US20070018396A1

US20070018396A1 - Method for making iron golf club set

Info

Publication number: US20070018396A1
Application number: US11/313,945
Authority: US
Inventors: Ryota Kajita
Original assignee: Bridgestone Sports Co Ltd
Current assignee: Bridgestone Sports Co Ltd
Priority date: 2005-07-25
Filing date: 2005-12-22
Publication date: 2007-01-25
Also published as: JP2007029257A

Abstract

A method for making an iron golf club set includes selecting a plurality of iron golf clubs including a pitching wedge, wherein a difference in carry between each pair of golf clubs, which have consecutive club numbers, is substantially equal to a particular value; further selecting a minimum-carry golf club, which has a loft angle in a range of 55 to 60 degrees and a club length in a range of 34.5 inches to 35.5 inches; measuring carries of at least the pitching wedge and the minimum-carry golf club to obtain a difference in the carry between the pitching wedge and the minimum-carry golf club and; and still further selecting at least one golf club on a basis of the obtained difference in the carry so that a difference in carry between each pair of golf clubs, which have consecutive club numbers, is substantially equal to the particular value.

Description

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-214230 on Jul. 25, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a method for making a an iron golf club set and, more particularly, to a method for making an iron golf club set including at least two iron clubs, each of which has a loft angle larger than that of a pitching wedge and equal to or larger than 45 degrees
2. Description of the Related Art
A golf club set of six irons consisting of clubs numbered from 5 to 9 and a PW (Pitching Wedge) has recently entered the mainstream of iron golf club sets for average golfers. The iron golf clubs are designed so that a difference in carry between each iron golf club and the next-numbered iron golf club is equal to about 10 yards. Hitherto, a iron golf club set of eight irons consisting of clubs numbered from 3 to 9 and a PW has commonly been used. As is seen from a graph shown in FIG. 4, experienced golfers can obtain carries by hitting with iron clubs Nos. 3 to 5, respectively, to realize the differences in carry among these iron clubs as designed. However, intermediate level golfers cannot realize the difference in carry between the iron clubs Nos. 3 and 4 as designed. Golfers, who are insufficient in power and have a low head speed, cannot realize the difference in carry between each pair of consecutively numbered iron clubs among the iron clubs Nos. 3 to 5 as designed. The No. 4 iron is unnecessary for the intermediate level golfers (that is, an iron golf club set consisting of iron clubs Nos. 3 and 5 to 9 and a PW is better for the intermediate level golfers in terms of equalizing the differences in carry between each pair of consecutively numbered iron clubs) Also, the iron clubs Nos. 3 and 4 are unnecessary for powerless golfers. The intermediate level golfers and the powerless golfers have come to obtain sufficient carries by using wood clubs Nos. 7, 9, and 11 and utility clubs, instead of the iron golf clubs Nos. 3 and 4 (see JP 2002-17902 (page 3 and FIG. 1)).
As described above, hitherto, countermeasures for a large carry region, which requires golfers power, have mainly been taken. The golf clubs Nos. 3 and 4 called “long irons” are unnecessary for most of the average golfers. The golfers have come to recognize that it is more useful for lowering their scores to obtain desired carries, which have been required for the long irons, using the wood clubs and the utility clubs.

