TWO-PIECE GOLF SHAFT
Various embodiments of a two-piece golf shaft are provided, which include a hollow upper section, a hollow or solid lower section formed from an injection-molded chopped carbon fiber/thermoplastic material, and a coupling insert configured to join the lower section to the upper section (and, optionally, to the golf club head as well).
1 . A two-piece golf shaft, comprising:
a hollow upper section;
a hollow or solid lower section; and
a coupling insert configured to join the upper section and the lower section together,
wherein the lower section is formed from an injection-molded carbon fiber-reinforced thermoplastic material, and
wherein the coupling insert comprises a hollow structure configured to fit into an inner diameter of the upper section and configured to receive an end of the lower section inserted therein.
2 . The two-piece golf shaft of claim 1 , wherein the carbon-reinforced thermoplastic material comprises short length chopped carbon fiber and thermoplastic resin.
3 . The two-piece golf shaft of claim 2 , wherein the carbon-reinforced thermoplastic material comprises about 30% to about 50% chopped carbon fiber.
4 . The two-piece golf shaft of claim 2 , wherein the carbon-reinforced thermoplastic material comprises a polyamide thermoplastic resin or derivative thereof
5 . The two-piece golf shaft of claim 1 , wherein at least one end of the lower section has an exterior surface configured to mate with an interior surface of the coupling insert.
6 . The two-piece golf shaft of claim 5 , wherein the exterior surface of at least one end of the lower section and at least a portion of the interior surface of the coupling insert are smooth.
7 . The two-piece golf shaft of claim 5 , wherein the exterior surface of at least one end of the lower section comprises a plurality of convex ridges configured to mate with a plurality of concave grooves on the interior surface of the coupling insert.
8 . The two-piece golf shaft of claim 1 , wherein the coupling insert is formed from a machined metal or alloy.
9 . The two-piece golf shaft of claim 8 , wherein the coupling insert comprises aluminum, titanium, or stainless steel.
10 . The two-piece golf shaft of claim 1 , wherein the coupling insert is formed from an injection-molded carbon fiber-reinforced thermoplastic material or metal mesh composite material.
11 . The two-piece golf shaft of claim 1 , wherein the coupling insert includes a flange or head portion on one end, the flange or head portion configured to form a bridge that is visible between the upper section and the lower section after they are joined together.
12 . The two-piece golf shaft of claim 1 , wherein the coupling insert has an exterior surface comprising at least one shoulder configured to provide an interference fit with the inner diameter of the upper section.
13 . The two-piece golf shaft of claim 1 , wherein the coupling insert has an exterior surface comprising a knurled surface on at least a portion thereof.
14 . The two-piece golf shaft of claim 1 , wherein the lower section has a cross-sectional shape that is circular, hexagonal, octagonal, or fluted.
15 . The two-piece golf shaft of claim 1 , wherein the lower section is hollow.
16 . The two-piece golf shaft of claim 1 , wherein the lower section is tapered, decreasing in diameter from a proximal end toward a distal end thereof.
17 . The two-piece golf shaft of claim 1 , wherein the lower section is molded into a non-linear shape with a variety of longitudinal axes.
18 . The two-piece golf shaft of claim 1 , wherein the lower section has a density ranging from about 1.2 grams/cubic centimeter to about 10 grams/cubic centimeter.
19 . The two-piece golf shaft of claim 1 , wherein the lower section has a density gradient, whereby the density increases from a proximal end toward a distal end thereof
20 . The two-piece golf shaft of claim 1 , wherein the lower section includes a metal mesh or rod.