle α 6  may be within a range from 0 degree to 30 degrees, and is 15 degrees in the present embodiment. The sixth edge surface  126  is connected to the top surface  128  via a top surface connecting line b 83  inclined with respect to the front-rear direction at a tilting angle α 83 . The tilting angle α 83  may be within a range from 0 degree to 30 degrees, and is 15 degrees in the present embodiment. As illustrated in  FIG.  8   , the sixth edge surface  126  is disposed at a sixth angle θ 6  with respect to the slide surface  129 . The sixth angle θ 6  may be within a range from 20 degrees to 45 degrees, and is 30 degrees in the present embodiment. The fifth angle θ 5  is larger than a sixth angle θ 6 . A ratio of the fifth angle θ 5  to the sixth angle θ 6  may be within a range from 1:1 to 7:2, and is 3:2 in the present embodiment. The fifth edge surface  125  is connected to the first edge surface  121  at its front side and connected to the third edge surface  123  at its rear side. 
     As illustrated in  FIG.  5   , the fifth edge surface  125  has a fifth width d 5  in a direction orthogonal to the fifth connecting line b 5  as viewed from above. The fifth width d 5  is a distance between the fifth connecting line b 5  and the sixth connecting line b 6 . The sixth edge surface  126  has a sixth width d 6  in a direction orthogonal to the sixth connecting line b 6  as viewed from above. The sixth width d 6  is a distance between the sixth connecting line b 6  and the top surface connecting line b 83 . A ratio of the fifth width d 5  to the sixth width d 6  may be within a range from 7:80 to 5:7, and is 1:4 in the present embodiment. The fifth width d 5  may be within a range from 0.28 mm to 0.8 mm, and the sixth width d 6  may be within a range from 1.12 mm to 3.2 mm. In the present embodiment, the fifth width d 5  is 0.4 mm and the sixth width d 6  is 1.6 mm. 
     As illustrated in  FIG.  8   , the edge portion  120  is formed such that a thickness t 5  of the fifth edge surface  125  in the up-down direction is 0.3 times or less the thickness T of the edge portion  120  in the up-down direction. 
     (Operation of Pair of Blades  12 ) 
     Hereafter, operation when the pair of blades  12  is actuated will be described. In  FIG.  9 A  to  FIG.  9 D , the upper blade  12   b  is illustrated in solid lines and the lower blade  12   c  is illustrated in two-dot chain lines to distinguish the upper blade  12   b  and the lower blade  12   c . As described above, in the present embodiment, when the upper blade  12   b  and the lower blade  12   c  are actuated by the motor  26 , each blade reciprocates in the front-rear direction relative to the housing  14 , however, in  FIG.  9 A  to  FIG.  9 D , reciprocation of the lower blade  12   c  relative to the upper blade  12   b  is illustrated with respect to the upper blade  12   b . Each of  FIG.  10 A  to  FIG.  10 D  is equivalent to a figure obtained by viewing its corresponding example of  FIG.  9 A  to  FIG.  9 D  from the left side of an object B to be cut. 
     As illustrated in  FIG.  9 A  to  FIG.  9 D , in the present embodiment, a distance by which the lower blade  12   c  moves in the front-rear direction relative to the upper blade  12   b  when the pair of blades  12  reciprocates is equal to an interval between the edge portions  120   b ,  120   c . When the pair of blades  12  reciprocates, the edge portion  120   c  alternately repeats operation to move in the rearward direction and overlap with one edge portion  120   b  and operation to move in the forward direction and overlap with another edge portion  120   b . As illustrated in  FIG.  9 D  and  FIG.  10 D , the edge portions  120   b ,  120   c  slide and overlap at the slide surfaces  129   b ,  129   c  upon the operation to overlap with each other. When the object B to be cut is positioned between the edge portion  120   b  and the edge portion  120   c  in the reciprocating direction of the edge portion  120   b  and the edge portion  120   c  (front-rear direction), the object B is cut by the overlapping operation of the edge portions  120   b ,  120   c . Hereafter, the operation to cut the object B by the edge portions  120   b ,  120   c  will be described in detail. 
