Movement No. 47 presents a frictional clutch-box — one of the most practically important mechanisms in 19th-century industrial machinery, used specifically for connecting and disconnecting heavy machinery from a continuously running drive shaft without stopping the prime mover. The mechanism consists of two main elements on the same shaft: a continuously rotating driving element, and a driven disk that can be slid axially along the shaft to engage or disengage from it. The driven disk is ingeniously mounted using a slot in its central hub — called the eye — which slides over a long key or feather fixed lengthwise along the shaft. This keyed slot arrangement means that the disk can slide freely back and forth along the shaft’s length (allowing engagement and disengagement), but is rotationally locked to the shaft — whenever the disk is in the engaged position, it rotates with the shaft as a single unit, transmitting full torque. Engagement and disengagement is controlled by an external lever at the bottom of the mechanism. When the lever is operated, it pushes or pulls the driven disk axially along the shaft, pressing its friction surface firmly against the driving element to engage, or withdrawing it to disengage. The transmission of power between the driving element and the driven disk occurs entirely through friction at their mating surfaces — no teeth, no rigid coupling, just controlled surface friction. This frictional engagement provides a smooth, shock-free connection, allows for gradual engagement under heavy load, and provides overload slip protection. The frictional clutch-box was a fundamental enabling technology of the Industrial Revolution, allowing a single continuously running line shaft to power multiple machines independently, with each machine connected or disconnected at will by its operator.
47. A frictional clutch-box, thrown in and out of gear by the lever at the bottom. This is used for connecting and disconnecting heavy machinery. The eye of the disk to the right has a slot which slides upon a long key or feather fixed on the shaft.