Way of displaying real-world objects on a flat surface, showing only height and width. This system uses only the X and Y axes.


Way of displaying real-world objects in a natural way by showing depth, height and width. This system uses the X, Y and Z axes.


Substance used for grinding, honing, lapping, superfinishing and polishing. Examples include garnet, emery, corundum, silicon carbide, cubic boron nitride and diamond in various grit sizes.

abrasive band

Endless band coated with diamond or other abrasive that is fitted to a special band machine for machining difficult-to-cut materials.

abrasive belt

Abrasive-coated belt used for production finishing, deburring and similar functions. See coated abrasive.

abrasive cutoff disc

Blade-like disc with abrasive particles that cuts/parts stock in a slicing motion.

abrasive cutoff machine

Machine that uses blade-like discs impregnated with abrasive particles to cut/part stock. See saw, sawing machine.

abrasive flow machining

Finishing and deburring operation for holes, inaccessible areas or restricted passages. Done by clamping the workpiece in a fixture, then extruding semisolid abrasive media through the passage. Often, multiple parts are loaded into a single fixture and finished simultaneously.

abrasive machining

Various grinding, honing, lapping and polishing operations that utilize abrasive particles to impart new shapes, improve finishes and part stock by removing metal or other material.

abrasive waterjet (AWJ)

System that uses high-pressure waterjets in combination with a slurry of fine abrasive grains to machine materials. See waterjet cutting.

abrasive-wire bandsawing

Variation of bandsawing that uses a small-diameter wire with diamond, cubic boron nitride or aluminum-oxide abrasives bonded to the surface as the cutting blade. Alternative to electrical-discharge machining for producing dies, stripper plates, electrodes and cams from difficult-to-machine conductive and nonconductive materials. See bandsawing.


Sulfur, chlorine and other materials added to cutting fluids to improve lubricity, stabilize oil emulsions and prevent chipwelding under high heat and pressure. See cutting fluid.


Mixture of concentrate and water prepared to restore depleted cutting fluid to its original state.

age hardening

Hardening of a heat-treated material that occurs slowly at room temperature and more rapidly at higher temperatures. Usually follows rapid cooling or cold working.

alloy steels

Steel containing specified quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, sulfur and phosphorus) added to cause changes in the metal’s mechanical and/or physical properties. Principal alloying elements are nickel, chromium, molybdenum and silicon. Some grades of alloy steels contain one or more of these elements: vanadium, boron, lead and copper.

alloying element

Element added to a metal to change its mechanical and/or physical properties.


Substances having metallic properties and being composed of two or more chemical elements of which at least one is a metal.

alpha iron

The body-centered cubic form of pure iron. Each of eight atoms is located in the corner of a cube, and one atom is located in the center of the cube. Alpha iron is stable below 1,670º F (910º C).


Formation of an aluminum or aluminum-alloy coating on a metal by hot dipping, hot spraying or diffusion.

aluminum alloys

Aluminum containing specified quantities of alloying elements added to obtain the necessary mechanical and physical properties. Aluminum alloys are divided into two categories: wrought compositions and casting compositions. Some compositions may contain up to 10 alloying elements, but only one or two are the main alloying elements, such as copper, manganese, silicon, magnesium, zinc or tin.

aluminum oxide

Aluminum oxide, also known as corundum, is used in grinding wheels. The chemical formula is Al2O3. Aluminum oxide is the base for ceramics, which are used in cutting tools for high-speed machining with light chip removal. Aluminum oxide is widely used as coating material applied to carbide substrates by chemical vapor deposition. Coated carbide inserts with Al2O3 layers withstand high cutting speeds, as well as abrasive and crater wear.


Not having a crystal structure; noncrystalline.

angle of entry

Determined by the position of the milling cutter’s centerline relative to the edge of the workpiece. Depending on the cutter diameter and the radial width of cut, the angle of entry can be negative or positive. A negative angle of entry occurs when the cutter’s centerline is located on the workpiece. Such an angle is recommended because the insert contacts the workpiece by its strong front rake, not by its weak cutting edge. To produce a negative angle of entry, the radial width of cut should exceed the cutter radius. A positive angle of entry occurs when the cutter’s centerline is not located on the workpiece. It happens when the radial width of cut is less than the cutter radius. A positive angle of entry should be avoided because the insert contacts the workpiece by its weakest part—the cutting edge.

angle plate

Solid adjustable or nonadjustable plate that holds work at a precise angle to the spindle during machining. Also used for inspection.


Softening a metal by heating it to and holding it at a controlled temperature, then cooling it at a controlled rate. Also performed to produce simultaneously desired changes in other properties or in the microstructure. The purposes of such changes include improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties and increase in stability of dimensions. Types of annealing include blue, black, box, bright, full, intermediate, isothermal, quench and recrystallization.

approach angle

Angle between the insert’s side-cutting edge and the line perpendicular to the milling cutter’s axis of rotation. Approach angle, which is also known as cutting edge angle, is used with metric units of measurement. See lead angle.

APT file

A file for automatically programmed tools that consists of the input language, an APT processor, an APT postprocessor and a computer of sufficient size to run the APT program. The APT system was initially developed for 3-, 4- and 5-axis milling machines, but because of further development, is capable of a range of applications, including point-to-point and turning work.


Shaft used for rotary support in machining applications. In grinding, the spindle for mounting the wheel; in milling and other cutting operations, the shaft for mounting the cutter.

arithmetic average (AA)

The mathematical expression denoting one of several parameters that describe surface texture (same as average roughness Ra). Average roughness is the arithmetic average height deviation of the measured surface profile from the profile centerline. See surface texture.


Joining together two or more parts to complete a structure.


Hot deformation of metastable austenite within controlled ranges of temperature and time that avoids formation of nonmartensitic transformation products.


Heat-treatment for ferrous alloys in which a part is quenched from the austenitizing temperature at a rate fast enough to avoid formation of ferrite or pearlite, and then held at the to achieve the desired characteristics. Austempering at lower temperatures (240° C to 270° C) produces a part with maximum strength, while austempering at higher temperatures (360° C to 380° C) yields high ductility and toughness.appropriate transformation temperature


Solid solution of one or more elements in face-centered cubic iron. Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon. Austenite can dissolve up to 2 percent carbon. Austenite is relatively soft, ductile and nonmagnetic.


Heating an alloy above its transformation temperature and then quenching it in a salt bath or other medium that extracts the heat at a sufficiently high rate to prevent formation of undesirable high-temperature-transformation qualities on its surface or in its microstructure. See austenite; martensite; martensiting.

automatic bar machine

Machine for turning bar stock. Similar to an automatic chucking machine, except that stock size is limited to through-the-spindle capacity and workpiece is held by push, draw or stationary collets rather than by chucks. See automatic chucking machine; turning machine.

automatic chucking machine

Machine with multiple chucks and toolholding spindles that permits processing of several parts simultaneously or multiple machining steps in one pass through the machine. See automatic bar machine.

automatic screw machine

Turning machine designed to produce parts automatically from coil or bar stock. The two basic types are cam (mechanical) and programmable (computer-controlled). Usually single-spindle, but Swiss types often have multiple spindles. See lathe; turning machine.

automatic toolchanger

Mechanism typically included in a machining center that, on the appropriate command, removes one cutting tool from the spindle nose and replaces it with another. The changer restores the used tool to the magazine and selects and withdraws the next desired tool from the storage magazine. The changer is controlled by a set of prerecorded/predetermined instructions associated with the part(s) to be produced.


Approach under which all or part of a machining or manufacturing process is accomplished by setting in motion a sequence that completes the process without further human intervention. May be mechanical (controlled by stops, cams, etc.), electrical (controlled by relays, contact switches, etc.) or electronic (computer- or microprocessor-controlled). “Fully automated” implies computer-integrated manufacturing. See CIM, computer-integrated manufacturing.

axial force

When drilling, a force that is directed axially—along the direction of machining. The magnitude of an axial force rises with the drill’s diameter and the chisel edge’s width. Axial force is also known as thrust. When turning and boring, the term “feed force” is commonly used instead of “axial force.” See cutting force.

axial rake

On angular tool flutes, the angle between the tooth face and the axial plane through the tool point.


Joint, rotational, directional or transversal movement of which the robot is capable. See degrees of freedom.


Smoothing and shining a surface by pressing an abrasive compound, embedded in a soft wheel or belt, against the workpiece.


1. Flexible portion of a bandsaw blade. 2. Support material behind the cutting edge of a tool. 3. Base material for coated abrasives.


Reaction in dynamic motion systems where potential energy that was created while the object was in motion is released when the object stops. Release of this potential energy or inertia causes the device to quickly snap backward relative to the last direction of motion. Backlash can cause a system’s final resting position to be different from what was intended and from where the control system intended to stop the device.


Rapid withdrawal of the tool from the workpiece.


Support that mounts on a cylindrical grinder to prevent deflection when grinding long, small-diameter stock.


Additive to cutting fluids to inhibit bacterial growth. See fungicide.


1. Heating to a low temperature to remove gases. 2. Curing or hardening surface coatings, such as paints, by exposure to heat. 3. Heating to drive off moisture, as in the baking of sand cores after molding. Often used after plating or welding, or when the presence of hydrogen is suspected, to prevent embrittlement.

band polishing

Variation of bandsawing that uses an abrasive band to polish parts previously sawed or filed. See bandsawing.


Machine that utilizes an endless band, normally with serrated teeth, for cutoff or contour sawing. See saw, sawing machine.

bandsaw blade (band)

Endless band, normally with serrated teeth, that serves as the cutting tool for cutoff or contour band machines.


Long, endless band with many small teeth traveling over two or more wheels (one is a driven wheel, and the others are idlers) in one direction. The band, with only a portion exposed, produces a continuous and uniform cutting action with evenly distributed low, individual tooth loads. Often called band machining.

barrel finishing

Mass finishing process that involves low-pressure abrasion resulting from tumbling workpieces in a barrel (usually of hexagonal or octagonal cross section) together with an abrasive slurry. See finishing.

bend test

Test for determining relative ductility of metal that is to be formed (usually sheet, strip, plate or wire) and for determining soundness and toughness of metal (after welding, for example). The specimen is usually bent over a specified diameter through a specified angle for a specified number of cycles.

black oxide

Black finish on a metal produced by immersing it in hot oxidizing salts or salt solutions.


Hole or cavity cut in a solid shape that does not connect with other holes or exit through the workpiece.


Workholding devices used on milling machines. Styles include step, finger-holding, telescoping and quick-clamp.

blue brittleness

Brittleness exhibited by some steels after being heated to a temperature within the range of about 200° C to 370° C, particularly if the steel is worked at the elevated temperature.

bonded abrasive

Abrasive grains mixed with a bonding agent. The mixture is pressed to shape and then fired in a kiln or cured. Forms include wheels, segments and cup wheels. Bond types include oxychloride, vitrified, silicate, metal, resin, plastic, rubber and shellac. Another type of bond is electroplated, wherein the abrasive grains are attached to a backing by a thick layer of electroplated material.

Boolean operation

Command that allows the addition, subtraction or intersection of solid objects in CAD.


Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

boring bar

Essentially a cantilever beam that holds one or more cutting tools in position during a boring operation. Can be held stationary and moved axially while the workpiece revolves around it, or revolved and moved axially while the workpiece is held stationary, or a combination of these actions. Installed on milling, drilling and boring machines, as well as lathes and machining centers.

boring cutter (or boring tool)

Cutting tool mounted in a boring bar (the holder) that enlarges a cored or drilled hole. May be a single-point or multiple-cutting-edge tool. Can be adjustable.

boring head

Single- or multiple-point precision tool used to bring an existing hole within dimensional tolerance. The head attaches to a standard toolholder and a mechanism permits fine adjustments to be made to the head within a diameter range.

boring machine

Similar to a turning machine except that the cutting tool (single-point or multiple-cutting-edge), rather than the workpiece, rotates to perform internal cuts. However, boring can be accomplished by holding the tool stationary and turning the workpiece. Takes a variety of vertical, slanted and horizontal forms, and has one or more spindles. Typically a large, powerful machine, it can readily hold tolerances to 0.0001". See jig boring; lathe; turning machine.

boundary additives

Sulfur, chlorine, phosphorus and other compounds added to cutting fluids to fill in surface irregularities at the tool/workpiece interface, creating a lubricating film. See cutting fluid; lubricity.

Brinell hardness number (HB)

Number related to the applied load (usually, 500 kgf and 3,000 kgf) and to the surface area of the permanent impression made by a 10mm ball indenter. The Brinell hardness number is a calculated value of the applied load (kgf) divided by the surface area of the indentation (mm2). Therefore, the unit of measure of a Brinell hardness number is kgf/mm2, but it is always omitted.

Brinell hardness test

Test for determining the hardness of a material by forcing a hardened steel or carbide ball of specified diameter into the material under a specified load. The result is expressed as the Brinell hardness number. See Knoop hardness test; Rockwell standard hardness test; Rockwell superficial hardness test; Scleroscope hardness test; and Vickers hardness test.

brittle fracture

Separation of a solid accompanied by little or no macroscopic plastic deformation. Typically, brittle fracture occurs by rapid crack propagation with less expenditure of energy than for ductile fracture.


Tapered tool, with a series of teeth of increasing length, that is pushed or pulled into a workpiece, successively removing small amounts of metal to enlarge a hole, slot or other opening to final size.


Operation in which a cutter progressively enlarges a slot or hole or shapes a workpiece exterior. Low teeth start the cut, intermediate teeth remove the majority of the material and high teeth finish the task. Broaching can be a one-step operation, as opposed to milling and slotting, which require repeated passes. Typically, however, broaching also involves multiple passes.

broaching machine

Machine designed specifically to run broaching tools. It is typically designated by operating characteristics (pull, push, rotary, continuous, blind-spline), type of power used (hydraulic, mechanical) and tonnage ratings. Broaching is also performed on arbor presses (manual and powered).


Generic term for a curve whose shape is controlled by a combination of its control points and knots (parameter values). The placement of the control points is controlled by an application-specific combination of order, tangency constraints and curvature requirements. See NURBS, nonuniform rational B-splines.


Use of rapidly spinning wires or fibers to effectively and economically remove burrs, scratches and similar mechanical imperfections from precision and highly stressed components. The greatest application is in the manufacture of gears and bearing races where the removal of sharp edges and stress risers by power methods has increased the speed of the operation.

built-up edge (BUE)

1. Permanently damaging a metal by heating to cause either incipient melting or intergranular oxidation. 2. In grinding, getting the workpiece hot enough to cause discoloration or to change the microstructure by tempering or hardening.


Tool-condition problem characterized by the adhesion of small particles of workpiece material to the cutting edge during chip removal.


Rotary tool that removes hard or soft materials similar to a rotary file. A bur’s teeth, or flutes, have a negative rake.


Finishing method by means of compressing or cold-working the workpiece surface with carbide rollers called burnishing rolls or burnishers.


Stringy portions of material formed on workpiece edges during machining. Often sharp. Can be removed with hand files, abrasive wheels or belts, wire wheels, abrasive-fiber brushes, waterjet equipment or other methods.


Cylindrical sleeve, typically made from high-grade tool steel, inserted into a jig fixture to guide cutting tools. There are three main types: renewable, used in liners that in turn are installed in the jig; press-fit, installed directly in the jig for short production runs; and liner (or master), installed permanently in a jig to receive renewable bushing.

button cutter

Round insert that is able to spread the stresses generated by the cutting forces over a larger area than other insert shapes. However, a round insert generates higher axial forces, which transfer into the workpiece.


Checking measuring instruments and devices against a master set to ensure that, over time, they have remained dimensionally stable and nominally accurate.

cam-actuated assembly

Assembly machine, rotary or linear, utilizing cam mechanisms to orient and/or assemble parts.

cam-cutting attachment

Device for cutting face, peripheral or cylindrical cams from flat cam-former stock.

canned cycle (fixed cycle)

Subroutine or full set of programmed NC or CNC steps initiated by a single command. Operations are done in a set order; the beginning condition is returned to when the cycle is completed. See CNC, computer numerical control; NC, numerical control.


Compound of carbon and one or more metallic elements. For cutting tools, tungsten carbide, titanium carbide, tantalum carbide or a combination of these in a cobalt or nickel matrix provides hardness, wear resistance and heat resistance. Other elements added to carbide include vanadium, niobium, silicon, boron and hafnium.

carbon steels

Known as unalloyed steels and plain carbon steels. Contains, in addition to iron and carbon, manganese, phosphorus and sulfur. Characterized as low carbon, medium carbon, high carbon and free machining.


Casehardening metal by heating it in a mixture of carbon and nitrogen and by controlling the cooling rate. Allows carbon to enter the surface microstructure.


Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature above the transformation range, in contact with a suitable carbonaceous material. A form of casehardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperature or by cooling to room temperature, then reaustenitizing and quenching.

carriage stop

Mechanical device placed on the lathe head or ways to prevent over-travel that might damage the machine or workpiece.


Generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen or a mixture of the two and, by diffusion, create a concentration gradient. Processes commonly used are carburizing, quench hardening, cyaniding, nitriding and carbonitriding.

cast alloys

Alloys cast from the molten state. Most high-speed steel is melted in an electric-arc furnace and cast into ingots.

cast cobalt-base alloys

Used as wear-resistant (largest application area), corrosion-resistant and heat-resistant materials. They have different names depending on the manufacturers, such as Stellite, Tribaloy, Haynes alloys and MP35N. These alloys are hard, brittle and difficult to use for making cutting tools.

cast irons

Cast ferrous alloys containing carbon in excess of solubility in austenite that exists in the alloy at the eutectic temperature. Cast irons include gray cast iron, white cast iron, malleable cast iron and ductile, or nodular, cast iron. The word “cast” is often left out.

cavity cutting

Machining entirely within the body of a workpiece.

cavity type laser machining

Process that removes material by focusing a concentrated laser beam onto the workpiece. The material is melted and vaporized. In the cavity process, the beam is carefully controlled to prevent burning through the workpiece.

cell manufacturing

Grouping processes, equipment and people together to manufacture a specific family of parts. Highly automated and able to changeover quickly to produce a different part within the family of parts. See family of parts.

cemented carbides

Typical powder-metallurgical products. They are sintered compounds of cobalt (or another binder metal) and carbides of refractory metals suitable for use as a cutting tool material. The majority of metalcutting indexable inserts are multicarbide compounds of tungsten carbide, titanium carbide, tantalum carbide and/or niobium carbide with cobalt as a binder metal.


Compound of iron and carbon known as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. Cementite contains 6.67 percent carbon. When it occurs as a phase in steel, the chemical composition is altered by the presence of manganese and other carbide-forming elements. Cementite is hard and brittle. It is magnetic below 1,670º F (910º C).

center drill

Drill used to make mounting holes for workpiece to be held between centers. Also used to predrill holes for subsequent drilling operations. See centers.

center drilling

Drilling tapered holes for mounting workpiece between centers. Center-drilled holes also serve as starter holes for drilling larger holes in the same location. See centers; drilling.

center rest

Support provided at the center of the working area of a cylindrical grinder to prevent part deflection during grinding.


1. Process of locating the center of a workpiece to be mounted on centers. 2. Process of mounting the workpiece concentric to the machine spindle. See centers.

centerless grinding

Grinding operation in which the workpiece rests on a knife-edge support, rotates through contact with a regulating or feed wheel and is ground by a grinding wheel. This method allows grinding long, thin parts without steady rests; also lessens taper problems. Opposite of cylindrical grinding. See cylindrical grinding; grinding.


Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.

centrifugal feeder (rotary feeder)

Utilizes centrifugal force to continuously orient and deliver parts, at a specified feed rate, to an assembly machine.


Filtering device that uses a spinning bowl and the differences in specific gravities of materials to separate one from another. A centrifuge can be used to separate loosely emulsified and free oils from water-diluted metalworking fluid mixes and to remove metalworking fluids from chips.


Cutting tool materials based on aluminum oxide and silicon nitride. Ceramic tools can withstand higher cutting speeds than cemented carbide tools when machining hardened steels, cast irons and high-temperature alloys.


Cutting tool materials based mostly on titanium carbonitride with nickel and/or cobalt binder. Cermets are characterized by high wear resistance due to their chemical and thermal stability. Cermets are able to hold a sharp edge at high cutting speeds and temperatures, which results in exceptional surface finish when machining most types of steels.


Machining a bevel on a workpiece or tool; improves a tool’s entrance into the cut.

chamfering tool

Cutter or wheel that creates a beveled edge on a tool or workpiece.

Charpy test

Impact test in which a V-notched, keyhole-notched or U-notched specimen, supported at both ends, is struck behind the notch by a striker mounted at the lower end of a bar that can swing as a pendulum. The energy absorbed in fracture is calculated from the height to which the striker would have risen if there had been no specimen, and the height to which it actually rises after fracture of the specimen. See Izod test.


Condition of vibration involving the machine, workpiece and cutting tool. Once this condition arises, it is often self-sustaining until the problem is corrected. Chatter can be identified when lines or grooves appear at regular intervals in the workpiece. These lines or grooves are caused by the teeth of the cutter as they vibrate in and out of the workpiece and their spacing depends on the frequency of vibration.

chemical vapor deposition (CVD)

High-temperature (1,000° C or higher), atmosphere-controlled process in which a chemical reaction is induced for the purpose of depositing a coating 2µm to 12µm thick on a tool’s surface. See coated tools; PVD, physical vapor deposition.


Small piece of material removed from a workpiece by a cutting tool or grinding wheel.

chip clearance

In milling, the groove or space provided in the cutter body that allows chips to be formed by the inserts.


Groove or other tool geometry that breaks chips into small fragments as they come off the workpiece. Designed to prevent chips from becoming so long that they are difficult to control, catch in turning parts and cause safety problems.


Surface treatment at elevated temperature, generally carried out in a pack, vapor or salt bath, in which an alloy is formed by the inward diffusion of chromium into the base metal.


Workholding device that affixes to a mill, lathe or drill-press spindle. It holds a tool or workpiece by one end, allowing it to be rotated. May also be fitted to the machine table to hold a workpiece. Two or more adjustable jaws actually hold the tool or part. May be actuated manually, pneumatically, hydraulically or electrically. See collet.

circular saw

Cutoff machine utilizing a circular blade with serrated teeth. See saw, sawing machine.

circular-saw blade

Cutting tool for a cold or circular saw. Blade is round with serrated cutting teeth.


