Patent Publication Number: US-7718879-B2

Title: Hammer shank of piano and method of manufacturing the same

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a hammer shank for a piano, which pivotally moves in accordance with key depression, and a method of manufacturing the same. 
   2. Description of the Related Art 
   Conventionally, a hammer of a piano, which has a hammer shank, has been disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 2005-77455. The hammers are provided in association with respective keys, and each of the hammers is pivotally supported by a hammer shank flange (hereinafter simply referred to as “the shank flange”). Each of the hammers includes a long, slender wooden hammer shank and a hammer head fixed to a rear end of the hammer shank. The hammer shank has a front end thereof bifurcated into two left and right arms extending forward in facing and parallel relation to each other. The shank flange is formed by a synthetic resin molded article, and screwed to a hammer shank rail. The shank flange has a rear end thereof formed with an engaging part projecting rearward, and the two arms of the hammer shank are engaged on the opposite sides of the engaging part. Further, a pin is horizontally passed through the two arms and the engaging part. This pin is rigidly secured to the engaging part, but is supported by the two arms in a pivotally movable manner. Thus, the hammer is pivotally supported by the shank flange via the pin integral with the shank flange. The opposite side surfaces of the engaging part of the shank flange are formed parallel to each other, and each of the side surfaces of the engaging part of the shank flange is opposed to the inner side surface of an associated arm of the hammer shank with a slight clearance. 
   With the above-mentioned arrangement, as an associated key is depressed, an associated action operates to push up the hammer shank, whereby the hammer pivotally moves upward, and the hammer head strikes an associated string to thereby generate a piano tone. During the pivotal motion of the hammer, the hammer shank is guided by the two arms and the engaging part of the shank flange, so that the hammer can perform the pivotal motion without deflecting laterally. 
   However, the hammer shank, which is made of wood, is susceptible to a use environment of the piano, particularly to dryness and wetness, and hence there is a fear that smooth and stable pivotal motion of the hammer cannot be obtained due to a change in the dimension between the two arms. Specifically, when the dimension between the arms of the hammer shank is reduced due to shrinkage caused by dryness (see  FIG. 5B ), the clearances between the two arms and the engaging part is sometimes lost, which causes a defective operation of the hammer, such as incapability of smooth pivotal motion of the hammer (which will be hereinafter referred to as “a stick”). On the other hand, when the dimension between the arms of the hammer shank is increased due to expansion caused by wetness (see  FIG. 5A ), the clearances between the two arms and the engaging part become larger. As a result, there is a fear that the hammer deflects laterally or wobbles during pivotal motion, thereby hindering the hammer from properly striking the string. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in order to solve the above problem, and an object thereof is to provide a hammer shank for a piano, which is capable of suppressing a change in the dimension between two arms due to dryness and wetness to thereby ensure smooth and stable operation of a hammer, and a method of manufacturing the hammer shanks. 
   To attain the above object, in a first aspect of the present invention, there is provided a hammer shank for a piano, which is supported by a flange and pivotally moves in accordance with key depression, comprising a shank body that is formed of wood, two bifurcated arms that are formed on one end of the shank body in a manner extending in facing and parallel relation to each other along respective opposite sides of the flange, and are pivotally supported by the flange, and displacement suppression members that are attached on outer side surfaces of the respective two arms so as to suppress displacement of the two arms in a direction in which the arms face each other. 
   With the construction of the hammer shank for a piano according to the first aspect of the present invention, the wooden shank body has the one end bifurcated into the two arms extending in facing and parallel relation to each other along the respective opposite sides of the flange, and the two arms are pivotally supported by the flange. This causes, according to key depression, the hammer shank to perform pivotal motion while being guided by the two arms and the flange. Further, the displacement suppression members are attached on the outer side surfaces of the respective two arms. The displacement suppression members function as splints, so to say, for the respective associated arms to restrain these. As a consequence, displacement of the arms in the direction in which they face each other is suppressed. This makes it possible to stably maintain the dimension between the arms to thereby maintain the size of the clearance between each of the inner side surfaces of the respective arms and the shank flange, so that occurrence of a stick due to dryness and wetness, and lateral deflection and wobbling of the hammer during its pivotal motion can be prevented. Therefore, it is possible to ensure smooth and stable operation of the hammer irrespective of whether it is dry or wet. 