     (Cutting Operation of Edge Portions  120   b ,  120   c ) 
     As illustrated in  FIG.  9 A  and  FIG.  10 A , when the lower blade  12   c  moves in the rearward direction relative to the upper blade  12   b , the first edge surface  121   b  of the edge portion  120   b  and the third edge surface  123   c  of the edge portion  120   c  enter into the object B to be cut. As illustrated in  FIG.  9 B  and  FIG.  10 B , very high load is applied on the first edge surface  121   b  and the third edge surface  123   c  when the edge portions  120   b ,  120   c  enter the object B. However, since the first angle θ 1   b  between the first edge surface  121   b  and the slide surface  129   b  is 45 degrees, the edge portion  120   b  exhibits great durability against the load applied on the first edge surface  121   b . Since the first width d 1   b  of the first edge surface  121   b  is 0.4 mm, the first edge surface  121   b  will not cause a substantial decrease in sharpness of the edge portion  120   b . Similarly, since the third angle θ 3   c  between the third edge surface  123   c  and the slide surface  129   c  is 45 degrees, the edge portion  120   c  exhibits great durability against the load applied on the third edge surface  123   c . Since the third width d 3   c  of the third edge surface  123   c  is 0.4 mm, the third edge surface  123   c  will not cause a substantial decrease in sharpness of the edge portion  120   c.    
     As illustrated in  FIG.  9 C  and  FIG.  10 C , after  FIG.  9 B  and  FIG.  10 B , the edge portions  120   b ,  120   c  which have entered into the object B to be cut press and expand the cut surface in the object B using the second edge surface  122   b  and the fourth edge surface  124   c  to cut the object B. Overall sharpness of the edge portions  120   b ,  120   c  depends on resistance which the second edge surface  122   b  and the fourth edge surface  124   c  receive in the cutting direction when they press and expand the object B. Here, since the second angle θ 2   b  between the second edge surface  122   b  and the slide surface  129   b  is 30 degrees, resistance received in the cutting direction is reduced, and the edge portion  120   b  as a whole exhibits great sharpness. Since the second width d 2   b  of the second edge surface  122   b  is 1.6 mm, the second edge surface  122   b  will not cause a substantial decrease in sharpness of the edge portion  120   b . Similarly, since the fourth angle θ 4   c  between the fourth edge surface  124  and the slide surface  129   c  is 30 degrees, resistance received in the cutting direction is reduced, and the edge portion  120   c  as a whole exhibits great sharpness. Since the fourth width d 4   c  of the fourth edge surface  124   c  is 1.6 mm, the fourth edge surface  124   c  will not cause a substantial decrease in durability of the edge portion  120   c.    
     In the present embodiment, the shape of the lower blade  12   c  is the same as the shape of the upper blade  12   b , and the shape of each of the edge portions  120   b  on the right side of the upper blade  12   b  is a mirror image of the shape of each of the edge portions  120   c  on the right side of the lower blade  12   c . Therefore, the operation for the edge portions  120   b ,  120   c  to cut the object B to be cut when the lower blade  12   c  moves in the forward direction relative to the upper blade  12   b  corresponds to the operation when the upper blade  12   b  moves in the forward direction relative to the lower blade  12   c  in the example illustrated in  FIG.  9 A  to  FIG.  9 D  and  FIG.  10 A  to  FIG.  10 D . Accordingly, the above explanation about the case in which the lower blade  12   c  moves in the rearward direction relative to the upper blade  12   b  similarly applies to the case in which the lower blade  12   c  moves in the frontward direction relative to the upper blade  12   b.    
     Here, when the tilting angle α 1  at which the first connecting line b 1  of the edge portion  120  is inclined relative to the front-rear direction or the tilting angle α 3  at which the third connecting line b 3  is inclined relative to the front-rear direction is too large, the object B to be cut adversely is displaced to the side of the pair of blades  12  when the edge portions  120  are entering into the object B, by which the object B may not be cut. In the pair of blades  12  of the present embodiment, since the tilting angle α 1  at which the first connecting line b 1  of the edge portion  120  is inclined relative to the front-rear direction is 80 degrees and the titling angle α 3  at which the third connecting line b 3  is inclined relative to the front-rear direction is 80 degrees, the object B can be cut without the object B being displaced to the side of the pair of blades  12 . Further, since the titling angle α 5  at which the fifth connecting line b 5  of the edge portion  120  is inclined relative to the front-rear direction is 15 degrees, the object B on the side of the pair of blades  12  is easily guided to a position between the edge portion  120   b  and the edge portion  120   c.    
     (Variant) 
     In the above embodiment, the hedge trimmer  100  was described as an example of the working machine including the pair of blades  12 . Unlike this, the working machine may be a working machine other than the hedge trimmer  100 . For example, the working machine may for example be a pole hedge or a ground trimmer. 
