JPH11285550A - Shaft set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shaft set for simply producing a golf club set capable of swinging all the clubs in the same timing by nearly equalizing the inertia moments of the respective clubs. SOLUTION: In this shaft set for golf club set consisting of plural clubs gradually increasing the weight of a head and gradually reducing the length of a shaft as the increase of the numeral figure of a number, the shaft set for a golf club set consisting of iron clubs gradually reduces the inertia moment of the shaft within the range of 5 to 9% according to the increase of the numeral figure of the number by one and a shaft set for a golf club set consisting of wood clubs gradually reduces the inertia moments of the shaft within the range of 2 to 4% according to the increase of the numeral figure of the number by one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shaft set for a golf club, and more particularly to a shaft set used for manufacturing a golf club set including a plurality of clubs having substantially the same moment of inertia.

[0002]

2. Description of the Related Art A set of iron clubs and a set of wood clubs are configured such that the head weight gradually increases and the length of the shaft gradually decreases as the number of the club increases. It is necessary that the golfer be designed to fly a predetermined distance by drawing a trajectory set in advance for each club (counter) when the golfer hits the ball with a certain swing. Therefore, a club set has been developed in which a golfer can swing all clubs in the club set with a uniform swing feeling by setting the moments of inertia of the respective clubs constituting the club set to be the same.

[0003]

On the other hand, a golf club shaft made of a fiber reinforced resin using carbon fiber or the like is lighter in weight and longer in hitting distance than a conventional steel shaft. The use rate of such materials as shafts for irons and shafts for iron clubs has been dramatically increased. Such a shaft made of fiber-reinforced resin is usually manufactured by a sheet winding method, an internal pressure molding method, or the like using a prepreg sheet in which fibers are impregnated with a resin. As the fibers constituting the prepreg sheet, carbon fibers, boron fibers, aramid fibers, titanium fibers, and the like are used, and various modified resins are also used as the resin impregnated in the fibers, and the fibers are used for shafts. The prepreg sheets to be used are various. Therefore, it is possible to develop a golf club shaft having desired characteristics by combining different prepreg sheets.

Conventionally, a shaft set designed for a club set is manufactured by manufacturing a shaft designed to have predetermined characteristics and cutting the shaft at a predetermined length for each count. Many, and in part, there are shaft sets consisting of individually manufactured shafts with the desired properties for each count.

However, no matter which of the conventional shaft sets is used, it is difficult to make the moments of inertia of the clubs of the respective counts substantially the same only by mounting the head on the tip portion and the grip on the butt portion. It was difficult. That is, the weight of a wood head or an iron head is determined with a certain width for each count, but a shaft given predetermined characteristics by combining different prepreg sheets or the like has a moment of inertia of the shaft. Is irregular or does not adapt to the change in head weight for each count, so that the manufactured club has an uneven moment of inertia. For this reason, in order to make the moments of inertia of the clubs substantially the same, it is necessary to make fine adjustments to the individual shafts constituting the shaft set, and there has been a problem that the club manufacturing process is extremely complicated.

The present invention has been made in view of such circumstances, and a shaft set for easily manufacturing a golf club set in which each club has substantially the same moment of inertia and can swing all clubs at the same timing. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a plurality of irons configured such that the head weight gradually increases and the length of the shaft gradually decreases as the number increases. A shaft set for a golf club set comprising a club, wherein the moment of inertia of the shaft increases from 5 to 9 as the number of the count increases by one.
%.

The present invention is also a shaft set for a golf club set comprising a plurality of wood clubs, wherein the head weight gradually increases and the length of the shaft gradually decreases as the number increases. The configuration is such that the moment of inertia of the shaft gradually decreases within the range of 2 to 4% as the number of the count increases by one.

According to the present invention, each shaft has one bulging portion between the tip side and the butt side, and the distance from the tip side to the bulging portion gradually decreases as the count number increases. The configuration was adopted.

Further, the present invention provides a structure in which the bulging portion contains at least one kind of metal powder, metal fiber and metal wire in a resin, wherein the metal powder, metal fiber and metal wire are made of tungsten, titanium, aluminum,
The structure was made of at least one of lead, copper and low carbon steel.

