US20040116207A1

US20040116207A1 - Golf club head and method of manufacture

Info

Publication number: US20040116207A1
Application number: US10/316,453
Authority: US
Inventors: Drew De Shiell; Michael Burnett; Benoit Vincent
Original assignee: TaylorMade Golf Co Inc
Current assignee: TaylorMade Golf Co Inc
Priority date: 2002-12-11
Filing date: 2002-12-11
Publication date: 2004-06-17
Also published as: US20150038262A1; US20170001082A1; US9839821B2; US8568248B2; US9452325B2; US8287402B2; US10252122B2; US20180200587A1; US20110092311A1; US20130337939A1; US20120142451A1; US20130040758A1; US8096896B2

Abstract

The present invention resides in a golf club head having a high COR that is durable and has desirable acoustic qualities. The club head includes a body portion, a striking face and a crown forming a hollow cavity of at least 150 cc in volume. The body portion defines a front opening and an upper opening, and it includes a sole and a side section that extends rearward of the front opening. The striking plate is secured to the body portion, enclosing the front opening. While partially assembled, final weighting and/or other attachment of other members to the inner surface of the club head can be preformed, as desired. The crown is secured to the body portion, enclosing the upper opening. The crown has a maximum thickness no greater than about 2 mm. The density of the crown is less than the density of the body portion. At least one of the striking plate and the crown is attached to the second portion by adhesive bonding, and the golf club head has a maximum coefficient of restitution of at least 0.80.

Description

FIELD OF THE INVENTION

The invention relates generally to a wood-type golf club head and, more particularly, to a golf club head having a non-metal crown.

BACKGROUND OF THE INVENTION

A wood-type golf club head includes a load-bearing outer shell with an integral or attached strike plate. Today's club head is typically formed of metal material and has a hollow cavity. The metal body may comprise several portions welded together or may include a cast body with a separate sole plate or strike plate that is welded in the appropriate location.

Most club heads today are made of a strong, yet lightweight material such as, for example, a titanium, steel or aluminum alloy. There have also been heads formed of carbon fiber composite material. The use of these materials is advantageous for the larger club heads now sought by golfers, i.e., at least 300 cc and up to about 500 cc in volume. The larger sized, yet conventionally weighted, club heads strive to provide larger “sweet spots” on the striking face and club moments of inertia that, for some golfers, make it easier to get a golf ball up in the air and with greater accuracy.

Various attempts have been made to attain an improved coefficient-of-restitution (“COR”) for golf club heads, with much attention paid to the design of face plates having variable thicknesses. However, the durability of very thin portions of the face plate continues to be a problem. Such face plate designs are limited by the high impact loads to which these club heads are subject, in particular at the junctions of the face plate with the crown and sole of the club head.

Titanium alloys are particularly favored in club head designs for their combination of strength and light weight. However, the material can be quite costly. Steel alloys are more economical; however, since the density of steel alloys is greater than for titanium alloys, steel club heads are limited in size in order to remain within conventional head weights while maintaining durability.

Composite club heads, such as a carbon fiber reinforced epoxy or carbon fiber reinforced polymer, for example, are an alternative to metal club heads. A notable advantage is the relatively light weight compared to stainless steel alloys. However, these club heads have suffered from durability and performance qualities associated with composite materials. These include higher labor costs in manufacture, undesirable acoustic properties of the composite material, shearing and separation of the layers of composite plies used to form the striking surface of the club head and relatively low COR for composite faces.

The areas of the club head that are subject to the greatest wear, the face and sole, have been reinforced in some instances by providing a metal plate in one or both regions. Integrated face and hosel constructions have also been done. However, durability at the junctions of the composite and metal materials continues to be a problem. Further, when the majority of the body of the club head is of composite material, there may still remain the problem of adequately fixing one or more weighting elements within the head body. The mere increase in volume of the club head may not provide the proper location of the center of gravity of the club head for greater forgiveness in off-center hits.

