JPH0657274B2 - Method for manufacturing golf club shaft - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a stepped shaft used in a golf club.

[Prior Art] Steel stepped shafts used for golf club shafts are manufactured, for example, by step processing using a seamless pipe as a raw pipe. In the step processing, the outer diameter of the shaft is formed so as to gradually decrease toward the head side.

The stepped shaft has a lower cost than the carbon shaft and the like, and has less twisting during a swing. Therefore, both professional golfers and amateur golfers,
Frequent use of stepped shafts.

A shaft for a golf club has a role of connecting a player and a golf head, and includes important factors that determine a flight direction and a flight distance. Above all, in order to prevent the head from shaking at the moment of impact and to fly the ball in a desired direction, it is necessary that the shaft has little twist. Regarding the flight distance of the ball, the hardness of the shaft (flex) and the bending point (kick point) that match the player's individuality are taken into consideration when the club is selected so that the player's ability is fully exerted. For this reason, stepped shafts have been favored by a great number of people, and the variety of types is also increasing.

Recently, not only club selection based on physical factors such as kick point and flex, but also club selection based on the quality of feeling when actually gripping or shaking a golf club is increasing. The feeling is
It varies from player to player.

A swing weight is used as an index indicating feeling. For example, an index in which the feeling is divided into about 30 stages from B5 to E4 is announced by Kenny Smith, and each rank is determined based on the player's physical strength. Generally, even with the same weight, a club with a large grip does not feel the weight of the head and is shaken lightly. Conversely, if the grip is thin, it feels heavy.

On the other hand, American Persimmon, which is a hard and beautiful grain, is often used for the wood head of golf clubs. However, when American Persimmon is attached to the conventional steel stepped shaft, the swing weight becomes too large, and it becomes a golf club that only advanced players can use. Therefore, the frequency of American Persimmon being used for the driver's club head is 10 to 20%.
And very low.

[Problems to be Solved by the Invention] When American Persimmon or the like and wood are used as a head material, one of the causes for increasing the swing weight is the weight balance of the stepped shaft.
According to the molding result, the thickness of the conventional stepped shaft gradually increases toward the club head side for each step. The kick point of the stepped shaft shifts to the grip side according to this variation in wall thickness. Therefore, if a wood head with a large specific gravity such as American Persimmon is attached, the swing weight becomes too heavy.

The present invention has been devised to solve such a problem, and a head having a large specific gravity such as American Persimmon is also attached by making the thickness of each step from the grip side to the head side substantially equal. An object of the present invention is to provide a shaft for a golf club that is capable of providing a good feeling when swinging.

[Means for Solving the Problems] In order to achieve the object, the manufacturing method of the present invention, when forming a steel pipe into a stepped shaft by step processing, the wall thickness T _{n of} each step is _expressed by the following formula (1). ), The stepped processing is performed so that the conditions specified in () are satisfied.

However, in the formula (1), t ₁ is the thickness on the grip side,
D ₁ is the outer diameter on the grip side, D _n is the outer diameter of each step, and α is a value in the range of 0.60 to 0.80 determined by the material of the pipe, the diameter reduction ratio, the elongation of the shaft, and the like.

In this shaft, a raw tube with the same thickness in the longitudinal direction is initially thick on the grip side and set to a predetermined thin thickness on the head side, and the wall thickness gradually changes from the grip side to the head side. The taper pipe is manufactured by forming the taper pipe into a stepped shape and subjecting the taper pipe to a stepped process so that the wall thickness T _{n of} each step satisfies the condition defined by the equation (1).

[Operation] The stepped shaft is formed by die-casting a raw pipe having a constant wall thickness in the longitudinal direction, that is, a normal steel pipe. The diameter of each step is reduced to a predetermined diameter according to the size of the die during molding. At this time,
Since the excess thickness is consumed as the thickness due to the diameter reduction, the thickness of the step portion on the small diameter side is increased.

In the step processing, when the thickness between the steps satisfies the requirement defined by the formula (1), the increase in the thickness of the step portion on the small diameter side is suppressed. Expression (1) is a relational expression found by experiments by the present inventors and is also effective in satisfying the characteristics required for the golf club shaft.

