Shaft stiffened by axial pre-stress

Abstract

A long shaft comprising a number of axially pre-stressed members, one inside the other, the sum of the bending rigidities of the axially tensioned members is greater than the sum of the bending rigidities of the compression members, is enhanced in bending stiffness such that the end deflection of the shaft under a simultaneous transverse load and the axial force has an end deflection less than the end deflection of the same shaft, which has no pre-stress. The long shaft may be a golf club shaft. An example shows a flex “s” golf shaft, which ordinarily has an end deflection of 3.5 inch, measured from the deflection board, is stiffened into a super stiff shaft with end deflection of 1.54 inch, without having a weight increase or a change of material.

What is claimed is:  
     
         1 . A shaft, comprising two or more long, concentric, cylindrical members, being joined together at their common end regions, said sleeves are permanently pre-stressed along its axis, in compression or in tension, constitutes a self equilibrating internal force system.  
     
     
         2 . The shaft as defined in  claim 1  wherein each of said concentric members has its own bending rigidity, and the sum of the bending rigidities of all tension members is greater than the sum of the compression members' bending rigidities.  
     
     
         3 . The shaft as defined in  claim 2  wherein the outmost member is in tension.  
     
     
         4 . The shaft as defined in  claim 2  wherein when the shaft is held as a cantilever beam having its free end under a transverse load, the end deflection will be less as compared to the same shaft under the same load but its internal pre-stress is removed; and said end deflection would be further reduced when the pre-stress in the members is further increased.  
     
     
         5 . The shaft as defined in  claim 2  wherein the shaft has three concentric members and at least the outer member is in tension.  
     
     
         6 . The shaft as defined in  claim 2  wherein there is a spring device installed at the grip end to create the required axial force to the compression members.  
     
     
         7 . The shaft as defined in  claim 1  wherein the pre-stress is adjustable after it was first installed in the factory.  
     
     
         8 . The shaft as defined in  claim 1  is a golf club shaft.  
     
     
         9 . The shaft as defined in  claim 1  is a part of a fishing rod.  
     
     
         10 . The shaft as defined in  claim 1  wherein a said cylindrical member for compression may be a slender shaft with spacers, which remains concentric but is not necessarily having surface to surface contact with the outer member.  
     
     
         11 . The shaft as defined in  claim 2  wherein at least one of the compression members has a physical arrangement made during manufacturing process such that its bending rigidity is significantly reduced because of the arrangement so that the ratio of the bending rigidity of the tension members to that of the compression members can be increased.  
     
     
         12 . The shaft as defined in  claim 11  wherein said physical arrangement is shallow cuttings on the member's surface along a major part of the length of the member.  
     
     
         13 . The shaft as defined in  claim 6  wherein the force at the spring device is adjustable.