Milling machines are the most versatile of all machine tools. Flat or contoured surfaces may be machined with excellent finish and accuracy. Angles, slots, gear teeth, and recess cuts can be made by using various cutters. Drilling and Boring Machines Hole-making machine tools are used to drill a hole where none previously existed; to alter a hole in accordance with some specification or to lap or hone a hole to create an accurate size or a smooth finish. Drilling machines vary in size and function, ranging from portable drills to radial drilling machines, multispindle units, automatic production machines, and deep-hole-drilling machines. Boring is a process that enlarges holes previously drilled, usually with a rotating single-point cutter held on a boring bar and fed against a stationary workpiece. Boring machines include jig borers and vertical and horizontal boring mills. Grinders Grinding is the removal of metal by a rotating abrasive wheel; the action is similar to that of a milling cutter.
The wheel is composed of many small grains of abrasive, bonded together, with each grain acting as a miniature cutting tool. The process produces extremely smooth and accurate finishes. Because only a small amount of material is removed at each pass of the wheel, grinding machines require fine wheel regulation. The pressure of the wheel against the workpiece can be made very slight, so that grinding can be carried out on fragile materials that cannot be machined by other conventional devices. See Grinding and Polishing. GSaws Commonly used power-driven saws are classified into three general types, according to the kind of motion used in the cutting action: reciprocating, circular, and band-sawing machines. They generally consist of a bed or frame, a vise for clamping the workpiece, a feed mechanism, and the saw blade. Cutting Tools and Fluids Because cutting processes involve high local stresses, frictions, and considerable heat generation, cutting-tool material must combine strength, toughness, hardness, and wear resistance at elevated temperatures.
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