Space provided behind a tool’s land or relief to prevent rubbing and subsequent premature deterioration of the tool. See land; relief.

climb milling (down milling)

Rotation of a milling tool in the same direction as the feed at the point of contact. Chips are cut to maximum thickness at the initial engagement of the cutter’s teeth with the workpiece and decrease in thickness at the end of engagement. See conventional milling.

closed-loop system

CNC system in which the program output, or the distance the slide moves, is measured and compared to the program input. The system automatically adjusts the output to be the same as the input.

coated abrasive

Flexible-backed abrasive. Grit is attached to paper, fiber, cloth or film. Types include sheets, belts, flap wheels and discs.

coated tools

Carbide and high-speed-steel tools coated with thin layers of aluminum oxide, titanium carbide, titanium nitride, hafnium nitride or other compounds. Coating improves a tool’s resistance to wear, allows higher machining speeds and imparts better finishes. See CVD, chemical vapor deposition; PVD, physical vapor deposition.

cold working

Deforming metal plastically under conditions of temperature and strain rate that induce strain hardening. Working below the recrystallization temperature, which is usually, but not necessarily, above room temperature.


Flexible-sided device that secures a tool or workpiece. Similar in function to a chuck, but can accommodate only a narrow size range. Typically provides greater gripping force and precision than a chuck. See chuck.

commercial-grade tool steel

Low-grade tool steel; not controlled for hardenability.

compacted graphite iron

Cast iron having a graphite shape intermediate between the flake form typical of gray cast iron and the spherical form of fully spherulitic ductile cast iron. Also known as CG iron, CGI or vermicular iron, it is produced in a manner similar to that of ductile cast iron but using a technique that inhibits the formation of fully spherulitic graphite nodules.


Materials composed of different elements, with one element normally embedded in another, held together by a compatible binder.

computer numerical control (CNC)

Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

computer-aided design (CAD)

Product-design functions performed with the help of computers and special software.

computer-aided engineering (CAE)

Engineering functions performed with the help of computers and special software. Includes functions such as determining a material’s ability to withstand stresses.

computer-aided manufacturing (CAM)

Use of computers to control machining and manufacturing processes.

computer-integrated manufacturing (CIM)

Theoretically, an approach under which all phases of production—including management, sales, order processing, design, quality control and chipmaking—are controlled or monitored by interconnected computers. Practically, a term applied to systems approximating the ideal.


Agents and additives that, when added to water, create a cutting fluid. See cutting fluid.

continuous casting

Casting technique in which a cast shape is continuously withdrawn through the bottom of the mold as it solidifies, so that its length is not determined by mold dimensions. Used chiefly to produce semifinished mill products such as billets, blooms, ingots, slabs and tubes.

contouring attachment

Handwheel-operated mechanism for holding and guiding the workpiece while sawing contours on a contour bandsaw.

conventional milling (up milling)

Cutter rotation is opposite that of the feed at the point of contact. Chips are cut at minimal thickness at the initial engagement of the cutter’s teeth with the workpiece and increase to a maximum thickness at the end of engagement. See climb milling.

conversational programming

Method for using plain English to produce G-code file without knowing G-code in order to program CNC machines.


Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.


Process of reducing the heat content of a tool, part, assembly or material. Cooling may be required for a variety of reasons: to improve tool life, increase cutting speeds and ensure workpiece tolerances by controlling expansion. When heat-treating metal parts, part of the process is cooling, either by air, water or oil.

copper alloys

Copper containing specified quantities of alloying elements added to obtain the necessary mechanical and physical properties. The most common copper alloys are divided into six groups, and each group contains one of the following major alloying elements: brasses—major alloying element is zinc; phosphor bronzes—major alloying element is tin; aluminum bronzes—major alloying element is aluminum; silicon bronzes—major alloying element is silicon; copper-nickels and nickel-silvers—major alloying element is nickel; and dilute-copper or high-copper alloys, which contain small amounts of various elements such as beryllium, cadmium, chromium or iron.


Chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties.

corrosion fatigue

Process in which a metal fractures prematurely under conditions of simultaneous corrosion and repeated cyclic loading at lower stress levels or fewer cycles than would be required in the absence of the corrosive environment.

corrosion resistance

Ability of an alloy or material to withstand rust and corrosion. These are properties fostered by nickel and chromium in alloys such as stainless steel.


Use of weights or mechanisms to balance a workpiece, grinding wheel, rotating tool or other device. Minimizes machining vibration and maximizes cutting force.


Tool, guided by a pilot, that expands a hole to a certain depth.


Enlarging one end of a drilled hole. The enlarged hole, which is concentric with the original hole, is flat on the bottom. Counterboring is used primarily to set bolt heads and nuts below the workpiece surface.


Tool that cuts a sloped depression at the top of a hole to permit a screw head or other object to rest flush with the surface of the workpiece.


Cutting a beveled edge at the entrance of a hole so a screw head sits flush with the workpiece surface.


Depressions formed on the face of a cutting tool caused by heat, pressure and the motion of chips moving across the tool’s surface.

creep-feed grinding

Grinding operation in which the grinding wheel is slowly fed into the workpiece at sufficient depth of cut to accomplish in one pass what otherwise would require repeated passes. See grinding.

crush grinding

Method of producing intricate forms in a part by using a grinding wheel dressed to the shape of the form desired. See grinding.

cubic boron nitride (CBN)

Crystal manufactured from boron nitride under high pressure and temperature. Used to cut hard-to-machine ferrous and nickel-base materials up to 70 HRC. Second hardest material after diamond. See superabrasive tools.

curtain application

Arrangement of multiple nozzles that apply fluid to a broad cutting area, as is found on a horizontal, post-type band machine or a large hacksaw.


Step that prepares a slug, blank or other workpiece for machining or other processing by separating it from the original stock. Performed on lathes, chucking machines, automatic screw machines and other turning machines. Also performed on milling machines, machining centers with slitting saws and sawing machines with cold (circular) saws, hacksaws, bandsaws or abrasive cutoff saws. See saw, sawing machine; turning.

cutoff blade

Blade mounted on a shank or arbor and held in a milling-machine spindle for simple cutoff tasks.

cutoff wheel

Rotating cutting wheel that cuts bar stock, pipe, etc., to a desired length.

cutter compensation

Feature that allows the operator to compensate for tool diameter, length, deflection and radius during a programmed machining cycle.

cutting fluid

Liquid used to improve workpiece machinability, enhance tool life, flush out chips and machining debris, and cool the workpiece and tool. Three basic types are: straight oils; soluble oils, which emulsify in water; and synthetic fluids, which are water-based chemical solutions having no oil. See coolant; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

cutting force

Engagement of a tool’s cutting edge with a workpiece generates a cutting force. Such a cutting force combines tangential, feed and radial forces, which can be measured by a dynamometer. Of the three cutting force components, tangential force is the greatest. Tangential force generates torque and accounts for more than 95 percent of the machining power. See dynamometer.

cutting speed

Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).

cutting tool materials

Cutting tool materials include cemented carbides, ceramics, cermets, polycrystalline diamond, polycrystalline cubic boron nitride, some grades of tool steels and high-speed steels. See HSS, high-speed steels; PCBN, polycrystalline cubic boron nitride; PCD, polycrystalline diamond.


Casehardening method that introduces carbon and nitrogen to the workpiece simultaneously.

cylindrical grinding

Grinding operation in which the workpiece is rotated around a fixed axis while the grinding wheel is fed into the outside surface in controlled relation to the axis of rotation. The workpiece is usually cylindrical, but it may be tapered or curvilinear in profile. See centerless grinding; grinding.

cylindrical-grinding attachment

Device that mounts to the table of a surface grinder or lathe, permitting both straight and tapered grinding of round stock.


Loss of carbon from the surface layer of a carbon-containing alloy due to reaction with one or more chemical substances in a medium that contacts the surface. Frequently occurs in steel exposed to air at high temperatures, resulting in loss of hardness and strength at the surface.

degrees of freedom

Number of axes along which a robot, and thus the object it is holding, can be manipulated. Most robots are capable of maneuvering along the three basic Cartesian axes (X, Y, Z). More sophisticated models may move in six or more axes. See axis.


Removal of ions from a water-based solution. See semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

depth of cut

Distance between the bottom of the cut and the uncut surface of the workpiece, measured in a direction at right angles to the machined surface of the workpiece.

depth-to-diameter ratio

Ratio of the depth of a hole compared to the diameter of the tool used to make the hole.


Cubic crystalline form of carbon produced under extreme pressures at elevated temperatures. The hardest natural substance, it has approximately five times the indentation hardness of carbide. Its extreme hardness, though, makes it susceptible to fracturing. See superabrasive tools.

diamond bandsawing

Machine operation in which a band with diamond points is used to machine carbides, ceramics and other extremely hard materials.

die casting

Casting process wherein molten metal is forced under high pressure into the cavity of a metal mold.


1. Spreading of a constituent in a gas, liquid or solid, tending to make the composition of all parts uniform. 2. Spontaneous movement of atoms or molecules to new sites within a material.

diffusion coating

Any process whereby a basis metal or alloy is either coated with another metal or alloy and heated to a sufficient temperature in a suitable environment, or exposed to a gaseous or liquid medium containing another metal or alloy, thus causing diffusion of the coating or of the other metal or alloy into the basis metal or alloy with resultant changes in the composition and properties of its surface.

direct numerical control (DNC)

Method of transferring CNC code from the CAD/CAM system to the machine tool.

disc grinding

Operation in which the workpiece is placed against the side of a wheel rather than the wheel’s periphery. See grinding.

disc-cutting attachment

Adjustable device for a contour bandsaw that positions stock to allow the sawing of arcs and circular shapes on a contour bandsaw.


Form of relief given to the face of an endmill to prevent undesirable contact with the work. Similar to clearance.

dividing head

Attaches to a milling-machine table and precisely indexes the workpiece. Allows equally spaced cuts to be made when machining gear and sprocket teeth, spline keys, serrations, etc.

dovetail cutter

Cutter for milling dovetail slots. See milling cutter.


Removal of undesirable materials from “loaded” grinding wheels using a single- or multi-point diamond or other tool. The process also exposes unused, sharp abrasive points. See loading; truing.

drill jig

Accessory that holds a workpiece securely while guiding a drill or other tool into the workpiece. Ensures accurate, repeatable location.

drill-grinding gage

Used to check a drill’s entry angle into a workpiece. Also used to check accuracy when grinding drills.


Operation in which a rotating tool is used to create a round hole in a workpiece. Drilling is normally the first step in machining operations such as boring, reaming, tapping, counterboring, countersinking and spotfacing.

drilling machine (drill press)

Machine designed to rotate end-cutting tools. Can also be used for reaming, tapping, countersinking, counterboring, spotfacing and boring.

drilling tool (drill or drill bit)

End-cutting tool for drilling. Tool has shank, body and angled face with cutting edges that drill the hole. Drills range in size from “microdrills” a few thousandths of an inch in diameter up to spade drills, which may cut holes several inches in diameter. Drills may have tapered shanks with a driving tang and fit directly into a spindle or adapter, or they may have straight shanks and be chuck-mounted. The rake angle varies with the material drilled. Styles include twist drills, straight-flute drills, half-round and flat drills, oil-hole drills, indexable drills and specials.

drive plate

Attaches to a lathe spindle and has a slot or slots that engage a driving dog to turn the work. Usually used in conjunction with centers. See centers; driving dog.

driving dog

Device having a ring or clamp on one end that slips over the workpiece to be turned; a screw secures the workpiece in place. The dog’s opposite end (tail) fits into a drive plate attached to the machine spindle. See centers; drive plate.

ductile cast irons

Ferrous alloys in which graphite is present as tiny balls or spherulites. The spheroidal graphite structure is produced by adding one or more elements to the molten metal, among which magnesium and cerium are commercially important. Approximate composition of ductile cast irons is: 3.0 to 4.0 percent carbon, 0.1 to 1.0 percent manganese, 1.8 to 2.8 percent silicon, 0.1 percent (maximum) phosphorus and 0.03 percent (maximum) sulfur. Typical ductile cast iron grades are D-4018, D-4512, D-5506 and D-7003 by definition of the Society of Automotive Engineers; 60-40-18, 65-45-12, 80-55-06, 100-70-03 and 120-90-02 by definition of the American Society for Testing and Materials. Also known as nodular cast irons.

ductile fracture

Fracture characterized by tearing of metal accompanied by appreciable gross plastic deformation and expenditure of considerable energy.


