Patent Publication Number: US-2023158373-A1

Title: Golf club having a low modulus crown

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 17/364,508 filed Jun. 30, 2021, which is a divisional U.S. application Ser. No. 16/746,277, filed Jan. 17, 2020, now Issued U.S. Pat. No. 11,077,340, which is a continuation of U.S. application Ser. No. 15/913,347, filed Mar. 6, 2018, now Issued U.S. Pat. No. 10,583,334 and which applications are incorporated herein by reference in their entireties. To the extent appropriate a claim of priority is made to each of the above disclosed applications. 
    
    
     BACKGROUND 
     The flight characteristics of a golf ball after being struck by a golf club are dependent on not only on the swing of the golf club but also on the construction of the golf club itself. For instance, flight characteristics of a golf ball, such as spin of the ball and ball speed, are impacted by the design and construction of the golf club. By modifying the golf club design, the flight characteristics can be improved. Some modifications to golf clubs that improve flight characteristics of a golf ball, however, may also reduce durability of the golf club, increase its overall weight, cause undesirable acoustic responses, or create other disadvantageous features of the golf club. As such, improvements to golf club designs that both improve ball flight characteristics and limit disadvantageous consequences are desired. 
     SUMMARY 
     In an aspect, the technology relates to a golf club head including a sole positioned on a bottom side of the golf club head, a striking face positioned toward the front of the golf club head and attached to at least a portion of the sole, and a crown positioned on a top side of the golf club head such that a cavity is formed between the sole, the striking face, and the crown. The crown includes an outer portion made of a first material and an inner portion made of a second material. The outer portion defines: an opening to the cavity, wherein the opening has a center, a riser extending into the cavity, the riser having a bottom edge, and a ledge extending from the edge of the riser towards the center. The ledge defines a first channel and a second channel that extend around the ledge, and the first channel is filled with an adhesive to secure the inner portion of the crown to the ledge. The inner portion of the crown is attached to the ledge such that the opening is covered by the inner portion of the crown. In an example, the first channel has a volume greater than a volume of the second channel. In another example, a distance between the first channel and the riser is less than a distance between the second channel and an inner edge of the ledge. In yet another example a width of the ledge varies around a perimeter of the opening such that a maximum ledge width is disposed proximate the striking face of the golf club head and a minimum ledge width is disposed proximate a rear of the golf club head. In still yet another example, a ratio between the maximum ledge width and the minimum ledge width is at least 2:1. 
     In another example, a thickness of the ledge is less than a thickness of a remainder of the outer portion of the crown. In yet another example, the inner portion of the crown comprises at least about 85% of an exterior surface area of the crown. In still yet another example, the second material is at least one of a wood-based material and a material displaying an elastic modulus of about 10 GPa to about 50 GPa. In another aspect, an offset distance between the striking face and the inner portion of the crown is between about 10 mm to about 20 mm. 
     In another aspect, the technology relates to a golf club head including a sole positioned on a bottom side of the golf club head, a striking face positioned toward the front of the golf club head and attached to at least a portion of the sole, a crown positioned on a top side of the golf club head such that a cavity is formed in between the sole, the striking face, and the crown, wherein the crown includes an outer portion made of a first material and an inner portion made of a second material, wherein the outer portion defines an opening to the cavity, wherein the opening has a center, a shelf attached to an internal surface of the outer portion of the crown around a perimeter of the opening, wherein the shelf extends towards the center, and wherein the inner portion of the crown is attached to the shelf such that the opening is covered by the inner portion of the crown. In an example, the first material is titanium and the second material is one of a wood-based material and a magnesium-based material. In another example, the second material displays an elastic modulus of between about 5 GPa to about 20 GPa. In yet another example, the inner portion of the crown is formed from a polyphenylene sulfide (PPS) material and a composite material. In still yet another example, the PPS material comprises at least about 90% of a volume of the inner portion of the crown. 
     In another example, the inner portion is separated from the outer portion by one of the shelf or a polymer spacer around a perimeter of the inner portion. In yet another example, the shelf is adhesively attached to the internal surface of the outer portion of the crown and the inner portion of the crown is adhesively attached to the shelf. 
     In another aspect, the technology relates to a golf club head including a sole positioned on a bottom side of the golf club head. The sole includes an outer sole portion made of a first material and an inner sole portion made of a second material. The golf club head also includes a striking face positioned toward the front of the golf club head and attached to at least a portion of the sole. The golf club head also includes a crown positioned on a top side of the golf club head such that a cavity is formed between the sole, the striking face, and the crown. The crown includes an outer crown portion made of the first material and an inner crown portion made of the second material. The outer crown portion defines a first opening to the cavity, wherein the first opening has a center, a crown riser extending into the cavity, the crown riser having a bottom edge, and a crown ledge extending from the bottom edge of the crown riser towards the center of the first opening. The outer sole portion defines a second opening to the cavity, wherein the second opening has a center, a sole riser extending into the cavity, the sole riser having a top edge, and a sole ledge extending from the top edge of the sole riser towards the center of the second opening. The inner crown portion is attached to the crown ledge such that the first opening is covered by the inner crown portion. The inner sole portion is attached to the sole ledge such that the second opening is covered by the inner sole portion. In an example, the first opening and second opening are portions of a single continuous opening. In another example, the inner sole portion and the inner crown portion are portions of a single continuous portion made of the second material. In yet another example, the sole ledge defines a first channel and a second channel that extend around the sole ledge, wherein the first channel is filled with an adhesive to secure the inner sole portion to the sole ledge. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive examples are described with reference to the following Figures. 
