Machine Tools

There are many different types of grinding machines available which are used to obtain very close tolerances and fine finishes. Grinding machines are used for grinding flat surfaces, external and cylindrical surfaces, tapered surfaces, and irregular surfaces. Production parts are typically ground to tolerances of plus or minus 0.0001 in and special parts for precision instruments are ground to plus or minus 0.000020 in (20 microinches). All grinding machines utilize a rotating abrasive wheel or moving belt in contact with a workpiece to remove metal. Various combinations of wheel feed, either along or normal to the axis of wheel rotation, and also rotary or linear workpiece motion, are provided by the different types of grinding machines. To produce shapes of cylindrical section, workpiece and wheel both rotate on parallel axes while one or the other is fed along its own axis of rotation. Contact between workpiece and wheel is on the outside diameter of the wheel and the work is mounted between centers, chucked, or rotated without centers by a back-up wheel (this is called "centerless" grinding). To produce flat surfaces, the workpiece is mounted on a table and traversed along a line parallel to the surface to be ground or rotated about an axis at right angles to the surface to be ground. The axis of grinding wheel rotation can either be parallel or perpendicular to the surface to be ground, applying either the side or face of the wheel. Complex shapes are routinely ground such as thread forms, cam contours, gear teeth, and cutting tool edges. The same basic devices that control motion between the cutting tool and workpiece in other machine tools are also used in grinding machines such as lead screws, cams, special fixtures and tracer mechanisms. Grinding machines have limitations as to how fast and how much material can be removed but modern manufacturing, with the help of more accurate castings and forgings, is utilizing grinders more and more for both sizing and finishing operations. Some finished parts are produced by grinding only.

The major types of grinding machines available are cylindrical grinders, internal and chucking grinders, universal grinders, centerless grinders, surface grinders, face grinders, disc grinders, and tool and cutter grinders.