INSERT FOR BICYCLE CRANK ARM
A crank arm is provided, having a body made of a composite material, the body defining two apertures, each aperture defining a plurality of recesses. Each of the recesses extends outwardly a distance from a center of the corresponding aperture and widens as the distance increases. Inserts made of a material surrounding the inside edge of each aperture, and each insert has extensions fitting within a corresponding recess. When the crank arm is cooled, the material shrinks relative to the body, and the recesses maintain the insert in position during the cooling process.
1 . A crank arm, comprising:
a body made of a composite material, said body defining an aperture, said aperture defining a plurality of recesses, each of said recesses having an opening, and at least one of said recesses having a width from a first side of said recess to a second side of said recess exceeding the length of said opening;
an insert made of a material surrounding the edge of said aperture, said insert having a plurality of extensions, each of said extensions fitting within a corresponding recess;
wherein said material shrinks relative to said composite material during cooling of said crank arm.
2 . The crank arm of claim 2 wherein said body defines a second aperture, said second aperture defining a plurality of recesses, each of said recesses having an opening, each of said second plurality of recesses wherein a width from a first side of said recess to a second side of said recess exceeds the length of said opening;
an second insert made of a material surrounding the inside edge of said second aperture, said second insert having a plurality of extension, each of said extensions fitting within a corresponding recess.
3 . The crank arm of claim 2 wherein said composite material is carbon fiber.
4 . The crank arm of claim 3 wherein said material is aluminum.
5 . The crank arm of claim 3 wherein said material is steel.
6 . The crank arm of claim 3 wherein said material is titanium.
7 . The crank arm of claim 3 wherein said recesses each have a first edge adjacent a second edge, and said second edge also adjacent a third edge, wherein said first edge is at a 72° to 79° angle to said second edge.
8 . The crank arm of claim 7 wherein said third edge is at an 72° to 79° angle to said second edge.
9 . The crank arm of claim 8 wherein a plurality of said recesses are defined in a row along said edge of said first aperture.
10 . The crank arm of claim 9 further comprising a second row of a plurality of said recesses along said edge of said first aperture.
11 . The crank arm of claim 10 wherein a plurality of said recesses are defined in a row along said edge of said second aperture.
12 . The crank arm of claim 11 further comprising a second row of a plurality of recesses along said edge of said first aperture.
13 . The crank arm of claim 10 wherein said first row of recesses is parallel to said second row of recesses.
14 . A method of cooling a crank arm during the moulding process, comprising the steps of:
a) providing an insert made of a material, said insert defining an aperture, said insert having a plurality of extensions, each of said extensions fitting within a corresponding recess, wherein the neck of said insertions is narrower than a distance between a first side of said insertion and a second side of said insertion;
b) heating said crank arm whereby composite material cures around said extensions, thereby defining a crank arm having a body made of said composite material, said body defining a plurality of recesses, each of said recesses having an opening, and at least one of said recesses having a width from a first side of said recess to a second side of said recess exceeding the length of said opening;
c) cooling said crank arm, whereby said material shrinks relative to said composite material during cooling of said crank arm.