Shaft having axial pre-stress

Abstract

A shaft, having a length and two ends, a handle end and an opposite end, is arranged to have two or more concentric, longitudinal members in at least along a major portion of its length; when a lateral load acts at the opposite end, the shaft bends in the conventional primary bending mode of a cantilever beam; the structural members of the shaft is characterized by said concentric members having a substantial, permanent axial pre-stress, wherein each member is either in compression or in tension, constitutes an internal self equilibrating force system.

What is claimed is:  
     
         1 . A shaft device having a handle end and an opposite end, comprising at least two or more concentric, longitudinal members in at least along a major portion of its length, and being adapted to deflect, in the primary conventional bending mode of a cantilever beam; when a transverse load acts against said opposite end while holding said handle end immobile, said concentric members having a substantial, permanent axial pre-stress in either compression or in tension, thereby constituting an internal self-equilibrating force system.  
     
     
         2 . The shaft device as defined in  claim 1  wherein each of said members has its own bending rigidity, and is arranged wherein the sum of the bending rigidities of all tension members is greater than the sum of the bending rigidities of the compression members.  
     
     
         3 . The shaft device as defined in  claim 1  wherein each of said members has its own bending rigidity, and it is arranged wherein the sum of the bending rigidities of all compression members is greater than the sum of the bending rigidities of the tension members.  
     
     
         4 . The shaft device as defied in  claim 2  being adapted whereby said end deflection of the shaft device under a transverse end load will be decreased as compared to the shaft device under the same load but with internal pre-stress removed, and said end deflection will further decrease when the pre-stress in said members is further increased.  
     
     
         5 . The shaft device as defined in  claim 3  being adapted whereby said end deflection of the shaft device under a transverse end load will be increased as compared to the shaft device under the same load but with internal pre-stress removed, and said end deflection will further increase when the pre-stress in said members is further increased.  
     
     
         6 . The shaft device as defined in  claim 1  wherein the shaft device has two concentric members.  
     
     
         7 . The shaft device as defined in  claim 1  wherein the shaft device is a golf club shaft.  
     
     
         8 . The shaft device as defined in  claim 1  including a screw device arranged in said handle end being adapted for producing said axial force system.  
     
     
         9 . The shaft device as defined in  claim 1  including a spring device arranged in said handle end for maintaining said axial force constant.  
     
     
         10 . The shaft device as defined in  claim 1  wherein said concentric members have an interface therebetween which has a portion partly fixed whereby said members can not slide relative to each other after internal stresses are permanently established.  
     
     
         11 . The shaft device as defined in  claim 5  wherein the innermost member is a thin wire-like structural element held in tension thereby subjecting the outermost member in compression.  
     
     
         12 . A conversion kit adapted to be incorporated into a hollow shaft device, such as a golf club, for controlling the flexing thereof when the same is deflected at one end during swinging of the shaft device, comprising a wire-like elongated, structural element connected adjacent its spaced ends to spaced points within and along the shaft device, means for producing tension on said structural element thereby producing compression in the shaft device between said points of connection.  
     
     
         13 . The conversion kit as defined in  claim 12  including means positioned at one of said ends of said structural element for adjusting said tension on said structural element and thereby adjusting said compression accordingly.  
     
     
         14 . The shaft device as defined in  claim 1  wherein at least one or more of said members may not be pre-stressed, or pre-stressed only partially along its length, or its length is less than the full length from said handle end to said opposite end.