Shears(redirected from plaster shears)
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a manual tool or device or a machine for cutting various materials. Shears were found during the excavation of artifacts from the La Tène culture, which indicates that they were in use as early as the third century B.C. These early shears consisted of two knives connected by an arch-shaped spring plate; similar shears are still used for shearing sheep. Shears of the modern type, consisting of two knives connected by a hinge, appeared in the Near East around the eighth century A.D. In Russia the oldest hinged shears, dating from the tenth century A.D., were found in the Gnezdovo burial mounds.
Manual shears are used to cut fabrics, paper, and similar materials. A distinction is made between such types as household shears, metal snips, roofing shears, tailor’s scissors, and surgical shears. Stationary and portable mechanical shears with disc or bar cutters (such as bench shears) are used, especially in repair shops, to cut various materials. More powerful machines are used to cut sheet materials and strips, pipes, rolled and formed metal shapes, and similar materials. These shears are classified, according to the design of the working parts, into such types as hewing shears, guillotine shears, lever (alligator) shears, and circular shears.
Such machines are capable of cutting sheet steel up to 60 mm thick and rolled steel up to 165 mm thick. In such cutting, the cutting force reaches as much as 25 meganewtons (2,500 tons). Shears for similar work that weigh less than 8 kg, have a power rating below 1 kilowatt, and are capable of cutting sheet steel up to 5 mm thick are classified as portable machine tools.