Further, the present invention is configured such that the outer maximum diameter at the maximum point of the bulging portion is within a range of 1.01 to 2.0 times the outer diameter of the shaft near the butt side of the bulging portion. The length of the bulging portion in the axial direction occupies 5 to 40% of the length of the shaft.

In the present invention, since the moment of inertia of the shaft is set to gradually decrease within a certain range as the number of the count increases by one, the head corresponding to the count is provided on the tip side. Just by putting on and attaching the grip to the bat side, it is possible to produce a club set with almost the same moment of inertia of each count, and it is possible to adjust the pre-tone and original tone by the position of the bulging part,
By gradually decreasing the distance from the tip side to the bulging portion as the number of the count increases, it is possible to gradually change from the previous tone to the original tone.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiment of the present invention will be described.

First, a method for calculating the moment of inertia of a shaft according to the present invention will be described.

Now, there are four types of prepregs used for producing the shaft, as shown in FIGS. 1A to 1D, and the dimensions of each prepreg are indicated by a, b, c, and d as shown. In this case, the distance L from the tip of each prepreg (the position indicated by the reference line M in FIG. 1) to the center of gravity g is obtained by the following equations.

Prepreg of type A: L = a (b + 2c) / 3 (b + c) Prepreg of type B: L = (a ² + ac + c ² ) / 3 (a + c) Prepreg of type C: L = (2a ² + 2ac-c) ² ) / 3 (c + a) Prepreg of type D: L = a / 2 The above prepreg is a resin sheet containing fibers. As the fibers, use carbon fibers, polyamide fibers, boron fibers, metal fibers, glass fibers, and unidirectional fibers composed of two or more kinds of these fibers, woven fibers, braided fibers, nonwoven fibers, and the like. Can be. As the resin, an epoxy resin, a melamine resin, a phenol resin, a thermoplastic nylon, a polycarbonate resin, a polyphenylene sulfide resin, a polyetheretherketone resin, a polyetherimide resin, or the like can be used. Further, as the prepreg, a sheet containing at least one of a metal powder, a metal fiber, and a metal wire in a resin may be used. In this case, as the metal powder, metal fiber, and metal wire, those made of tungsten, titanium, aluminum, lead, copper, low carbon steel, or the like can be used.

Next, as shown in FIG. 2, for example, the prepregs of type A, type B and type D are used, and the prepregs of type A and type B
, The prepreg of type D has a distance x from the reference line O.
The shaft S is formed by arranging them at remote positions. The distance from the tip of each prepreg to the center of gravity g is calculated from the above equation, and is defined as L ₁ , L ₂ , L _3. The weight of each prepreg is defined as W ₁ , W ₂ , W ₃ , and the shaft S
Is the weight L _s (= W ₁ + W ₂ + W ₃ ), the distance L _g from the tip side (reference line O) of the shaft S to the center of gravity G
Is obtained by the following equation. The dimensions and weight of the prepreg are dimensions and weight after a curing treatment performed in a conventional manufacturing method such as a sheet winding method or an internal pressure molding method.

L _g = [(L ₁ × W ₁ ) + (L ₂ × W ₂ ) +
((L ₃ + x) × W ₃ )] / W _{s Further} , the moment of inertia I around the center of gravity of the shaft S
_sg is obtained by the following equation.

I _sg = W ₁ (L ₁ -L _g ) ² + W ₂ (L ₂ -L _g )
² + W ₃ ((L ₃ + x) -L _g ) ² Therefore, the moment of inertia of the shaft S (the moment of inertia around the butt, hereinafter the same) _Iso can be obtained by the following equation.

I _so = I _sg + W _s × L _g ^{2 In the} present invention, in the shaft set for the iron club set, the inertia moment I _{so of the} shaft is in the range of 5 to 9% as the number of the iron number increases by one. Set to gradually decrease within. Further, the shaft set for wood club set, the moment of inertia I _so of the shaft according to figures count is increased by one set to gradually decrease in the range of 2-4%.

The equations for calculating L _g , I _sg and I _so are as follows:
Although this corresponds to the arrangement example of the prepreg shown in FIG. 2, in the present invention, the change in the moment of inertia between the shafts may be within the above range. Is not particularly limited and can be appropriately set. According to each case, L _g , I _sg and I _so can be calculated as described above.

