Arrow or Crossbow Bolt Shafts Having a Profiled Inner Diameter

Abstract

Composite arrow or crossbow bolt shafts have a hollow core, where the inner diameter of the shafts vary along the length of the shaft, but the outer diameter of the shafts remains constant. The hollow inner core may vary gradually in size along the length of the shaft, or it may vary in discrete stepped portions so that the shaft is more hollow in some portions in comparison to others. The hollow composite shafts may be manufactured by wrapping a tapered or stepped inner mandrel with fibers of a composite material and curing that composite material, or by triaxially braiding composite fibers around a tapered or stepped inner mandrel before curing those composite fibers.

We claim: 
     
         1 . An arrow or crossbow bolt shaft comprising:
 a shaft inner diameter that varies along a length of the shaft;   a shaft outer diameter that remains constant along the length of the shaft; and   a hollow core comprising an outer diameter that varies along the length of the shaft.   
     
     
         2 . The shaft of  claim 1 , wherein the shaft inner diameter and hollow core outer diameter vary along the entire length of the shaft. 
     
     
         3 . The shaft of  claim 1 , wherein the hollow core outer diameter and the shaft inner diameter vary continuously along the length of the shaft. 
     
     
         4 . The shaft of  claim 1 , wherein:
 the shaft is a stepped shaft comprising a plurality of portions; and   each of the plurality of portions has a constant shaft inner diameter that is different than a shaft inner diameter of each of the other portions.   
     
     
         5 . The shaft of  claim 4 , wherein the stepped shaft comprises at least three portions. 
     
     
         6 . The shaft of  claim 4 , wherein each of the plurality of portions of the stepped shaft has the same length. 
     
     
         7 . The shaft of  claim 4 , wherein at least one of the plurality of portions of the stepped shaft has a different length than another of the plurality of portions. 
     
     
         8 . The shaft of  claim 4 , wherein the stepped shaft comprises a tapered portion, in which the shaft inner diameter and hollow core outer diameter vary continuously along the length of the tapered portion. 
     
     
         9 . The shaft of  claim 1 , wherein the center of mass of the shaft is closer to a tip portion of the shaft than to a tail portion of the shaft. 
     
     
         10 . The shaft of  claim 9 , wherein the center of mass of the shaft is between approximately 10% and approximately 20% front of center. 
     
     
         11 . The shaft of  claim 1 , wherein the shaft comprises fibers of one or more materials. 
     
     
         12 . The shaft of  claim 11 , wherein the fibers of one or more materials comprise carbon fibers, stainless steel fibers, spring steel fibers, steel fibers, titanium fibers, magnesium fibers, aluminum fibers, linearized polyethylene or spectra fibers, silicon carbide fibers, cellulose fibers, or fiberglass fibers. 
     
     
         13 . The shaft of  claim 1 , wherein the shaft comprises thermoset resin or thermoplastic resin. 
     
     
         14 . The shaft of  claim 13 , wherein the thermoset resin comprises epoxy, polyester, vinylester, phenolic, or urethane. 
     
     
         15 . The shaft of  claim 13 , wherein the thermoplastic resin comprises polyether ether ketone (PEEK), polymethyl methacrylate (PMMA), acrylic, nylon, or polyethylene. 
     
     
         16 . A method of manufacturing an arrow or crossbow bolt shaft, comprising:
 shaping an inner mandrel so that an outer diameter of the inner mandrel varies along the length of the inner mandrel;   wrapping the inner mandrel with wrapping material;   heating the inner mandrel and the wrapping material to form a shaft around the inner mandrel;   removing the inner mandrel from the interior of the shaft; and   mechanically processing the shaft to shape the shaft to its desired final dimensions.   
     
     
         17 . The method of  claim 16 , wherein shaping the inner mandrel comprises turning the inner mandrel on a lathe. 
     
     
         18 . The method of  claim 16 , wherein the wrapping material comprises fibers of one or more materials. 
     
     
         19 . The method of  claim 18 , wherein the fibers of one or more materials comprise carbon fibers, stainless steel fibers, spring steel fibers, steel fibers, titanium fibers, magnesium fibers, aluminum fibers, linearized polyethylene or spectra fibers, silicon carbide fibers, cellulose fibers, or fiberglass fibers. 
     
     
         20 . The method of  claim 19 , wherein the wrapping material comprises thermoset resin or thermoplastic resin. 
     
     
         21 . The method of  claim 20 , wherein:
 the wrapping material comprises a dry carbon fiber mat that has been coated with liquid thermoset resin; and   wrapping the inner mandrel with wrapping material comprises manually wrapping the coated carbon fiber mat around the inner mandrel.   
     
     
         22 . The method of  claim 21 , wherein heating the inner mandrel and the wrapping material comprises placing the inner mandrel and the coated carbon fiber mat in a press and molding the coated carbon fiber mat at an elevated temperature. 
     
     
         23 . The method of  claim 20 , wherein:
 the wrapping material comprises a thermoplastic, pre-impregnated carbon fiber tape and one of a polypropylene type or a nylon tape; and   wrapping the inner mandrel with wrapping material comprises wrapping the pre-impregnated carbon fiber tape around the inner mandrel and then wrapping the polypropylene tape or the nylon tape around the carbon fiber tape.   
     
     
         24 . The method of  claim 23 , wherein heating the inner mandrel and the wrapping material comprises placing the inner mandrel wrapped with the tapes into an oven and curing the tapes at an elevated temperature. 
     
     
         25 . The method of  claim 19 , wherein:
 the wrapping material comprises a self-adhesive, pre-impregnated carbon fiber fabric; and   wrapping the inner mandrel with the wrapping material comprises wrapping the fabric around the inner mandrel.   
     
     
         26 . The method of  claim 16 , wherein mechanically processing the shaft comprises sanding or grinding the shaft to its desired final dimensions. 
     
     
         27 . The method of  claim 26 , wherein sanding or grinding the shaft to its desired final dimensions comprises sanding or grinding the shaft until the shaft has a constant outer diameter along the entire length of the shaft. 
     
     
         28 . The method of  claim 27 , further comprising coating the shaft having its desired final dimensions with a thin polymeric tube or fabric to reduce the friction on the exterior of the shaft. 
     
     
         29 . The method of  claim 28 , wherein the thin polymeric tube or fabric comprises polypropylene, polyethylene, vinyl, or nylon. 
     
     
         30 . The method of  claim 16 , wherein the inner mandrel comprises steel, aluminum, or titanium. 
     
     
         31 . A method of manufacturing an arrow or crossbow bolt shaft, comprising:
 shaping an inner mandrel so that the outer diameter of the inner mandrel varies along a length of the inner mandrel;   tri-axially braiding fibers of one or more materials around the inner mandrel;   heating the inner mandrel and the tri-axially braided fibers to form a shaft around the inner mandrel; and   removing the inner mandrel from the interior of the shaft.   
     
     
         32 . The method of  claim 31 , wherein the fibers of one or more materials comprise carbon fibers, titanium fibers, stainless steel fibers, spring steel fibers, steel fibers, aluminum fibers, cellulose fibers, fiberglass fibers, silicon carbide fibers, or magnesium fibers. 
     
     
         33 . The method of  claim 32 , wherein the carbon fibers are high-modulus carbon fibers or intermediate-modulus carbon fibers. 
     
     
         34 . The method of  claim 31 , wherein tri-axially braiding fibers of one or more materials around the inner mandrel comprises varying a speed at which the inner mandrel moves longitudinally during the tri-axial braiding of the fibers around the inner mandrel.