Hacksaw: Bent and Flattened Frame, Bi-Metal Blade

A hacksaw is a C-shaped frame holding a narrow blade under tension from a screw. In a 1936 patented frame, each upright is made from a piece of wire rod, bent to shape and then pressed, rolled or hammered flat, with its end flattened at right angles to carry the blade, and the uprights are held in a channel-section top member. Bi-metal blades, patented in 1976, start as a metal block with a central strip of cutting tool steel; it is rolled flat into a sheet, the sheet is divided into two blades whose edges are the tool steel, the teeth are cut in that edge, and the blades are hardened by heating, quenching and tempering. The teeth are given a wavy set.