With regard to hybrid metal-composite club heads, U.S. Pat. Nos. 5,328,176, 5,410,798, and 5,624,331 to Kun-Nan Lo disclose composite-metal golf club heads having a metal casing with an inner member or core of composite material. The inner member reinforces the thin walls of the metal casing in U.S. Pat. Nos. 5,410,798 and 5,624,331. The crown comprises one or two carbon fiber composite portions. The single composite crown portion of U.S. Pat. No. 5,410,798 is attached to the upper ends of the composite member during the heating portion of the manufacturing process. The double composite crown portions of U.S. Pat. No. 5,624,331 are separated by a reinforcing central rib of the metal casing. U.S. Pat. No. 5,328,176 discloses a metal reinforcing plate that is fixed to the front face and wraps around the composite head from front to back.

Published U.S. Patent Application No. 2002/0049310 to Cheng et al. discloses a metal golf club head having a carbon-fiber cover that incorporates the entirety of the upper wall and a majority of the side walls at the toe, rear and heel ends of the head body. The position of the center of gravity of the head is accomplished by the size and placement of weight plugs in the sole and rear side wall. The attachment of the carbon-fiber cover is accomplished by insertion of a bladder through the hole for the plug in the sole and application of aluminum oxide sand where the carbon-fiber cover contacts the metal base and face of the head. The bladder is inflated, and the aluminum-oxide sand adhesively attaches the cover to the rest of the club head during a heating process.

Published Japanese Application No. 05-317465 discloses a golf club head having a hole cut into the crown part. The hole may be closed with a plate of a transparent and lightweight resin. This device allows the weight of the replaced metal material to be substantially distributed to the sole, lowering the center of gravity. An initial speed of a ball is increased and an amount of spin can be decreased, whereby distance can be increased.

Metal, composite and hybrid metal-composite club heads have long suffered from poor acoustic properties. That is, golfers are accustomed to—and desire—a particular range in pitch tone generated by the golf ball impacting the striking face. Some prior club heads have used a foam filling in order to alter the sound while attempting to minimize any adverse impact on performance. While metal club heads have become better matched to golfers' acoustic preferences, composite club heads generally lack acoustic appeal.

It should, therefore, be appreciated, there is a need for a golf club head having a high COR and improved durability and acoustic qualities, which is cost effective and simple to manufacture. The present invention fulfills this need and others.

SUMMARY OF THE INVENTION

The present invention provides a golf club head having a high COR that is durable and has desirable acoustic qualities. The club head includes a body portion, a striking face and a crown forming a hollow cavity of at least 150 cc in volume. The body portion defines a front opening and an upper opening, and it includes a sole and a side section that extends rearward of the front opening. The striking plate is secured to the body portion, enclosing the front opening. The crown is secured to the body portion, enclosing the upper opening. The crown has a maximum thickness no greater than about 2 mm. The density of the crown is less than the density of the body portion. At least one of the striking plate and the crown is attached to the second portion by adhesive bonding, and the golf club head has a maximum coefficient of restitution of at least 0.80.

In a detailed aspect of a preferred embodiment, the body portion is preferably formed of a metal having a density of at least about 1.8 g/cc and preferably at least about 4 g/cc. The crown has a density between 1 g/cc and 2 g/cc.

In another detailed aspect of a preferred embodiment, the crown may be formed of plies of composite material having a fiber area weight of between 20 g/m ²and 200 g/m². The weight of the composite crown being at least 20% less than the weight of a similar sized piece formed of the metal of the body. The composite crown may be formed of an uppermost ply and at least one layer of four plies of uni-tape standard modulus graphite, the plies of uni-tape oriented at 0°, +45°, −45° and 90°.

In yet another detailed aspect of a preferred embodiment, the striking plate is separately formed and attached to the front of the body of the club head. At least one of the crown and striking plate is adhesively attached to the main body of the club head. The striking plate is made of metal and is welded to a cast second portion of the body having an opening at its front, with a lightweight crown adhesively bonded to the top opening of the body.

