The magnitude of the force. Different types of machine tools have different working conditions. For example, the working conditions of spindle for high-speed and precision machine tools differ from those for heavy-duty machine tools in terms of bending or torsional fatigue characteristics. Type of shaft, such as on plain bearings, the journal needs to have high wear resistance. Spindle shape and possible defects in heat treatment. The spindle with complex structure and shape is prone to deformation and even rupture during heat treatment.