     In the above embodiment, the configuration including the motor  26  as an example of the prime mover was described. Unlike this, the prime mover may be a prime mover other than the motor  26 . For example, the prime mover may be an engine. 
     In the above embodiment, the configuration in which the prime mover (motor  26 ) is a brushless motor was described. Unlike this, the prime mover (motor  26 ) may be a motor other than a brushless motor. For example, the prime mover (motor  26 ) may be a brushed motor. 
     In the above embodiment, the configuration in which the working machine (hedge trimmer  100 ) includes the power cable  20  and supplies external power to the hedge trimmer  100  through the power cable  20  was described. Unlike this, the working machine (hedge trimmer  100 ) may include a battery pack (not illustrated) configured to be attached to and detached from the rear handle  18  and may supply power to the working machine (hedge trimmer  100 ) from the battery pack. 
     In the above embodiment, the configuration in which each of the pair of blades  12  is configured to reciprocate relative to the housing  14  was described. Unlike this, only one of the pair of blades  12  may be configured to reciprocate relative to the housing  14  and the other of the pair of blades  12  may be fixed to the housing  14 . 
     In the above example, the configuration in which each of the upper blade  12   b  and the lower blade  12   c  includes the plurality of edge portions  120   b ,  120   c  on the both side in the left-right direction was described. Unlike this, each of the upper blade  12   b  and the lower blade  12   c  may include the plurality of edge portions  120   b ,  120   c  only on the left side. Alternatively, each of the upper blade  12   b  and the lower blade  12   c  may include the plurality of edge portions  120   b ,  120   c  only on the right side. 
     In the above embodiment, the configuration in which stainless steel is used for the upper blade  12   b  and the lower blade  12   c  was described. Unlike this, for example, steel, copper, silver, gold, aluminum, titan or nickel may be used for the upper blade  12   b  and the lower blade  12   c , or an alloy of the aforementioned materials may be used for the upper blade  12   b  and the lower blade  12   c.    
     In the above embodiment, the tilting angle α 1  of the first connecting line b 1 , the tilting angle α 2  of the second connecting line b 2 , the tilting angle α 3  of the third connecting line b 3 , the tilting angle α 4  of the fourth connecting line b 4 , the tilting angle α 5  of the fifth connecting line b 5 , the tilting angle α 6  of the sixth connecting line b 6 , the tilting angle α 81  of the top-surface connecting line b 81 , the tilting angle α 82  of the top-surface connecting line b 82 , and the tilting angle α 83  of the top-surface connecting line b 83  of each of the edge portions  120  of the pair of blades  12  may be suitably changed in the process of forming the pair of blades  12 . 
     In the above embodiments, the first angle θ 1 , the second angle θ 2 , the third angle θ 3 , the fourth angle θ 4 , the fifth angle θ 5 , the sixth angle θ 6 , the first width d 1 , the second width d 2 , the third width d 3 , the fourth width d 4 , the fifth width d 5  and the sixth width d 6  of each of the edge portions  120  of the pair of blades  12  may be suitably changed in the process of forming the pair of blades  12 . Since in reality required sharpness and required durability vary in accordance with the type of the object B to be cut, the pair of blades  12  of the present embodiment may be formed in accordance with a type of the object B. In particular, when the object B to be cut is a thick branch and the pair of blades  12  is actuated at a high voltage and high torque, durability is more prioritized than sharpness as compared to the usual case, however, sufficient durability can be realized by setting the first angle θ 1 , the third angle θ 3  and the fifth angle θ 5  of the edge portion  120  to relatively large angles within the respective angle ranges. 
     In the above embodiment, the configuration in which the lower portion of each of the edge portions  120  is flat was described. Unlike this, as illustrated in  FIG.  11   , a cavity  127  may be defined in the lower portion of each of the edge portions  120 . The cavity  127  may be defined so that an area of the slide surface  129  is decreased without a substantial decrease in durability of the edge portion  120  as compared to the case in which the lower portion of the edge portion  120  is flat. In this case, slide resistance generated in one edge portion  120  sliding with respect to another edge portion  120  is decreased, by which energy loss due to the slide resistance in the working machine (the hedge trimmer  100 ) can be decreased. Further, a weight of the pair of blades  12  per se is reduced, by which maneuverability of the working machine (the hedge trimmer  100 ) is increased and energy required to actuate the pair of blades  12  cand be reduced. 
