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Abrasives

Basics of the Centerless Grinder 233

Basics of the Centerless Grinder provides a comprehensive introduction to centerless grinding. Centerless grinding includes both internal and external grinding operations. During centerless grinding, a rotating regulating wheel moves a workpiece, supported by a work rest blade, along a rotating grinding wheel. This abrasive process removes a layer of material from the surface of the workpiece. Its cutting variables include wheel speed, spindle speed, surface or work speed, and feed rate. During throughfeed and endfeed grinding, workpieces move along the length of the grinding wheel, while infeed grinding pushes a shaped workpiece into the grinding wheel.

Centerless grinding produces accurate parts with improved surface finish. An operator cannot use a centerless grinder without understanding how the machine functions. After this class, users should be able to describe the general machine components, controls, and basic function of a centerless grinder.

Difficulty Intermediate
Format Online
Number of Lessons 14
Language English

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Introduction to Centerless Grinding
Centerless Grinder Components
Centerless Grinder Controls
Abrasive Wheels
Throughfeed Centerless Grinding
Centerless Grinding Basics
Infeed Centerless Grinding
Endfeed Centerless Grinding
Internal Centerless Grinding
Centerless Grinding in Action
Varieties of Centerless Grinding
Grinding Wheel Maintenance and Grinding Fluid
Cutting Variables on the Centerless Grinder
Centerless Grinding Review

Describe the basic centerless grinding process.
Identify the essential components of the centerless grinder.
Identify the controls on the centerless grinder.
Describe the different abrasive wheels used in centerless grinding.
Describe throughfeed centerless grinding.
Describe infeed centerless grinding.
Describe endfeed centerless grinding.
Describe internal centerless grinding.
Describe common practices for wheel maintenance.
Describe the different cutting variables used in centerless grinding.

Vocabulary Term

Definition

abrasive grains

A hard, sharp particle of material, generally aluminum oxide or silicon carbide and sometimes diamond or cBN. Abrasives are used to wear down or rub away material.

angle of inclination

The angle at which the centerline of the regulating wheel spindle is set in relation to the centerline of the grinding wheel. The regulating wheel angle of inclination provides axial thrust that feeds the workpiece past the grinding wheel during centerless grinding.

angular-bed grinders

A type of centerless grinder that uses the regulating wheel to rotate the workpiece until it reaches the desired speed. On an angular-bed grinder, the workpiece contacts the grinding wheel only after it has reached the desired speed.

axial

Running straight along or parallel to the axis of a workpiece. Axial as well as rotational movement are required for a workpiece to be properly ground during centerless grinding.

backing plate

A component that, along with the grinding wheel, rotates a workpiece and pushes it into two hard shoes during shoe-type internal centerless grinding. A backing plate is often a magnetic chuck.

bar stock

Raw material purchased from metal manufacturers in the form of long bars. Bar stock may be round, square, or hexagonal.

bed

The foundation of a grinding machine that supports all other machine components. The bed on a grinder is the bottom portion of the machine.

bond

The material that holds abrasive grains together in a grinding wheel. Bond, or bonding material, can be vitrified, resin, rubber, or metal.

bonding material

The material that holds abrasive grains together in a grinding wheel. Bonding material, or bond, can be vitrified, resin, rubber, or metal.

centerless grinding

A type of cylindrical grinding in which a cylindrical part is supported on a work rest blade and guided between a grinding wheel and a regulating wheel. Centerless grinding requires that both the workpiece and the grinding wheel rotate.

chip

A small piece of material that is removed from a workpiece. Chips are formed when a tool cuts or grinds a material.

circumference

The boundary or perimeter around a circle. Circumference measures the distance around a circle.

concentric

Having a common center or sharing the same axis. Concentric circles on a grinding wheel should share a center point at this axis.

concentricity

A geometric tolerance that describes the location of opposing points in cylindrical features with respect to their center axes. Concentricity can be achieved on a cylindrical part using shoe-type internal centerless grinding.

coolant

A complex liquid consisting of several chemicals that is used during grinding to clean, cool, and lubricate the wheel and workpiece. Coolant, or grinding fluid, also washes away swarf.