Ability of a material to be bent, formed or stretched without rupturing. Measured by elongation or reduction of area in a tensile test or by other means.

dynamic stiffness

Measure of a machining system’s ability to dampen vibration from a forced input. If the dynamic stiffness of a system is not sufficient to dampen vibration, chatter occurs. See static stiffness; stiffness.


When drilling, a device for measuring the generated torque and axial force (thrust). When milling, a device for measuring the generated torque and feed force. When turning, a device for measuring the tangential, feed and radial forces.

eddy-current testing

Electromagnetic, nondestructive testing method in which eddy-current flow is induced in the test object. Detects changes in flow caused by variations in the object.

edge finder

Gage mounted in the spindle of a vertical mill and used, while rotating, to find the center of a part relative to the toolholder.

edge preparation

Conditioning of the cutting edge, such as a honing or chamfering, to make it stronger and less susceptible to chipping. A chamfer is a bevel on the tool’s cutting edge; the angle is measured from the cutting face downward and generally varies from 25° to 45°. Honing is the process of rounding or blunting the cutting edge with abrasives, either manually or mechanically.

effectuating device

Hand, gripper, toolholder, magnet, spray gun, drill, welding head or other electronic/mechanical device for holding workpieces and/or performing functions.

elastic limit

Maximum stress that a material can sustain without deforming.


Property of a material to deform under stress and recover its original shape and dimensions after release of stress.

electrical-discharge grinding (EDG)

Process similar to conventional electrical-discharge machining except a grinding-wheel type of electrode is used. See EDM, electrical-discharge machining.

electrical-discharge machining (EDM)

Process that vaporizes conductive materials by controlled application of pulsed electrical current that flows between a workpiece and electrode (tool) in a dielectric fluid. Permits machining shapes to tight accuracies without the internal stresses conventional machining often generates. Useful in diemaking.

electrochemical deburring

Variation on electrochemical machining designed to remove burrs and impart small radii to corners. The process normally uses a specially shaped electrode to carefully control the process to a specific area. The process works on material regardless of hardness.

electrochemical grinding

Variation on electrochemical machining that uses a conductive, rotating abrasive wheel. Chemical solution is forced between the wheel and the workpiece. Shape of the wheel determines the final shape.

electrochemical machining (ECM)

Operation in which electrical current flows between a workpiece and conductive tool through an electrolyte. Initiates a chemical reaction that dissolves metal from the workpiece at a controlled rate. Unlike with traditional cutting methods, workpiece hardness is not a factor, making ECM suitable for difficult-to-machine materials. Takes such forms as electrochemical grinding, electrochemical honing and electrochemical turning.

electrochemical-discharge grinding

Combination of electrochemical grinding and electrical-discharge machining. Material is removed by both processes. The workpiece and the grinding wheel never come into contact as in any other electrical-discharge-machining process. See EDG, electrical-discharge grinding.


In tensile testing, the increase in the gage length, measured after fracture of the specimen within the gage length, usually expressed as a percentage of the original gage length.


Reduction in the normal ductility of a metal due to a physical or chemical change. Examples include blue brittleness, hydrogen embrittlement and temper brittleness.


Suspension of one liquid in another, such as oil in water.


Milling cutter held by its shank that cuts on its periphery and, if so configured, on its free end. Takes a variety of shapes (single- and double-end, roughing, ballnose and cup-end) and sizes (stub, medium, long and extra-long). Also comes with differing numbers of flutes.


Operation in which the cutter is mounted on the machine’s spindle rather than on an arbor. Commonly associated with facing operations on a milling machine.

endurance limit

Limit below which a material will not fail.


1. Isothermal reversible reaction in which a liquid solution is converted into two or more intimately mixed solids on cooling, the number of solids formed being the same as the number of components in the system. 2. Alloy having the composition indicated by the eutectic point on an equilibrium diagram. 3. Alloy structure of intermixed solid constituents formed by the eutectic reaction.

extreme pressure additives (EP)

Cutting-fluid additives (chlorine, sulfur or phosphorus compounds) that chemically react with the workpiece material to minimize chipwelding. Good for high-speed machining. See cutting fluid.


Conversion of an ingot or billet into lengths of uniform cross section by forcing metal to flow plastically through a die orifice.


Flat surface, usually at right angles and adjacent to the ground hole.

face plate

Flat, round workholder with slots used to hold regular- or irregular-shaped stock. If stock is markedly asymmetrical, counterbalances may be needed to prevent vibration.


Milling cutter for cutting flat surfaces.


Form of milling that produces a flat surface generally at right angles to the rotating axis of a cutter having teeth or inserts both on its periphery and on its end face.


Preliminary “cleanup” operation that provides a true reference surface before beginning another operation.

family of parts

Parts grouped by shape and size for efficient manufacturing.


Phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material. Fatigue fractures are progressive, beginning as minute cracks that grow under the action of the fluctuating stress.

fatigue life

Number of cycles of stress that can be sustained prior to failure under a stated test condition.

fatigue resistance

Ability of a tool or component to be flexed repeatedly without cracking. Important for bandsaw-blade backing.

fatigue strength

Maximum stress that can be sustained for a specified number of cycles without failure, the stress being completely reversed within each cycle unless otherwise stated.

feather burr

Very fine or thin burr.

feather edge

Same as a feather burr, except that feather edge can also refer to a very thin machined ridge located at the ends of a lead-in or lead-out thread. It is sometimes called a wire-edge or whisker-type burr.

feature-based CAD/CAM

Construction methodology. It means the model is constructed using 3-D objects (features), as opposed to individual lines, arcs, splines and surfaces.


Rate of change of position of the tool as a whole, relative to the workpiece while cutting.


Solid solution of one or more elements in body-centered cubic iron. Unless otherwise designated, for instance, as chromium ferrite, the solute is generally assumed to be carbon. On an equilibrium diagram, there are two ferrite regions separated by an austenite area. The lower area is alpha ferrite and the upper area is delta ferrite. If there is no designation, alpha ferrite is assumed. Not more than 0.04 percent carbon can be dissolved in alpha iron. Ferrite is stable below 1,670º F (910º C); it is soft, highly ductile, and magnetic. Ferrite loses its magnetic property above 1,414º F (768º C).

file band

Segmented files mounted on an endless band for use on a powered band-type filing machine or on a contour band machine with a filing attachment.


Operation in which a tool with numerous small teeth is applied manually to round off sharp corners and shoulders and remove burrs and nicks. Although often a manual operation, filing on a power filer or contour band machine with a special filing attachment can be an intermediate step in machining low-volume or one-of-a-kind parts.

filing attachment

Mounts on a contour bandsaw for power-filing operations.


Rounded corner or arc that blends together two intersecting curves or lines. In three dimensions, a fillet surface is a transition surface that blends together two surfaces.

film strength

Relative ability of a fluid to form a film between workpiece and tool, under the influence of temperature and pressure, to prevent metal-to-metal contact. See lubricity.

finish cut

Final cut made on a workpiece to generate final dimensions or specified finish. Often made using reduced feeds and higher speeds. Generally, the better the surface finish required, the longer the finish cut takes. Also, the final cut taken on an electrical-discharge-machined part.

finish feed

Feeding in small increments for finishing the part.


Any of many different processes employed for surface, edge and corner preparation, as well as conditioning, cleaning and coating. In machining, usually constitutes a final operation.

finishing tool

Tool, belt, wheel or other cutting implement that completes the final, precision machining step/cut on a workpiece. Often takes the form of a grinding, honing, lapping or polishing tool. See roughing cutter.


Device, often made in-house, that holds a specific workpiece. See jig; modular fixturing.

flame hardening

Hardening process in which an intense flame is applied to the surfaces of hardenable ferrous alloys, heating the surface layers above the upper transformation temperature, whereupon the workpiece is immediately quenched.

flank wear

Reduction in clearance on the tool’s flank caused by contact with the workpiece. Ultimately causes tool failure.


Thin web or film of metal on a casting that occurs at die partings and around air vents and movable cores. This excess metal is due to necessary working and operating clearances in a die. Flash also is the excess material squeezed out of the cavity as a compression mold closes or as pressure is applied to the cavity.

flat (screw flat)

Flat surface machined into the shank of a cutting tool for enhanced holding of the tool.

flexible assembly system

System that can be programmed to assemble a family or group of similar assemblies. This typically is done with programmable robots. This system is contrasted to dedicated or fixed assembly systems.

flexible manufacturing system (FMS)

Automated manufacturing system designed to machine a variety of similar parts. System is designed to minimize production changeover time. Computers link machine tools with the workhandling system and peripherals. Also associated with machine tools grouped in cells for efficient production. See cell manufacturing.

flood application

Fluid applied in volume by means of a recirculating system composed of a reservoir, filters, chip-removal components, pump, hoses and positionable application nozzles, along with movable splash shields, valves for adjusting flow and other controls. Fluids normally permit the highest metal-removal rates possible.

flow stress

Uniaxial true stress at the onset of plastic deformation in a metal.


Unintentional surface irregularities that occur at infrequent or varying intervals, such as cracks, blowholes, checks, ridges and scratches. The effect of flows is not included in roughness average measurement. See lay; roughness; waviness.

flushing hose

Hand-operated hose and nozzle added to machine’s cutting-fluid-application system to permit manual flushing of table and workpiece areas.


Grooves and spaces in the body of a tool that permit chip removal from, and cutting-fluid application to, the point of cut.


Cutting straight or spiral grooves in drills, endmills, reamers and taps to improve cutting action and remove chips.

fly cutter

Rotary cutting tool employing one or more single-point tools for plane surfacing.

follower rest

Workpiece rest or supporting device attached to the carriage that “follows” the cutting tool, keeping support near the point of cut. See steady rest.

form cutter

Cutter shaped to cut stepped, angular or irregular forms in the workpiece. The cutting-edge contour corresponds to the workpiece shape required. The cutter can often be reground repeatedly without changing the cutting-edge shape. Two general classes: straight and circular.

form-rolling machine

Used to roll splines, gears, worms and threads. Cold-forming machine for production processing of previously machined parts. See broaching machine.

fracture stress

1. Maximum principal true stress at fracture. Usually refers to unnotched tensile specimens. 2. True stress (hypothetically) that will cause fracture without further deformation at any given strain.

fracture toughness

Critical value (KIC) of stress intensity. A material property.

free machining steels

Group of carbon steels designated by the American Iron and Steel Institute numerical classification are free machining grades: AISI 1108, 1109, 1110, etc., up to AISI 1151 for a total of 14 grades. AISI 1211, 1212, 1213, 1215 and 12L14 carbon steels are also free machining grades. Free machining steels contain one or more additives, which enhance machining characteristics and lower machining cost. Increased sulfur content (from 0.20 to 0.33 percent in some grades) improves chip control. Addition of lead (from 0.15 to 0.35 percent in some grades) reduces friction and buildup of heat between the cutting edge of the tool and the workpiece.


