TOOL, an implement or appliance used by a worker in the treatment of the substances used in his handicraft, whether in the preliminary operations of setting out and measuring the materials, in reducing his work to the required form by cutting or otherwise, in gauging it and testing its accuracy, or in duly securing it while thus being treated. (For the tools of prehistoric man see ARCHAEOLOGY; FLINTS; and EGYPT.) In beginning a survey of tools it is necessary to draw the dis tinction between hand and machine tools. The former class includes any tool which is held and operated by the unaided hands; e.g., a chisel, plane or saw. Attach one of these to some piece of operating mechanism, and it, with the environment of which it is the central essential object, becomes a machine tool. Simple examples are the common power-driven hack saw for metal, the small high-speed drill, and the wood-boring auger held in a frame and turned by a winch handle and bevel-gears. The difference between these and a big frame-saw cutting down a dozen boards simultaneously, or the immense machine boring the cylinders of an ocean liner, etc., is so vast that the relationship is hardly
apparent. Often the tool itself is absolutely dwarfed by the machine, of which nevertheless it is the central object and around which the machine is designed and built. A milling machine weighing several tons will often be seen rotating a tool of but two or three dozen pounds' weight. Yet the machine is fitted with elaborate slides, self-acting movements and provision for taking up wear, and is worth some hundreds of pounds sterling, while the tool may not be worth two pounds. Such apparent anomalies are in constant evidence. This article is a survey of the principles that underlie the forms of tools. The subject of their embodiment in machine tools will be found and treated under MACHINE TOOLS, LATHE, PLANING-MACHINES, MILLING MACHINES, SAWING MACHINES, WOOD-WORKING MACHINERY, etc.
An analysis of the essential methods of operation gives a broad grouping as follows: line where the results obtained are practically those due to cutting, as in some of the shears, saws, milling cutters and grinding wheels.