         FIG.  1 A  depicts a top view of an example of a golf club. 
         FIG.  1 B  depicts a perspective view of the golf club of  FIG.  1 A  showing a partial section view of the golf club head. 
         FIG.  1 C  depicts a partial section view of the golf club head of  FIGS.  1 A- 1 B . 
         FIG.  1 D  is a plot showing effects of elastic modulus and crown thickness on ball speed for an example golf club head. 
         FIG.  1 E  is a plot showing the effects of elastic modulus and an inner crown portion&#39;s proximity to the striking face on ball speed for an example golf club head. 
         FIG.  1 F  is a plot showing the effect of elastic modulus on launch angle for an example golf club. 
         FIG.  1 G  is a plot showing the effect of elastic modulus on backspin of a golf ball for an example golf club head. 
         FIG.  1 H  is a table of example material quantities suitable for an inner portion of a crown for an example golf club head. 
         FIG.  2 A  depicts an example of a golf club head with an inner portion of the crown removed. 
         FIG.  2 B  depicts a partial section view of the golf club head of  FIG.  2 A  proximate the face of the golf club head. 
         FIG.  2 C  depicts a partial section view of the golf club head of  FIGS.  2 A- 2 B  proximate the rear of the golf club. 
         FIG.  2 D  depicts another partial section view of the golf club head of  FIGS.  2 A- 2 C . 
         FIG.  3    depicts a process for attaching an inner portion of the crown of the example golf club head depicted in  FIGS.  2 A- 2 D . 
         FIGS.  4 A- 4 G  depict example attachment configurations for attaching an inner portion of a crown to a golf club head. 
         FIG.  5 A  depicts a top view of an example golf club with a low modulus inner crown portion and a low modulus inner sole portion. 
         FIG.  5 B  depicts a bottom view of the example golf club of  FIG.  5 A . 
         FIG.  5 C  depicts a section view of the example golf club of  FIGS.  5 A- 5 B . 
         FIG.  5 D  is a plot showing the effect of elastic modulus on ball speed for the example golf club of  FIGS.  5 A- 5 C . 
         FIG.  5 E  is a plot showing the effect of elastic modulus on backspin for the example golf club of  FIGS.  5 A- 5 C . 
         FIG.  6 A  depicts a bottom view of another example golf club with a low modulus inner crown portion and a low modulus inner sole portion. 
         FIG.  6 B  depicts a top view of the example golf club of  FIG.  6 A . 
         FIG.  6 C  is a plot showing the effect of elastic modulus on ball speed for the example golf club of  FIGS.  6 A- 6 B . 
         FIG.  6 D  is a plot showing the effect of elastic modulus on backspin for the example golf club of  FIGS.  6 A- 6 B . 
         FIG.  7    depicts a bottom view of an example golf club with a low modulus inner sole portion. 
     
    
    
     DETAILED DESCRIPTION 
     The technologies described herein contemplate a golf club head, such as a fairway metal, driver, or other golf club head, that includes a crown and/or a sole that has an inner portion having a low elastic modulus (also known as the Young&#39;s Modulus) and may also have a low density. One goal of golf club construction is often to reduce the overall mass of the golf club head or at least reduce the mass of particular components. The reduction of mass, however, can often lead to less durable golf club heads. The present technologies provide for a golf club head that with a crown that has at least two portions: an outer portion that is made of traditional materials, such as titanium, and an inner portion that made from a low density or low elastic modulus material. By reducing the density of a portion of the crown, the overall mass of the crown and the club can be reduced. Reducing the amount of mass dedicated to the crown also allows for incorporation of active recoil channels or discretionary mass, such as removable weights, to modify a center-of-gravity (CG) location. Incorporating a low modulus material into the crown also provides performance improvements, such as increased ball speed and ball spin improvements, by increasing the flexibility of the crown while maintaining durability. Similar techniques for increasing the flexibility of the crown may also be applied to the sole of the golf club head. Prior attempts to modify the crown of a golf club to increase performance have generally utilized a slot, but the present technology eliminates the need for such a structure. 
       FIG.  1 A  depicts a top view of a golf club head  100 ,  FIG.  1 B  depicts a perspective view of the golf club head  100  showing a partial section view of the golf club head  100 .  FIGS.  1 A- 1 B  are described concurrently. The golf club head  100  has a crown  102  on the top side of the golf club head  100  attached to a striking face  108  positioned towards the front of the golf club head  100  and a sole  110  on the bottom side of the golf club head  100 . The crown  102 , the striking face  108 , and the sole  110  are attached so as to form a cavity  116  in the golf club head  100 . In some examples, a skirt may also be included between the crown  102  and the sole  110 . In such examples, for purposes of this application, the crown  102  is still considered to be attached or connected to the sole  110 . 
