Shears
A machine used in forges and rolling-mills for cutting up puddle-bars into suitable lengths for piling, trimming the edges of sheets, plates, etc. Crocodile or alligator shears are generally some form of lever-shears consisting of a fixed bottom jaw or knife, to which at the root of the knife is attached the vibrating-arm or lever-jaw. A crank or excentric at the opposite end of the lever causes the upper jaw to open and shut after the manner of an alligator's mouth; hence the name. The plate-shearing machine is made with diagonal-edged knives of considerable length; the bottom one is fixed, and the upper has a vertical motion within parallel guides. These are employed for sheet and plate work. Guillotine-shears are similar in design to plate-shears; but, as their use is for cutting up the hot steel ingots into lengths suitable for subsequent operations in the mill, the knives are much shorter and the guides closer together, giving the machine an appearance of the instrument from which it derives its name. There are also numerous designs of combined shear and punch, both of which motions are derived from gear connection with the fly-wheel. Hydraulic shears may be of two forms: the stroke is either upward or downward, according to the position of the press.