     (Corresponding Relationships) 
     In one or more embodiments, the hedge trimmer  100  (an example of the working machine) comprises: the pair of blades  12 ; and the motor  26  (an example of the prime mover) configured to reciprocate the pair of blades  12  relative to each other. Each of the pair of blades  12  (the upper blade  12   b  and the lower blade  12   c ) comprises the plurality of edge portions  120  ( 120   b ,  120   c ) disposed along the reciprocating direction (the front-rear direction). Each of the plurality of edge portions  120  ( 120   b ,  120   c ) of one of the pair of blades  12  (the upper blade  12   b , the lower blade  12   c ) comprises: the slide surface  129  ( 129   b ,  129   c ) configured to slide with respect to the plurality of edge portions  120  ( 120   c ,  120   b ) of the other of the pair of blades  12  (the lower blade  12   c , the upper blade  12   b ) as the pair of blades  12  reciprocates relative to each other; the first edge surface  121  ( 121   b ,  121   c ) connected to the slide surface  129  ( 129   b ,  129   c ) via the first connecting line b 1  and disposed at the first angle θ 1  with respect to the slide surface  129  ( 129   b ,  129   c ), the first connecting line b 1  being inclined with respect to the reciprocating direction (front-rear direction); and the second edge surface  122  ( 122   b ,  122   c ) connected to the first edge surface  121  ( 121   b ,  121   c ) via the second connecting line b 2  and disposed at the second angle θ 2  with respect to the slide surface  129  ( 129   b ,  129   c ), via the second connecting line b 2  being inclined with respect to the reciprocating direction (the front-rear direction). The first angle θ 1  is greater than the second angle θ 2 . 
     In one or more embodiments, the pair of blades  12  is the pair of blades  12  configured to be attached to the hedge trimmer  100  comprising the motor  26  and reciprocated relative to each other by the motor  26 . Each of the pair of blades  12  (the upper blade  12   b  and the lower blade  12   c ) comprises the plurality of edge portions  120  ( 120   b ,  120   c ) disposed along the reciprocating direction (the front-rear direction). Each of the plurality of edge portions  120  ( 120   b ,  120   c ) of one of the pair of blades  12  (the upper blade  12   b , the lower blade  12   c ) comprises: the slide surface  129  ( 129   b ,  129   c ) configured to slide with respect to the plurality of edge portions  120  ( 120   c ,  120   b ) of the other of the pair of blades  12  (the lower blade  12   c , the upper blade  12   b ) as the pair of blades  12  reciprocates relative to each other; the first edge surface  121  ( 121   b ,  121   c ) connected to the slide surface  129  ( 129   b ,  129   c ) via the first connecting line b 1  and disposed at the first angle θ 1  with respect to the slide surface  129  ( 129   b ,  129   c ), the first connecting line b 1  being inclined with respect to the reciprocating direction (the front-rear direction); and the second edge surface  122  ( 122   b ,  122   c ) connected to the first edge surface  121  ( 121   b ,  121   c ) via the second connecting line b 2  and disposed at the second angle θ 2  with respect to the slide surface  129  ( 129   b ,  129   c ), the second connecting line b 2  being inclined with respect to the reciprocating direction (the front-rear direction). The first angle θ 1  is greater than the second angle θ 2 . 
     According to the above configuration, each of the edge portions  120  ( 120   b ,  120   c ) of the pair of blades  12  has two edge surfaces. The first edge surface  121  ( 121   b ,  121   c ) positioned at the cutting edge of each of the edge portions  120  ( 120   b ,  120   c ) of the pair of blades  12  is disposed at the first angle θ 1  with respect to the slide surface  129  ( 129   b ,  129   c ), and the second edge surface  122  ( 122   b ,  122   c ) positioned away from the cutting edge is disposed at the second angle θ 2 , which is smaller than the first angle θ 1 , to the slide surface  129  ( 129   b ,  129   c ). Therefore, the sharpness is increased by reducing resistance received in the cutting direction when the edge portions  120  tear and open the object B to be cut, and durability against the load applied upon cutting is also increased. In other words, according to the above configuration, both sharpness and durability can be achieved in the edge portions  120  ( 120   b ,  120   c ) of the pair of blades  12 . 
     In one or more embodiments, the first edge surface  121  ( 121   b ,  121   c ) has the first width d 1  in the direction orthogonal to the first connecting line b 1 , as viewed from above (an example of the direction orthogonal to the slide surface), and the second edge surface  122  ( 122   b ,  122   c ) has the second width d 2  in the direction orthogonal to the second connecting line b 1 , as viewed from above. The ratio of the first width d 1  to the second width d 2  is 1:4. 