In the shaft set of the present invention as described above,
As shown in FIG. 3, a club set can be manufactured by mounting a head corresponding to the count on the tip side of the shaft S and mounting a grip on the butt side. Such a distance H _c from the butt side of the club (grip end (shown by reference line O')) to the club center of gravity of club set produced, the moment of inertia I _cg around the center of gravity of the club, by the following equation Desired.

[0023] _{H c = (H g · W} g + H s · W s + H h · W h) / W c I cg = W g (H g -H c) 2 + W s (H s -H c) 2 + W _h (H _h
-H _c) ² H _g: distance from the grip end to grip the center of gravity H _s: distance H _h from grip end to the shaft center of gravity distance from the grip end to the center of gravity W _g: Grip weight W _s: shaft weight W _h : Head weight W _c : club weight (W _g + W _s + W _h ) Therefore, the inertia moment of the club (moment of inertia around the grip end, the same applies hereinafter) I _co can be obtained by the following equation.

I _co = I _cg + W _c × H _c ² By using the shaft set of the present invention, the inertia moment I _co of the manufactured club set becomes almost the same, and the golf club can swing all clubs at the same timing. Set.

FIG. 4 is a side view showing one shaft constituting a shaft set according to an embodiment of the present invention.
In FIG. 4, the shaft 1 has a tip part 2, a shaft part 3, and a butt part 4 in this order from one end along the axial direction of the shaft.

The tip portion 2 is a portion which is inserted and fixed in the hosel of the club head, and comprises a base shaft 11 described later. The shape of the tip portion 2 is usually a straight shape having the same outer diameter, but a tapered shape having a thin tip portion, an inverted tapered shape having a slightly thick tip portion, and the like.
Any of them may be used.

The butt portion 4 includes a base shaft 1 to be described later.
1 in the illustrated example, the end 4 on the shaft 3 side.
Although the outer diameter of the golf club shaft 1 has a tapered shape in which the outer diameter increases toward the end portion of the golf club shaft 1, the outer diameter may be a straight shape having the same outer diameter.

The shaft portion 3 is a characteristic portion of the golf club shaft 1 of the present invention, and includes a base shaft 11 described later.
And one bulge 3A along the axial direction of the base shaft 11. In the present invention, the distance l ₂ from the tip side to the bulge 3A as the number of the count increases.
Is set to decrease gradually. It is possible to adjust the pre-tone and the original tone by the position of the bulging portion 3A. By gradually decreasing the distance from the chip side to the bulging portion 3A as the number of the count increases, the pre-toning and the original tone are changed. Can be changed gradually.

The external maximum diameter D at the maximum point a of the bulging portion 3A is near the butt portion 4 side of the bulging portion 3A (11a).
It is preferable to set so as to be in a range of 1.01 to 2.0 times the outer diameter of the shaft portion 3 of the above. Further, the axial length L ₃ of the bulge portion 3A is preferably set to be 5-40% of the length l ₁ of the shaft 1.

In the shaft set of the present invention comprising the shaft having the bulging portion as described above, in the shaft set for the iron club set, the inertia moment I _{so of the} shaft increases as the number increases by one. It is set so as to gradually decrease within the range of 5 to 9%. Further, the shaft set for wood club set, the moment of inertia I _so of the shaft according to figures count is increased by one set to gradually decrease in the range of 2-4%.

FIG. 5 is a partial sectional view along the axial direction of the shaft portion 3 of the shaft 1 of the present invention as shown in FIG. The shaft 1 shown in FIG. 5 is manufactured by a sheet winding method, and the shaft portion 3 includes a base shaft 11 that extends over the entire length of the shaft 1.
And the thick part 12 constituting the bulging part 3A.

The base shaft 11 is formed by laminating prepregs of a desired shape from prepregs of various shapes as shown in FIG. For example, the inner layer side of the base shaft 11 may be a high elastic fiber reinforced resin layer and the outer layer side may be a high strength fiber reinforced fiber layer, or all layers may be formed of a high strength fiber reinforced fiber layer. It can be set appropriately. The thickness t of the base shaft 11 is
It is preferable to set in the range of 0.4 to 5.0 mm,
Further, the shape of the portion corresponding to the shaft portion 3 of the base shaft 11 may be either a straight shape having the same external diameter or a tapered shape having a thin tip portion 2 side.