   Preferably, each of the displacement suppression members is formed of a material containing a predetermined synthetic resin. 
   In general, a synthetic resin is lighter and easier to be shaped than metals or the like. Therefore, with the construction of the preferred embodiment, by forming the displacement suppression members out of a material containing such a synthetic resin, it is possible to easily manufacture the displacement suppression members according to the shape and size of the arms to which the displacement suppression members are to be attached, respectively. Further, e.g. by employing a synthetic resin having a relatively high rigidity and a relatively high dimensional stability, it is possible to reliably obtain the above-mentioned action and advantageous effect of the hammer shank according to the first aspect of the present invention. It should be noted that the above-mentioned “material containing a synthetic resin” is intended to mean not only a composite material comprising a synthetic resin and a material other than the synthetic resin, but also a synthetic resin material comprising only a single synthetic resin or a plurality of synthetic resins. 
   More preferably, the displacement suppression members are phenol backers. 
   In general, the phenol backer (phenolic resin-impregnated paper) has a high rigidity and a high dimensional stability against dryness and wetness. Further, the phenol backer has is relatively inexpensive, and has a characteristic of high adhesiveness to wood. Therefore, with the construction of the preferred embodiment, by employing the phenol backer as the displacement suppression member and attaching the phenol backer onto the outer side surface of each arm e.g. by bonding, it is possible to easily realize a hammer capable of performing smooth and stable pivotal motion, at low costs. 
   To attain the above object, in a second aspect of the present invention, there is provided a method of manufacturing a hammer shank for a piano, comprising a preparation step of preparing a wooden hammer shank member which has one end thereof bifurcated into two arm parts continuously extending in facing and parallel relation to each other, and two plate-shaped displacement suppression members, an attachment step of attaching the displacement suppression members onto the hammer shank member by bonding the two displacement suppression members onto outer side surfaces of the respective two arm parts, and a cutting step of cutting the hammer shank member having the displacement suppression members attached thereon, at predetermined space intervals in a direction of extension of the arm parts along a direction orthogonal to the direction of extension, to thereby cut out a plurality of hammer shanks. 
   With the configuration of the method of manufacturing a hammer shank for a piano according to the second aspect of the present invention, first, the above-mentioned wooden hammer shank member and the two displacement suppression members are prepared. This wooden hammer shank member has the two bifurcated arm parts formed at one end thereof such that they continuously extend in facing and parallel relation to each other, and the displacement suppression members are each formed into a plate shape. Next, the two displacement suppression members are bonded onto the outer side surfaces of the respective two arm parts of the hammer shank member, whereby the displacement suppression members are attached onto the hammer shank member. Then, the hammer shank member are cut at predetermined space intervals in the direction of extension of the arm parts, along the direction orthogonal to the direction of extension, whereby a plurality of hammer shanks are cut out. This makes it possible to obtain a plurality of hammer shanks each having displacement suppression members attached on the outer side surfaces of the two arms, i.e. the same hammer shanks according to the first aspect of the present invention. Further, since the hammer shank member is cut after the two displacement suppression members have been attached onto the hammer shank member, it is possible to manufacture the hammer shanks more efficiently than in a case where displacement suppression members corresponding in size to each hammer shank are attached on a hammer shank-by-hammer shank basis. 
   Preferably, each of the displacement suppression members is a phenol backer. 
   With the construction of the preferred embodiment, since the phenol backer is employed as a displacement suppression member, it is possible to easily obtain the same hammer shank as the more preferred embodiment of the first aspect of the present invention. 
