1. Field of the Invention
The present invention relates to shafts and particularly shafts for use in arrows.
2. Prior Art
In the prior art there exists several different methods for making shafts. The earliest method of shaft manufacturing was to make cylindrical solid wooden shafts. Shafts were later produced out of plastic, fiber glass, carbon fiber, aluminum tubing and composite materials made of two or more dissimilar materials, e.g., particularly thin wall aluminum tubing with carbon fiber overlaid and bonded thereto.
Shafts used for arrows require that they be designed and constructed for particular stiffnesses. Indeed, in many applications, the stiffer the better. To achieve this higher stiffness without resorting to very heavy construction, composite materials, and particularly thin-wall aluminum tubing with carbon fiber overlaid and bonded thereto, have been adopted. While this construction is capable of providing sufficient stiffness in varying amounts, these types of shafts are often very expensive.
Arrows have additional characteristics which are different as compared to shafts for golf clubs. In particular, arrows must be able to provide the required stiffness while being light in weight and small in diameter. The lightness of the weight of the arrow allows the arrow to be shot faster in a flatter trajectory; the small diameter reduces the wind drag, which means that the arrow will retain more of its speed over long distances and be less affected by cross winds. Again, the construction that has been adopted is that of composite construction consisting of thin-walled aluminum tubing with carbon fiber overlaid and bonded thereto. While such a composite structure can provide the required stiffness with small diameter and lightweight, it is again expensive and difficult to manufacture.
Accordingly, it is a general object of the present invention to provide a shaft which overcomes the disadvantages of the prior art.
In particular, it is an object of the present invention to provide a shaft which can be made stiff, low in weight and small in diameter while being manufactured for a reasonable cost.
In view of the objects set forth above, the present invention comprises a filled shaft and a method for making the filled shaft. In particular, the shaft includes a cylindrical tube and at least one foamed resin filling the cylindrical tube. Preferably the cylindrical tube is made from a thin-wall aluminum tubing and the foamed resin comprises a foam polystyrene resin, commonly called styrofoam. The polystyrene resin is injected as a liquid into the cylindrical tube in an amount sufficient to fill the entire cylindrical tube once the styrene resin foams up and solidifies.