     The crown  102  is made from at least two components: an outer portion  104  made from a first material and an inner portion  106  made from a second material. The outer portion  104  of the crown  102  may be made from a traditional golf club material, such as a titanium-based or a steel-based material. The inner portion  106  of the crown  102  is made from a non-traditional material that may have a low elastic modulus and/or a low density. For example, the inner portion  106  of the crown  102  may be formed of a material that has an elastic modulus between 10-50 GPa. The performance advantages resulting from the use of materials having an elastic modulus within this range are discussed further below with reference to  FIGS.  1 D- 1 G . 
     Some examples of materials that may be used for the inner portion  106  of the crown  102  include wood-based materials, lignin-based materials, cellulose-based materials, or magnesium-based materials. Wood-based materials generally display an elastic modulus between 1-20 GPa, whereas magnesium-based materials generally display an elastic modulus of about 45 GPa. The use of wood-based materials also include additional benefits of having a low density, sound-dampening characteristics, and flexibility. The flexibility of the wood-based material allows the inner portion  106  to be more easily shaped or formed to match the contours of the outer portion  104  of the crown  102 . In examples where a wood-based material is used, a veneer may be also be attached to the top side of the wood-based material. The use of magnesium-based materials also provides the benefit of being low density, can be easily cast, and are resistant to scratching. 
     Other suitable materials for the inner portion  106  include a glass fiber reinforced plastic (displaying an elastic modulus of about 20-50 GPa), a composite or Kevlar fiber reinforced nylon or plastic (displaying an elastic modulus of about 5-50 GPa), or a thermoplastic combination (displaying an elastic modulus of about 1-10 GPa). Each of these materials also includes the benefit of being able to be 3D printed. In addition, a material with a polyphenylene sulfide (PPS) in combination with a composite is also be suitable. The use of the PPS provides a desirable metallic sound when the golf club head  100  strikes a golf ball, and the composite is used in combination to raise the elastic modulus of the resultant materials. Fractional volumes of PPS and composites for a suitable material are discussed further below with reference to  FIG.  1 H . 
     The inner portion  106  of the crown  102  is shaped so as to match the contours of the outer portion  104  of the crown  102 . The size of the inner portion  106  may be about 50-100% of the exterior surface area of the crown  102 . In some examples, the size of the inner portion  106  is at least 85% of the exterior surface area of the crown  102 . The inner portion  106  is also offset from the striking face  108  or the front edge of the crown by an offset distance (D O ). The offset distance (D O ) may range from about 10-30 mm, 10-20 mm, 20-30 mm, or 15-25 mm. In some examples, the offset distance (D O ) is about 15 mm. The performance effects of the offset distance (D O ) are discussed further below with reference to  FIG.  1 E . The inner portion  106  may also be shaped to substantially match the shape of the outer portion  104  and be offset from the outer edges of the crown  102  by an amount sufficient to not interfere with the hosel  112 . 
     The inner portion  106  of the crown  102  is attached to the outer portion  104  via a ledge  118  formed by the outer portion  104  of the crown  102 . The outer portion  104  defines an opening to the cavity  116  of the golf club head  100 . The ledge  118  extends towards the center of the opening to create a bonding surface for the inner portion  106  to be attached. The inner portion  106  may be attached to the ledge  118  with an adhesive or other bonding mechanism. 
     The arrangement of the outer portion  104 , ledge  118 , and the inner portion  106  can be further seen in  FIG.  1 C , which depicts a partial section view of the golf club head  100 . To form the ledge  118 , the outer portion  104  defines a riser  120  that that extends into the cavity  116 . The ledge  118  extends from the bottom edge of the riser  120  towards the center of the opening  114 . The thicknesses of the respective components can also be seen in  FIG.  1 C . The inner portion  106  of the crown  102  has a thickness (T IC ), the outer portion has a thickness (T OC ), and the ledge has a thickness (T L ). In some examples, the inner portion thickness (T IC ) is substantially the same as the outer portion thickness (T OC ). In such examples, the riser  120  extends further into the cavity  116  such that the top surface of the inner portion  106  and the top surface of the outer portion  104  are substantially flush with one another. In general, the height of the riser  120  is substantially the same as the inner portion thickness (T IC ). In other examples, the inner portion thickness (T IC ) is less than the outer portion thickness (T OC ). For instance, the inner portion thickness (T IC ) may be about 0.4-0.6 mm thick, such as 0.4 mm, 0.5 mm, or 0.6 mm. In other examples, the inner portion thickness may be between about 0.4-1.0 mm. In examples where the inner crown thickness (T IC ) is less than the outer crown thickness (T OC ), the ratio of the inner crown thickness (T IC ) to the outer crown thickness (T OC ) may be about 2:3 or 1:2. The performance effects due to the inner crown thickness (T IC ) are discussed further below in FIG.  1 D. In some examples, the ledge thickness (T L ) may be the same as the outer portion thickness (T OC ) or the inner portion thickness (T IC ). In other examples, the ledge thickness (T L ) may be substantially equal to the difference between the outer portion thickness (T OC ) and the inner portion thickness (T IC ). 
