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TYPES OF GRINDING MACHINES

The versatility and wide application of the grinding processes have led to the development of many types of grinding machines. Your shop will probably have two, three, or more of the common types. As a machinist, you should be familiar with the many types of these machine tools and the processes they perform. Surface Grinders One of the most common grinding machines is the surface grinder. Types of surface grinders include
Type I : Horizontal spindle with reciprocating table
Type II: Horizontal spindle with rotary table
Type III: Vertical spindle with either reciprocating or rotary table

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Type I On this type of surface grinder (Figure L-1) the grinding wheel is on a horizontal spindle. The face (periphery) of the wheel is presented to the workpiece. The workpiece, if it is made of a ferrous material, is usually held on a magnetic chuck and moved back and forth under
the rapidly rotating grinding wheel. The chuck (or the wheelhead) may also be moved in and out. Depth of cut is controlled by raising and lowering the wheelhead. Sizes of surface grinders range from a small machine that will grind an area of 4 by 8 in. to large machines with the capacity to grind an area of 6 by 16 ft, or even larger. The 6- by 18-in.capacity machine is common in machine shops (FigureL-2).
produce a flat surface on a workpiece within a tolerance of less than in. Special shaping of the grinding wheel allows contoured surfaces to be ground.

Type II On the type II surface grinder the face of the wheel is also brought into contact with the workpiece (Figure L-3).
Parts to be ground are mounted on a rotary table and run under the wheel. The table may also be tilted to provide special grinding geometry, such as hollow grinding of the sides of a circular saw.
Type III The type III surface grinder has a vertical spindle, and the side (also called the grinding face) of the wheel is brought into contact with the workpiece. The worktable may be reciprocating (Figure L-4) or rotary (Figure L-5).
Figure L-3 Principle of the type II surface grinder. Sometimes circular parts are centered on this grinder; the resulting concentric scratch pattern is excellent for metal-to-metal seals of mating parts.

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Accessory spindles and special wheel shaping (dressing) add to the versatility of this (reciprocating table version) grinding machine (Figure L-6). Vertical spindle grinding  machines are often seen in large sizes (Figure L-7).Cylindrical Grinders Cylindrical grinders are used to grind the diameters of cylindrical workpieces.

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Types of cylindrical grinders include
1. Center-type
2. Roll-type
3. Centerless
4. Internal cylindrical
5. Tool and cutter
Center-Type Grinder The center-type cylindrical grinder, sometimes called a center grinder, grinds the outside diameter of a cylindrical workpiece mounted between centers (Figure L-8). The workpiece is traversed past the grinding wheel while being rotated from 50 to 100 sfpm
against the rotation of the grinding wheel (Figure L-9).

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Swiveling the table allows conical shapes can be ground. This machine is also used for plunge grinding, in which the work and wheel are brought together without table traverse.

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Steep conical shapes can be ground on the universal cylindrical grinder (Figure L-10). Long, slender workpieces can be ground using a steady rest (Figure L-11). The angular type center grinder (FigureL-12) can grind into a shoulder (Figure L-13) and can form cylindrical geometry by using wheels (Figure L-14) accurately dressed to produce a mirror image of their form in the workpiece.

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Cylindrical grinders with computer numerical control (CNC) are being produced (Figure L-15) that can perform the functions of the universal cylindrical grinder under program control.

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Roll-Type Grinder Roll grinders are used to grind and resurface large steel rolling mill rolls (Figure L-16). Because these rolls are usually heavy, they are supported in bearings Wheel spindle Figure L-10 Universal cylindrical grinder (Courtesy of MAG Industrial Automation Systems, LLC).
(rather than on centers) while in the grinding machine. In most of the larger roll grinding machines, the wheelhead is traversed along the rotating workpiece to accomplish the grinding.
Centerless Grinder The centerless grinder, as the name suggests, permits the grinding of cylindrical workpieces
without the use of centers for support. It can be used for narrow parts, such as the outside grinding of bearing races, or for the grinding of long workpieces, such as lengths of drill rod. Machines may even be lined up in tandem, to permit roughing and finishing of parts in a continuous
process so that large numbers of parts can be quickly and Figure L-11 Use of a steady rest for grinding slender workpieces (Courtesy of MAG Industrial Automation Systems, LLC).
Figure L-15 Computer numerically controlled (CNC) cylindrical grinder showing a variety of applications that can be accomplished under computer control (Courtesy of Maximum Advantage—Carolinas).
accurately ground to close tolerances. An example is the O.D. grinding of bearing rings.

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The workpiece is fed between the grinding wheel and regulating wheel (Figure L-17). The work rest located between the grinding and regulating wheel supports the workpiece. The regulating wheel is usually a rubber-bonded wheel of the same grit characteristics as the grinding wheel. It Figure L-16 Roll grinding machine for grinding steel mill rolls. Figure L-17 Principle of the centerless grinder. The grinding wheel travels at normal speeds, and the regulating wheel travels at a slower speed to control the rate of spin of the workpiece.
rotates in the same direction as the grinding wheel but at a much slower speed, acting as a brake on the workpiece. The feeding action for moving the workpiece between the grinding feeding action also may be used with a stop for the workpiece. A good example is the grinding of stems on automotive valves. Centerless grinding is also suited to the grinding of conical parts (Figure L-19) and parts with different diameters
(Figure L-20). It is even possible to grind threads on headless setscrews, employing the through-feed method with the spiral thread form dressed into the grinding wheel.

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A common through-feed centerless grinding operation is the grinding of wrist pins for automotive pistons. Sometimes this centerless
grinding operation is followed by a centerless lapping process utilizing the same principle, but employing a much smaller abrasive grit size.

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Internal Cylindrical Grinder Cylindrical grinding processes apply to internal (Figure L-21) as well as external surfaces. Internal grinding uses mounted abrasive wheels (Figure L-22). These are grinding wheels cemented onto a shank for mounting into the machine’s grinding spindle
(Figure L-23). Internal grinding can be done on concentric workpieces parallel to the machine spindle axis. Internal tapers may also be ground. When fitted with special faceplate tooling, internal grinders can also be used for nonconcentric parts.

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The centerless principle can also be applied to internal concentric parts, with the part held and driven between three rolls (Figure L-24) while the inside is ground with a mounted wheel.

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Tool and Cutter Grinder The universal tool and cutter grinder (Figure L-25) is a type of cylindrical grinder.
However, this machine can also perform some limitedsurface grinding. On these machines, the grinding head can be rotated around the vertical axis, and the workhead can be rotated and tilted in a variety of directions. On several designs, the grinding spindle can also be tilted. A variety of grinding wheel shapes and a variety of abrasives can be used with tool and cutter grinders. The primary application of
tool and cutter grinders is in the resharpening of milling cutters (Figure L-26).Miscellaneous Grinding Machines Gear grinders are another interesting specialized family of grinding machines. These machines fall into two categories: form grinders (Figure L-27), on which the grinding wheel is dressed to a precise “mirror image” of the shape of the tooth to be ground, and generating grinders (Figure L-28), on
which the completed form results from the combined action of the wheel and workpiece.

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Thread grinders (Figure L-29) are important in the production of precise lead screws and other precision screw forms.

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