A method of manufacturing a golf club head having a maximum coefficient of restitution of at least 0.80 is also provided. The method includes forming a body potion of a metal material, the body having walls forming a front, a side section, a sole and a top section, an opening formed in each of the front and the top section. A striking plate adapted to enclose the front opening of the body is also formed. A crown is formed to enclose the opening in the top section. The crown has a density less than 2 g/cc and a maximum thickness no greater than 2 mm. The striking plate is attached to the body portion, enclosing the front opening. At least one of the crown and the striking plate is attached to the body by adhesive bonding. The forming steps may be performed in any order, while the striking plate is attached prior to attachment of the crown to the body. The resulting access to the interior of the nearly complete golf club head allows final weighting and/or other members to be attached to any inner surface as desired.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings in which: [0020]
FIG. 1 is a partially exploded perspective view of a preferred embodiment of a club head in accordance with the invention, depicting a crown separated from a body portion. [0021]
FIG. 2 is a cross-sectional view of the club head of FIG. 1, depicting the crown in place. [0022]
FIG. 3 is a cross-sectional view a junction of the crown and body portion of the club head of FIG. 1. [0023]
FIG. 4 is a cross-sectional view of a second preferred embodiment of a golf club head in accordance with the invention. [0024]
FIG. 5 is a cross-sectional view of a junction of the crown and the body portion of the club head of FIG. 4. [0025]
FIG. 6 is a partially exploded view of another preferred embodiment of a club head in accordance with the invention, depicting the composite crown separated from the metal body. [0026]
FIG. 7 is a perspective view of a striking face and a body portion of a preferred embodiment of a golf club head in accordance with the invention, depicting a rear surface of the striking face.[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the illustrative drawings, and particularly FIG. 1, there is shown a [0028] golf club head 10 having a crown 12 formed of composite material not yet attached to a body 14 of a golf club head, to enclose an opening 16. The body is formed of any metal, such as an aluminum, steel or titanium alloy, for example. The body may be cast to form a front 18, a sole 20, a top portion 22 and a side portion 24. At the front, a striking plate 26 is separately formed and attached to the front of the body in any manner known to those skilled in the art (see FIGS. 4 and 5). The striking plate may be formed of a different alloy or grade of the same metal as the body, or the plate may be a different metal or a composite material, as desired. If metallic, the striking plate is welded to the front 18; if made of a composite material, the striking plate may be adhesively bonded to the front 18.
In alternative embodiments, the metal body may comprise three or more portions welded together, where the portions are forged, cast or stamped pieces or any mix thereof. Or, the body may be cast except for a separate sole plate that is attached in the appropriate location. The body may also include one or more attached members, such as weighting elements, that may comprise a metal or other material having a different density than the material of the rest of the main body. [0029]
The [0030] side portion 24 extends rearwardly of the front 18 and has a toe region 28, a rear region 30 and a heel region 32 formed above the sole 20. A hosel 34 is provided at the heel end of the body for attachment of a shaft (not shown). The top portion 22 of the body 14 extends rearwardly from an upper edge 36 of the front 18 of the club head, above the side portion 24. Thus, the sole 20, top portion 22, front 18 and side portion combine with the crown 12 to form a hollow body having a volume of at least 150 cubic centimeters (cc) and up to 500 cc.
As more clearly shown in FIG. 2, the [0031] cast body 14 includes an annular rim 38 at the opening 16 in the top portion 22 that includes a ledge 40 that acts as a support member for the crown 12. Alternatively, the support member may comprise a plurality of tabs. The size and shape of the support member is preferably chosen to minimize the required overlap with the crown or the mating surface area of the crown and top portion.
Referring to FIG. 3, the [0032] rim 38 extends a distance D₁of at least 7 mm rearward from the upper edge 36 of the front 18, with a shoulder 42 defining the ledge 40 which preferably extends an additional distance D₂of at least 7 mm. The rim preferably extends between 8 mm and 12 mm, and more preferably about 10 mm, from the upper edge 36 while providing advantages of the present invention. Similarly, the ledge preferably extends between 8 mm and 12 mm. Preferably, an adhesive such as Hysol® two part epoxy 9460 or, alternatively, 3M® DP460NS, is used to attach the crown 12 onto the ledge 40, abutting the shoulder 42.
The [0033] opening 16 in a central section 44 of the top portion 22 comprises at least 25% (see FIG. 6), and preferably comprises at least 60%, of the total area of the top portion 22. More preferably, the opening is at least 75% of the total area of the top portion. Thus, there is a significant weight savings afforded by replacing a similarly sized metal crown with the crown 12 described herein. The difference in weight between the metal and composite materials may be redistributed in the club head 10 to manipulate the center of gravity of the club head, such as by providing a weight pad 46 on an interior surface 48 of the sole as shown in FIG. 4. Such a weight pad is preferably formed of a softer metal of lower density than the material of the body 14 of the club head and is attached to the sole 20; although, a weight pad may alternatively be cast as a thickened portion of the sole.

