The paper presents a possible process for the designing the basic dimensions of the Cardan coupling shaft for the specified operating power and speed. It describes the process of designing and controlling the main shaft dimensions. The starting point is a static shaft load with the constant torque. This paper describes the metod of weld control in the cyclic loading. The following is a procedure for the analysis of shaft deformation and tension in mode of steady transverse oscillations in the vicinity of the resonance.