page_title: Crankshaft
section_title: Forging, casting and machining
hierarchical_section_title: Crankshaft / Construction / Forging, casting and machining
caption_attribution_description: English: Continental Engine marine crankshafts, 1942. Office of War Information Photograph Collection. Original caption: "Production. Marine engines. Marine engine crankshafts for the Navy are produced in great quantity at a Midwest plant. The finest of material and workmanship go into their manufacture. Continental Motors, Michigan."
context_page_description: A crankshaft is a rotating shaft which converts reciprocating motion of the pistons into rotational motion. Crankshafts are commonly used in internal combustion engines and consist of a series of cranks and crankpins to which the connecting rods are attached.
  The crankshaft rotates within the engine block through use of main bearings, and the crankpins rotate within the connecting rods using rod bearings. Crankshafts are usually made from metal, with most modern crankshafts being constructed using forged steel.
context_section_description: The most common construction methods for crankshafts are forging (usually through roll forging) or casting. Most crankshafts are made in a single piece; however, some smaller and larger engines use crankshafts assembled from multiple pieces.
  Recently, forging has become the most common construction method for crankshafts, due to their lighter weight, more compact dimensions and better inherent damping. With forged crankshafts, vanadium microalloyed steels are mostly used as these steels can be air cooled after reaching high strengths without additional heat treatment (aside from the surface hardening of the bearing journals). The low alloy content also makes the material cheaper than high alloy steels.
  Casting (using cast iron) is today mostly used for crankshafts in cheaper, lower performance engines.
  Crankshafts can also be machined out of a billet of steel. These crankshafts tend to be expensive due to the large amount of material that must be removed with lathes and milling machines, the high material cost, and the additional heat treatment required. Since no expensive tooling is needed, this production method is mostly used for low-volume engines. In a machined crankshafts, the fibre flow (local inhomogeneities of the material caused by the casting process) does not follow the shape of the crankshaft, however this is rarely a problem since machined crankshafts often use higher quality steels than forged crankshafts.
caption: Continental engine marine crankshafts, 1942
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