In which machining operation is a rotating cutting tool normally employed?

Milling is a machining operation where a rotating cutting tool is utilized to remove material from a workpiece. This process allows for precise and effective cutting capabilities, enabling the creation of complex shapes, slots, and surfaces with a high degree of accuracy. The rotating cutter in milling can move in multiple axes, allowing for various types of machining operations to be performed, including face milling and end milling.

In contrast, planing typically uses a linear cutting tool that moves over the workpiece, while turning employs a workpiece that rotates against a stationary cutting tool, which fundamentally differs from the milling process. Jig boring primarily focuses on achieving high precision in positioning holes rather than the general material removal characteristic of milling. Therefore, the defining feature of milling is its use of a rotating cutting tool, making this option the correct choice.