       FIG.  1 D  is a plot showing effects of elastic modulus (labeled Young&#39;s Modulus) and crown thickness on ball speed for an example golf club head. Multiple data points are shown for an inner crown portion having a thickness of 0.4 mm, 0.5 mm, and 0.6 mm. In general, the plot indicates that for most elastic modulus values, a thicker inner crown portion results in higher ball speed values for resultant ball strikes with the example golf club. In addition, the plot also shows an unexpected result of an increase in ball speed resulting from the use of an inner crown portion having an elastic modulus value within a particular range. More specifically, ball speed increases are observed for inner crown portions having an elastic modulus value from about 10-40 GPa. Each thickness of inner crown portion also has its own respective optimal elastic modulus as well. For instance, for an inner crown portion having a 0.5 mm thickness, an optimal elastic modulus occurs at about 20 GPa. Higher thicknesses of an inner crown portion generally resulted in a lower optimal elastic modulus value. The results for the plot were created via finite element analysis for an example golf club similar to that depicted in  FIGS.  1 A- 1 C  with the TITLEIST 917 D3 Driver being the base model for the example golf club. 
       FIG.  1 E  is plot showing the effects of elastic modulus and an inner crown portion&#39;s proximity to the striking face on ball speed for an example golf club head. Multiple data points are shown for an inner crown portion having an offset distance (D O ) of 15 mm and 25 mm. From the plot, it can be seen that moving the inner crown portion closer to the striking face results in higher ball speeds for certain ranges of elastic modulus values. For instance, for an elastic modulus value between about 20-30 GPa, ball speeds are increased where the inner crown portion has an offset distance (D O ) of 15 mm rather than 25 mm. The results depicted in the plot were generated using finite element analysis for the same example golf club used for the plot in  FIG.  1 D . 
       FIG.  1 F  is a plot showing the effect of elastic modulus on launch angle for an example golf club having an inner portion with a 0.5 mm thickness. Multiple data points are shown for high ball strikes (about a half inch above face center) on the example golf club utilized for the plots in  FIGS.  1 D- 1 E . As can be seen from the plot, the launch angle generally decreases as the elastic modulus increases. 
       FIG.  1 G  is a plot showing the effect of elastic modulus on the backspin of a golf ball for an example golf club head having an inner portion with a 0.5 mm thickness. Multiple data points are shown for high ball strikes (about a half inch above face center) on the example golf club utilized for the plots in  FIGS.  1 D- 1 F . As can be seen from the plot, there is a reduction in backspin for inner crown portions having elastic modulus values within particular ranges. For instance, the unexpected result of backspin decrease for elastic modulus values of 15-60 GPa is seen. In particular, a decrease in backspin occurs for elastic modulus values between about 20-25 GPa. By reducing backspin, additional carry distance of a golf ball can be achieved. 
       FIG.  1 H  is table of example materials suitable for an inner portion of a crown for an example golf club head. As discussed above, a material with a polyphenylene sulfide (PPS) in combination with a composite may be suitable for use in an inner crown portion. The table in  FIG.  1 H  provides different fractional volumes of PPS with composites having varied elastic modulus values to achieve a target elastic modulus of 20 GPa. The first column of the table lists the elastic modulus value for PPS (about 5 GPa), the second column lists the elastic modulus of a sample composite material, the third column lists the target elastic modulus (20 GPa for the present example), the fourth column lists the fractional volume of composite needed to result in the target elastic modulus, and the fifth column lists the fractional volume of PPS needed to result in the target elastic modulus. As an example from the table, for a composite having an elastic modulus of 200 GPa, a material suitable for an inner crown portion having an elastic modulus of about 20 GPa has 7.69% composite and 92.31% PPS by volume. In light of this disclosure, similar fractional volumes may be determined for other target elastic modulus values. By having a large amount of PPS as compared to the composite amount (such as greater than 90% PPS), the acoustic properties of the PPS are dominant. Any material having the combination of PPS and composite listed in the able in  FIG.  1 H  may be suitable for use in an inner portion of a crown. 
       FIG.  2 A  depicts an example of a golf club head  200  with an inner portion of the crown  202  removed. The golf club head  200  is substantially similar to the golf club head  100  depicted above in  FIGS.  1 A- 1 C  except the golf club head  200  includes channels  222 ,  224  for receiving adhesive to attach the inner portion of the crown to the ledge  218 . The channels  222 ,  224  increase the surface area for the adhesive to adhere, which creates a stronger bond. In addition, the channels  222 ,  224  help prevent overflow of the adhesive into the cavity  216 , which would cause an undesirable rattle or noise in the golf club head  200 . As an example, adhesive may be added to the main or first channel  222 , but not the second channel  224 . As the inner portion is pressed against the ledge  218  to be attached, the adhesive flows from the first channel  222  across the ledge  218  to the overflow or second channel  224 , where the excess adhesive is captured before being able to flow into the cavity  216 . The process of attaching the inner portion to the ledge  218  is discussed in further detail below with reference to  FIG.  3   . As another advantage, the amount of adhesive can also be controlled through the use of the channels  222 ,  224 . In other golf clubs, parts are often attached with large globs of epoxy, which results in unnecessary additional mass in the golf club. With the present technology, however, the amount of adhesive added can be controlled and based on the volume of the first channel  222  and/or the second channel  224  to provide a consistent amount of adhesive. 
