What is a spindle's function in a milling machine?

The spindle serves a crucial role in a milling machine by creating rotary motion for the cutting tools. It is the component that rotates the tool at high speeds, enabling it to effectively slice through various materials during the machining process. This rotary action is essential for cutting operations, as it facilitates the tool's ability to engage with the workpiece and perform tasks like milling, drilling, or tapping.

The other options, while related to the overall functioning of a milling machine, do not accurately describe the primary function of the spindle. For instance, holding down the workpiece is typically accomplished by vises or clamps, and measuring the depth of cut is done using measuring tools or indicators. Enhancing stability is more about the design of the machine itself, such as its base and structural support systems, rather than a specific function of the spindle. Thus, understanding the spindle's primary role in generating the rotational motion required for cutting tools is key to grasping the operation of a milling machine.