A spindle on a CNC (Computer Numerical Control) machine is the rotating shaft that holds and drives the cutting tool. It is located at the center of the machine and is driven by a motor. The spindle is responsible for rotating the cutting tool at high speeds, which allows it to remove material from the workpiece. The spindle is also the mechanism by which the cutting tool is positioned and held in place, and is typically designed to accept a variety of different cutting tools.

On a CNC lathe, the spindle is located in the center of the machine and rotates the workpiece while the cutting tool is moved across it. On a CNC milling machine, the spindle holds the cutting tool and moves it to remove material from the workpiece.

The speed of the spindle is controlled by the CNC controller and can be adjusted to suit the specific machining operation. Some CNC machines also have the ability to change the direction of the spindle rotation, which allows for more versatile machining capabilities.

Overall, the spindle plays a crucial role in the CNC machining process, as it holds, rotates and drives the cutting tool, and is responsible for creating the final shape of the part.