     Similar to the golf club head  100  depicted in  FIGS.  1 A- 1 C , the golf club head  200  includes a crown  202  attached to a sole and a striking face  208  to form a cavity  216 . The outer portion  204  of the crown  202  also defines a ledge  218  for attaching the inner portion of the crown  202 . A first channel  222  and a second channel  224  are formed in the ledge  218  to receive an amount of adhesive to bond the inner portion of the crown  202  to the ledge  218 . The first channel  222  extends around the ledge and is offset from the outer edges of the golf club head  200  by a smaller distance than the second channel  224 , which also extends around ledge  218 . 
     Further details of the channels  222 ,  224  can be seen in  FIGS.  2 B and  2 D , which depict partial section views of the golf club head  200 . In the example depicted, the first channel  222  and the second channel  224  have a substantially semi-circle or half-circle contour. The first channel  222  has a radius (R 1 ) and the second channel  224  has a radius (R 2 ). Accordingly, the volume (V 1 ) of the first channel  222  may be defined as V 1 =πR 1   2 L 1 /2, where L 1  is the length of the first channel  222 . Similarly, the volume (V 2 ) of the second channel  224  may be defined as V 2 =πR 2   2 L 2 /2, where L 2  is the length of the second channel  224 . While the channels  222 ,  224  in the example depicted have a half-circle shape, other shapes could also be used and one having skill in the art would understand how to determine the volumes of such channels. In some examples, the radius (R 1 ) of the first channel  222  may be between about 0.2-0.4 mm and the radius of the second channel may be between about 0.1-0.2 mm. In a particular example, the radius (R 1 ) of the first channel  222  is about 0.25 mm and the radius (R 2 ) of the second channel  224  may be about 0.15 mm. The ratio between the radius (R 1 ) of the first channel  222  and the radius (R 2 ) of the second channel  224  may be about 2:1, 5:3, or 3:2. 
     The first channel  222  is offset from the riser by a distance D 1 . The second channel  224  is offset from the first channel  222  by a distance D 2 , and the second channel  224  is offset from the inner edge of the ledge  218  by a distance D 3 . In some examples, the distance D 3  is greater than the distance D 1 , which is greater than the distance D 2  (i.e., D 3 &gt;D 1 &gt;D 2 ). Increasing distance D 3  further prevents any adhesive from flowing into the cavity  216 . In other examples, D 3  is greater than D 2 , which is equal to D 1  (i.e., D 3 &gt;D 2 =D 1 ). In yet other examples, distance D 1 , distance D 2 , and distance D 3  are equal (i.e., D 1 =D 2 =D 3 ). In still other examples, distance D 1  is equal to distance D 3 , which is greater than distance D 2  (i.e., D 1 =D 3 &gt;D 2 ). 
     The ledge  218  has a width (W L ) that is wide enough to fit both of the channels  222 ,  224 . In some examples, the ledge width (W L ) may be between 5-10 mm, and in a particular example the ledge width may be about 8 mm. The ledge width (W L ) may also be variable as it extends around the golf club  200  and the perimeter of the opening. For example, near the front of the golf club head (near the striking face  208 ), the ledge width (W L ) may be the greatest as the largest amount of stress occurs near the striking face  208 . As such, it may be more desirable to have the bonding surface of the ledge  218  be the largest near the striking face  208 . The stresses occurring near the rear of the golf club head  200 , however, are less than those near the striking face  208 . Accordingly, the maximum ledge width is where the ledge  218  is disposed proximate the striking face  208  of the golf club head  200  and the minimum ledge width is where the ledge is disposed proximate a rear of the golf club head  200 . A section view of the golf club  200  near the rear of the golf club head  200  is shown in  FIG.  2 C . The width (W L ) of the ledge  218  may be smaller near the rear the golf club head  200  because the bonding surface does not need to be as large. By having a variable width (W L ) of the ledge  218 , the overall mass of the golf club head  200  can be reduced without sacrificing any substantial performance or durability. In some examples, the ratio between the maximum ledge width and the minimum ledge width may be about 2:1. 
     The volume of the channels  222 ,  224  may also vary with the size of the ledge  218 . For example, the channels  222 ,  224  may have a maximum volume near the front of the golf club head  200  and the channels  222 ,  224  may have a minimum volume near the rear of the golf club head  200 . By varying the volume of the channels  222 ,  224 , the amount of adhesive added to the channels may also vary based on the varied volume of the channels  222 ,  224  such that the adhesive does not overflow into the cavity  216 . 