Characteristic of abrasive grains that describes their tendency to fracture or break apart when hit or placed under pressure. Highly friable abrasives cut more easily, but wear faster than other abrasives. Friable abrasives are usually used on soft, gummy materials or where heat produced by worn grits must be carefully controlled. Friability is usually related to the levels of impurities in the manufactured abrasive mineral.

friction sawing

Sawing with a special band machine capable of achieving band velocities of 15,000 sfm or more. Metal removal is accomplished in two steps: Frictional heat softens the metal, then the teeth scoop out the molten material. Carbon-steel bands are used for flexibility and to maximize band life. Excellent for cutting extremely hard alloys but cannot be used on most aluminum alloys or other materials that load the teeth of conventional blades. See sawing.

full annealing

Imprecise term that denotes an annealing cycle designed to produce minimum strength and hardness. For the term to be meaningful, the composition and starting condition of the material and the time-temperature cycle used must be stated.


Additive to cutting fluids to inhibit fungi. See bactericide.

G-code programming

Programs written to operate NC machines with control systems that comply with the ANSI/EIA RS-274-D-1980 Standard. A program consists of a series of data blocks, each of which is treated as a unit by the controller and contains enough information for a complete command to be carried out by the machine.


Measure of the grinding performance defined as the volume of metal removed divided by the volume of grinding wheel worn away in the operation.


Condition whereby excessive friction between high spots results in localized welding with subsequent spalling and further roughening of the rubbing surface(s) of one or both of two mating parts.

gamma iron

Face-centered cubic form of pure iron. Each of eight atoms of gamma iron are located in the corner of a cube, and each of six atoms are located in the center of the cube’s face. Gamma iron is stable from 1,670º F (910º C) to 2,550º F (1,400º C).

gang cutting (milling, slitting)

Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.

gantry robot

Robot positioned by means of an overhead supporting structure such as a crane or bridge-type support.

gear cutter

Cutter, such as a mill, broach and hob, designed for machining gears.

gear shaper

Machine that, in contrast to mills and hobbing machines, reciprocates the tool to cut the gear. See hobbing machine.

graphitic corrosion

Deterioration of gray cast iron in which the metallic constituents are selectively leached or converted to corrosion products leaving the graphite intact. The term graphitization is commonly used to identify this form of corrosion but is not recommended because of its use in metallurgy for the decomposition of carbide to graphite.

gray cast irons

Alloys of iron, carbon and silicon in which more carbon is present than can be retained in austenite. The carbon in excess of austenite solubility in iron precipitates as graphite flakes. Approximate composition of gray irons is: 2.5 to 4.0 percent carbon, 0.5 to 1.0 percent manganese, 1.0 to 3.0 percent silicon, 0.05 to 0.15 percent sulfur and 0.05 to 0.8 percent phosphorus. Some Society of Automotive Engineer grades are G-1800, G-2500, G-3000, G-3500 and G-4000.


Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.

grinding machine

Powers a grinding wheel or other abrasive tool for the purpose of removing metal and finishing workpieces to close tolerances. Provides smooth, square, parallel and accurate workpiece surfaces. When ultrasmooth surfaces and finishes on the order of microns are required, lapping and honing machines (precision grinders that run abrasives with extremely fine, uniform grits) are used. In its “finishing” role, the grinder is perhaps the most widely used machine tool. Various styles are available: bench and pedestal grinders for sharpening lathe bits and drills; surface grinders for producing square, parallel, smooth and accurate parts; cylindrical and centerless grinders; center-hole grinders; form grinders; facemill and endmill grinders; gear-cutting grinders; jig grinders; abrasive belt (backstand, swing-frame, belt-roll) grinders; tool and cutter grinders for sharpening and resharpening cutting tools; carbide grinders; hand-held die grinders; and abrasive cutoff saws.

grinding ratio

Ratio of work material removed to grinding-wheel material lost.

grinding wheel

Wheel formed from abrasive material mixed in a suitable matrix. Takes a variety of shapes but falls into two basic categories: one that cuts on its periphery, as in reciprocating grinding, and one that cuts on its side or face, as in tool and cutter grinding.

grit size

Specified size of the abrasive particles in grinding wheels and other abrasive tools. Determines metal-removal capability and quality of finish.


Machining grooves and shallow channels. Example: grooving ball-bearing raceways. Typically performed by tools that are capable of light cuts at high feed rates. Imparts high-quality finish.


In cast iron, a permanent increase in dimensions resulting from repeated or prolonged heating at temperatures above 480° C due either to graphitizing of carbides or to oxidation.


Self-guided drill for producing deep holes with good accuracy and fine surface finish. Has coolant passages that deliver coolant to the tool/workpiece interface at high pressure.


Drilling process using a self-guiding tool to produce deep, precise holes. High-pressure coolant is fed to the cutting area, usually through the gundrill’s shank.

H-band steel

Alloy steel produced to specified limits of hardenability. The chemical-composition range may be slightly different from that of the corresponding grade of ordinary alloy steel.

hacksaw blade

Serrated blade for a manual or power hacksaw that cuts on the forward or return stroke. See sawing.

hard chromium

Chromium electrodeposited for engineering purposes (such as to increase the wear resistance of sliding metal surfaces) rather than as a decorative coating. It is usually applied directly to basis metal and is customarily thicker than a decorative deposit, but not necessarily harder.

hard tooling

Tooling made for a specific part. Also called dedicated tooling.

hard turning

Single-point cutting of a workpiece that has a hardness value higher than 45 HRC.


Relative ability of a ferrous alloy to form martensite when quenched from a temperature above the upper critical temperature. Hardenability is commonly measured as the distance below a quenched surface at which the metal exhibits a specific hardness (50 HRC, for example) or a specific percentage of martensite in the microstructure.


Process of increasing the surface hardness of a part. It is accomplished by heating a piece of steel to a temperature within or above its critical range and then cooling (or quenching) it rapidly. In any heat-treatment operation, the rate of heating is important. Heat flows from the exterior to the interior of steel at a definite rate. If the steel is heated too quickly, the outside becomes hotter than the inside and the desired uniform structure cannot be obtained. If a piece is irregular in shape, a slow heating rate is essential to prevent warping and cracking. The heavier the section, the longer the heating time must be to achieve uniform results. Even after the correct temperature has been reached, the piece should be held at the temperature for a sufficient period of time to permit its thickest section to attain a uniform temperature. See workhardening.


Hardness is a measure of the resistance of a material to surface indentation or abrasion. There is no absolute scale for hardness. In order to express hardness quantitatively, each type of test has its own scale, which defines hardness. Indentation hardness obtained through static methods is measured by Brinell, Rockwell, Vickers and Knoop tests. Hardness without indentation is measured by a dynamic method, known as the Scleroscope test.

headchanging machine

Multifunction, NC machine tool. It differs from machining centers in that single- or multiple-spindle heads, rather than tools, are transferred to a single workstation in proper sequence to perform the required series of operations. The single workstation is equipped with a spindle drive and slide feed unit; the workpiece remains in a fixed or indexable position. Additional workstations can be added on some machines if required.

heat-affected zone

That portion of the base metal that was not melted during brazing, cutting or welding, but whose microstructure and mechanical properties were altered by the heat.


Process that combines controlled heating and cooling of metals or alloys in their solid state to derive desired properties. Heat-treatment can be applied to a variety of commercially used metals, including iron, steel, aluminum and copper.

heeling (heel drag)

Rubbing that occurs on the cutter’s heel, the area just behind the tooth’s cutting edge.

helical cutter

Endmill or other cutter with spiral or helical flutes. May be right- or left-hand.

helix angle

Angle that the tool’s leading edge makes with the plane of its centerline.

high-speed steels (HSS)

Available in two major types: tungsten high-speed steels (designated by letter T having tungsten as the principal alloying element) and molybdenum high-speed steels (designated by letter M having molybdenum as the principal alloying element). The type T high-speed steels containing cobalt have higher wear resistance and greater red (hot) hardness, withstanding cutting temperature up to 1,100º F (590º C). The type T steels are used to fabricate metalcutting tools (milling cutters, drills, reamers and taps), woodworking tools, various types of punches and dies, ball and roller bearings. The type M steels are used for cutting tools and various types of dies.

hydrodynamic machining

General term for various forms of waterjet and abrasive waterjet machining. In all cases, a fine, highly pressurized jet of water cuts and removes the material. See AWJ, abrasive waterjet; waterjet cutting.

impact test

Test to determine the behavior of materials when subjected to high rates of loading, usually in bending, tension or torsion. The quantity measured is the energy absorbed in breaking the specimen by a single blow, as in Charpy and Izod tests.

in-process gaging (in-process inspection)

Quality-control approach that monitors work in progress, rather than inspecting parts after the run has been completed. May be done manually on a spot-check basis but often involves automatic sensors that provide 100 percent inspection.

inches per minute (ipm)

Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.

inches per tooth (ipt)

Linear distance traveled by the cutter during the engagement of one tooth. Although the milling cutter is a multi-edge tool, it is the capacity of each individual cutting edge that sets the limit of the tool, defined as: ipt = ipm/number of effective teeth 5 rpm or ipt = ipr/number of effective teeth. Sometimes referred to as the chip load.

inclination angle

Angle that the cutter edge makes with a plane that is perpendicular to the direction of tool travel. Determines the direction the chip curls.

included angle

Measurement of the total angle within the interior of a workpiece or the angle between any two intersecting lines or surfaces.

indexable insert

Replaceable tool that clamps into a tool body, drill, mill or other cutter body designed to accommodate inserts. Most inserts are made of cemented carbide. Often they are coated with a hard material. Other insert materials are ceramic, cermet, polycrystalline cubic boron nitride and polycrystalline diamond. The insert is used until dull, then indexed, or turned, to expose a fresh cutting edge. When the entire insert is dull, it is usually discarded. Some inserts can be resharpened.

indexing machine

Assembly machine designed to assemble parts sequentially. Each station consists of tooling for subsequent operations. Parts are moved through their assembly sequence by an intermittent rotary motion.

indicator drop measurement

Method of determining if the primary and secondary reliefs on an endmill or other cutter have been properly ground. See clearance; relief.

induction hardening

Surface-hardening process in which only the surface layer of a suitable ferrous workpiece is heated by electromagnetic induction to above the upper critical temperature and immediately quenched.

industrial robot

Robot designed for industrial use. Primarily used as a material-handling device but also used for changing tools, assembling parts, and manipulating special tools and measuring devices. Depending on design, an industrial robot can be programmed to perform a task by means of a controller, or it can be “walked” through the required movements by utilizing a digitizing system that translates movements into commands that the robot can be “taught.” See robot; teaching pendant.

inner diameter (ID)

Dimension that defines the inside diameter of a cavity or hole. See OD, outer diameter.

inscribed circle (IC)

Imaginary circle that touches all sides of an insert. Used to establish size. Measurements are in fractions of an inch and describe the diameter of the circle.


Process of physically checking a part or product to ensure that it meets specific, predetermined dimensions. Because errors can be caused by out-of-tolerance measuring instruments as well as out-of-spec parts, it is important to periodically check the measuring tools for accuracy. See calibration.

interchangeable parts

Parts and components produced to specified tolerances, permitting them to be substituted for one another. Essential to mass production, permitting the high-volume output that results in economies of scale. Less critical to operating costs in computer-integrated manufacturing operations but facilitates maintenance and repair. See CIM, computer-integrated manufacturing; modular design, construction.