SUMMARY OF THE INVENTION

There are, however, no countermeasures, which considers a difference in carry between each pair of consecutively numbered iron clubs whose loft angles are larger than that of the PW, that is, a difference in carry between the consecutively numbered clubs whose desired carries are in so-called a small carry region (the opposite of the large carry region). For example, it is more difficult for a golfer, who can hit a distance of 100 yards with a PW on a full shot, to hit a distance of 70 yards with a PW on a control shot than to hit a distance of 100 yards with a PW on a full shot. Golfers should perform control shots with considering an initial speed of a ball and an amount of spin. It is easier to hit a full shot than to hit a control shot in order to obtain a stable carry and make a ball quickly stop after landing.
JP 2002-17902 teaches adding a utility golf club to an iron golf club set instead of the lowest numbered club in the golf club set. However, there has been no golf club set, which is made according to an idea that a carry in the small carry region is obtained by hitting a full shot using a golf club with a higher number than that of a PW.
Accordingly, the invention provides a method for making an iron golf club set including at least two iron golf clubs wherein differences in carry between consecutively numbered golf clubs for the small carry region are equalized.
According to one aspect of the invention, a method for making an iron golf club set includes: selecting a plurality of iron golf clubs including a pitching wedge, wherein a difference in carry between each pair of golf clubs, which are selected from the plurality of iron golf clubs and have consecutive club numbers, is substantially equal to a particular value; further selecting a minimum-carry golf club, which has a loft angle in a range of 55 to 60 degrees and a club length in a range of 34.5 inches to 35.5 inches; measuring carries of at least the pitching wedge and the minimum-carry golf club to obtain a difference in the carry between the pitching wedge and the minimum-carry golf club and a loft angle of the pitching wedge and the loft angle of the minimum-carry golf club; and still further selecting at least one golf club on a basis of the obtained difference in the carry, the obtained loft angle of the pitching wedge and the obtained loft angle of the minimum-carry golf club so that a difference in carry between each pair of golf clubs, which are selected from the group consisting of the pitching wedge, the minimum-carry golf club and the at least one golf club and have consecutive club numbers, is substantially equal to the particular value.
When a sole surface of a head body of the minimum-carry golf club is placed on the ground, a leading edge of a face surface of the head body may be located at or below a geometric contact point between the face surface and a golf ball placed on the ground. Also, the minimum-carry golf club may include a fillet portion, which is posterior to the leading edge, and a curved surface between a tip end of the fillet portion and the sole surface, the curved surface being concaved downward.
According to the above-described structure, in a small carry region, carries can stably be obtained using the golf clubs of such a golf club set. This results in improvement in a score.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a relation between club number and carry of each golf club.
FIG. 2 is a section view showing shape of a golf club head whose desired carry is less than that of a PW.
FIG. 3 is a graph showing a relation in a small carry region between club number and carry of each golf club, and indicating golf clubs to be added to a golf club set.
FIG. 4 is a graph showing the relation between the club number and the carry of each golf club included in a golf club head according to a related art.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Hereinafter, embodiments of the invention are described by referring to the accompanying drawings.
A graph shown in FIG. 1 illustrates a range on full shot of an iron golf club set in the case of an average golfer. This graph also illustrates an example of adding golf clubs, carries obtained with which are smaller than that obtained with the PW, to the iron golf club set, that is, an example of adding two golf clubs “EXT1” and “EXT2” thereto for expansion of the range. The two golf clubs “EXT1” and “EXT2” meet conditions that a carry is stably obtained by hitting with each of these golf clubs on a full shot, and that the obtained carry is in a small carry region and is smaller than that obtained with the PW. Such a club, the carry obtained with which is in the small carry region, is designed according to the following relational expression showing a relation between the initial speed V_bof a ball and the weight M_hof a head: $V_{b} = (\frac{1 + e}{\frac{1 + m_{b}}{M_{h}}}) \cdot V_{h} \cdot \cos (loft angle)$