     If the ratio of the first width d 1  of the first edge surface  121  ( 121   b ,  121   c ) entering into the object B to be cut to the second width d 2  of the second edge surface  122  ( 122   b ,  122   c ) tearing and opening the object B is too small, the sharpness upon cutting is adversely decreased. Contrary to this, if the ratio of the first width d 1  of the first edge surface  121  ( 121   b ,  121   c ) to the second width d 2  of the second edge surface  122  ( 122   b ,  122   c ) is too large, the durability against the load applied upon cutting is adversely decreased. According to the above configuration, both the sharpness and durability can more suitably be achieved in the edge portions  120  ( 120   b ,  120   c ) of the pair of blades  12 . 
     In one or more embodiments, the first width d 1  is within a range from 0.28 mm to 0.8 mm. 
     When the first width d 1  of the first edge surface  121  ( 121   b ,  121   c ) is too small, it is difficult to achieve an effect of improving the durability. On the other hand, when the first width d 1  of the first edge surface  121  ( 121   b ,  121   c ) is too large, this may cause a substantial decrease in the sharpness. According to the above configuration, in the edge portions  120  ( 120   b ,  120   c ) of the pair of blades  12 , the effect of improving the durability can sufficiently be obtained without causing a substantial decrease in the sharpness. 
     In one or more embodiments, the second width d 2  is within a range from 1.12 mm to 3.2 mm. 
     When the second width d 2  of the second edge surface  122  ( 122   b ,  122   c ) is too small, it is difficult to achieve an effect of improving the sharpness. On the other hand, when the second width d 2  of the second edge surface  122  ( 122   b ,  122   c ) is too large, this may cause a substantial decrease in the durability. According to the above configuration, in the edge portions  120  ( 120   b ,  120   c ) of the pair of blades  12 , the effect of improving the sharpness can sufficiently be obtained without causing a substantial decrease in the durability. 
     In one or more embodiments, the ratio of the first angle θ 1  to the second angle θ 2  is 3:2. 
     When the ratio of the first angle θ 1  between the first edge surface  121  ( 121   b ,  121   c ) and the slide surface  129  ( 129   b ,  129   c ) to the second angle θ 2  between the second edge surface  122  ( 122   b ,  122   c ) and the slide surface  129  ( 129   b ,  129   c ) is too small, sharpness upon cutting is adversely decreased. On the other hand, when the ratio of the first angle θ 1  to the second angle θ 2  is too large, durability against the load applied upon cutting is adversely decreased. According to the above configuration, both the sharpness and durability can more suitably be achieved in the edge portions  120  ( 120   b ,  120   c ) of the pair of blades  12 . 
     In one or more embodiments, the first angle θ 1  is within a range from 45 degrees to 70 degrees. 
     When the first angle θ 1  is too small, it is difficult to achieve an effect of improving durability. On the other hand, when the first angle θ 1  is too large, this may cause a substantial decrease in sharpness. According to the above configuration, in the edge portions  120  ( 120   b ,  120   c ) of the pair of blades  12 , the effect of improving the durability can sufficiently be obtained without causing a substantial decrease in the sharpness. 
     In one or more embodiments, the second angle θ 2  is within a range from 20 degrees to 45 degrees. 
     When the second angle θ 2  is too small, this may cause a substantial decrease in durability. On the other hand, when the second angle θ 2  is too large, it is difficult to achieve an effect of improving sharpness. According to the above configuration, in the edge portions  120  ( 120   b ,  120   c ) of the pair of blades  12 , the effect of improving the sharpness can sufficiently be obtained without causing a substantial decrease in the durability. 
     In one or more embodiments, the first edge surface  121  ( 121   b ,  121   c ) and the second edge surface  122  ( 122   b ,  122   c ) are formed by die forging. 
     When the first edge surface  121  ( 121   b ,  121   c ) and the second edge surface  122  ( 122   b ,  122   c ) are formed on each of the edge portions  120  ( 120   b ,  120   c ), it is contemplated to perform polishing. In that case, however, the polishing needs to be separately performed on each of the plurality of edge portions  120  ( 120   b ,  120   c ), which makes mass production of the pair of blades  12  (upper blade  12   b , lower blade  12 ) (examples of the blades) difficult. According to the above configuration, the first edge surface  121  ( 121   b ,  121   c ) and the second edge surface  122  ( 122   b ,  122   c ) can be formed in one processing, thus mass production of the pair of blades  12  (upper blade  12   b , lower blade  12   c ) is facilitated.