The crank was considered as a beam with rectangular cross section. In real case it is not a rectangular and by the side there are two circular holes. For hand calculations those holes were neglected and considered both were filled with material. In hand calculation considered all edges were sharpen but in CAD model there were no sharp edges all are curved.
Mass and volume of the two sections were different.
Geometry was different in both cases. In hand calculation not considered any chamfers and curved surfaces but considered all in FEA.