Grinding Variables 301

abrasive

A hard particle of material used to remove workpiece material. Abrasives are bonded in the shape of a wheel for grinding operations.

arc of cut

The length of contact between the grinding wheel and the workpiece. Arc of cut describes the length of the cutting zone, the area of contact between the wheel and workpiece.

axis

An imaginary straight line that passes through the center of a point or object used to describe the positions of objects in three-dimensional space. Axes refer to locations or movements along and across the worktable in grinding operations, as well as vertical locations or movements.

bond material

The adhesive material in grinding wheels that holds the abrasive grains together. Bonding materials can be vitrified, organic, and metal.

brittle

The tendency to break when drawn, stretched, or formed. Brittleness typically accompanies hardness.

carbon

A nonmetallic chemical element that combines readily with metallic elements. Carbon is found in steel, carbide, diamond, and other materials.

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.

centers

A hardened, pointed, cylindrical component used to hold the end of a workpiece by inserting its tip into a matching hole in the part. Centers are often used to hold cylindrical grinding workpieces.

chemical resistance

The ability to resist chemical changes. Chemically resistant materials do not react with abrasives or their bonds.

chips

Pieces of material that are removed from a workpiece when a tool cuts or grinds the workpiece material. During grinding, small chips are formed by the grinding wheel’s abrasive grains.

chuck

A device that holds a workpiece in place as it rotates. The chuck commonly has three or four jaws that can be adjusted to fit various sizes.

collet

A slitted workholding device that uses tension or pressure to hold a workpiece. Collets hold and rotate a workpiece in the headstock spindle.

computer numerical control

CNC. A self-contained system of computers and precise motors that executes program instructions to guide machine tool components. Computer numerical control allows operators to program sequences of machining operations.

creep-feed grinding

A grinding process in which the depth of cut is increased dramatically while the feed rate is decreased. Creep-feed grinding is used for large amounts of material removal.

creep-feed grinding

A grinding process in which the feed into the workpiece is increased dramatically over conventional surface grinding while the feed rate of the workpiece is decreased. Creep-feed grinding is used to remove large amounts of material and produce a fine surface finish.

crossfeed

In surface grinding, the rate of a grinding wheel’s linear movement across a workpiece surface. In cylindrical grinding, crossfeed is a type of infeed and describes the wheel’s movement into the workpiece.

cubic inches

in³. A unit of volume measurement in the English system. One cubic inch is the volume of a cube with one-inch-long sides.

cubic millimeters

mm³. A unit of volume measurement in the metric system. One cubic millimeter is the volume of a cube with one-millimeter-long sides.

cutting tools

A tool with one or more cutting edges designed to engage a workpiece and remove material in the form of chips. Cutting tools preferably exhibit excellent hardness, toughness, and wear resistance.

cutting zone

The area of contact between the grinding wheel and the workpiece. Cutting zone is the arc of cut multiplied by the contact width in grinding.

cylindrical grinding

A common grinding process in which a cylindrical workpiece is held on one or both ends during grinding. Cylindrical grinding rotates both the workpiece and grinding wheel in order to finish a part.

depth of cut

The amount of penetration a tool makes, or the distance from the uncut surface to the machined surface. In grinding, depth of cut refers to the total depth of cut from the beginning to the end of the process or the incremental depth of cut per pass of the grinding wheel, which is the infeed.

downfeed

The feed of the grinding wheel into the workpiece in surface grinding. Downfeed is a type of infeed.

dressing

Removing 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 axial motion of the workpiece. End stops are used in some centerless grinding operations to position a taper on the workpiece or hold a position for plunge grinding.

feed rates

The rates at which the workpiece moves in relation to the grinding wheel. Feed rates vary depending on the operation according to factors such as tolerance and surface finish.

feeds

Movement of the workpiece or machine component from one point to another. Feeds may be either along or across the wheel periphery in grinding operations.

ferrous

A metal that contains iron. The most common ferrous metal is steel.

