The machine tool spindle refers to the axis on the machine that drives the workpiece or the tool to rotate.The main shaft components are usually composed of a main shaft, a bearing and a transmission member (gear or pulley). In the machine, gears and pulleys are mainly used to support transmission parts, machine tool spindles are used to support transfer motion and torque, some are used to clamp workpieces, such as mandrels.Most machine tools have spindle components, except for planers, broaching machines, etc., where the main motion is linear.The motion accuracy and structural rigidity of the spindle components are important factors in determining the machining quality and cutting efficiency.The indicators that measure the performance of the spindle components are mainly the accuracy of rotation, stiffness and speed.

Rotation accuracy：The radial and axial runout (see geometrical tolerance) that occurs in the direction of the machining accuracy is mainly determined by the manufacturing and assembly quality of the spindle and bearing.

Dynamic and static stiffness are mainly determined by the bending stiffness of the main shaft, the stiffness and damping of the bearing.

Speed adaptability:the maximum allowable speed and speed range is determined by the structure and lubrication of the bearing, as well as the heat dissipation conditions.