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ndition without being turned or otherwise machined.Thus many types of forgings and other parts are finished pletely with the grinding wheel at appreciable savings of time and expense.Classes of grinding machines include the following:cylindrical grinders,centerless grinders,internal grinders,surface grinders,and tool and cutter grinders.The cylindrical and centerless grinders are for straight cylindrical or taper work;thus splines,shafts,and similar parts ale ground on cylindrical machines either of the moncenter type or the centerless machine.Thread grinders are used for grinding precision threads for thread gages, and threads on precision parts where the concentricity between the diameter of the shaft and the pitch diameter of the thread must be held to close tolerances.The internal grinders are used for grinding of precision holes.Cylinder bores,and similar operations where bores of all kinds ale to be finished.The surface grinders are for finishing all kinds of flat work,or work with plain surfaces which may be operated upon either by the edge of a wheel or by the face of a grinding wheel.These machines may have reciprocating or rotating tables.Grinding machines utilize abrasive grains,bonded into various shapes and sizes of wheels and belts to be used as the cutting agent.Grinding operations are used to impart a high‘quality surface finish on the workpiece.In addition,the dimensional accuracy of the workpiece is improved since tolerances of 0.00025mm are possible in grinding operations.Grinding machines are classified according to the type of surface produced.Common surfaces and classifications ofgrinding machines are surface,cylindrical,and special machines.The grinding process is of extreme importance in production work for several reasons.(1)It is the most mon method for cutting hardened tool steel or other heattreated steel. Parts are first machined in the unheattreated condition,and then ground to the desired dimensions and surface finish.(2)It c