Tables I and II show exemplary materials for the

body

14 of the club head and the crown 12, respectively. The body 14 preferably has a thin-wall construction, wherein the thicknesses of the sole 20 and side portion 24 is in the range of 0.8 mm to 2 mm and the top portion thickness is in the range of 0.7 mm to 2 mm. The thickness of the front portion 16 is preferably in the range of 1.5 mm to 4 mm. The crown is also of a thin construction, having a thickness T_cof no more than about 2 mm, preferably less than 1.5 mm, and more preferably about 1 mm. In the preferred embodiment of FIGS. 1-3, the thickness of the top portion 22, including the ledge 40, is approximately 1 mm so that the shoulder 42 extends about 2 mm from an outer surface 50 of the top portion to an inner surface 52 of the ledge.

TABLE I


EXAMPLES OF METALS FOR THE BODY OF A CLUB HEAD

		Ult.	Mod.
	Density	Tens. Str.	of Elast.
Material Type	(g/cc)	(MPa)	(GPa)	Hardness

Mg AZ81A-T4	1.8	275	45	Brinell 55
Al 1201 Alloy	2.85	430	72	—
Ti 6A1-4V	4.43	950	113.8	Brinell 334
				Rockwell C 36
Ti 15-3-3-3	4.76	790	82	Rockwell B 95
Carpenter	7.76	1100	200	Brinell 318
Custom 455 ®				Rockwell C	34

[0035]

TABLE II

EXAMPLES OF COMPOSITE MATERIALS FOR A CLUB

HEAD CROWN

Ult. Tens.

Density Str. Modulus of

Composite Fiber Material (g/cc) (MPa) Elasticity (GPa)