   The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a keyboard, an action, and a hammer for a grand piano using a hammer shank according to an embodiment of the present invention, in a key-off state; 
       FIG. 2  is a perspective view of the hammer and a hammer shank flange; 
       FIG. 3  is an exploded perspective view showing the hammer shank and the hammer shank flange in  FIG. 2  on an enlarged scale; 
       FIG. 4A  is a plan view of an expanded-width part of the hammer shank according to the present embodiment, which is subjected to a dry/wet test; 
       FIG. 4B  is a plan view of an expanded-width part of a hammer shank according to the prior art, which is subjected to a dry/wet test; 
       FIGS. 5A and 5B  are views useful in explaining deformation of two arms after humidification and drying in the dry/wet test; 
       FIGS. 6A and 6B  are views showing tables of results of the dry/wet test; and 
       FIGS. 7A ,  7 B and  7 C are views useful in explaining the method of manufacturing a hammer shank. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The invention will now be described in detail with reference to the drawings showing a preferred embodiment thereof.  FIG. 1  shows a keyboard  1 , an action  2 , a hammer  3 , etc. of a grand piano to which is applied a hammer shank for a piano, according to the embodiment of the present invention, in a key-off state. 
   The keyboard  1  is comprised of lots of keys  1   a  (only one of which is shown) arranged in a longitudinal direction of the grand piano. Each key  1   a  extends in a front-rear direction (the left-right direction as viewed in  FIG. 1 ), and is supported in a manner pivotally movable about a balance pin erected on a keyframe on a keybed (none of which are shown). 
   The action  2  is disposed above the rear part of the keyboard  1 , and includes a wippen  11 , a jack  12 , a repetition lever  13 , etc. provided for each of the keys  1   a . The wippen  11  extends in the front-rear direction, and has a rear end thereof supported by a wippen flange  14 . The wippen flange  14  extends vertically, and is screwed to a wippen rail  16  extending between a plurality of brackets  15  (only one of which is shown in  FIG. 1 ) arranged in the longitudinal direction of the grand piano in a manner spaced from each other. Further, the wippen flange  14  has an upper end thereof bifurcated into two left and right arms  14   a  and  14   a  (only a left one of which is shown in  FIG. 1 ). The rear end of the wippen  11  is engaged between the two arms  14   a  and  14   a , and a center pin  17  is horizontally passed through the two arms  14   a  and the wippen  11 . Thus, the wippen  11  is supported by the wippen flange  14  in a manner pivotally movable about the center pin  17 . Further, a heel section  11   a  projects downward from a central part of the wippen  11  in the front-rear direction. The wippen  11  is placed on a capstan screw  1   b  provided on a rear part of the key  1   a , via the heel section  11   a . The jack  12  is supported on a front end of the wippen  11 . 
   The jack  12  is formed into an L-shape in side view by a vertically extending hammer push-up part  12   a  and a regulating button abutment part  12   b  extending forward from the lower end of the hammer push-up part  12   a  substantially at right angles thereto. The front end of the wippen  11  is bifurcated into two left and right arms  11   b  and  11   b  (only a left one of which is shown in  FIG. 1 ). The jack  12  has its corner engaged between the two arms  11   b  and  11   b , and a center pin  18  is horizontally passed through the two arms  11   b  and the jack  12 . Thus, the jack  12  is supported by the front end of the wippen  11  in a manner pivotally movable about the center pin  18 . An upper end of the hammer push-up part  12   a  is engaged in a jack guide hole  13   a , referred to hereinafter, of the repetition lever  13 , and is opposed to a shank roller  26  with a slight space therebetween. Further, the jack  12  is urged in a returning direction (counterclockwise direction as viewed in  FIG. 1 ) by a repetition spring  22 , referred to hereinafter. 
