alligator

An alligator is a shearing machine with two heavy jaws: one fixed, one hinged and driven by mechanical or hydraulic force. The moving jaw closes down against the fixed jaw like an animal's bite, cutting through sheet metal, plate, or bar stock in a single stroke. The fixed jaw sits at the bottom; the upper jaw swings down from a pivoting arm, usually powered by a foot treadle, lever, or motor-driven cam or hydraulic ram. Cutting happens in the gap between the jaws, where material is held flush against the fixed jaw.

Alligators come in sizes from small manual benchtop shears cutting thin sheet up to heavy floor-standing machines that sever plate several inches thick. Jaw length ranges from about 12 inches on a light machine to 4 feet or more on industrial models. The depth of the throat, the space between the hinge and the edge of the jaws, limits the width of material that can enter. Most have adjustable stops or gauges to set repeat cut lengths.

Variants and capability

A guillotin shear works on the same principle but uses a large falling blade rather than hinged jaws. Some alligators have compound leverage arms to multiply cutting force; others use a screw mechanism instead of direct pivot action. Hydraulic models allow precise pressure control and are safer than lever-driven machines, which can jam fingers or catch loose clothing in the hinge. Electric foot pedals and two-hand safety controls became standard on industrial units to prevent accidental operation.

Material must be positioned carefully so it seats fully against the fixed jaw before closing. Misalignment causes uneven cutting, bent edges, or jamming. Dull jaws produce crushed rather than sheared edges; jaw faces are hardened steel and must be resharpened or replaced when worn. Burrs left by the cut often need filing or deburring on precision work.

The name comes directly from the resemblance: strong hinged jaws that snap shut on their prey. The term has been used for such machines since the late 1800s and remains standard in American metalworking shops, though British metalworkers more often use guillotine or power shears for larger machines.