the club head 10 illustrated in fig1 to 10 is preferably constructed of a titanium alloy such as 6av4 , which signifies a high titanium alloy of 6 % aluminum , 4 % vanadium , and the balance pure titanium . the club head 10 has a volume of 280 cm . 3 , and ball striking face area of 43 . 25 cm . 3 . aspects of the present invention are applicable to “ wood ” type club heads having total volumes in the range of 150 to over 300 cm . 3 , as well as face areas in the range of 25 to 45 cm . 3 . the club head 10 illustrated in fig1 to 7 is constructed of three pieces that are joined together in assembly ; namely , a club head forward portion 11 illustrated in fig9 a club head rear portion 12 illustrated in fig1 , and a power shaft 13 shown in fig1 and 15 . the power shaft 13 is cast or formed separately from the rear portion , attached to the rear portion by welding or press - fitting it therein . viewing fig1 to 10 , the club head 10 is seen to generally include a grooved ball striking face wall 15 having an area of about 43 . 25 cm . 3 and a wall thickness as viewed in the plane of fig1 to 14 that progressively decreases in the club line from fig1 to fig1 . in this regard , the wall thicknesses throughout the club head 10 are in the range of 2 to 3 mm . except for the face wall 15 , which varies in the line . a crowned top wall 17 extends integrally and rearwardly from the upper portion of the face wall 15 , and it has a short integral hosel segment 18 projecting upwardly therefrom with a shaft receiving bore 19 therein that extends through spaced hosel segments 20 and 21 illustrated in fig9 . a heel wall 23 is integral with and extends in an arcuate path rearwardly from the right side of the face wall 15 as viewed in fig1 . a toe wall 24 is formed integrally with the face wall 15 and extends rearwardly in an arcuate path from the extreme toe end of the face wall 15 and is also integrally formed with the top wall 17 , as is the heel wall 23 . as seen in fig1 and 2 , there is a cavity 26 formed in the bottom of the club head 10 that conforms to the shape of the rear of the power shaft 13 . cavity 26 is defined by a sole plate 27 that is not a separate piece but formed by the forward and rear portions of the club head sub - assemblies illustrated in fig9 and 10 . sole plate 27 has a toe rail 29 and a heel rail 30 ( see fig1 and 7 ) that are coplanar as seen when comparing fig5 and 6 and provide the set - up geometry for the club head ; i . e ., face angle ( open - closed ), face loft , club head lie , etc . the forward sole plate portion 32 is recessed upwardly from the plane of the set - up rails 29 and 30 and is arcuate when viewed from the bottom of the club head . sole plate portion 32 connects with an integral upwardly extending semispheroidal wall 33 that defines the cavity 26 and extends upwardly from the arcuate rear ends 34 and 35 ( fig6 ) of the set - up rails 30 and 29 respectively . as seen in fig8 semi - spheroidal wall 33 is formed entirely in club head rear sub - assembly 12 . the heel wall 23 and the toe wall 24 smoothly connect tangentially with a club head rear wall 37 that has a semi - ellipsoidal segment 38 welded to and enclosing the rear end of the power shaft 13 . as seen in fig1 , the upper semi - annular portion 39 of the spheroidal cavity wall 33 runs along a line parallel to the power shaft 13 and is welded to the sides of the power shaft 13 to increase the modulus of elasticity of the power shaft in the columnar or axial direction . as seen in fig3 and 4 , the club head 10 has a somewhat pointed heel 41 that projects outwardly from the hosel 18 in a direction perpendicular to the axis of the hosel a distance of 15 . 8 mm . this dimension is taken from the furthest extent of the heel when viewed in the plane of fig3 which is somewhat further from hosel axis 42 than the furthest extent 43 of the face wall 15 because of the radius 44 of the heel wall 23 as seen in fig4 . this relationship conforms with the rules of the usga . viewing fig3 the total heel to toe length of the club head 10 , dimension b , is 110 mm ., while the total heel to toe length of face wall 15 ( c + d ) in a horizontal direction is somewhat less , about 105 mm . the furthest toe extension on the face wall from a vertical plane containing geometric center 46 , dimension c in fig3 is 48 mm ., while the furthest extent of the face wall from the heel to the vertical plane of point 46 , dimension d , is 57 mm . maximum face wall height , dimension e , is 48 mm . and geometric point 46 is spaced a distance of 25 mm . ( f ) from the ground . viewing fig5 total club head length from the lower leading edge of the club face , dimension g , is 90 mm ., while the rear end of the top wall 17 , dimension h , is 24 mm . off the ground , and the lower rear end of the power tube 13 is 9 . 5 mm . off the ground ( j in fig8 ). viewing fig7 the forward - most portion of the cavity portion 39 , from the lower leading edge of the face wall 15 ( dimension k ) is 36 mm ., while the rear end of the set - up rails 29 are spaced a distance l from the lower leading edge of the face wall of 54 mm ., and the forward portion of the sole plate portion 32 is spaced 22 mm . from the face wall leading edge identified by the letter m in fig7 . viewing fig9 upper hosel segment 20 has an axial length n of 14 mm ., while lower hosel segment 21 has an axial extent p of 12 mm . distance q is the horizontal distance from geometric center 46 to the furthest toe extent of the rear portion casting 17 , and that value is 50 mm . the power shaft 13 has an outer diameter of 13 mm . and a wall thickness of 0 . 