   The repetition lever  13  obliquely extends upward in the front-rear direction, and is supported by a lever flange  21  projected upward from the central part of the wippen  11  in the front-rear direction. The lever flange  21  has an upper end thereof bifurcated into two left and right arms  21   a  and  21   a  (only a left one of which is shown in  FIG. 1 ). A central part of the repetition lever  13  is engaged between the two arms  21   a  and  21   a , and a center pin  19  is horizontally passed through the two arms  21   a  and the repetition lever  13 . Thus, the repetition lever  13  is supported by the upper end of the lever flange  21  in a manner pivotally movable about the center pin  19 . The repetition lever  13  is urged in a returning direction (counterclockwise direction as viewed in  FIG. 1 ) by the repetition spring  22  attached to the lever flange  21 . Further, the repetition lever  13  has the jack guide hole  13   a  formed to extend vertically through a front portion thereof, and the hammer  3  is placed on the repetition lever  13  via the shank roller  26  in contact with the repetition lever  13  at a location at or around the upper opening of the jack guide hole  13   a.    
     FIG. 2  shows the hammer  3  and a shank flange  23  (flange) for supporting the hammer  3 . The hammer  3  is comprised of a hammer shank  24  extending in the front-rear direction and a hammer head  25  mounted to a rear end of the hammer shank  24 . The hammer head  25  is opposed to a string S (see  FIG. 1 ) stretched above. The hammer shank  24  is formed of wood, such as hornbeam, and has a slender rod-like shank body  24   a . The hammer shank body  24   a  has its fibers extending in the direction of length thereof, and has a front end thereof formed to have a larger width in the longitudinal direction of the grand piano than the other part of the shank body  24   a . The upper and lower surfaces of the front end are formed as planes parallel with each other. It should be noted that in the following description, the large-width front end of the shank body  24   a  will be referred to as the “expanded-width part  24   b”.    
   The expanded-width part  24   b  of the shank body  24   a  is bifurcated into two left and right arms  24   c  and  24   c . As shown in  FIG. 3 , the two arms  24   c  and  24   c  are opposed to each other in the longitudinal direction of the grand piano with a predetermined space therebetween, and extend forward parallel to each other. Each of the arms  24   c  is formed with a pin hole  24   d  extending therethrough in the longitudinal direction of the grand piano, and a hollow cylindrical bearing  27  formed of felt is fitted in the pin hole  24   d . Further, the shank roller  26  is mounted to the lower surface of the expanded-width part  24   b  of the shank body  24   a  via a support member  26   a . Further, phenol backers  28  and  28  (displacement suppression members) in the form of a thin plate and identical in shape and size are attached on the respective left and right outer side surfaces of the expanded-width part  24   b.    
   Each of the phenol backers  28  is formed of paper impregnated with a phenolic resin, and has a high rigidity and a high dimensional stability against dryness and wetness. The phenol backer  28  has a predetermined thickness (e.g. 0.7 mm), and is formed into a rectangular shape which is long sideways (e.g. 6.3 mm high and 28 mm wide) which is substantially the same as the shape of the outer side surface of the expanded-width part  24   b  of the shank body  24   a . Further, the phenol backer  28  has a predetermined portion formed with a through hole  28   a  through which the associated bearing  27  is fitted and a cutout  28   b  for engagement with the support member  26   a  of the shank roller  26 . The phenol backers  28  formed as above are bonded on the respective opposite outer side surfaces of the expanded-width part  24   b  of the shank body  24   a  in a manner entirely covering these. 