where “e” designates a coefficient of restitution, and “V_h” denotes a hitting speed. The lower the coefficient “e” of restitution, the lower the initial speed of the ball. The smaller the weight M_hof the head, the lower the initial speed of the ball. The lower the hitting speed V_h, the larger the loft angle. It is important for the club, the carry obtained with which is short, to suppress the initial speed of the ball.
Hereunder, the feasibility of the aforementioned four factors for suppressing the initial speed of the ball will be discussed. First, with regard to reduction in the coefficient of restitution, approach from a material aspect such as using various shock absorbing materials and using plastic materials (e.g., clay) is conceivable. Second, reduction in the weight of the head can be expected to have an advantage in decreasing the initial speed of the ball. According to inventor's past experience, however, there is a fear that golfers sensitively feel difference about the weight of the head of a golf club, and is likely to avoid using such a golf club. This is because the weight of the head seriously affects swing balance, so that swing becomes unstable. Thus, the reduction in the weight of the head is inadequate to be applied to the clubs, which are required to obtain short carry stably. Third, reduction in the hitting speed has hitherto been achieved by decreasing the lengths of clubs. However, when the length of a presently shortest club is decreased, a swing plane is changed, so that a golfer's swing becomes unstable. Therefore, this method is unsuitable for being applied to the clubs, which are required to obtain short carry stably. Fourth, increase in the loft angle results in an acute angle formed between the face portion and the sole portion of each club. Thus, a leading edge of the head is sunk into the ground. Alternatively, a ball is hit at the tip end of the leading edge of the head to thereby top the ball. Consequently, it is necessary to take countermeasures to both of these. A ball contact point between the ball and the club face is positioned low in the case of the wedge whose loft angle is large. The leading edge is positioned high in the case of the wedge having a large bounce angle. Therefore, in a case where a ball placed on a fairway is hit with a wedge whose ball contact point is positioned low and whose leading edge is positioned high, it is incontrovertible that a golfer may top the ball. To prevent the ball from being topped, the inventor has devised the shapes of the leading edge and the sole as follows. That is, the leading edge and the sole are shaped as shown in FIG. 2 FIG. 2 shows a section view taken along the central plane of a face surface 2 of a wedge when a ball 4 placed on the ground is hit with the wedge whose face surface 2 is set up to be perpendicular to the direction of a target of the ball 4, at prescribed loft angle of 60 degrees. A head body 1 is shaped so that no cavity is defined in the rear surface of the face portion thereof. The material of the head body 1 is copper alloy. However, the head body 1 may have a structure in which a part in the vicinity of a leading edge 3 is made of stainless steel, thereby to enhance the durability thereof. Incidentally, the head body 1 means a part obtained by removing a hose 1 portion at which the club head is attached to a shaft. The leading edge 3, which is the bottom of the face surface 2, is provided at a place (H′) downwardly extending about 2 mm along the face surface from a geometric contact point that has a height (H) and that is defined as a point at which the face surface 2 is put into tangential contact with the ball 4 placed on the ground at a normal loft angle (60 degrees) when normal hitting is performed. That is, in a state where the sole surface 5 is brought into contact with the ground while the face surface 2 is adjusted to the normal loft angle (θ=60 degrees), a point (H) at which the face surface 2 is in tangential contact with the ball 4 placed on the ground is obtained. Then, a point (H′) is obtained by extending a line along the face surface 2 about 2 mm downwardly. The leading edge 3 is positioned at the thus-obtained point H′ It is noted that the length, by which the face surface 2 is extended, is limited within a range in which the bottom (A) of a fillet portion (to be described later) does not interfere with the ground.
An arc 6, which has this leading edge 3 as the center of a circle and has a radius of about 2 mm, is drawn. Then, an intersection point between this arc 6 and a segment 7 extending perpendicularly to the face surface 2 from the leading edge 3 is obtained. The obtained intersection point is set to be the bottom (A) of the fillet portion 8. Incidentally, the position of the bottom (A) is not limited to that determined in this embodiment and may freely be set on the arc 6 within an angular range of 90° from a point positioned vertically just under the center of a circle (the point H′). Further, a part extending between the bottom (A) of the fillet portion 8 and the leading edge 3 (H′) may be connected by a circular arc, whose radius is equal to or larger than 2 mm, or a straight line (in this embodiment, a straight line is employed). The reason for employing such a large arc whose radius is equal to or larger than 2 mm or the straight line is that the fillet portion 8 is prevented from being formed like an acute-angled part and from having a small thickness to thereby reduce the strength thereof, and that it is prevented to sink the leading edge 3 into the ground.