cylindrical grinding

A common grinding process that holds a cylindrical part on each end or uses a chuck or collet to hold the part during grinding. Cylindrical grinding rotates both the part and grinding wheel.

cylindricity

A three-dimensional form tolerance that describes the allowable variability in the shape and appearance of a cylinder. Cylindricity states how close a part is to being perfectly cylindrical.

dressing

To remove swarf, dull grains, and bonding material from a grinding wheel by fracturing away the wheel surface. Dressing also sharpens the wheel.

end stop

A device that halts or prevents workpiece motion once the workpiece is ground to a specified location and depth. End stops are used in endfeed centerless grinding.

endfeed

A method of centerless grinding in which the workpiece is fed into the grinding and regulating wheels until the workpiece contacts an end stop. Endfeed centerless grinding is used to taper the end of a workpiece.

external cylindrical centerless grinder

The most common form of centerless grinder. External cylindrical centerless grinders perform either throughfeed or infeed centerless grinding.

fracturing

The breaking apart of grains in an abrasive wheel during grinding to create new cutting edges. Fracturing is part of the wheel’s self-sharpening process.

glazing

The unwanted formation of a smooth surface on a grinding wheel. Glazing occurs when the heat from grinding reacts with a wheel.

grinding

Using an abrasive to wear away a workpiece surface and achieve highly accurate measurements. Grinding operations commonly use abrasive grains bonded into a wheel shape.

grinding fluid

A complex liquid consisting of several chemicals that is used during grinding to clean, cool, and lubricate the wheel and workpiece. Grinding fluid also washes away swarf.

grinding variables

The measureable rates of movement of grinding wheels and workpieces. Grinding variables include speed, feed, and depth of cut.

grinding wheel

A wheel made of abrasive grains that are held together by a bonding material. A grinding wheel rotates and grinds away microscopic chips of material and can produce very fine surface finishes.

hard shoes

A component against which the workpiece is pushed during internal centerless grinding to provide accurate concentricity. Two hard shoes are used in shoe-type internal centerless grinding.

horizontal-bed grinders

A type of centerless grinder that causes the workpiece to rotate only after it touches the rotating grinding wheel. Horizontal-bed grinders are the most common design of centerless grinders.

infeed centerless grinding

A centerless grinding process in which workpieces do not move all the way through the machine. Infeed centerless grinding involves the regulating wheel and work rest pushing the workpiece into the grinding wheel.

inner diameter

ID. The interior surface of a spherical or cylindrical object. Inner diameter is also known as internal diameter.

loading

A buildup of swarf in a grinding wheel that clogs the spaces between grains. Dressing and truing a grinding wheel prevent loading.

lower slide

The device that moves the regulating wheel and work rest blade toward and away from the grinding wheel. The lower slide is attached to the swivel plate.

machine tool

A power-driven machine that uses a cutting tool or abrasive wheel to remove material from a workpiece. Machine tools include centerless and cylindrical grinders.

meters per second

m/s. A measurement of speed that is a direct function of the workpiece or tool diameter and its rate of rotation. Meters per second is a metric measurement.

outer diameter. The external surface of a workpiece. OD centerless grinding operations include throughfeed, infeed, and endfeed grinding.

outer diameter

OD. The external surface of a workpiece. Outer diameter centerless grinding operations include throughfeed, infeed, and endfeed grinding.

periphery

The perimeter, or edge, of an object. Many types of grinding wheels grind with their periphery.

pressure roll

A wheel that, along with the support roll, helps to hold the workpiece during internal centerless grinding. A pressure roll is used in roll-type internal centerless grinding.

recessed wheel

An abrasive wheel that resembles a flat disk with a depressed area surrounding the wheel center. Recessed wheels are wider at their periphery than their center.

regulating roll

A wheel used to rotate the workpiece and pull it through the internal centerless grinding process. A regulating roll is used in roll-type internal centerless grinding.

regulating wheel

A grinding wheel commonly made of resin bond that is used to slow a workpiece's rotation against a grinding wheel. A regulating wheel, or control wheel, also drives the workpiece axially across the work rest blade.