   The shank flange  23  is formed of a synthetic resin, and screwed onto an upper surface of a hammer shank rail  29  (see  FIG. 1 ) extending between the plurality of brackets  15 . As shown in  FIG. 3 , the shank flange  23  extends in the front-rear direction, and is formed to have a rectangular shape in cross section. The shank flange  23  has a rear end thereof formed as an engaging part  23   a  having a slightly smaller width than a dimension between the arms  24   c  and  24   c  of the hammer shank  24  and projecting rearward for engagement between the arms  24   c  and  24   c . The engaging part  23   a  is formed with a pin fitting hole  23   b  extending therethrough in the longitudinal direction of the grand piano. A center pin  20  is passed through bearings  27  and  27  and the pin fitting hole  23   b  between the bearings  27  and  27  with the engaging part  23   a  engaged between the arms  24   c  and  24   c  with a slight clearance from each of the inner surfaces of the respective arms  24   c  and  24   c . The center pin  20  has its central part fixed in the pin fitting hole  23   b  and its opposite ends pivotally supported by the respective bearings  27  and  27 . Thus, the hammer  3  is pivotally supported by the shank flange  23  via the center pin  20  integral with the shank flange  23 . 
   With the above-described arrangement, as the key  1   a  is depressed in a key-off state illustrated in  FIG. 1 , the wippen  11  is pushed up via the capstan button  1   b  to pivotally move upward about the center pin  17 , and the jack  12  and the repetition lever  13  also pivotally move upward about the respective center pins  18  and  19 . At the same time, the hammer  3  is pushed up by the jack  12  via the shank roller  26  to pivotally move about the center pin  20  in the clockwise direction, as viewed in  FIG. 1 , while being guided by the arms  24   c  and  24   c  of the hammer shank  24  and the engaging part  23   a  of the shank flange  23 . This causes the hammer  3  to strike the string S to thereby generate a piano tone. 
   Next, a description will be given of a dry/wet test carried out on a hammer shank.  FIGS. 4A and 4B  show the expanded-width part of the hammer shank subjected to the dry/wet test.  FIG. 4A  shows the hammer shank  24  according to the embodiment, and the phenol backer  28  having a thickness of 0.7 mm is bonded on each of the left and right outer side surfaces of the expanded-width part  24   b  by a predetermined adhesive (e.g. an aqueous vinylurethane-based adhesive) in a manner entirely covering the associated outer side surface. On the other hand,  FIG. 4B  shows a generally used hammer shank  30  according to the prior art. Differently from the present example, the phenol backers  28  are not attached to an expanded-width part  30   b  of the hammer shank  30 . Further, the shank body  24   a  of the hammer shank  24  and a shank body  30   a  of the hammer shank  30  are both made of hornbeam, and each have its fibers extending in the direction of the length thereof (i.e. a vertical direction as viewed in  FIG. 4 ). 
   The hammer shank  24  according to the embodiment, constructed as above, and the hammer shank  30  according to the prior art were produced under normal conditions (e.g. a temperature of 20° C. and a humidity of 50%), and the following two types of dry/wet tests were carried out on the hammer shanks  24  and  30 : 
   (1) Normal Conditions→Humidification→Drying 
   In this dry/wet test, first, the above-described hammer shanks  24  and  30  were left in a test chamber for four days under predetermined humidifying conditions (a temperature of 25° C. and a humidity of 85%). Then, the hammer shanks  24  and  30  after humidification are let standing under predetermined drying conditions (a temperature of 45° C. and a humidity of 10±5%) for four days. 
   (2) Normal Conditions→Drying→Humidification 
   This dry/wet test is distinguished from the above dry/wet test (1) only in that the order of humidification and drying is reversed, and the other conditions are the same as in the dry/wet test (1). 
   In either of the dry/wet tests (1) and (2), 20 pieces of each of the hammer shank  24  according to the embodiment and the hammer shank  30  according to the prior art were prepared, and the dimension between the arms  24   c  and  24   c  of each hammer shank  24  and that between the arms  30   c  and  30   c  of each hammer shank  30  (the dimensions will be referred to as the “arm-to-arm dimension W”) were measured under the normal conditions before the test, after completion of the humidification, and after completion of the drying.  FIGS. 6A and 6B  show results obtained from the respective dry/wet tests (1) and (2). It should be noted that numerical values as the test results are average values of arm-to-arm dimensions W measured under the normal conditions, after the humidification, and after the drying, and respective average values of the difference between the dimensions of arm-to-arm dimension W measured before and after the humidification and that between the dimensions of the same measured before and after the drying. Parenthesized numerical values indicate respective standard deviation values. 