Meanwhile, the sole surface 5 is formed by the following designing procedure. That is, first, a segment i parallel to the face surface 2 is drawn at a distance, which is equal to a maximum value (T) of the thickness of the head, in a region of perpendicularly rearward of the face surface 2. An endpoint C of the sole surface 5 is disposed on this segment i. On the other hand, a segment k parallel to the face surface 2 is drawn at a distance of 2 mm in a region perpendicularly rearward of the face surface 2. A point B is disposed on this segment k. Subsequently, a segment j, which intersect with the segment k, is drawn from a point (a tentative point C) on the segment i in a direction of a prescribed bounce angle (10 degrees in this embodiment) An intersection point between the segment j and the segment k is set to be a tentative point B. Then, an arc is drawn, which has the segment j between the tentative points B and C as its chord. This arc is upwardly and downwardly moved along the segment i and the segment k if the tentative point C moves on the segment i. The tentative points B and C, which are in a case where this arc is in contact with the ground, are set to be a true point B and a true point C. An arc at that time is set to be a sole radius (R) . Also, a curved surface formed by an arc extending between the point B and the point C is the sole surface 5.
Subsequently, a curved surface (M) is formed by a downwardly concave arc so that the segment k and the sole surface 5 are in contact with each other. Further, an end part of the fillet portion 8 is formed by connecting a point, at which the curved surface M is in contact with the segment k, to the bottom A of the fillet portion 8 by a straight line. Incidentally, the segment k is set at a position at a distance of about 2 mm in a perpendicularly rearward region of the face surface 2. Also, the downwardly concave curved surface (M) is in contact with the segment k. This prevents the thickness of the end part of the fillet portion 8 from becoming extremely thin. Further, in a case where the segment k is set far away from the face surface 2 and where the radius of the circular arc constituting the curved surface (M) is too large, the thickness of the fillet portion 8 becomes too large, so that the fillet portion 8 is susceptive to interference from the ground, and that the bottom of the face surface 2 cannot sufficiently be projected between the ground and the ball. The lower limit of the radius of the circular arc constituting the curved surface (M) is determined with considering that the root part of the fillet portion 8, which part is in the vicinity of the point B, is prevented from being extremely thin. This is because the durability of the fillet portion 8 is prevented from becoming controversial.
The heads of the iron golf clubs, carries obtained with which are in the small carry region, are configured as described above. Thus, when a ball placed on the ground is hit, the normal hitting is realized on the face surface at the loft angle even in a case where the ball is hit with a part provided in the vicinity of the leading edge of the head. Consequently, occurrence of a topping shot, which is a mistaken shot, can be prevented, similarly to the related art. Also, in view of the fact that a ball frequently sits up on the top of the grass, the club head having this structure enables that the ball is always hit at the geometric contact point of the face surface.
Incidentally, the bounce angle is measured as an angle formed between the ground and a tangential line that is in tangential contact with a sole radius at the midpoint between the points B and C. The loft angle of the iron club to be used to obtain a carry in a small carry region is equal to or larger than 45°, preferably, 50°. The bounce angle thereof is equal to or larger than 4°.
The above-described golf club is employed as a minimum-carry golf club head having the minimum carry among golf clubs of a golf club set. That is, the minimum-carry golf club head has a loft angle in a range of 55 to 60 degrees and a club length in a range of 34.5 inches to 35.5 inches. When a sole surface of a head body of the minimum-carry golf club is placed on the ground, a leading edge of a face surface of the head body the minimum-carry golf club is located at or below a geometric contact point between the face surface and a golf ball placed on the ground. The minimum-carry golf club includes a fillet portion, which is posterior to the leading edge, and a curved surface between a tip end of the fillet portion and the sole surface. The curved surface is concaved downward. The loft angle of the minimum-carry golf club may be set up with considering a golfer's swing and/or facility of hitting a golf ball with it. Here, a minimum-carry golf club having a loft angle of 60 degrees is called as “W60,” and parameters of other short iron clubs (#8 and #9), PW and W60 are set up as shown in a table 1.