Thornel ® Graphite Cloth 1.4 103 13

DuPont Kevlar ® 49 Fiber, 1.44-1.45 2760 120-125

diam 11.9 um

Thornel ® VCB-20 Carbon 1.88 1380 138

Cloth
A graphite-epoxy composite material, for example, with a 50% to 70% fiber volume ratio would have a density between about 1.4 g/cc and 1.65 g/cc. [0036]
A golf club head constructed in this manner advantageously improves durability since the junction of the [0037] striking plate 26 with the top portion 22 is subject to a lesser force at impact with a golf ball. The use of the crown 12 on the metal body 14 also increases COR. Further, the golf club head having a crown on a metal body advantageously provides acoustic qualities judged to be more appealing to golfers.
In one club head tested by the inventors, a 300 cc hollow body was formed of a stainless steel alloy. A large area, 1 mm thick crown was formed of 5 plies including 4 plies of a uni-tape of standard modulus graphite and 1 ply of a woven graphite cloth. The 4 plies of uni-tape were assembled at 0, 45, −45 and 90 degrees and had a fiber area weight (FAW) of about 140 grams per meter squared (g/m[0038] ²). The standard modulus is approximately 33 Mpsi for the fiber with about 600 Kpsi tensile strength. In comparison, an alternative, and more expensive, ultrahigh modulus fiber (satellite grade) comprises about 57 Mpsi. FAW may range from about 20 to 200 g/m², and preferably the composite plies for the crown are in the range of 70 to 180 g/m². More preferably, the composite plies for the crown are in the range of 120 to 160 g/m².
The resultant mass of the [0039] crown 12 is about 10 grams. This is about a 50% reduction in the mass compared to a crown formed of the steel material of the rest of the club head. The calculations of the weight savings must take into account the presence of the ledge 40 with the crown, as well as the adhesive. Generally, the weight savings is at least 20% compared to an all metal body. The weight pad 46 may then be added to achieve a total mass approximately equivalent to an all metal body.
The [0040] crown 12 may alternatively be formed of more or less plies, and instead of the top ply being a woven graphite cloth, the top ply may be another uni-tape that is painted to achieve the desired aesthetic look of the club head. The top ply is preferably oriented at 0 or 90 degrees. The molding of the crown may be performed using methods known to those skilled in the art and preferably comprises a dual mold to achieve a net shape that requires little finishing and flash removal prior to its attachment to the body 14 of the club head.
Another club head tested by the inventors utilized a titanium alloy body for the club head, with a [0041] crown 12 formed of a thermoplastic material. Preferably, the crown is an injection-molded nylon or polyphenylene sulfide (PPS) material, using 3M® DP460NS adhesive for attachment to the metal body. The nylon may be used with or without glass or carbon fiber and preferably has a density between 1 g/cc and 1.7 g/cc. Alternatively, the PPS material maybe used with or without glass or carbon fiber and preferably has a density between 1.3 g/cc and 2.0 g/cc. Replacing the crown of the titanium alloy club head results in about a 35% savings in weight. In general, the weight savings is at least 15% compared to an all metal body.
The replacement of the crown of a metal club head provides the advantage of weight savings and/or redistribution of mass to the sole, for example. A weight pad on the sole, or elsewhere on the body, may be integrally formed or be a separately formed and attached mass, the resulting weight being comparable to an all metal club head of the same volume. [0042]
Because of the access afforded by the opening in the top of the club head, a rear of the [0043] striking face 54 is accessible during manufacture for the addition of a face reinforcing member 56 formed of metal or composite material and securely attached behind the sweet spot, as shown in FIG. 7. Thus, a thin titanium alloy striking face can be strengthened or otherwise enhanced in performance. Similarly, any number of additional members may be attached elsewhere on any inner surface of the club head.
The use of the aforementioned materials, composite or plastic, for the [0044] crown 12 allows the use of a lighter weight material that may result in the top of the club head having a stiffness similar to the heavier, metal sole. This stiffness matching may be advantageous for high COR golf club heads.
The [0045] golf club head 10 can be assembled with the aid of adhesive bonding. In a preferred method of manufacture, the striking face 22 is securely attached to the body 14, enclosing a front opening. While partially assembled, final weighting and/or other attachment of other members to the inner surface of the club head can be preformed, as desired. Next, the crown is secured in place, forming the top section of the club head. Preferably, the crown 12 is of a material having a density less than 2 g/cc has a thickness no greater than 2 mm. At least one of the crown and the striking plate is attached by adhesive bonding to the opening in the body. In one embodiment, the mating surfaces of the crown and ledge 40 may be prepared by sandblasting to enhance bonding. Other steps may be performed in order to prepare and/or finish the final club head, as known to those skilled in the art.
Although the invention has been disclosed in detail with reference only to the preferred embodiments, those skilled in the art will appreciate that additional golf club heads can be made without departing from the scope of the invention. Accordingly, the invention is only by the claims set forth below. [0046]

Claims

We claim:

1. A golf club head, comprising:

a body portion defining an upper opening and a front opening and having a sole and a side section, the side section extending rearward of the front opening and having toe, rear and heel regions, the body portion having a density of at least about 4 g/cc;

a striking plate securely attached to the body portion, enclosing the front opening; and

a crown securely attached to the body portion, enclosing the upper opening, the crown having a density between 1 g/cc and 2 g/cc and having a maximum thickness no greater than about 2 mm, wherein at least one of the striking plate and the crown is attached to the body portion by adhesive bonding, the golf club head having a maximum coefficient of restitution of at least 0.80 and a volume of at least 150 cc.

2. A golf club head as defined in claim 1, wherein the body portion is integrally formed by a metal casting method.

3. A golf club head as defined in claim 1, wherein the striking plate is formed of a metal material and is welded to the body portion.

4. A golf club head as defined in claim 3, wherein a rear surface of the striking plate has an attachment placed thereon after the striking plate is welded to the body portion and before the crown is adhesively bonded to the body portion.

5. A golf club head as defined in claim 1, wherein an inner surface of the sole has an attachment placed thereon after the striking plate is attached to the body portion and before the crown is attached to the body portion.