finishing passes

A movement of a grinding wheel along a workpiece that removes very small amounts of material. Finishing passes often require faster speeds and a lighter depth of cut.

flood cooling

A method of delivering coolant to the workpiece with a low-pressure pump. Flood cooling drenches the entire grinding area with coolant.

fracture

Complete separation or breaking apart due to force or impact. Fracturing occurs in the abrasive grain as part of the grinding wheel's self-sharpening process.

friability

The ability of abrasive grains to fracture and self-sharpen under stress. Abrasive grains with low friability may be worn too dull to grind effectively.

glazing

The unwanted formation of a smooth surface on a grinding wheel. Glazing occurs when the abrasive grains are worn dull and have not fractured or been released from the bonding material.

grade

The strength of the bond in an abrasive wheel. Soft-grade grinding wheels release grains more easily than hard-grade wheels.

grain sizes

The size of the abrasive grains that compose a grinding wheel. Grain sizes help to determine the tolerance and surface finish that the wheel can create.

grains

A small, hard particle or crystal of abrasive material. Abrasive grains are bonded together to create grinding wheels and other abrasive tools.

graphite

A soft, black formation of carbon. Graphite is brittle and has lubricating properties.

G-ratio

The cubic volume of workpiece material removed divided by the cubic volume of wheel wear. The G-ratio generally ranges from 20:1 to 80:1.

grinding

Using an abrasive tool to remove material from a workpiece surface. Grinding operations commonly use abrasive grains bonded into the shape of a grinding wheel.

grinding fluid

A liquid substance used in a grinding operation to control temperatures and add lubrication. Grinding fluids are generally either water-based fluids or straight oils, though some special operations use other substances.

grinding fluid

A liquid used during grinding to clean, cool, and lubricate. Grinding fluid is also referred to as coolant.

grinding wheel

A wheel made of a bonded abrasive used to remove material from the surface of a workpiece. A grinding wheel removes microscopic chips of material from a workpiece and can produce very fine surface finishes.

hardness

A material’s ability to resist penetration, indentation, or scratching. Hard materials tend to be brittle and resistant to wear.

honing

A precision abrasive process that removes a relatively small amount of material using abrasive stones. Honing can produce high precision parts and refined surface finishes.

inches per minute

ipm. A unit of measurement of feed that indicates how many linear inches the cutting tool or workpiece has traveled in one minute. Inches per minute is an English measurement.

infeed

The feed of the grinding wheel into the workpiece. Infeed can be continuous or incremental.

inside diameter

ID. The interior surface of a workpiece feature. Inside diameter operations may include grinding and metal-cutting operations, such as holemaking.

lapping

An abrasive finishing process that removes very small amounts of material from the surface of flat parts. Lapping can produce the highest degree of flatness and superior surface finishes with a reflective shine.

loading

To build up swarf in a grinding wheel and clog the pores between grains. Loading can be removed by dressing and truing the grinding wheel.

m/s

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

magnetic chuck

A device that uses magnetism to hold a workpiece. The magnetic chuck is the most common workholding device used on the surface grinder.

manual grinding machines

A grinding machine that requires an operator to control every part of the grinding process. Manual grinding machines have set spindle speeds.

material removal rate

The volume of material removed in a given amount of time. Material removal rate is measured in cubic inches or centimeters per minute.

meters per minute

m/min. A unit of measurement of feed that indicates how many linear meters the cutting tool or workpiece has traveled in one minute. Meters per minute is a metric measurement.