Process of generating a sufficient number of positioning commands for the servomotors driving the machine tool so the path of the tool closely approximates the ideal path. See CNC, computer numerical control; NC, numerical control.

interrupted cut

Cutting tool repeatedly enters and exits the work. Subjects tool to shock loading, making tool toughness, impact strength and flexibility vital. Closely associated with milling operations. See shock loading.

investment casting

1. Casting metal into a mold produced by surrounding (investing) an expandable pattern with a refractory slurry that sets at room temperature, after which the wax, plastic or frozen-mercury pattern is removed through the use of heat. Also called precision casting or lost-wax process. 2. Part made by the investment-casting process.

ion nitriding

Surface-hardening process in which nitrogen ions are accelerated under an electric potential in a closed chamber and become embedded in the surface of the parts being treated, where they interact with minor constituents of the treated metal to form nitrogen compounds.

Izod test

Impact test in which a V-notched specimen, fixed at one end, is subjected to a sudden blow delivered by the weight at the end of a pendulum arm. The energy required to break off the free end is a measure of the impact strength or toughness of the material. See Charpy test.


Tooling usually considered to be a stationary apparatus. A jig assists in the assembly or manufacture of a part or device. It holds the workpiece while guiding the cutting tool with a bushing. A jig used in subassembly or final assembly might provide assembly aids such as alignments and adjustments. See fixture.

jig boring

High-precision machining (a sophisticated form of milling) that originally pertained to jig and fixture manufacturing. Basic jig-boring processes include centering, drilling, reaming, through and step boring, counterboring and contouring.

jig grinder

Machine for grinding molds and dies where the positioning, shaping and finishing of holes and other surfaces are needed.

just-in-time (JIT)

Philosophy based on identifying, then removing, impediments to productivity. Applies to machining processes, inventory control, rejects, changeover time and other elements affecting production.

K factor

Power constant that represents the number of cubic inches of metal per minute that can be removed by one horsepower input.


Width of cut left after a blade or tool makes a pass.


Milling or grinding an internal keyway. See slotting.

killed steel

Steel treated with a strong deoxidizing agent such as silicon or aluminum to reduce the oxygen content so that no reaction occurs between carbon and oxygen during the solidification process.


Mechanism for releasing workpieces from a die. It is also called ejector, kickout, liftout or shedder.

Knoop hardness number (HK)

Number related to the applied load and to the projected area of the permanent impression made by a rhombic-based pyramidal diamond indenter having included edge angles of 172º 30' and 130º 0'. The Knoop hardness number is the ratio of the applied load (usually, 0.5 kgf and greater) to the projected area of indentation measured in mm2. The area of indentation is proportional to the length of the long diagonal squared and a constant equal to 0.07028.

Knoop hardness test

Test for determining the hardness of a material in which calibrated machines force a rhombic-base pyramidal diamond indenter having specified edge angles into the surface of the material. After the applied load is removed, the length of the long diagonal is measured and the area of indentation is calculated. The result is expressed as the Knoop hardness number. See Brinell hardness test; Rockwell standard hardness test; Rockwell superficial hardness test; Scleroscope hardness test; Vickers hardness test.


Chipless material-displacement process that is usually accomplished on a lathe by forcing a knurling die into the surface of a rotating workpiece to create a pattern. Knurling is often performed to create a decorative or gripping surface and repair undersized shafts.

knurling tool

Normally a lathe tool for impressing a design on a rod or handle to improve gripping or provide decoration.


Part of the tool body that remains after the flutes are cut.


Finishing operation in which a loose, fine-grain abrasive in a liquid medium abrades material. Extremely accurate process that corrects minor shape imperfections, refines surface finishes and produces a close fit between mating surfaces.

lapping compound, powder

Light, abrasive material used for finishing a surface.

laser machining

Intensified, pulsed beams of light generated by lasers—typically carbon dioxide or neodium-doped yttrium aluminum garnet (Nd:YAG)—that drill, weld, engrave, mark, slit and caseharden. Usually under CNC, often at both high cutting rates (100 linear in./sec.) and high power (5kW or more). Lasers also are used in conjunction with in-process quality-control monitoring systems allowing measuring accuracies of 0.00001".


Turning machine capable of sawing, milling, grinding, gear-cutting, drilling, reaming, boring, threading, facing, chamfering, grooving, knurling, spinning, parting, necking, taper-cutting, and cam- and eccentric-cutting, as well as step- and straight-turning. Comes in a variety of forms, ranging from manual to semiautomatic to fully automatic, with major types being engine lathes, turning and contouring lathes, turret lathes and numerical-control lathes. The engine lathe consists of a headstock and spindle, tailstock, bed, carriage (complete with apron) and cross slides. Features include gear- (speed) and feed-selector levers, toolpost, compound rest, lead screw and reversing lead screw, threading dial and rapid-traverse lever. Special lathe types include through-the-spindle, camshaft and crankshaft, brake drum and rotor, spinning and gun-barrel machines. Toolroom and bench lathes are used for precision work; the former for tool-and-die work and similar tasks, the latter for small workpieces (instruments, watches), normally without a power feed. Models are typically designated according to their “swing,” or the largest-diameter workpiece that can be rotated; bed length, or the distance between centers; and horsepower generated. See turning machine.

lathe bit (lathe tool)

Cutting tool for lathes and other turning machines. Normally a single-point cutting tool, square in cross section and ground to a shape suitable for the material and task. Intended for simple metal removal, threading, slotting or other internal or external cutting jobs. Clearance to prevent rubbing is provided by grinding back rake, side rake, end relief and side relief, as well as side- and end-cutting edges.

lathe turning

Machining operation in which a workpiece is rotated, while a cutting tool removes material, either externally or internally.


Direction of the predominant surface pattern, which is determined by the production method. See flows; roughness; waviness.


Use of scribers, ink and prick punches to create a part outline that machinists use to visually check part shape during machining of prototypes or during tool-and-die work.

lead angle

Angle between the side-cutting edge and the projected side of the tool shank or holder, which leads the cutting tool into the workpiece.

lean manufacturing

Companywide culture of continuous improvement, waste reduction and minimal inventory as practiced by individuals in every aspect of the business.

linear motor

Functionally the same as a rotary motor in a machine tool, a linear motor can be thought of as a standard permanent-magnet, rotary-style motor slit axially to the center and then peeled back and laid flat. The major advantage of using a linear motor to drive the axis motion is that it eliminates the inefficiency and mechanical variance caused by the ballscrew assembly system used in most CNC machines.

lip angle

Included angle between a cutter’s tooth and relieved land.


In grinding, the wheel’s tendency to accumulate workpiece material between its abrasive points. In milling, drilling and other operations, excessive packing of chips in cutter flutes or at cutter edge.


CNC feature that evaluates many data blocks ahead of the cutting tool’s location to adjust the machining parameters to prevent gouges. This occurs when the feed rate is too high to stop the cutting tool within the required distance, resulting in an overshoot of the tool’s projected path. Ideally, look-ahead should be dynamic, varying the distance and number of program blocks based on the part profile and the desired feed rate.

lost-wax process

Investment-casting process in which a wax pattern is used.

low-carbon steels

Group of carbon steels designated by American Iron and Steel Institute numerical classification as AISI 1005, 1006, 1008, etc., up to AISI 1026, for a total of 16 grades. They are softer and more ductile than other carbon steels. Composition of low-carbon steels is 0.06 to 0.28 percent carbon, 0.25 to 1.00 percent manganese, 0.040 percent (maximum) phosphorus and 0.050 percent (maximum) sulfur. See high-carbon steels; medium-carbon steels.


Substance that reduces friction between moving machine parts. Can be liquid (hydrocarbon oil), solid (grease) or gaseous (air). Important characteristics are to prevent metal-to-metal contact between moving surfaces, be a cooling medium, aid chip removal and protect surfaces from rust and corrosion.


Measure of the relative efficiency with which a cutting fluid or lubricant reduces friction between surfaces.

M-code programming

Miscellaneous, or auxiliary, functions constitute on/off type commands. Used to control actions such as starting and stopping of motors, turning coolant on and off, changing tools, and clamping and unclamping workpieces.


The relative ease of machining metals and alloys.

machinability rating

A relative measure of the machinability of a metallic work material under specified standard conditions. Machinability rating is expressed in percents, with the assumption that the machinability rating of AISI 1212 free-machining steel is 100 percent. If machinability ratings of work materials are less than 100 percent, it means that such work materials are more difficult to machine than AISI 1212 steel; and vice versa if machinability ratings are greater than that for AISI 1212 steel.


Process of giving a workpiece a new configuration by cutting or shaping it. Typically performed on a machine tool or machining center. Includes cutting and shaping all kinds of materials, not just metals. Generally associated with precision and high-quality fit. See metalcutting, material cutting; metalforming; metalworking.

machining center

CNC machine tool capable of drilling, reaming, tapping, milling and boring. Normally comes with an automatic toolchanger. See automatic toolchanger.

magnetic chuck

Workholding device used on surface grinders and milling machines for holding ferrous parts with large, flat sides. Holding power may be provided by permanent magnets or by an electromagnetic system. See chuck.

magnetic-particle inspection

Nondestructive method of inspection for determining the existence and extent of surface cracks and similar imperfections in ferromagnetic materials. Finely divided magnetic particles, applied to the magnetized part, are attracted to and outline the pattern of any magnetic-leakage fields created by discontinuities.

malleable cast iron

Cast iron made by prolonged annealing of white cast iron in which decarburization and/or graphitization take place to eliminate some or all of the cementite. The graphite is in the form of temper carbon. There are ferritic and perlitic malleable cast irons. Their typical composition ranges are: 2.2 to 2.9 percent carbon, 0.2 to 1.3 percent manganese, 0.9 to 1.9 percent silicon, 0.05 to 0.18 percent sulfur and 0.18 percent (maximum) phosphorus.


Workholder for turning that fits inside hollow workpieces. Types available include expanding, pin and threaded.


Arm or basic object-transferring device. Hands or gripping devices vary according to application, as do arm design and number of joints (axes or degrees of freedom). See degrees of freedom; effectuating device.

manufacturing resources planning

Management method, normally computer-aided, for cost-effective control of manufacturing support functions, such as inventory, production equipment and personnel. MRP was the initial, somewhat limited method; MRP-II implies a more sophisticated system.

maraging steels

Nickel in the amount of 18.5 percent is the principal alloying element in the maraging steels. Other alloying elements are cobalt, molybdenum, aluminum and titanium. With a maximum carbon content of 0.030 percent, these steels are essentially carbon-free. They utilize the soft, ductile, iron-nickel martensite, which can be age-hardened by additions of other alloying elements. The most common maraging steel grades are 18Ni(200), 18Ni(250), 18Ni(300) and 18Ni(350). The numerical designations represent ultimate tensile strength of these grades. Maraging steels are used in the aerospace industry and for making tools (various dies, trim knives and springs).


1. Hardening procedure in which an austenitized ferrous workpiece is quenched in a medium whose temperature is maintained substantially at the Ms temperature (temperature at which martensite starts to form from austenite) of the workpiece. It is held in the medium until its temperature is uniform throughout—but not long enough to permit bainite to form—and then cooled in air. The treatment is frequently followed by tempering. 2. When the process is applied to carburized (casehardened) material, the controlling Ms temperature is that of the case. This variation of the process is frequently called marquenching.


Formed during rapid cooling of austenite at the temperature rate higher than 500º F (260º C) per second. Such rapid cooling causes restructuring of crystalline lattice of gamma iron into crystalline lattice of alpha iron in which carbon is fully dissolved. Because only 0.04 percent carbon can be dissolved in alpha iron, the excessive amount of carbon transforms into supersaturated solution of carbon in alpha iron. This type of solution is called martensite, which is characterized by an angular needlelike brittle structure and high hardness (greater than 60 HRC).