In the manufactured shaft, the thickness of each step is approximately equal. Therefore, when a head made of wood material having a large specific gravity such as American Persimmon is attached, the weight balance of the shaft itself is biased toward the grip side, so that a feeling that is well balanced as a whole can be obtained during a swing. Further, since the kick point can be shifted to the head side, it is favorably used as a golf club shaft which is also preferable for amateur players.

[Example] In this example, a steel pipe having a constant wall thickness in the longitudinal direction was used as a raw pipe. The raw pipe was tapered to be a pipe having an inner peripheral surface tapered as shown in FIG. The outer diameter D _{1 of} this tapered tube is constant, and the wall thickness t between points A and B corresponds to the wall thickness as it is. Between points C~D is set to a predetermined thin thickness t _n. Between points B and C, the inner surface is formed in a tapered shape in which the wall thickness is gradually reduced as t ₁ → t _n . In FIG. 1, only the radial length of the pipe cross section is enlarged and displayed.

It has been experimentally confirmed that the wall thickness t satisfies the following relational expression when the wall thickness and outer diameter between C and D after processing are T and D, respectively.

Here, α is a value determined according to the material of the pipe, the elongation of the shaft, the diameter reduction ratio, etc., and is usually in the range of 0.60 to 0.80.

The tapered pipe of FIG. 1 is stepped to obtain a stepped shaft having the cross section shown in FIG. The stepped shaft 1 has a stepped portion whose outer diameter is gradually reduced as shown in FIG. 3, and has a grip 2 and a head 3 as shown in FIG.
It becomes a golf club to which is attached.

T _{1 to} T _{n in} FIG. 2 indicate the wall thickness of each stepped portion between points B to D, and are obtained by the following relational expression.

This relational expression is a relational expression found by the present inventors from many experiments. Note that D _n represents the outer diameter of the nth stepped portion.

Fig. 3 shows the inspection points of the obtained stepped shaft.
It is a model when the wall thickness of each part is measured by dividing it into 7 parts. 1st comparing the measurement result with the conventional stepped shaft
Shown in the table.

As is clear from Table 1, in the pipe material of the initial setting, the stepped shaft of the present invention has a difference of 0.03 mm.

The stepped shaft of the present invention has the balance point closer to the grip side and the kick point closer to the head side than the conventional stepped shaft. As a result, when compared with the conventional stepped shaft under the condition that the shaft weight is the same for professional clubs with the same flex, the stepped shaft of the present invention increases the weight of the club head 3 by 10 g, but the conventional shaft does not. It can be used with the same swing weight feeling of D ₆ rank.

This feeling is compared in Table 2.

As shown in Table 2, when the stepped shaft according to the present invention is used, the swing weight D ₆ is increased as compared with the conventional stepped shaft even if the total weight and the shaft weight are the same. You can lower D ₀ and 6 ranks.
Therefore, even an amateur golfer can obtain a golf club that can be swung sufficiently lightly.

In the above example, the variation when the inspection points were divided into 17 points and measured was a difference of 0.03 mm. When this variation is 0.06 mm or less, the good feeling described above is maintained.

[Effects of the Invention] As described above, in the present invention, the stepped shaft is manufactured from the steel pipe through the tapered pipe. At this time, by maintaining the wall thickness of each step in a predetermined relationship, the influence of the excess thickness at the time of processing is offset, and a stepped shaft in which the wall thickness of each step portion is approximately equal is obtained. Since the obtained stepped shaft has a uniform thickness as a whole,
Even if wood with a large specific gravity such as American Persimmon is used, the club will have swing weight for amateurs. Therefore, it is possible to use a hard material with beautiful wood grain such as American persimmon, and the kick point shifts to the head side, so that the club has a good feeling.

[Brief description of drawings]

Fig. 1 shows an intermediate stage pipe with a tapered inner surface, second
The figure shows the cross section after step processing, FIG. 3 shows the side surface of the shaft showing the position of the inspection point, and FIG. 4 shows the wood club using the step shaft. 1: Stepped shaft, 2: Grip, 3: Head

Claims (1)

[Claims] 1. A raw pipe having an equal wall thickness in the longitudinal direction is set to a predetermined thin wall thickness on the head side while maintaining the initial wall thickness on the grip side, and the wall thickness is sequentially increased from the grip side to the head side. A method for manufacturing a golf club shaft, characterized in that the taper tube is formed into a changed tapered tube, and stepped processing is performed on the tapered tube so that the wall thickness T _{n of} each step satisfies the condition defined by the following equation. .