The thick portion 12 is also formed by laminating prepregs of a desired shape from prepregs of various shapes as shown in FIG. As the prepreg to configure,
Although any prepreg used for the base shaft 11 can be used, in particular, by using a prepreg containing at least one of metal powder, metal fiber, and metal wire in a resin, the shaft constituting the shaft set of the present invention can be used. It is easy to adjust the rate of change of the moment of inertia between them, and the position of the thick portion 12 enables the adjustment of the initial tone and the original tone as described above. This thick part 1
The thickness of 2 can be a thickness that forms the bulging portion 3A having the shape described above. In the illustrated example, the cross-sectional shape of the thick portion 12 is the maximum thickness Ta at the local maximum point a, and the thickness is gradually reduced on both sides, but is not limited thereto. For example, as shown in FIG. 6, the maximum point a of the bulging portion 3A may have a certain width along the axial direction, and the thickness may gradually decrease on both sides.

Further, the shaft of the present invention shown in FIG. 4 may have a sectional structure as shown in FIGS. 7 and 8 manufactured by a sheet winding method.

In FIG. 7, the shaft portion 3 has a base shaft 11 extending over the entire length of the shaft 1, and this base shaft 11 is composed of an inner layer 11a and an outer layer 11b. Inner layer 1 above
This is a structure in which a thick portion 12 is formed between an interlayer 1a and an outer layer 11b.

In FIG. 8, the shaft portion 3 has a base shaft 11 extending over the entire length of the shaft 1, and a thick portion 12 is provided inside the base shaft 11 at a position where the bulging portion 3A is provided. Is formed.

The shaft 1 shown in FIGS.
Also, as shown in FIG. 6, the cross-sectional shape of the thick portion 12 is such that the maximum point a of the bulging portion 3A has a certain width along the axial direction, and the thickness gradually decreases on both sides. Is also good.

Further, the shaft of the present invention shown in FIG. 4 may have a sectional structure as shown in FIG. 9 manufactured by an internal pressure molding method. The shaft 1 shown in FIG. 9 is manufactured by an internal pressure molding method.
Base shaft 11 existing over the entire length of shaft 1
And a bulging portion 3A is formed at a predetermined position of the base shaft 11.

The base shaft 11 is formed by laminating prepregs of a desired shape from prepregs of various shapes as shown in FIG. For example, the inner layer side of the base shaft 11 may be a high elastic fiber reinforced resin layer and the outer layer side may be a high strength fiber reinforced fiber layer, or all layers may be formed of a high strength fiber reinforced fiber layer. It can be set appropriately. The thickness t of the base shaft 11 is
It is preferable to set in the range of 0.3 to 5.0 mm,
Further, the shape of the portion corresponding to the shaft portion 3 of the base shaft 11 may be either a straight shape having the same external diameter or a tapered shape having a thin tip portion 2 side.

The thick portion 12 is also formed by laminating prepregs of a desired shape from prepregs of various shapes as shown in FIG. As the prepreg to configure,
Although any prepreg used for the base shaft 11 can be used, in particular, by using a prepreg containing at least one of metal powder, metal fiber, and metal wire in a resin, the shaft constituting the shaft set of the present invention can be used. It is easy to adjust the rate of change of the moment of inertia between them, and the position of the thick portion 12 enables the adjustment of the initial tone and the original tone as described above.

The cross-sectional shape of the bulging portion 3A is such that the outer diameter is maximum at the local maximum point a and the outer diameter gradually decreases on both sides, but is not limited to this. For example, the maximum point a of the bulging portion 3A may have a certain width along the axial direction, and the outer diameter may gradually decrease on both sides.

Next, the production by the sheet winding method will be described using the shaft of the present invention having a sectional structure as shown in FIG. 5 as an example.

