| 摘要 |
A crank arm is formed with an enclosed hollow section, a first solid end fixed to one end of the hollow section and defining a first opening for fitting to a crank axle, and a second solid end fixed to a second end of the hollow section and defining a second opening for fitting to a pedal. The hollow section is constructed from a middle section having a longitudinal groove and a separate lid fixed to the middle section for enclosing the groove. The first solid end has a thicker cross section than the second solid end so that the stress applied to the crank is substantially constant. The hollow section may be keel-shaped to further enhance the strength of the crank arm without stress being concentrated in any particular location. To form the crank arm, a crank arm body is formed having a first opening on one end for fitting to a crank axle, a second opening on another end for fitting to a pedal, and a longitudinal groove. A lid member is positioned over the longitudinal groove, and then the lid member is welded to the crank arm body. Reverse beads are formed inside the longitudinal groove junctions between the lid member and the crank arm body, and any external beads formed by the welding step are shaved so that a surface of a junction between the middle section and the lid is even with a surface of the middle section and the lid along an entire length of the junction.
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