   As shown in  FIGS. 6A and 6B , in the case of the hammer shank  30  according to the prior art, the difference between the dimensions of the arm-to-arm dimensions W measured before and after the humidification and that between the dimensions of the same measured before and after the drying in the dry/wet test (1) were 0.13 mm and −0.23 mm, respectively, while the difference between the dimensions of the arm-to-arm dimensions W measured before and after the drying and that between dimensions of the same measured before and after the humidification in the dry/wet test (2) were −0.11 mm and 0.23 mm, respectively. It should be noted that in the case of the hammer shank  30 , as shown in  FIGS. 5A and 5B , after the humidification, there was perceived a change in which the two arms  30   c  and  30   c  were widened to increase the arm-to-arm dimension W, whereas after the drying, there was perceived a change in which the two arms  30   c  and  30   c  were narrowed to reduce the arm-to-arm dimension W. 
   In contrast, in the case of the hammer shank  24  according to the embodiment, the difference between the dimensions of the arm-to-arm dimensions W measured before and after the humidification and that between the dimensions of the same measured before and after the drying in the dry/wet test (1) were 0.05 mm and 0.00 mm, respectively, while the difference between the dimensions of the arm-to-arm dimensions W measured before and after the drying and that between the dimensions of the same measured before and after the humidification in the dry/wet test (2) were −0.02 mm and 0.09 mm, respectively. Further, the standard deviation values of the respective measured values were both very small ones of not more than 0.06, which means that variations between the hammer shanks  24  as test pieces are small. As can be understood from the above-described results, by attaching the phenol backers  28  and  28  onto the respective opposite outer side surfaces of the expanded-width part  24   b , it is possible to suppress an increase in the dimension between the arms  24   c  and  24   c  to less than one half of the increase in the arm-to-arm dimension W of the conventional hammer shank  30  under the wet environment, and to suppress reduction in the dimension between the arms  24   c  and  24   c  to less than one fifth of the reduction in the arm-to-arm dimension W of the conventional hammer shank  30  under the dry environment. 
   As described above, according to the present embodiment, the phenol backers  28  and  28  are bonded on the respective opposite outer side surfaces of the expanded-width part  24   b  of the hammer shank  24 , and function as splints, so to say, for the arms  24   c  and  24   c  to restrain these. As a consequence, displacement of the arms  24   c  and  24   c  in a direction in which they face each other is suppressed. This makes it possible to stably maintain the dimension between the arms  24   c  and  24   c  to thereby maintain the size of the clearance between each of the inner side surfaces of the respective arms  24   c  and  24   c  and the shank flange  23 , so that occurrence of a stick due to dryness or wetness, and lateral deflection or wobbling of the hammer  3  during its pivotal motion can be prevented. Therefore, smooth and stable operation of the hammer  3  can be ensured irrespective of whether it is dry or wet. Further, since the phenol backer  28  is not only relatively inexpensive, but also has a characteristic of high adhesiveness to wood, it is possible to easily attach the phenol backers  28  and  28  to the hammer shank  24 . Therefore, a hammer  3  which is capable of smooth and stable pivotal motion can easily be realized at low costs. 
   Further, since the phenol backers  28  and  28  can be additionally attached to a hammer shank in an existing grand piano, it is possible to ensure smooth and stable pivotal motion of each hammer in the existing grand piano as well. 
