Abstract:
A method for manufacturing golf club head includes: preparing a head blank for an iron type golf club head, the head blank having a recess serving as a measure of polishing or grinding at least in a portion of a sole part of the head blank; and polishing or grinding the head blank according to the recess.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-119806, filed on Jun. 10, 2014, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a method for manufacturing a golf club head, specifically, to a method for manufacturing an iron type golf club head including a step of machining a head blank by polishing or by grinding. 
         [0004]    2. Description of the Related Art 
         [0005]    A metal-made golf club head is manufactured through a step of finishing, by polishing or by grinding, a head blank manufactured by casting or by forging (for example, JP-A-2011-125611). 
         [0006]    As a method for polishing or grinding a head blank, in JP-A-H09-215789, there is disclosed a method for previously forming in a metal-made shell a large number of small grooves each having a depth corresponding to a grinding-off thickness and grinding the shell down to the depth of the small grooves. According to this method, a worker can polish the metal-made shell evenly down to a desired depth without requiring skill. 
         [0007]    In JP-A-H09-215789, the metal-made shell is the element of a wood type golf club head and has a hollow structure. In this document, small grooves are formed in the whole of the outer surface of the shell and the shell outer surface is ground evenly. 
         [0008]    In an iron type golf club head to be manufactured through a machining step of polishing or grinding a head blank, an operation to finish the back surface side of a sole portion requires skill. That is, the iron type golf club head is smoothly curved from its sole surface to its back surface and, therefore, not only the sole surface and back surface must be polished or ground but also the curved portion must be also polished or ground. When the amount of polishing or grinding of the curved portion is larger or smaller than a specified range, the shape of the sole portion is not finished according to a design value, thereby impairing the performance of the golf club. 
       SUMMARY 
       [0009]    An object of the invention is to provide a golf club head manufacturing method capable of finishing the sole part of an iron type golf club head with high precision. 
         [0010]    The invention provides a method for manufacturing golf club head includes: preparing a head blank for an iron type golf club head, the head blank having a recess serving as a measure of polishing or grinding at least in a portion of a sole part of the head blank; and polishing or grinding the head blank according to the recess. 
         [0011]    The recess may preferably be a groove. Also, the recess may preferably be formed on the back surface side of the sole part. 
         [0012]    According to an embodiment of the invention, when the depth of the recess is reduced down to a specified depth, polishing or grinding is ended. And, according to another embodiment of the invention, the recess has a shape having a width reducing toward its deeper side. 
         [0013]    According to a still embodiment of the invention, the recess includes first and second parts connected together in the depth direction, the second part situated deeper than the first part is smaller in width than the first part, and, when the outer surface of the head blank being polished or ground reaches a step surface constituting the boundary between the first and second parts or the second part, polishing or grinding is ended. 
         [0014]    According to a yet another embodiment of the invention, as the recess, there are formed a first recess and a second recess having a larger depth than the first recess, and, when the first recess is eliminated by polishing or by grinding, polishing or grinding is ended. 
         [0015]    In the golf club head manufacturing method of the invention, since the recess serving as a measure of the machining amount by polishing or by grinding is formed in the sole part, the sole part can be polished or ground to an expected shape with high precision. 
         [0016]    When the recess is formed on the back surface side of the sole part, intersecting portion between the sole part and the back surface of the golf club head can be finished to an expected shape with high precision. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawing which is given by way of illustration only, and thus is not limitative of the present invention and wherein: 
           [0018]      FIG. 1  is a perspective view of a head element, showing a method according to an embodiment; 
           [0019]      FIG. 2  is a front view of the sole portion of the head element; 
           [0020]      FIG. 3  is a section view of a groove; 
           [0021]      FIG. 4  is a section view of a groove; 
           [0022]      FIG. 5  is a section view of a groove; 
           [0023]      FIG. 6  is a section view of a groove; and 
           [0024]      FIGS. 7A and 7B  are front views of the sole portion. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Description is given below of an embodiment with reference to the drawings.  FIG. 1  is a perspective view of a head blank  1  when viewed from the back side and sole side thereof.  FIG. 2  is a front view of the head blank  1  when viewed from the sole side. 
         [0026]    The head blank  1  is a metal-made blank manufactured by casting or by forging. The head blank  1  includes a face part  2 , a sole part  3  constituting its bottom surface, a hosel part  4  for mounting a shaft thereon and a back surface  5 . On the back surface  5  side of the sole part  3 , there are formed grooves  10  constituted of recesses as a measure of the machining amount. In this embodiment, the groove  10  includes a first groove and a second groove. The first groove extends along a first direction crossing obliquely a ball flying direction and a direction defined by a line connecting the toe side with the heel side. The second groove extends along a second direction crossing obliquely the first direction so that the groove  10  provides a mesh-like appearance. 
         [0027]    The recess such as the groove  10  may be formed by a providing a projection on a mold for manufacturing the head blank  1 , or may be formed by machining, for example, by pressing or by cutting. 