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 measures the number of meters that a location on the periphery of a rotating component travels in one second.

milling

A machining operation that uses a multipoint horizontal or vertical cutter to remove metal from the surface of a workpiece. Milling is used to produce a variety of workpiece shapes and features, including contours, slots, and flat surfaces.

oxidation

The formation of deposits on the surface of a workpiece when grinding heat and/or pressures combine to create a chemical reaction between a metal and the oxygen in the environment. Oxidation may appear as a spot or mark on the workpiece surface.

parameters

A set of measurable factors or characteristics that define the scope of an operation. Parameters of a grinding operation include workpiece size and form as well as surface finish specifications.

peripheral

Relating to the outer edge or perimeter of an object. Peripheral speed in grinding refers to the speed of the wheel as opposed to the rotation of the spindle.

plowing

An action that occurs during grinding when dull grains push into the workpiece without cutting it. Plowing leaves grooves in the work surface.

properties

A measurable quality or attribute of a specific material that determines how it will respond to thermal and mechanical stresses applied during machining operations. Properties include aspects such as hardness and toughness.

regulating wheel

In centerless grinding, the wheel that rotates the workpiece and controls the workpiece speed. A regulating wheel is also known as the control wheel, as it moves the workpiece across the periphery of the grinding wheel and controls the feed rate.

revolutions per minute

rpm. The number of revolutions that a spindle, cutting tool, or any rotating component completes in one minute. Revolutions per minute is a measurement of speed.

roughing

The initial machining operation that removes material rapidly without regard to surface finish. Roughing achieves the basic workpiece shape and dimensions.

roughing passes

A movement of a grinding wheel along a workpiece that removes a large amount of material. Roughing passes grind a workpiece close to its finished size but without regard to surface finish.

rpm

Revolutions per minute. The number of revolutions that a spindle, tool, or any rotating component completes in one minute. Rpm is a measurement of speed.

rubbing

A sliding action that occurs during grinding when dull grains glide over the surface of a workpiece without cutting it.

sfm

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

speeds

The rate of rotational movement of the grinding wheel, rotary table, or regulating wheel. Speeds are measured in revolutions per minute and surface feet per minute or meters per second.

spindle

A rotating component of a machine that can hold and rotate tools. Grinding wheels are typically mounted onto a spindle.

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 specifies the distance that a location on the periphery of a rotating component travels in one minute.

surface finish

The texture of a workpiece surface after an operation. Surface finish is key to the performance of a finished part.

surface speed

The speed of the peripheral surface of any rotating machine component measured in sfm or m/s. The surface speed of the regulating wheel determines the rotational speed of the workpiece in centerless grinding.

swarf

The gritty combination of chips, abrasive grains, and worn bonding material that is produced during grinding. If not effectively evacuated, swarf can clog a grinding wheel and cause it to function improperly.

table feed

The rate of side-to-side movement of the worktable. Table feed is a type of work feed in surface grinding and cylindrical grinding and is also called the traverse rate.

tapered

A linear increase or decrease in the diameter of an object. In centerless grinding, a taper is ground into a workpiece using a tapered grinding wheel and an end stop.

through feed

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

tolerances

The allowable deviation from a given dimension that will still allow the part to perform its desired function. Tolerances indicate the allowable difference between a physical feature of a workpiece and its intended design.

tool steels

A grouping of alloy steels designed to be used as cutting tools, dies, punches, and other tools. Tool steels are designed for toughness, hardness, and wear resistance.

traverse rate

The rate of side-to-side movement of the worktable. The traverse rate is a type of work feed in surface grinding and cylindrical grinding and is also called the table feed.

turning

A machining operation that rotates a cylindrical workpiece while a single-point tool is guided along its length. Turning is performed on a lathe.

variables

The measurable rates of movement of abrasive tools and workpieces. Grinding variables include the adjustable or changeable aspects of a grinding operation.

velocity

The combination of an object's speed and direction of motion. Unlike speed, velocity always implies a direction.

wheel speeds

The rate at which a point on the periphery of the wheel moves at the point of contact with the workpiece. Wheel speed depends upon the spindle speed and wheel size.

wheelhead

A grinding machine component that contains the spindle and grinding wheel. The wheelhead moves up and down in surface grinding.

work feed

The rate of a workpiece’s linear movement past the grinding wheel. Table feed and through feed are types of work feed.

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.

workpiece

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

workpiece speed

The rate of workpiece rotation in cylindrical grinding. In cylindrical and centerless grinding, workpiece speed measures how quickly the workpiece is moving past the grinding wheel.