     In other examples, the channels  222 ,  224  may be located on the inner portion  206  rather than the ledge  218 . In such examples, the adhesive may be applied directly to the inner portion  206  rather than the ledge  218 . In other examples, both the inner portion  206  and the ledge  218  may include channels similar to channels  222 ,  224 . 
       FIG.  3    depicts an example method  300  for securing an inner portion  306  of a crown to a ledge  318  having a first channel  322  and a second channel  324 . At operation  301 , adhesive  326  is added to the first channel  322 . The amount of the adhesive is based on the volume of the first channel  322  and/or the volume of the second channel  324 . In some examples, the volume of adhesive  326  that is added into the first channel  322  is equal to about 150-200% of the volume of the first channel  322 . 
     At operation  303 , the interior portion  306  is pressed onto the adhesive  326  to secure the interior portion  306  to the ledge  318  and the remainder of the outer portion  304  of the crown. At operation  305 , the adhesive  326  is allowed to spread and set, dry, or cure to establish the bond between the interior portion  306  and the ledge  318 . As the adhesive  326  spreads from the first channel  322 , some of the adhesive  326  is captured by the second channel  324 , which serves as an overflow channel. The adhesive  326  also spreads towards the riser  320 . As such, the primary bonding surface is between the riser  320  and the inner edge of the second channel  324 . In some examples, the adhesive may also spread between the inner portion  306  and the riser  320 , which causes the inner portion  306  to be bonded directly to the riser  320 . In other examples, the adhesive  326  may not flow in between the riser  320  and the inner portion  306 . Once the adhesive  326  has set, dried, or cured, the crown can be polished to remove any excess adhesive  326  that may have flowed to the surface of the crown. 
       FIGS.  4 A- 4 G  depict multiple configurations for attaching an inner portion  406  of a crown to an outer portion  404  of the crown.  FIG.  4 A  depicts an example configuration that utilizes a shelf  430  rather than a ledge as discussed in the examples above. The shelf  430  is attached to the internal surface, or underside, of the outer portion  404  of the crown. The inner portion  406  is then attached directly to shelf  430 . The various components may be attached to one another by adhesive or other bonding techniques. The shelf  430  may be made of a composite material or other suitable materials. The outer portion  404  of the crown may also define a locating rib  432  on the underside of the outer portion  404 . The locating rib  432  assists in the placement of the shelf  430 . For instance, the shelf  430  can be inserted into the opening and placed against the locating rib  432  to help ensure proper placement of the shelf  430 .  FIG.  4 B  depicts another example configuration that utilizes a shelf  430  that is substantially similar to the example configuration depicted in  FIG.  4 A . In the configuration depicted in  FIG.  4 B , however, no locating rib is utilized. 
       FIG.  4 C  depicts another example configuration that utilizes a shelf  430 . In the configuration depicted in  FIG.  4 C , the shelf  430  defines a locating rib  434 . The locating rib  434  defined by the shelf  430  is placed between the outer portion  404  and the inner portion  406 . The locating rib  434  may have a width of about 5-10 mm. The locating rib  434  allows for easier placement of the shelf  430  during assembly or manufacturing of the golf club head. In addition, the locating rib  434  provides strength to the crown by protecting and separating the relatively weaker inner crown portion  406  from the outer crown portion  404 . 
       FIG.  4 D  depicts another example configuration that utilizes a shelf  430 . In the configuration depicted in  FIG.  4 D , the shelf  430  is attached to the top side of the outer portion  404  and the inner portion  406 . In such an example, the shelf  430  can be made of a material that is visually appealing to add additional effect to the top surface of the crown. In addition, the shelf  430  protects the joint between the inner portion  406  and the outer portion  404  from exterior debris or other interference. A spacer  436  may also be incorporated between the inner portion  406  and the outer portion  404 . The spacer  436  may be made from a polymer material or other material that is less rigid than the outer portion  404  and the inner portion  406 . The spacer  436  provides an additional buffer between the more rigid materials of the outer portion  404  and the inner portion  406 , which increases the durability of the joint and the golf club head. As such, a wider variety of materials may be selected for the inner portion  406 . In some examples, the spacer  436  may be omitted. 
       FIG.  4 E  depicts another example configuration that utilizes a shelf  430 . In the configuration depicted in  FIG.  4 E , the shelf  430  is also on the top side of the crown and the shelf  430  also defines a locating rib  434 . The shelf  430  and the locating rib  434  are substantially the same as the shelf  430  and the locating rib  434  depicted in  FIG.  4 C . However, the shelf  430  is attached to the top side of the inner portion  406  and the top side of the outer portion  404  such that the locating rib  434  protrudes downward towards the cavity. 