   Next, a description will be given of a method of manufacturing the hammer shanks.  FIGS. 7A ,  7 B and  7 C show part of steps of the method of manufacturing the hammer shanks, in the order of the procedure. As shown in  FIG. 7A , first, a wooden hammer shank member  31  and a pair of phenol backer plates  32  (displacement suppression members) are prepared (preparation step). Specifically, e.g. by cutting a plate of a predetermined shape and a predetermined size, the hammer shank member  31  is prepared which has one end thereof bifurcated into two arm parts  31   a  and  31   a  continuously extending parallel to each other in facing relation. Further, the two phenol backer plates  32  are prepared each of which is formed by a phenol backer having a predetermined thickness (e.g. 0.7 mm) and identical in shape and size to a flat surface  31   b  of the hammer shank member  31  including the outer side surface of the arm part  31   a.    
   Next, the same adhesive as mentioned hereinbefore is applied to the opposite flat surfaces  31   b  and  31   b  of the hammer shank member  31 , and then the phenol backer plates  32  and  32  are bonded onto the respective flat surfaces  31   b  and  31   b  (attachment step). Thus, as shown in  FIG. 7B , the two phenol backer plates  32  and  32  are securely attached on the respective flat surfaces  31   b  and  31   b  of the hammer shank member  31 . Then, as shown in  FIG. 7C , the hammer shank member  31  having the phenol backer plates  32  and  32  attached thereon is cut at predetermined space intervals of T (e.g. 6.3 mm) in a direction of extension of the arm parts  31   a  e.g. by crosscut sawing the hammer shank member  31  along a direction orthogonal to the direction of extension of the arms  31   a  (cutting step). This cuts out a plurality of hammer shanks (hereinafter referred to as “half-finished hammer shanks”) having approximately the same shape as the hammer shank having the above-described phenol backers  28  attached thereon. Thereafter, the half-finished hammer shank is cut or machined, as required, whereby the above-described hammer shank  24 , i.e. the hammer shank  24  having the phenol backers  28  and  28  attached on the respective outer side surfaces of the expanded-width part  24   b  is obtained. 
   According to the method of manufacturing the hammer shanks, the two phenol backer plates  32  and  32  are attached to the hammer shank member  31 , and then the hammer shank member  31  is cut. Therefore, it is possible to manufacture the hammer shanks  24  each having the phenol backers  28  and  28 , more efficiently than in a case where the phenol backers  28  and  28  are attached onto each shank body  24   a . Further, since the other steps than the step of attaching the two phenol backer plates  32  and  32  onto the hammer shank member  31  are the same as the generally employed conventional method of manufacturing hammer shanks, a conventional manufacturing line can be utilized for manufacturing the hammer shanks  24 , which makes it possible to suppress an increase in manufacturing costs. 
   It should be noted that the present invention is not limited to the above-described embodiment, but can be practiced in various forms. For example, although in the present embodiment, the phenol backers  28  are used as displacement suppression members for preventing displacement of the arms  24   c  and  24   c  of the hammer shank  24 , members containing other suitable synthetic resin having a relatively high rigidity and a relatively high dimensional stability may be employed in place of the phenol backers  28 . Further, some phenol backers have a so-called anisotropic property that rigidity is different depending on the direction, and hence when such a phenol backer is used as the phenol backer  28 , it is preferable to bond the phenol backer  28  such that a direction in which rigidity thereof is higher matches the direction of length of the hammer shank  24 . Furthermore, although in the present embodiment, the phenol backer  28  is entirely bonded onto each outer side surface of the expanded-width part  24   b  of the hammer shank  24 , the shape, size, and bonding position of a phenol backer to be bonded may be changed as deemed appropriate, insofar as change in the dimension between the arms  24   c  and  24   c  due to dryness and wetness can be suppressed. In addition, the phenol backer  28  may be attached by another suitable mounting method than bonding. Further, the construction of the hammer shank  24  in the present embodiment is shown only by way of example, and various changes and modifications can be made, as required, without departing from the spirit and scope of the present invention. 
   It is further understood by those skilled in the art that the foregoing are preferred embodiments of the invention, and that various changes and modifications may be made without departing from the spirit and scope thereof.