regulating wheel housing

The part of a centerless grinder on which the regulating wheel is mounted. The regulating wheel housing is mounted to the upper slide and contains the regulating wheel and regulating wheel spindle.

revolutions per minute

rpm. The number of revolutions that a spindle or grinding wheel completes in one minute. Revolutions per minute is a measurement of speed.

roll-type internal

A type of centerless grinding in which three rolls are used to rotate and support a workpiece while a grinding wheel machines its inner diameter. Roll-type internal centerless grinding involves one large regulating roll that rotates the workpiece while a pressure roll and a support roll hold the workpiece in place during the grinding process.

rotational speed

The rate of rotational movement of the workpiece or grinding or regulating wheel. Rotational speed is measured in revolutions per minute (rpm).

shoe-type internal

A type of centerless grinding in which a backing plate pushes a workpiece into two hard shoes while a grinding wheel machines its inner diameter. Shoe-type internal centerless grinding maintains concentricity between the workpiece's inner and outer diameter.

spindle

A rotating component of a machine tool. Typically, grinding and regulating wheels are mounted on a spindle.

spindle speed

The rate of rotational movement of the grinding or regulating wheel. Spindle speed is measured in revolutions per minute (rpm).

stock

Raw material used to make manufactured parts. Stock is available in standard shapes, such as long bars, plates, or sheets.

straight wheel

A common type of abrasive tool used in grinding and cutoff operations. Straight wheels generally appear as flat disks.

support roll

A wheel that, along with the pressure roll, helps to hold the workpiece during internal centerless grinding. A support roll is used in roll-type internal centerless grinding.

surface feet per minute

sfm. A measurement of speed that is a direct function of the workpiece or tool diameter and its rate of rotation. Surface feet per minute measures the number of feet that a location on a rotating component travels in one minute.

surface finish

The smoothness of a part surface after it has gone through all grinding operations. Surface finish is the complete, desired surface.

surface speed

The uniform rate at which the regulating wheel revolves against the workpiece during centerless grinding. Surface speed controls the work speed of the workpiece.

swarf

The gritty combination of chips, abrasive grains, and worn bonding material that is produced during grinding. Swarf can clog a grinding wheel and cause it to function improperly.

swivel plate

The device that tilts or aligns the regulating wheel parallel to the grinding wheel.The swivel plate is mounted to the bed of a grinder.

tapered

A linear increase or decrease in the diameter of an object. A taper is ground into a workpiece using endfeed grinding.

through feed rate

The rate at which the workpiece passes axially between the grinding and regulating wheels. Through feed rate is controlled by the regulating wheel.

throughfeed

A method of centerless grinding in which the regulating wheel and work rest guides feed the workpiece past the grinding wheel in a straight line. In throughfeed grinding, the regulating wheel moves the part completely past the grinding wheel.

tolerance

The allowable deviation from a given dimension. Tolerances indicate the allowable difference between a physical feature and its intended design.

truing

To restore a grinding wheel to its original, intended shape. Truing ensures that a wheel retains a concentric round shape.

upper slide

The device that moves the regulating wheel toward and away from the work rest blade. The upper slide is attached to the swivel plate.

wheel speed

The peripheral rate of movement of the grinding wheel. Wheel speed is measured in surface feet per minute or meters per second.

wheelhead

The part of the grinding machine on which the wheel is mounted. On a centerless grinder, the wheelhead contains the grinding wheel and grinding wheel spindle.

work rest

A centerless grinder component that supports the workpiece as it is ground. The work rest is mounted on the lower slide and supports the work rest blade.

work rest blade

A device that supports cylindrical parts during centerless grinding. Work rest blades often have an edge that angles toward the regulating wheel.

work rest guides

A centerless grinder component located at the beginning and end of the machine to position the workpiece as it enters and exits. Work rest guides are used for throughfeed centerless grinding.

work speed

The peripheral speed of the workpiece. Work speed is approximately equal to the surface speed of the regulating wheel.

workpiece

A part that is in the process of being manufactured. A workpiece may be a complete product by itself or one component of a product consisting of many parts.