8 mm ., although shown somewhat heavier in the drawings . viewing fig9 face wall 15 has integral reinforcing ribs 52 , 53 , 54 , 55 , 56 , 57 , and 58 extending outwardly from and integral with an annular socket 48 . ribs 52 and 55 extend generally horizontally while ribs 53 and 57 extend generally vertically . rib 52 connects with and is integral with rib 58 that is integral with and approximately midway up the heel wall 23 . as seen in fig8 rib 58 extends all the way to the rear end of the heel wall 23 . rib 53 connects with and is integral with top wall rib 59 that extends centrally in the top wall 17 and rearwardly to the rear end of the top of the power shaft 13 as seen in fig1 . face wall rib 55 connects with and is integral with toe wall rib 61 that extends rearwardly and generally centrally in the toe wall 24 to the rear end of the club head , as seen in fig1 . the top wall has additional ribs 62 and 63 that also extend to the rear end of the top wall 17 . connecting ribs 62 , 63 , 64 , 65 and 66 interconnect ribs 52 to 57 , 57 to 56 , 56 to 55 , 55 to 54 , and 54 to 53 respectively to provide additional reinforcement for face wall 15 . all of these ribs have a width slightly over 3 mm . and a thickness ( their extension from the inner surface of the walls from which they project ) of about 2 mm . as seen in fig8 the parting line between the forward portion 11 and the rear portion 12 , which are separate castings , is about 21 . 5 mm . from the lower leading edge of the face wall 15 in a rearward direction along a vertical plane extending along the target line through point 46 . a socket similar to socket 48 can be provided in the rear of the club head to receive the rear end of the power shaft 13 to eliminate welding the power shaft 13 to the rear end of the club . however , minor heat distortion caused by welding the rear end of the club to the rear wall of the club is not a significant problem . viewing fig1 , 12 , 13 and 14 , the four clubs in the present line of clubs are depicted with the highest swing speed club depicted in fig1 , and the lowest swing speed club depicted in fig1 . as may be seen in these figures , the face wall 15 a in the club head 10 a seen in fig1 has the heaviest face wall , and hence , the highest face wall modulus of elasticity , the face walls 15 b , 15 c , and 15 d are progressively thinner with wall 15 d having the lowest face wall modulus of elasticity . it should be understood , however , that any number of clubs may constitute a club line according to the present invention , and in fact , in the fig1 stress strain curves , five club heads are illustrated rather than the four shown in fig1 to 14 . ideally , there should be a greater number of clubs in the line to tailor the line to more golfers . if each club head was designed for a 5 mph swing speed range , there could be 15 or more clubs in the line . however , the number of clubs in the line should really not exceed about eight to minimize customer confusion when selecting the swing speed club for his or her range . for explanation purposes only , the club head 10 d in fig1 is assumed to be the 50 to 65 mph club head illustrated in fig1 ; the club head 10 c illustrated in fig1 will be assumed to be the 66 to 80 mph illustrated in fig1 ; the club head lob depicted in fig1 will be assumed to be the 81 to 95 club head in fig1 ; and the club head 10 a depicted in fig1 will be assumed to be the 96 to 105 mph club head in fig1 . the power tube assembly 13 includes an annular tube , welded to an annular socket 71 formed integrally in the rear of the club head , the closure cap 38 , the socket 48 , and piston 73 welded to the front end of the tube 70 and slidable in socket bore 75 . the piston 73 has a downwardly stepped rear portion 77 that fits inside tube 70 , an annular through bore 78 , and a central annular groove 79 that receives a rubber “ o ” ring 81 . the outer diameter of the “ o ” ring 80 is larger than the outer diameter of the piston 73 to minimize lateral vibration of the piston 73 against the walls of socket bore 83 and reduce the noise level at ball impact . hole 78 is necessary so that no air is compressed between the forward face of the piston and the socket 75 . the spacing of the piston forward wall 84 from the socket bottom wall 85 is an important aspect of the present invention and is not necessarily , but may be , the same in each of the club heads 10 a , 10 b , 10 c , and 10 d . in all of the club heads in the line , however , the swing speed at which the rear of the face wall 15 impacts the forward surface of the piston 84 have a specific relation to the swing speed range for which that club head is designed . for example , the low swing speed range club head 10 d ; i . e ., 50 to 65 mph , might be designed to have a piston impact at 65 mph . it could , however , be somewhat higher or somewhat lower than 65 mph , and the exact impact speed point should best be determined by club head testing . in any event , whatever the relation of piston impact speed to the club head speed range should be consistent with all of the clubs 10 a , 10 b , 10 c , and 10 d in the line . as noted above , the spacing between the forward face 84 of the piston and the bottom wall 85 of the cavity , is shown approximately the same in club head 10 a , 10 b , 10 c , and 10 d , but in practice the piston spacing or piston clearance may be different in each of the club heads depending upon the moduli of elasticity of face walls 15 a , 15 b , 15 c and 15 d . piston clearance is determined experimentally and is selected so that piston impact occurs at about 85 % of the strain at the yield point of the face wall . the yield point , of course , is that point on the stress strain curve whereupon relaxation of the face wall it does not follow the stress strain curve during compression . one method for making this determination is with a variety of face wall thicknesses . for example , ten part 11 s could be constructed having face wall thicknesses from 0 . 050 inches to 0 . 150 inches in 0 . 