Rapid quenching of carbon steel in the austenite state causes a new structure—martensite—to form. Martensite is extremely hard. See austenite; austenitizing; martensite.

material safety data sheet (MSDS)

Form containing safety, regulatory, physical and other pertinent information regarding a chemical.

materials handling

Methods, equipment and systems for conveying materials to various machines and processing areas and for transferring finished parts to assembly, packaging and shipping areas.

mechanical properties

Properties of a material that reveal its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications; for example, modulus of elasticity, tensile strength, elongation, hardness and fatigue limit.

medium-carbon steels

Group of carbon steels designated by American Iron and Steel Institute numerical classification as AISI 1029, 1030, 1034, etc., up to AISI 1053, for a total of 16 grades. They are often selected where higher strength is required. Most commonly used steels for machined components. Composition of medium-carbon steels is: 0.25 to 0.55 percent carbon, 0.30 to 1.00 percent manganese, 0.040 percent (maximum) phosphorus and 0.050 percent (maximum) sulfur. See high-carbon steels; low-carbon steels.

metal stereolithography

Process similar to plastic stereolithography but uses powder metal to build up the part. See stereolithography, plastic.

metal-removal factor

Volume of metal removed per unit of power in a given period of time (reciprocal of the specific power-consumption factor). Also known as the K-factor. Metal-removal factor depends on the depth of cut and feed rate. Increases in depth of cut and feed rate increases K-factor; decreases in depth of cut and in feed rate decrease K-factor.

metal-removal rate

Rate at which metal is removed from an unfinished part, measured in cubic inches or cubic centimeters per minute.

metalcutting (material cutting)

Any machining process used to part metal or other material or give a workpiece a new configuration. Conventionally applies to machining operations in which a cutting tool mechanically removes material in the form of chips; applies to any process in which metal or material is removed to create new shapes. See metalforming.


Manufacturing processes in which products are given new shapes either by casting or by some form of mechanical deformation, such as forging, stamping, bending and spinning. Some processes, such as stamping, may use dies or tools with cutting edges to cut as well as form parts.


Any manufacturing process in which metal is processed or machined such that the workpiece is given a new shape. Broadly defined, the term includes processes such as design and layout, heat-treating, material handling and inspection.


Science of measurement; the principles on which precision machining, quality control and inspection are based. See precision machining, measurement.


Hardness of a material as determined by forcing an indenter such as a Vickers or Knoop indenter into the surface of the material under very light load; usually, the indentations are so small that they must be measured with a microscope. Capable of determining hardness of different microconstituents within a structure or measuring steep hardness gradients such as those encountered in casehardening.


A precision instrument with a spindle moved by a finely threaded screw that is used for measuring thickness and short lengths.


Measure of length that is equal to one-millionth of a meter.


Cutting small or thin parts from a larger base part. Uses a special machine with a thin, tensioned blade that takes a minimum kerf. Process for cutting expensive materials such as silicon, germanium and other computer-chip materials.


Structure of a metal as revealed by microscopic examination of the etched surface of a polished specimen.


Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

milling arbor

Shaft or toolholder that inserts in the machine spindle and holds a peripheral-milling or facemilling cutter.

milling cutter

Loosely, any milling tool. Horizontal cutters take the form of plain milling cutters, plain spiral-tooth cutters, helical cutters, side-milling cutters, staggered-tooth side-milling cutters, facemilling cutters, angular cutters, double-angle cutters, convex and concave form-milling cutters, straddle-sprocket cutters, spur-gear cutters, corner-rounding cutters and slitting saws. Vertical cutters use shank-mounted cutting tools, including endmills, T-slot cutters, Woodruff keyseat cutters and dovetail cutters; these may also be used on horizontal mills. See milling.

milling machine (mill)

Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.

minimum-quantity lubrication

Use of cutting fluids of only a minute amount—typically at a flow rate of 50 to 500 ml/hr.—which is about three to four orders of magnitude lower than the amount commonly used in flood cooling. The concept addresses the issues of environmental intrusiveness and occupational hazards associated with the airborne cutting fluid particles on factory shop floors. The minimization of cutting fluid also saves lubricant costs and the cleaning cycle time for workpieces, tooling and machines. Sometimes referred to as “near-dry lubrication” or “microlubrication.”


Ability of a liquid to mix with another liquid. See emulsion.

mist application

Atomized fluid generally applied when a clear view of the cut point is needed, as in contour bandsawing or manual milling. The airborne mist can be directed precisely to the point of cut, sometimes reaching areas flood-applied coolant cannot penetrate. The water evaporates on contact, providing further cooling, and leaves oils and additives on the work. See flood application.

mixture ratio

Ratio of water to concentrate in certain cutting fluids. See semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

modular design (modular construction)

Manufacturing of a product in subassemblies that permits fast and simple replacement of defective assemblies and tailoring of the product for different purposes. See interchangeable parts.

modular fixturing

System in which fixtures are constructed from standardized, reusable components. Fixtures are assembled and disassembled quickly. Basic styles are subplate, dowel-pin and T-slot. See fixture; modular tooling.

modular robot

Robot with interchangeable components, such as gripping hands, that permit quick modification to suit a specific purpose.

modular tooling

1. Tooling system comprised of standardized tools and toolholders. 2. Devices that allow rapid mounting and replacement of tools. Commonly used with carousel toolchangers and other computerized machining operations. See toolchanger; toolholder.

modulus of elasticity

Measure of rigidity or stiffness of a metal, defined as a ratio of stress, below the proportional limit, to the corresponding strain. Also known as Young’s modulus.

modulus of rigidity

Ratio of shear stress to the corresponding shear strain for shear stress below the proportional limit of the material. Also known as shear modulus. MRP, MRP-II, materials requirements planning,

multifunction machines (multitasking machines)

Machines and machining/turning centers capable of performing a variety of tasks, including milling, drilling, grinding boring, turning and cutoff, usually in just one setup.


Introducing nitrogen into the surface layer of a solid ferrous alloy. This is done to increase hardness, wear resistance and fatigue strength.


Any of several processes in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material and, by diffusion, create a concentration gradient. Nitrocarburizing is done mainly to provide an antiscuffing surface layer and to improve fatigue resistance. See carbonitriding.

nondestructive inspection (nondestructive examination)

Inspection by methods that do not destroy the part or impair its serviceability.

nondestructive testing (NDT)

Same as nondestructive inspection but implying use of a method in which the part is stimulated and its response measured quantitatively or semiquantitatively.

nontraditional machining

Variety of chemical, electrical, mechanical and thermal processes for machining workpieces. Originally applied to new or emerging processes, it designates any process developed since 1945.

nonuniform rational B-splines (NURBS)

Type of curve or surface for which the difference between successive knots (parameter values) need not be expressed in uniform increments of 1. See B-spline.


Heating a ferrous alloy to a temperature above the transformation range and then cooling in air to a temperature below the transformation range.

numerical control (NC)

Any controlled equipment that allows an operator to program its movement by entering a series of coded numbers and symbols. See CNC, computer numerical control; DNC, direct numerical control.

offhand grinding

Hand-feeding a workpiece into a bench grinder. Usually utilized in the shop to resharpen tools. Attachments or other mechanical devices are required for increased efficiency and accuracy. See grinding.

orthogonal chip formation

Concentrated shear action at the point of cut that results in the formation of a continuous chip. See shear plane.

outer diameter (OD)

Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.


Deviation from nominal path caused by momentum carried over from previous step, as when a tool is rapidly traversed a considerable distance to begin a cut. Usually applies to CNC machining and is prevented if the control has the appropriate look-ahead capability. See look-ahead; undershoot.


Strip or block of precision-ground stock used to elevate a workpiece, while keeping it parallel to the worktable, to prevent cutter/table contact.

parametric-based CAD/CAM

Model features can be driven by rules or parameters set up by the user. They can be dimensions, geometric constraints (tangent, concentric, co-linear, etc.), equations and design tables, among others.

part orientation

Designing the assembly machine, feeding mechanism and the part itself so the parts to be assembled are properly aligned prior to and during the assembly operation.


When used in lathe or screw-machine operations, this process separates a completed part from chuck-held or collet-fed stock by means of a very narrow, flat-end cutting, or parting, tool.

parts feeder

Mechanism that delivers parts to the assembly machine at a specified rate and with proper orientation.

payload (workload)

Maximum load that the robot can handle safely.


Lamellar aggregate of ferrite and cementite in slowly cooled iron-carbon alloys occurring normally as a principle constituent of steel and cast iron. Fully annealed steel containing 0.85 percent carbon consists entirely of pearlite.


Mechanical working of a metal by hammer blows or shot impingement.

peripheral milling

Form of milling that produces a finished surface generally in a plane parallel to the rotating axis of a cutter having teeth or inserts on the periphery of the cutter body. See milling.

phase transformation

Heat generated by machining action that causes changes in the workpiece’s surface layers. This can result in softer- or harder-than-desired workpiece surfaces, as well as undesirable changes in cutting tools.

photochemical machining

Variation on chemical machining that uses a chemically resistant mask that is sensitive to light. Light activates the mask only in the areas to be protected. The remaining mask is washed away. The process is typically used to produce parts such as circuit boards and other delicate items.

physical vapor deposition (PVD)

Tool-coating process performed at low temperature (500° C), compared to chemical vapor deposition (1,000° C). Employs electric field to generate necessary heat for depositing coating on a tool’s surface. See CVD, chemical vapor deposition.

pick-and-place robot

Simple robot or piece of hard automation that is capable of the simple actions of picking an object from a fixed point and placing the object at another fixed point.


1. On a saw blade, the number of teeth per inch. 2. In threading, the number of threads per inch.


Localized corrosion of a metal surface, confined to a point or small area, that takes the form of cavities.


Machining operation that creates flat surfaces. The workpiece is reciprocated in a linear motion against one or more single-point tools. Also used to create contours or irregular configurations.

planing bit

Cutting tool similar in appearance to a turning tool but with a longer shank.

planing machine (planer)

Machines flat surfaces. Planers take a variety of forms: double-housing, open-side, convertible and adjustable open-side, double-cut and milling. Large multihead (milling, boring, drilling, etc.) planers and planer-type milling machines handle most planing work.

plastic deformation

Permanent (inelastic) distortion of metals under applied stresses that strain the material beyond its elastic limit.

plastic stereolithography

Process that uses a combination of lasers and photosensitive, liquid plastics to generate models. The desired workpiece is electronically “sliced” into thin sections. The laser beam scans over a bath of uncured polymer and only turns on where material should exist, duplicating the sliced section. The polymer partially hardens in these areas. By lowering the workpiece into the polymer bath and scanning successive layers, the part is developed. When the part is completely built up, it is removed from the bath and finish-cured with intense ultraviolet light. Can be used to generate complex models.

plunge milling

Highly productive method of metal removal in which an axial machining operation is performed in a single tool sequence. The tool makes a series of overlapping, drill-like plunges to remove part of a cylindrical plug of material one after another. Because of the increased rigidity of a Z-axis move, the tool can cover a large cross-section of material.

plunge turning

Form of hard turning that uses the entire cutting edge or a portion of the cutting edge to create an orthogonal cut.

point angle

Included angle at the point of a twist drill or similar tool; for general-purpose tools, the point angle is typically 118°.

point-to-point system

NC system normally used for drilling and other operations where center-point location is readily determined. Tool is rapidly moved to a position, then drills, taps, reams, bores, counterbores, countersinks or performs some other task.

polar additives

Animal, vegetable or synthetic oil that, when added to a mineral oil, improves its ability to penetrate the tool/workpiece interface.