       FIG.  4 F  depicts another example configuration for attaching an inner portion  406  of a crown to an outer portion  404  of the crown. In the configuration depicted in  FIG.  4 F , the outer portion defines a ledge  418  and also utilizes a shelf  430  underneath the outer portion  404  and the ledge  418 . In the configuration depicted in  FIG.  4 F , however, the inner portion  406  is attached to the shelf  430  and abuts the edge of the ledge  418 . A cover  438  is attached to the top side of the inner portion  406  and the ledge  418 . The cover  438  may be made of the same type of materials as the shelf  430 . The shape of the cover  438  may also be manufactured to fit with the shape of the ledge  418  defined by the outer portion  404 . The configuration depicted in  FIG.  4 F  allows for further protection of the inner portion  406 . 
       FIG.  4 G  depicts another example configuration for attaching an inner portion  406  of a crown to an outer portion  404  of the crown. In the configuration depicted in  FIG.  4 G , the outer portion  404  defines a ledge  418  and the inner portion  406  is attached to the ledge  418 , similar to the configurations discussed above with reference to  FIGS.  1 A- 1 C,  2 A- 2 C, and  3   . A shelf  430  is also added to the configuration. The shelf  430  is attached on the underside of the outer portion  404  and, at least in part, underneath the ledge  418 . The shelf  430  extends from underneath the ledge  418  towards the center of the opening to provide further support for the inner portion  406 , which is attached to the shelf  430  with an adhesive or other bonding material. The shelf  430  is also shaped in manner such that the portion of the shelf  430  extending beyond the ledge  418  is flush with the ledge  418 . Thus, the ledge is sandwiched between the shelf  430  and the inner portion  406 . Any of the configurations depicted in  FIGS.  4 A- 4 G  may also include channels in the shelf  430  similar to the channels  222 ,  224  described above with reference to  FIGS.  2 A- 2 C . 
       FIGS.  5 A- 5 C  depict different views of an example golf club head  500  with a low modulus inner crown portion  506  of a crown  502  and a low modulus inner sole portion  524  of a sole  510 . In particular,  FIG.  5 A  depicts a top view of the example golf club head  500 ,  FIG.  5 B  depicts a bottom view of the example golf club head  500 , and  FIG.  5 C  depicts a section view of the example golf club head  500 .  FIGS.  5 A- 5 C  are discussed concurrently. The inner crown portion  506  of the golf club head  500  is similar to the inner portions of a crown discussed above. For instance, the inner crown  506  is attached to an outer crown portion  504 . The outer crown portion  504  may define an opening into a cavity of the golf club head. The outer crown portion  504  may similarly define a crown riser extending into the cavity and a crown ledge extending towards the center of the opening. The inner crown portion  506  is then attached to the crown ledge. The inner crown portion  506  may also be attached to the outer crown portion  504  by any of the configurations discussed above (e.g., those attachment configurations that utilize a discrete shelf). 
     The golf club head  500  also includes an inner sole portion  524  that is connected to an outer sole portion  522  of the sole  510 . The inner sole portion  524  is similar to the inner crown portion  506 , and can be attached to the outer sole portion  522  by substantially similar configurations as discussed above with reference to configurations for attaching the inner crown portion  506  to the outer crown portion  504 . For instance, the outer sole portion  522  may define an opening to the cavity. The outer sole portion  522  may also define a sole riser extending into the cavity and a ledge extending from the top edge of the sole riser towards the center of the opening in the sole  510 . The inner sole portion  524  may be attached to the sole ledge. In addition, the sole ledge and the crown ledge may also include channels for adhesive, such as the channels discussed above in  FIGS.  2 A-C  and  3 . 
     The inner sole portion  524  and the inner crown portion  506  may form a single continuous piece that is attached to the outer crown portion  504  and the outer sole portion  522 . For instance, the inner crown portion  506  wraps around the heel and toe of the golf club head  500  and connects with the inner sole portion  524 . In such an example, the opening defined by the outer crown portion  504  and the opening defined by the outer sole portion  522  may form a single continuous opening. The size and shape of the combined inner crown portion  506  and the inner sole portion  524  may vary in different examples. In some examples, the inner crown portion  506  may be about 50-100% of the exterior surface area of the crown  502 . In some examples, the size of the inner crown portion  506  is at least 85% of the exterior surface area of the crown  502 . The inner sole portion  524  may make up similar proportions of the sole  510 . In other examples, the inner sole portion  524  may make up less of the total exterior surface area of sole  510  due to other components located on the sole  510 . For instance, in some examples, the inner sole portion  524  is shaped so as to avoid sole components such as active recoil channels, weights or weight ports, and openings for adjusting a hosel, among other components (as can be seen in the example depicted in  FIGS.  6 A- 6 B ). The inner crown portion  506  also has a variable width (W IC ) and the inner sole portion  524  has a variable width (W IS ) as well. The widths W IC  and W IS  may be measured on an arc following the shape of the crown or the sole, respectively, and running orthogonal to the striking face  508 . The ratio of the maximum width W IC  to the maximum width W IS  may be about 2:1, 3:2, 1:1, 1:2 or within the range of about 1:1 to 2:1. The particular ratio between the maximum width W IC  to the maximum width W IS  may depend on other elements incorporated into the sole  510  or crown  502  of the golf club head  500 . For instance, in examples where the sole  510  includes other elements for improved flexibility, such as an active recoil channel, the width W IS  may be substantially less than that of the width W IC . 