         [0028]    The width of the groove  10  may preferably be 0.1 mm or more, and may more preferably be 0.2 mm or more. The width of the groove  10  may preferably be 1 mm or less, and may more preferably be 0.8 mm or less. The excessively large groove width can raise a fear of giving a bad influence on the impact resilience property or the like of the sole part. The excessively small groove width can raise a fear of collapsing the groove in polishing or in grinding, or disturbing visual confirmation of the groove. 
         [0029]    The depth of the groove  10  may preferably be 0.1 mm or more, and may more preferably be 0.2 mm or more. The depth of the groove  10  may preferably be 1 mm or less, and may more preferably be 0.6 mm or less. The excessively large groove depth may be excessively larger than necessary with respect to the polishing amount or grinding amount, or can raise a fear of giving a bad influence on the impact resilience property or the like of the sole part. The excessively small groove depth can raise a fear of eliminating the groove before a necessary amount of polishing or grinding is performed. 
         [0030]    The section shape of the groove  10  may be square as shown in  FIG. 3 , or may be a U-like shape (not shown). Also, like a groove  11  shown in  FIG. 4 , it may be a trapezoidal section shape the groove width of which becomes smaller toward the deep (groove bottom surface) side. Or, like a groove  12  shown in  FIG. 5 , it may be a composite section shape in which the entrance side is a large width portion  12   a , the deep side is a small width portion  12   b , and the boundary between them is a step surface  12   c . That is, the section shape of the large width portion  12   a  is a first trapezoidal section shape the width of which becomes smaller toward the deep (groove bottom surface) side, whereas the section shape of the small width portion  12   b  is a second trapezoidal section shape the width of which becomes smaller toward the deep (groove bottom surface) side and is smaller than that of the first trapezoidal section shape. The first and second trapezoidal section shapes are connected together and the bottom surface of the first trapezoidal section shape provides a step surface  12   c.    
         [0031]    In polishing or grinding the back surface  5  side of the sole part of the head blank  1  having the grooves  10 , when the depth of the groove  10  is reduced down to a specified depth, polishing or grinding may preferably be ended. Since the specified depth is corresponding to an expected shape, the polishing or grinding amount provides a specified amount, thereby enabling the sole shape to provide the expected shape with high precision. 
         [0032]    In the case of a groove  11  shown in  FIG. 4 , when the groove width of the groove  11  is reduced down to a specified width, polishing or grinding may preferably be ended. To measure the groove width is often easier than to measure the groove depth. However, in the case of the groove  11  as well, when the depth of the groove  11  is reduced down to a specified depth, polishing or grinding may be ended. Besides, the specified width is corresponding to the expected shape. 
         [0033]    In the case of a groove  12  shown in  FIG. 5 , when the outer surface of the head blank  1  being polished or ground becomes flush with the stepped surface  12   c , polishing or grinding may preferably be ended. When machining reaches the stepped surface  12   c , since the groove width is reduced and the groove is no longer a two-step-shaped groove, an operator can confirm the machining amount simply by viewing the appearance of the head blank  1 . However, in this case as well, when polishing or grinding advances to the second trapezoidal section shape  12   b  and thus the groove width becomes small, polishing or grinding may be ended. 
         [0034]    In the invention, as shown in  FIG. 6 , there are previously formed a first groove  13  having a comparatively small depth and a second groove  14  having a depth larger than the depth of the first groove, and when the first groove  13  disappears but the second groove  14  remains, polishing or grinding may be ended. Since the groove  13  disappears and the groove  14  remains, the operator can confirm the machining amount simply by viewing the appearance of the blank. 
         [0035]    In all cases shown in  FIGS. 4 to 6 , the polishing or grinding amount can be secured as accurately as specified and thus a golf club head the sole shape of which becomes an expected shape with high precision can be manufactured. By allowing the groove to remain after polishing or grinding, in a checking operation to be executed later, an operator can confirm at a glance that that it is not machined excessively. 
         [0036]      FIGS. 7A and 7B  show an example for machining (polishing or grinding) a head blank  1  having, on the back surface  5  side of the sole part  3 , grooves  10  serving as a measure for maintaining the shape of the sole part  3 .  FIG. 7A  is a front view of the sole part  3  before machined, and  FIG. 7B  is a front view of the sole part  3  when machined excessively. A broken line in  FIG. 7B  shows the rear edge of the sole part before machined. In this example, as shown in  FIG. 7B , it can be seen at a glance that the half of the groove  10  is eliminated by machining and the sole shape is not maintained. In this manner, the groove  10  can also be used as a measure for maintaining the sole shape before machined. 
         [0037]    In the above embodiment, the grooves  10  have a meshed shape. However, it may also be a parallel-lines shape, a zigzag shape, or an undulated shape. Also, the grooves may have any one of various shapes, for example, a circular shape, an oval shape, a square shape, a U-like shape, an L-like shape, a cruciform. 
         [0038]    In the above embodiment, as the recesses, there are formed the grooves  10 . However, recessed holes may also be formed, or grooves and recessed holes may be both formed. Also, in the above embodiment, the grooves are formed on the back surface side of the sole part  3 . However, the recesses may also be formed in other portions. 
         [0039]    The invention can be applied not only to the iron type golf head but also to golf heads having other shapes.