The mechanical spindle refers to the axis on the machine tool that drives the workpiece or tool to rotate. Spindle components are usually composed of the main shaft, bearings and transmission parts (gears or pulleys). The motion accuracy and structural rigidity of the spindle components are important factors that determine the machining quality and cutting efficiency. The main parameters for measuring the performance of the main shaft component are the rotation accuracy, stiffness and speed adaptability. Rotation accuracy: The radial and axial runout (see shape and position tolerance) that appear in the direction that affects the machining accuracy when the spindle rotates is mainly determined by the manufacturing and assembly quality of the spindle and bearings.