Making of a 180 Degree Crankshaft
By Ken Hurst

Selection of the right materials
Mild steel--this material will work on engines that have no loads and that are just spinning a flywheel.
4130-4340--this material is heat treatable and will make a tough crankshaft and will take torque load of the engine.

Planning your machining operation
The setup is the key to having a straight & true running crankshaft. Mill your material to the desired length ,width & thickness.
I machine it to the sizes on the plan Establish the center of the journals --

Center drilling- Use a center that will support your work, if drilling more than 1 center insure that all centers are drilled at the same depth.

Machine slots for rod journals -- Establish the center lines for the rods & center distance, this is to put the piston in the center of the bore. I machine the slot to size. Example plan has .375 that is were I put it. Leave enough material to machine journal later. Now we are ready for the lathe operation of turning the journals.
Make special turning tool for the machining of the journals, high speed is the material I use. I turn all the rod journals before machining the main bearings --- this is were fixtures are critical to hold minimum run out & make the crankshaft rigid. Machine to .015 oversize for grinding. Machine journal closest to the lathe chuck. End for end the crankshaft to do the other journal. Now I finish the journals by grinding to size using a tool post grinder.
Now all the rod journals are machined true & sized we can start machining the main bearing journals. Mill all excess material on ends and remove the rod journal centers & machine excess material of the center main bearing same as the rods. Install fixtures on the rod journal to support the crankshaft so as not to twist & so you can apply center pressure without distortion. Machine ends & center bearing .015 oversize & final grind after all material is removed. All that is left is threading the ends , removing the excess material between the rod journals & Drilling oil passages.
After all machining is done check for straightness, correct as necessary to get run out within .001 Total Indicator Runout (TIR). If heat treating is done leave all journal oversize, drill oil passages & after heat treating and check for straightness & final grind.