010 increments . these part 11 s are then placed in a compression machine with a plotting stylus , parting line surface downwardly and face wall 15 upwardly . a semihemisphere golf ball is then placed between the upper platen and the club face , arcuate surface against the base , of course , and compression testing is conducted using a dial indicator for measuring face flection from below on the rear of the face wall . the yield point is quite easily determined in a plotting compression testing machine by cycling up and down the stress strain curve with increasing cycle length until the stylus fails to return exactly down the compression line . the maximum deflection at the yield point on the dial indicator is then tabulated for each of the club heads , and since these club heads have reached the yield point , they have been damaged and cannot be used for further testing . then duplicates of these heads are utilized to make assembled club heads with the clearance space of the piston being 85 % of the tabulated yield strains noted in the compression testing . this 15 % safety factor is desirable because there is a mild amount of stress repetition fracture in golf club heads , even those that are well made . after the club heads 10 a to 10 d have been assembled , or however many are being tested , with the appropriate piston clearance for each club head , the club heads are tested utilizing a mechanical club swinging device with accurate club head speed measurement capability . the swing speed range for each head is determined by noting the club head swing speed at which piston impact occurs . piston impact produces a significant change in ball impact sound and is easily noted by the testing crew . for example , club head 10 d was noted to have piston impact at 65 mph swing speed so that swing speed ( or something close to that speed ) is assigned to club head 10 d as the upper limit of its swing speed range . the lower limit for the slowest swing speed in the low swing speed club in the line , of course , is an arbitrary value . obviously , the golfer that swings near the upper end of the range is going to benefit most from this club head line design , and that is why ideally there should be more than four clubs in the line . in fig1 , the strain line 86 represents the strain at 85 % of the yield point . as noted above , while the strain is shown equal for all the clubs in fig1 , they are not necessarily equal , but may be as a consequence of coincidence . line 86 thus represents the strain at which the piston impacts the bottom of the socket 85 in each of the club heads . in each of these curves , 10 a , 10 b , 10 c , and 10 d , the slope of the lower portion of the curve 87 is proportional to the modulus of elasticity of the face wall unsupported by the power piston assembly 13 , and the slope of the second portion 89 of the curves represents the modulus of elasticity of the face wall after it impacts the power piston assembly 13 and , of course , in each case is seen to be substantially higher than the slope of portion 87 . it should be noted that the slope of the stress strain curves in fig1 is proportional to modulus of elasticity . as discussed briefly above , the fundamental principles of the present invention can be applied with a lesser benefit to a single club as opposed to a multiple club line . some manufactures may prefer to utilize these design principles in a single club because they may view the custom clubfitting process as being customer confusing or retailer confusing because it requires measuring the customer &# 39 ; s swing speed , usually with an electronic swing speed measuring device . most average golfers have swing speeds in the range of 60 to 90 mph . if a club manufacturer preferred to make a one club line , the club could be designed so that face wall impact with the front face of the piston would occur at a 90 mph swing speed . this design , of course , would benefit the 85 to 90 mph swing speed the most , with a lesser benefit for those players in the 60 to 85 mph range . and if a player above 90 mph used the club , he would not damage the club because of the increased modulus of elasticity above 90 mph . this benefit is also characteristic of the multiple club line designs described above when using swing speeds above each of the designed ranges .
a line of golf clubs tailored to the swing speed of the golfer . the basic principles of the present invention can be applied to a single club , but optimally these principles are applied to a plurality of different club heads designed to the specific speed range of the golfer ; namely , 50 to 65 mph , 66 to 80 mph , 81 to 95 mph , 96 to 105 mph , and 106 to 140 mph . maximum ball exit speed from the club head is achieved from club face deflection in each of these ranges near the maximum at which the face wall reaches its permanent elastic deformation . to achieve these principles , the face wall firstly is designed so that the face wall modulus of elasticity increases from a low modulus for the low swing speed range to progressively higher moduli for the higher swing speed ranges . face modulus can be altered by a variety of a techniques including face wall thinning and face wall reinforcement or a combination of both . in each of the swing speed ranges , the face has a first modulus of elasticity determined by the face itself and after the face deflects to a predetermined value , the face modulus is significantly increased by a stationary power piston that is impacted by the back of the face wall . the power piston impacts the rear of the face wall in each of the clubs within the swing speed range for that specific club . that is , in the low speed , 50 to 60 mph club , the face wall will impact the piston below 65 mph . where exactly that impact occurs depends upon the design criteria of the club head designer .