6. A golf club head as defined in claim 1, wherein the body portion includes a support surrounding the upper opening for adhesive bonding of the crown to the body portion.

7. A golf club head as defined in claim 1, wherein each of the body portion, the striking plate and the crown are formed of different material.

8. A golf club head as defined in claim 7, wherein two of the body portion, the striking plate and the crown are formed of different alloys of the same metal.

9. A golf club head as defined in claim 1, wherein two of the body portion, the striking plate and the crown are formed of composite materials that are attached to the remaining non-composite portion by epoxy adhesive.

10. A golf club head as defined in claim 1, wherein at least one of the body portion, the striking plate and the crown is formed of at least two materials.

11. A golf club head as defined in claim 10, wherein the body portion includes a cast titanium alloy having a higher density weight attached thereto.

12. A golf club head as defined in claim 1, wherein a weight pad substantially equal to the weight savings provided by the crown is provided on the body portion.

13. A golf club head as defined in claim 1, wherein the crown is formed of a graphite-epoxy composite having a 50% to 70% fiber volume ratio and a density of 1.4 to 1.65 g/cc.

14. A golf club head as defined in claim 1, wherein the crown is formed of nylon material having a density ranging between 1 g/cc and 1.7 g/cc.

15. A golf club head as defined in claim 1, wherein the crown is formed of polyphenylene sulfide material having a density ranging between 1.3 g/cc and 2 g/cc.

16. A golf club head as defined in claim 1, wherein the volume is at least 350 cc.

17. A golf club head, comprising:

a crown securely attached to the body portion, enclosing the upper opening, the crown being formed of plies of composite material having a fiber area weight of between 20 g/m²and 200 g/m²and having a maximum thickness no greater than about 2 mm, the weight of the crown being less than the weight of a similar sized piece formed of the material of the body portion; wherein at least one of the striking plate and the crown is attached to the body portion by adhesive bonding, the golf club head having a maximum coefficient of restitution of at least 0.80 and a volume of at least 150 cc.

18. A golf club head as defined in claim 17, wherein the crown is formed of an uppermost fabric ply and at least one layer of four plies of uni-tape standard modulus composite, the plies of uni-tape oriented at 0°, +45°, −45° and 90°.

19. A golf club head as defined in claim 17, wherein the crown is formed of an uppermost ply of uni-tape standard modulus composite oriented at 0° or 90°, the ply of uni-tape being painted along with a top section of the body portion.

20. A golf club head as defined in claim 17, wherein the crown is formed of an uppermost ply of woven graphite cloth oriented at 0° or 90°

21. A method of manufacturing a hollow golf club head having a volume of at least 150 cc, comprising the steps of:

forming a body of a metal material, the body having walls forming a front that defines a front opening, a side section, a sole and a top section that defines an upper opening,

forming a striking plate adapted to be secured to the body and enclose the front opening;

securely attaching the striking plate to the body, enclosing the front opening;

forming a crown of a material having a density less than 2 g/cc, the crown having a maximum thickness no greater than 2 mm, the crown adapted to be secured to the body, enclosing the upper opening; and

securely attaching the crown to the body, enclosing the upper opening; wherein at least one of the crown and the striking plate is attached by adhesive bonding to the opening in the body, the golf club head having a maximum coefficient of restitution of at least 0.80.

22. A method as defined in claim 21, wherein the step of forming the body comprises casting a metal material, the front and upper openings are formed in the casting step.

23. A method as defined in claim 21, wherein the step of forming the striking plate comprises cold-forming a metal material to the desired thickness, shape and size, and the step of attaching the striking plate comprises welding.

24. A method as defined in claim 21, wherein the step of forming the striking plate comprises forming a composite plate, and the step of attaching the striking plate comprises adhesive bonding to a support at the front opening of the body.

25. A method as defined in claim 21, wherein the step of forming the crown comprises forming an uppermost ply and at least one layer of four plies of uni-tape standard modulus graphite.

26. A method as defined in claim 21, further comprising the step of attaching a member to a rear of the striking plate after the striking plate has been attached and before the crown has been attached.

27. A method as defined in claim 21, further comprising the step of attaching a member to an inner surface of the body after the striking plate has been attached and before the crown has been attached.