       FIG.  5 D  is a plot showing the effect of elastic modulus of an inner crown portion and an inner sole portion on ball speed for the example golf club of  FIGS.  5 A- 5 C . Multiple data points are shown for high ball strikes, center ball strikes, and low ball strikes. A high ball strike is a strike of a golf ball at about a half inch above face center, a center ball strike is a ball strike occurring at about face center, and a low ball strike is a ball strike occurring at about a half inch below face center. From the plot, the unexpected result is seen that ball speed is increased for all types of ball strikes for elastic modulus values between about 20-40 GPa. Accordingly, by incorporating both an inner crown portion and an inner sole portion having a particular elastic modulus value, ball speed performance can be improved for all ball strikes, whether the ball strikes are high, center, or low on the face. 
       FIG.  5 E  is a plot showing the effect of elastic modulus of an inner crown portion and an inner sole portion on backspin for the example golf club of  FIGS.  5 A- 5 C . Multiple data points are shown for high ball strikes, center ball strikes, and low ball strikes. Each respective ball strike type has a range of elastic modulus values that provide lower backspin values, which results in further carry distance. For example, at an elastic modulus value of about 20-40 GPa, the backspin characteristics are relatively low for all ball strike types compared to other elastic modulus values. Accordingly, utilization of a material having an elastic modulus between about 20 GPa to 40 GPa results in both lower backspin and increased ball speed. 
       FIGS.  6 A- 6 B  depict different views of another example golf club head  600  with a low modulus inner crown portion  606  of a crown  602  and a low modulus inner sole portion  624  of a sole  610 . In particular,  FIG.  6 A  depicts a bottom view of the example golf club head  600  and  FIG.  6 B  depicts a top view of the example golf club head  600 .  FIGS.  6 A- 6 B  are discussed concurrently. The golf club head  600  is substantially the same as the golf club head  500  depicted in  FIGS.  5 A- 5 C  and discussed above, except for the shape of the inner crown portion  606  and the inner sole portion  624 . The inner sole portion  624  is narrower than that of the inner sole portion  524  depicted in  FIGS.  5 A- 5 C  to avoid interference with the adjustable weight  630  and the active recoil channel  632 . As such, the outer sole portion  622  comprises more of the sole  610  than the inner sole portion  624 . 
       FIG.  6 C  is a plot showing the effect of elastic modulus of an inner crown portion and an inner sole portion on ball speed for the example golf club of  FIGS.  6 A- 6 B . Multiple data points are shown for high ball strikes, center ball strikes, and low ball strikes. From the plot, the unexpected result is seen that ball speed is increased for all types of ball strikes for elastic modulus values between about 15-40 GPa. Accordingly, by incorporating both an inner crown portion and an inner sole portion having a particular elastic modulus value, ball speed performance can be improved for all ball strikes, whether the ball strikes are high, center, or low on the face. 
       FIG.  6 D  is a plot showing the effect of elastic modulus of an inner crown portion and an inner sole portion on backspin for the example golf club of  FIGS.  6 A- 6 B . Multiple data points are shown for high ball strikes, center ball strikes, and low ball strikes. Each respective ball strike type has range of elastic modulus values that provides lower backspin values, which results in further carry distance. For example, at an elastic modulus value of about 15-40 GPa, the backspin characteristics are relatively low for all ball strike types compared to other elastic modulus values. Accordingly, utilization of a material having an elastic modulus between about 15-40 GPa results in both lower backspin and increased ball speed. 
       FIG.  7    depicts an example of a golf club head  700  having a low modulus inner sole portion  724  in the sole  710 . The inner sole portion  724  may be substantially similar to the inner sole portion  524  depicted in  FIGS.  5 A- 5 C  and the inner sole portion  624  depicted in  FIGS.  6 A- 6 B , with the exception that the inner sole portion  724  may be discrete from any inner crown portion. In some examples, the golf club head  700  may not incorporate an inner crown portion. The inner sole portion  724  may be about 30-90% of the exterior surface area of the sole  702 . In some examples, the size of the inner sole portion  724  is at least 65% of the exterior surface area of the crown. The inner sole portion  724  may be attached to the outer sole portion  722  through any of the means or configurations discussed above. As the inner sole portion  724  is located closer to the striking face  708 , backspin of a golf ball from resulting strikes at or below face center is further reduced. 
     Although specific embodiments and aspects were described herein and specific examples were provided, the scope of the technology is not limited to those specific embodiments and examples. For instance, while many of the present examples have been depicted for use with a driver, the present technology may be applied to any metal wood, fairway metal or wood, or hybrid golf club. Further, each of the above examples may be combined with another. One skilled in the art will recognize other embodiments or improvements that are within the scope and spirit of the present technology. Therefore, the specific structure, acts, or media are disclosed only as illustrative embodiments. In addition, if the limits of the terms “about,” “substantially,” or “approximately” as used in the following claims are unclear from the foregoing specification to one having skill in the art, those terms shall mean within ten percent of the value described. The scope of the technology is defined by the following claims and any equivalents therein.