First, the base shaft 11 is placed on the mandrel.
Wind a prepreg sheet to form The prepreg sheet to be used is a prepreg having a desired shape as shown in FIG. 1. A prepreg sheet in which reinforcing fibers are oriented at a desired angle with respect to the axial direction of the shaft can be used. The fiber reinforced resin prepreg sheet is used. The type of the prepreg and the position of the prepreg are set in advance so that the change in the moment of inertia between the shafts is within the above range.

Next, a prepreg sheet for forming the thick part 12 is provided at a desired position on the fiber reinforced resin prepreg sheet. The prepreg sheet to be used may be one in which reinforcing fibers are oriented at a desired angle with respect to the axial direction of the shaft. Further, at least one of metal powder, metal fiber and metal wire is contained in the resin.
Prepregs containing seeds can also be used. The types and positions of the prepregs are also set in advance so that the change in the moment of inertia between the shafts is within the above range, and the distance from the tip side is gradually reduced as the number of the number increases.

Thereafter, the resin of each prepreg sheet is cured by heating, and the mandrel is pulled out to obtain the shaft of the present invention.

Next, the production by the internal pressure molding method will be described with reference to the shaft of the present invention having a sectional structure as shown in FIG. 9 as an example.

First, a prepreg sheet for forming the base shaft 11 is wound through a stretchable tube on a mandrel having a hollow structure having an air injection hole on the surface. The prepreg sheet to be used is a prepreg having a desired shape as shown in FIG. 1, and a fiber-reinforced resin prepreg sheet in which reinforcing fibers are oriented at a desired angle with respect to the axial direction of the shaft can be used. Usually, a plurality of types of fiber reinforced resin prepreg sheets are used. The type of the prepreg and the position of the prepreg are set in advance so that the change in the moment of inertia between the shafts is within the above range.

Further, a prepreg sheet for forming the thick portion 12 is provided at a desired position on the fiber reinforced resin prepreg sheet. The prepreg sheet to be used may be one in which reinforcing fibers are oriented at a desired angle with respect to the axial direction of the shaft. Further, at least one of metal powder, metal fiber and metal wire is contained in the resin.
Prepregs containing seeds can also be used. The types and positions of the prepregs are also set in advance so that the change in the moment of inertia between the shafts is within the above range, and the distance from the tip side is gradually reduced as the number of the number increases.

Next, after the prepreg sheet wound around the mandrel is set in a molding die, air is injected from the air injection holes of the mandrel to apply internal pressure to the prepreg sheet, press it against the molding die, and heat it. Then, each prepreg sheet is thermoformed, and then the mandrel and the stretchable tube are pulled out, whereby the shaft of the present invention is obtained.

[0050]

Next, the present invention will be described in more detail by showing examples of a shaft set for an iron club set and a shaft set for a wood club set.

First, using a prepreg of type A to D shown in FIG. 1, a shaft set for iron club set (eight pieces of No. 3 to 10) and a shaft set for wood club set (No. 1 to No. 1) No. 5) were produced by the sheet winding method described above. Position of prepreg on each shaft (distance from tip side of shaft), type of prepreg to be used, weight of prepreg, dimensions of prepreg (a, b, c, d), center of gravity of prepreg from tip side of shaft The distance L up to this is shown in Tables 1 to 13 below. Table 1
The shafts of each count shown in Table 13 are produced by winding the prepregs described in the upper row of the table in order at a predetermined position on the mandrel by a sheet winding method.

The following table shows the moment of inertia I _so of each shaft constituting the shaft set of the present invention, the reduction rate of the moment of inertia I _so between the shafts, and the distance from the tip side to the bulging portion. The results are shown in FIG.

In the shaft set described above, a prepreg of type D containing tungsten powder was used for forming the bulge.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

[0057]

[Table 4]

[0058]

[Table 5]

[0059]

[Table 6]

[0060]

[Table 7]

[0061]

[Table 8]

[0062]

[Table 9]

[0063]

[Table 10]

[0064]

[Table 11]

[0065]

[Table 12]

[0066]

[Table 13]

[0067]

[Table 14] The head set and the grip shown in Table 15 below were attached to the shaft set of the present invention prepared as described above to prepare an iron club set and a wood club set. The weight W _{h of} the head used, the weight W _{g of} the clip,
The distance H _h from the club butt side (grip end) to the center of gravity of the head, the distance H _g from the center of gravity of the grip, and the shaft weight W _s , the distance H _s from the butt side of the club (grip end) to the center of gravity of the shaft, Further, the club weight W
_c , distance H _c from the club butt side (grip end) to the center of gravity of the club, moment of inertia I around the center of gravity of the club
_cg and the moment of inertia I _{co of the} club were measured or obtained by the above formula, and are shown in Table 15 below.

