Machine tool spindle

A machine tool spindle is the shaft that drives the workpiece or the tool to rotate. A spindle assembly normally consists of the spindle, its bearings and transmission parts such as gears or pulleys. In a machine it mainly supports rotating parts such as gears and pulleys and transmits motion and torque, as in a machine tool spindle; in other cases it holds the workpiece, as in a mandrel. Apart from planers, broaching machines and other machine tools whose main motion is linear, most machine tools have a spindle assembly. The motion accuracy and structural stiffness of the spindle assembly are decisive factors in machining quality and cutting efficiency.

The main measures of spindle assembly performance are rotational accuracy, stiffness and speed adaptability.

1. Rotational accuracy: the radial and axial runout that appears in the direction affecting machining accuracy while the spindle rotates. It depends mainly on the manufacturing and assembly quality of the spindle and bearings.

2. Static and dynamic stiffness: determined mainly by the bending stiffness of the spindle and by the stiffness and damping of the bearings.

3. Speed adaptability: the maximum permissible speed and the speed range, determined mainly by the bearing construction and lubrication, as well as by the heat dissipation conditions.