Cage: from drum to enclosure
In the mine, a cage is the drum itself. Everywhere else, it is what the drum holds or protects.
To most people, a cage is an enclosure: bars or mesh that confine an animal, secure a space, or provide protection. A bird cage, a roll cage in a car, a squirrel-cage motor that spins inside a housing. All of these surround something to limit or protect it.
In mining and extraction, the cage is the hoisting drum itself, the mechanical device on which the wire rope winds as it lowers or raises the cage conveyance through the shaft. The cager, a specialist operator or automated system, manages the speed and direction of this drum to move workers, materials, and ore up and down the mineshaft. The terminology can confuse newcomers: the cage you ride in the shaft is called a skip or kibble; the cage that pulls it is the drum.
This inversion of meaning arose from the shape and function of the drum itself. Early hoisting drums were fitted with a helical or spiral groove, wound with rope, that resembled a cage or basket when viewed from the side. The word transferred first to the rope-winding mechanism, then metonymically to the entire hoisting assembly, and finally to the conveyance that hung from it. In modern mining vocabulary, the distinction has survived: the cage is the machine; the conveyance is what descends.
Other trades borrowed the word in its everyday sense, for physical enclosure. Agricultural equipment uses battery cages and queen-cages to confine hens and bees. The squirrel-cage motor takes its name from the rotor design, where conducting bars arranged in a circle resemble the rotating wheel of a caged squirrel. The tomato cage is literally a framework that encloses and supports a plant. In each case, the enclosure is the named thing itself, not the mechanism that operates it.
The mining sense persists because the hoisting drum remains a discrete, named component of colliery equipment. The shift in meaning reflects how trades preserve old terms for old machines, while general language evolves toward the more intuitive metaphor: a cage is what you keep things in, not what keeps things moving.
The dictionary entry
cage
(noun, mining and extraction)
The drum on which the rope is wound in a hoisting whim.