Abstract: Marine diesel engines is the "heart" of marine manufacturing, and large marine crankshaft is the core component of manufacturing engine. A dedicated lathe for machining the main journal of large marine diesel crankshafts is designed, adopting by means of "one-clamp-one-support with intermediate bearing" approach. The key points of design include special fixtures, headstocks, tailstocks, center rests, and sliding saddles. Through variable-pressure floating clamping tests and finite element analysis (FEA) for calculating tailstock tightening forces, the crankshaft clamping and machining processes were optimized. The test results show that the average precision of variable pressure clamping is 3.3 times higher than that of constant pressure clamping. Adopting the FEA validates the influence of tailstock tightening force on crankshaft deformation, confirming that a tightening force of 5-6 kN satisfies processing requirements. Practical production shows that all aspects of the machine’s precision, cycle time, and qualification rate meet the design expectations.