How to model a Single cylinder crank shaft in simple steps: it's just simple and refer the tutorial in below.
Answered with a tutorial: https://grabcad.com/tutorials/how-to-model-a-single-cylinder-crank-shaft-in-simple-steps
I'd download some SolidWorks models of crank shafts. You will be able to roll back the 'tree' and see what other designers have done, step by step.
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