Abstract: An operating head for automatic machine tools of the type mounted on a structure for moving along a set of three Cartesian axes having a first support, fitted to the structure for rotation around a first axis, and a chuck unit fitted to the first support, wherein the chuck unit is interchangeable and projects from the first support, and is designed to allow angular positioning around a second axis orthogonal to the first axis. The first support includes a power transmission system for the chuck unit. The connection of the chuck unit to the first support permits changing from rough to finish work by simply replacing the chuck unit, rather than replacing the entire operating head.