TABLE 1

Club No.

8 9 PW W60

Loft Angle (degrees) 36 40 45 60

Lie Angle (degrees) 62.5 63 63.5 63.5

Length (inches) 36.25 35.75 35.25 35.25

Swing Weight D0 D0 D1 D0
The trial hitting of each golf club designed as described in Table 1 was performed by “intermediate level” golfers and “powerless” golfers. Results are described in the following Table 2. The unit of carries described in Table 2 is “yards”.

TABLE 2

Club No.

8 9 PW W60

Intermediate Level Golfer 140 129 117 73

Powerless Golfer 119 108 95 55
A graph illustrated in FIG. 3 shows golf clubs (newly added clubs X), which “intermediate level golfers” and “powerless” golfers should add to their golf club set between the PW and the W60 in the small carry region, according to the results of the trial hitting, which are shown in Table 2. The golf clubs X corresponding to a difference in carry between each pair of consecutively numbered clubs among the #8 club to the PW are added. That is, a difference in carry between each pair of consecutively numbered clubs among PW, W60 and the clubs X is equal to a difference in carry between the #8 club and #9 club and that between the #9 club and the PW.
Many golfers really feel that most of golfers can realize the uniform difference in carry between consecutively numbered short irons even without sufficient power and skill. This is corroborated by data shown in Table 2 and FIG. 3. In FIG. 3, as indicated by solid lines, a trial-model club W60 is numbered next to the PW. However, the reduction in the carry between the PW and the club W60 is large. Thus, in the case of the intermediate level golfer, three clubs designated with “X” between the PW and W60 are added to the club set. Further, in the case of the powerless golfers, two clubs designated with “X” between the PW and W60 are added to the club set. Thus, as indicated by dashed lines in FIG. 3, a new golf club set can be configured so that the carries obtained by the consecutively numbered clubs are uniformly and discretely changed with a uniform variance. That is, when golfers find golf clubs, which provide carries in the small carry region stably on a full shot, he/she can make an iron club set, which can cover a range on full shot shorter than that of short iron clubs as well as the range of full shot achieved by his/her current iron club set, by adding new clubs having loft angles discretely changed with a uniform variance, such as “X” shown in the drawings.
In this example, the golfers swung a wedge-like club on full shot. Generally, it is rare to swing a wedge with on a full shot. Additionally, the loft angle thereof is 60°. Thus, two golfers felt odd to some extent. The odd feeling occurs due to the fact that a ball hitting speed and the energy of a ball hit with the club on a full shot are low. These golfers might have feel that they hit ping-pong balls. Therefore, from the viewpoint of sensory evaluation, the maximum loft angle is set at 60° in this example.
The golf clubs, the carries obtained with which are between those respectively obtained by the W60 (the minimum carry club) and the PW are determined as illustrated in FIG. 3. That is, the carries respectively obtained by the W60 and the PW are measured by actually hitting balls with these clubs or by using a golf club carry measuring system. Then, the loft angles and the difference in carry therebetween are obtained. Subsequently, a graph showing such data is plotted. Thereafter, the difference between the carries respectively obtained by the W60 and the PW is equally divided according to the need. Then, the iron golf clubs indicated by “X” in FIG. 3 are added to the iron golf club set.
It is desirable that the shape of the head of each of the golf clubs indicated by “X” in FIG. 3 is similar to the shape of the head of the W60. These golf clubs, the carries obtained with which are in the small carry region, are frequently used in a case where it is necessary to hit a ball on a relatively short shot around the green and in a bunker by setting the loft angle at a large value, which is equal to or larger than 45°, and by spinning the ball with the face surface 2. The aforementioned head shape can prevent occurrence of a so-called topping shot, which is a mistaken shot, that is, prevent a ball from being directly hit by the leading edge 3 provided at the bottom of the face surface 2. A ball can be always hit at the geometric contact point in a state in which the face surface 2 is in tangential contact with the outer periphery of the ball. Thus, a ball is lotted with a desired amount of spin. Consequently, accurate carries and orientation can be obtained.
Further, in a case of employing such a large loft angle, the leading edge 3 takes the form of an acute angle, so that when hitting a ball, what is called a “duff shot” is liable to occur when hitting a ball. To prevent occurrence of a duff shot, hitherto, the setting of a large bounce angle to be equal to or larger than 4°, and the employment of a small sole radius and a wide sole width have been applied to the golf clubs. Consequently, the height of the leading edge 3 is increased still more. This has tended to easily cause the topping shot. However, the application of the aforementioned shape of the head results in that the leading edge 3 is always disposed under the geometric contact point, that occurrence of a topping shot, which is a mistaken shot, is almost prevented, and that the advantages of the large loft angle can be obtained enough.

Claims

1. A method for making an iron golf club set, the method comprising:

selecting a plurality of iron golf clubs including a pitching wedge, wherein a difference in carry between each pair of golf clubs, which are selected from the plurality of iron golf clubs and have consecutive club numbers, is substantially equal to a particular value;

further selecting a minimum-carry golf club, which has a loft angle in a range of 55 to 60 degrees and a club length in a range of 34.5 inches to 35.5 inches;

measuring carries of at least the pitching wedge and the minimum-carry golf club to obtain a difference in the carry between the pitching wedge and the minimum-carry golf club and a loft angle of the pitching wedge and the loft angle of the minimum-carry golf club; and

still further selecting at least one golf club on a basis of the obtained difference in the carry, the obtained loft angle of the pitching wedge and the obtained loft angle of the minimum-carry golf club so that a difference in carry between each pair of golf clubs, which are selected from the group consisting of the pitching wedge, the minimum-carry golf club and the at least one golf club and have consecutive club numbers, is substantially equal to the particular value.

2. The method according to claim 1, wherein:

when a sole surface of a head body of the minimum-carry golf club is placed on the ground, a leading edge of a face surface of the head body is located at or below a geometric contact point between the face surface and a golf ball placed on the ground, and

the minimum-carry golf club comprises:

a fillet portion, which is posterior to the leading edge; and

a curved surface between a tip end of the fillet portion and the sole surface, the curved surface being concaved downward.

3. The method according to claim 1, further comprising:

plotting the obtained carries in a graph, wherein:

the at least one golf club head is selected using the graph.

4. The method according to claim 2, wherein the at least one golf club has the same head structure as that of the minimum-carry golf club.

5. A method for making an iron golf club set, the method comprising:

selecting a pitching wedge and a minimum-carry golf club, which has a loft angle in a range of 55 to 60 degrees and a club length in a range of 34.5 inches to 35.5 inches;

measuring carries of the pitching wedge and the minimum-carry golf club to obtain a difference in the carry between the pitching wedge and the minimum-carry golf club and a loft angle of the pitching wedge and the loft angle of the minimum-carry golf club; and

further selecting at least one golf club on a basis of the obtained difference in the carry, the obtained loft angle of the pitching wedge and the obtained loft angle of the minimum-carry golf club so that a difference in carry between each pair of golf clubs, which are selected from the group consisting of the pitching wedge, the minimum-carry golf club and the at least one golf club and have consecutive club numbers, is substantially equal to each other.