[0068]

[Table 15] As is clear from Table 15, in the iron club set manufactured using the shaft set of the present invention, the moment of inertia I _{co of} each club is almost the same around 244.8 g · m ² , and the wood club set However, the moment of inertia I _{co of} each club is almost the same centering on 262.8 g · m ² .

The above-described heads for iron clubs and wood clubs are merely examples, and in the present invention, any of the heads in the range usually used for golf club shafts made of fiber reinforced resin is used. Even so, a golf club set having substantially the same moment of inertia can be manufactured.

[0070]

As described in detail above, according to the present invention, the head corresponding to the count is mounted on the tip side of each count shaft in the shaft set, and the grip is mounted on the butt side. The manufactured club set is a golf club set in which the moments of inertia of each count are almost the same, and all clubs can swing at the same timing,
Also, by gradually decreasing the distance from the tip side of the bulging portion provided on the shaft as the number of the number increases, the golf club set gradually shifts from the previous tone to the original tone as the number of the number increases in the golf club set. By making the bulging portion contain at least one of a metal powder, a metal fiber and a metal wire in the resin, the moment of inertia of the shaft falls within a predetermined range as the number of the number increases. Thus, the adjustment for the gradual decrease is further facilitated, and the adjustment of the preceding tone and the original tone is also facilitated.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining prepregs of various shapes used for manufacturing a shaft set of the present invention.

FIG. 2 is a view for explaining an example of a shaft using the prepreg shown in FIG.

FIG. 3 is a view for explaining a golf club manufactured using the shaft set of the present invention.

FIG. 4 is a side view showing one embodiment of a shaft constituting the shaft set of the present invention.

FIG. 5 is a partial cross-sectional view of a shaft portion of the shaft shown in FIG. 4 along an axial direction.

FIG. 6 is a partial cross-sectional view of a shaft portion of the shaft shown in FIG. 4 along an axial direction.

FIG. 7 is a partial cross-sectional view of a shaft portion of the shaft shown in FIG. 4 along an axial direction.

FIG. 8 is a partial cross-sectional view of a shaft portion of the shaft shown in FIG. 4 along an axial direction.

FIG. 9 is a partial cross-sectional view of the shaft portion of the shaft shown in FIG. 4 along the axial direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, S ... Shaft 2 ... Tip part 3 ... Shaft part 3A ... Swelling part 4 ... Butt part 11 ... Base shaft 12 ... Thick part

Claims (7)

[Claims] 1. A shaft set for a golf club set comprising a plurality of iron clubs, wherein the head weight gradually increases and the length of the shaft gradually decreases as the number increases. The shaft set wherein the moment of inertia of the shaft gradually decreases within the range of 5 to 9% as the value of the shaft set increases by one. 2. A shaft set for a golf club set comprising a plurality of wood clubs, wherein the head weight gradually increases and the length of the shaft gradually decreases as the number increases. A shaft set wherein the moment of inertia of the shaft gradually decreases within a range of 2 to 4% as the value of the shaft set increases by one. 3. Each of the shafts has one bulge between the tip side and the butt side, and the distance from the tip side to the bulge gradually decreases as the number of numbers increases. The shaft set according to claim 1 or 2. 4. The shaft set according to claim 1, wherein the bulging portion contains at least one of a metal powder, a metal fiber, and a metal wire in a resin. 5. The shaft set according to claim 4, wherein the metal powder, metal fiber and metal wire are made of at least one of tungsten, titanium, aluminum, lead, copper and low carbon steel. 6. An outer maximum diameter at a maximum point of the bulge portion is within a range of 1.01 to 2.0 times an outer diameter of a shaft near a butt side of the bulge portion. The shaft set according to any one of claims 3 to 5. 7. The shaft set according to claim 3, wherein an axial length of the bulge occupies 5 to 40% of a length of the shaft.