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Hi al, A billet crank is one that has been "carved" out of a solid chunk of material. Moldex(one of the oldest and best custom crank companys) was only a few blocks from where I lived for 24 years. I've been there several times. There are cranks all over the place tagged with the names of famous racers, famous race teams, and names of expensive exotic cars. A billet crank could be made from a bar of iron, but why would someone go to all this trouble to custom machine a crank out of the weakest possible material. The type of steel depends on the application. Most aircraft crankshafts, and some automative crankshafts, are nitrided, and must therefore be made from a special alloy that can be nitrided. Most custom cranks are made from 4100 series steel, but I'm not sure about 4340. Although 4340 is the best material for many parts, it may lack the ductility needed for a crankshaft. Moldex has no CNC equipment. The parts are roughed out on big milling machines using roughing mill cutters. In spite of all the operations it takes to finish a one-off crank, they seldom scrap one. I think everything they do is heat treated, so the stresses are dealt with at that point. Heat treating and tempering crankshafts is as much art as science, and they don't give out much information about it. After heat treating the part is finish ground. A good forging has the potential to be a little stronger and more fatigue resistant than a billet. Today most of the race cranks for common applications are made from crome-moly steel forgings. A note on billet....hot rodders have give billet a "bad" name. In the hot rodding world billet has come to mean anything that has a machined all over look. There are lots of wheels, pulleys, air filters, steering wheels, door handles, etc., etc., etc., that started out as a casting or stampings and were then CNC machined or brushed finished, and then referred to as billet. In this case it is a look, and not a process. "Real" billet is whittled from a brick. Hope this isn't more than you wanted to know...Al English
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