Abrasive process that improves surface finish and blends contours. Abrasive particles attached to a flexible backing abrade the workpiece.

polishing attachment

Abrasive grinding device that mounts on a contour bandsaw and uses fine-grit belts to grind and polish.

polycrystalline cubic boron nitride (PCBN)

Cutting tool material consisting of polycrystalline cubic boron nitride with a metallic or ceramic binder. PCBN is available either as a tip brazed to a carbide insert carrier or as a solid insert. Primarily used for cutting hardened ferrous alloys.

polycrystalline diamond (PCD)

Cutting tool material consisting of natural or synthetic diamond crystals bonded together under high pressure at elevated temperatures. PCD is available as a tip brazed to a carbide insert carrier. Used for machining nonferrous alloys and nonmetallic materials at high cutting speeds.

powder metallurgy

Processes in which metallic particles are fused under various combinations of heat and pressure to create solid metals.

power brushing

Any process that uses a power-driven, rotating industrial brush to deburr, clean or finish a metal part. Depending on the application, the brush fibers, collectively known as brush fill material, may be metal wires; fiberglass-coated, abrasive-filled plastics; synthetics such as nylon and polypropylene; natural animal hairs such as horsehair; or vegetable fibers such as tampico and bahia.

power hacksaw

Machine fitted with serrated blade held taut in a reciprocating frame that cuts in one direction, either on the forward or return stroke. See saw, sawing machine.

power hacksawing

Sawing process that uses the back-and-forth motion of a short, straight-toothed blade to cut the workpiece. Hacksawing machines are generally electrically driven and may or may not provide for application of cutting fluid to the saw blade or workpiece.

precision machining (precision measurement)

Machining and measuring to exacting standards. Four basic considerations are: dimensions, or geometrical characteristics such as lengths, angles and diameters of which the sizes are numerically specified; limits, or the maximum and minimum sizes permissible for a specified dimension; tolerances, or the total permissible variations in size; and allowances, or the prescribed differences in dimensions between mating parts.


Heating before some further thermal or mechanical treatment.

probability theory

Discipline based on the likelihood of any given event happening; mathematical techniques built around sampling methods, combinations and permutations. Key to understanding statistical-process-control systems. See SPC, statistical process control.

process annealing

Imprecise term denoting various treatments used to improve workability. For the term to be meaningful, the condition of the material and the time-temperature cycle used must be stated.

process control

Method of monitoring a process. Relates to electronic hardware and instrumentation used in automated process control. See in-process gaging, inspection; SPC, statistical process control.


Measure of the efficiency with which human and material resources are used to produce goods and services. Output per man-hour has traditionally been the most stable measure, but, since direct labor is sharply reduced by CAD, CAM and computer-integrated manufacturing, alternative methods of measuring may be more accurate. Software and other support/service functions must be factored into the equation.


Machining vertical edges of workpieces having irregular contours; normally performed with an endmill in a vertical spindle on a milling machine or with a profiler, following a pattern. See mill, milling machine.

quality assurance (quality control)

Terms denoting a formal program for monitoring product quality. The denotations are the same, but QC typically connotes a more traditional postmachining inspection system, while QA implies a more comprehensive approach, with emphasis on “total quality,” broad quality principles, statistical process control and other statistical methods.

quench cracking

Fracture of a metal during quenching. Most frequently observed in hardened carbon steel, alloy steel or tool steel parts of high hardness and low toughness. Cracks often emanate from fillets, holes, corners or other stress raisers and result from high stresses due to the volume changes accompanying transformation to martensite.

quench hardening

1. Hardening alpha-beta alloys (most often copper or titanium alloys) by solution-treating and quenching to develop a martensite-like structure. 2. In ferrous alloys, hardening by austenitizing and then cooling so that austenite transforms to martensite.


Rapid cooling of the workpiece with an air, gas, liquid or solid medium. When applicable, more specific terms should be used to identify the quenching medium, the process and the cooling rate.

quick-change toolholder

Cutter holder that permits rapid tool changes. Generally associated with automatic or semiautomatic machining operations. See toolholder.

rack-milling attachment

Attachment for cutting gear teeth, usually in a straight line, but, when used in conjunction with universal spiral-index centers on a universal mill, it allows the machining of worms.

radial drill

Large drill with an arm that pivots about a column to provide positioning flexibility and great reach and stability. See drilling machine, drill press.

radial rake

Also known as the tool back rake, the angle between the tooth face and the radial plane through the tool point.


Angle of inclination between the face of the cutting tool and the workpiece. If the face of the tool lies in a plane through the axis of the workpiece, the tool is said to have a neutral, or zero, rake. If the inclination of the tool face makes the cutting edge more acute than when the rake angle is zero, the rake is positive. If the inclination of the tool face makes the cutting edge less acute or more blunt than when the rake angle is zero, the rake is negative.

ram EDM

Process using a shaped electrode made from graphite or copper. The electrode is separated by a nonconductive liquid and maintained at a close distance (about 0.001"). A high DC voltage is pulsed to the electrode and jumps to the conductive workpiece. The resulting sparks erode the workpiece and generate a cavity in the reverse shape of the electrode, or a through-hole in the case of a plain electrode. Permits machining shapes to tight accuracies without the internal stresses conventional machining often generates. Also known as “die-sinker” or “sinker” electrical-discharge machining.

ramp milling

Milling process in which the machine tool spindle is feeding simultaneously in an axial and radial direction.


Bacterial and fungal growths in water-miscible fluids that cause unpleasant odors, stained workpieces and diminished fluid life.

rapid traverse

Movement on a CNC mill or lathe that is from point to point at full speed but, usually, without linear interpolation.

reaction injection molding (RIM)

Molding process that allows the rapid molding of liquid materials. The injection-molding process consists of heating and homogenizing plastic granules in a cylinder until they are sufficiently fluid to allow for pressure injection into a relatively cold mold, where they solidify and take the shape of the mold cavity. For thermoplastics, no chemical changes occur within the plastic, and, consequently, the process is repeatable. The major advantages of the injection-molding process are the speed of production; minimal requirements for postmolding operations; and simultaneous, multipart molding.


Rotating cutting tool used to enlarge a drilled hole to size. Normally removes only a small amount of stock. The workpiece supports the multiple-edge cutting tool. Also for contouring an existing hole.


1. Increasing the carbon content of molten cast iron or steel by adding a carbonaceous material, a high-carbon pig iron or a high-carbon alloy. 2. Carburizing a metal part to return surface carbon lost in processing; also known as carbon restoration.


A turning operation in which a groove is produced on the periphery or inside a hole of a workpiece. The grooving tool moves at right angles to the axis of rotation.


Reduction or removal of workhardening effects, without motion of large-angle grain boundaries.


1. Formation of a new, strain-free grain structure from that existing in cold-worked metal, usually accomplished by heating. 2. Change from one crystal structure to another, as occurs on heating or cooling through a critical temperature.

recrystallization temperature

Approximate minimum temperature at which complete recrystallization of a cold-worked metal occurs within a specified time.

red hardness

Ability of a cutting tool material to withstand high temperatures at the point of cut without softening and degrading.


Optical instrument that measures the refractive index of a liquid, such as a water-diluted metalworking fluid mix. The refractive index can by used to determine the concentration of a fresh metalworking fluid mix.

refractory metal

Metal having an extremely high melting point; for example, tungsten, molybdenum, tantalum, niobium (columbium), chromium, vanadium and rhenium. In the broad sense, this term refers to metals having melting points above the range of iron.


Space provided behind the cutting edges to prevent rubbing. Sometimes called primary relief. Secondary relief provides additional space behind primary relief. Relief on end teeth is axial relief; relief on side teeth is peripheral relief.

residual stress

Stress present in a body that is free of external forces or thermal gradients.


Device capable of performing various combinations of movements, manipulations and actions. Normally computerized but may be electromechanical. Computerized units normally consist of three basic components: machinery or mechanical parts, controller/computer system and software. See industrial robot.


Discipline involving self-actuating and self-operating devices. Robots frequently imitate human capabilities, including the ability to manipulate physical objects while evaluating and reacting appropriately to various stimuli. See industrial robot; robot.

Rockwell hardness number (HR)

Number derived from the net increase in the depth of impression as the load on the indenter is increased from a fixed minor load to a major load and then returned to the minor load. The Rockwell hardness number is always quoted with a scale symbol representing the indenter, load and dial used. Rockwell A scale is used in connection with carbide cutting tools. Rockwell B and C scales are used in connection with workpiece materials.

Rockwell standard hardness test

Indentation hardness test uses a calibrated machine that utilizes the depth of indentation, under constant load, as a measure of hardness. There are 15 standard hardness scales. The most common are the A, B and C scales. The A and C scales utilize the 120º spheroconical diamond indenter and different major loads: 60 kgf is for scale A; 150 kgf is for scale C. The B scale utilizes the 1¼16" (1.588mm) ball and the major load of 100 kgf. The result is expressed as the Rockwell hardness number. See Brinell hardness test; Knoop hardness test; Scleroscope hardness test; Vickers hardness test.

Rockwell superficial hardness test

Indentation hardness test uses a calibrated machine that utilizes the depth of indentation, under constant load, as a measure of hardness. There are five superficial hardness scales (N, T, W, X and Y) and three different loads (15, 30 and 45 kgf) that can be applied to the appropriate indenter. The most common scales are N and T. The 120º spheroconical diamond indenter is used with scale N and the 1¼16" (1.588mm) ball is used with scale T. The 15-, 30- or 45-kgf load can be used for both scales. The result is expressed as the Rockwell hardness number.


Rotation about an axis, as with a rotatable wrist.

rotary attachment

Bolts to a milling machine to permit machining such shapes as circular T-slots and cams.

rotary transfer machine

Type of CNC machine tool for high-volume, extended-length production runs of a family of parts. A workpiece is transferred from station to station in a rotary fashion and a tool or tools at each station performs one or more operations until the part is completed.

roughing cutter

Tool for high-volume metal removal; normally followed by finishing passes. See finishing tool.


Irregularities on the surface of a workpiece caused by production process. Includes traverse feed marks within the limits of the instrument cutoff setting (sampling length). See flows; lay; waviness.

S-N diagram

Plot showing the relationship of stress, S, and the number of cycles, N, before fracture in fatigue testing.

salt fog test (salt spray test)

Accelerated corrosion test in which specimens are exposed to a fine mist of a solution usually containing sodium chloride but sometimes modified with other chemicals. Used to determine resistance to, and rates of, corrosion exhibited by various materials.


Machining operation in which a powered machine, usually equipped with a blade having milled or ground teeth, is used to part material (cutoff) or give it a new shape (contour bandsawing, band machining). Four basic types of sawing operations are: hacksawing (power or manual operation in which the blade moves back and forth through the work, cutting on one of the strokes); cold or circular sawing (a rotating, circular, toothed blade parts the material much as a workshop table saw or radial-arm saw cuts wood); bandsawing (a flexible, toothed blade rides on wheels under tension and is guided through the work); and abrasive sawing (abrasive points attached to a fiber or metal backing part stock, could be considered a grinding operation).

sawing machine (saw)

Machine designed to use a serrated-tooth blade to cut metal or other material. Comes in a wide variety of styles but takes one of four basic forms: hacksaw (a simple, rugged machine that uses a reciprocating motion to part metal or other material); cold or circular saw (powers a circular blade that cuts structural materials); bandsaw (runs an endless band; the two basic types are cutoff and contour band machines, which cut intricate contours and shapes); and abrasive cutoff saw (similar in appearance to the cold saw, but uses an abrasive disc that rotates at high speeds rather than a blade with serrated teeth).


Wavy surface condition caused by deflection, unbalanced tool, loose workpiece or tooling or worn machine.

Scleroscope hardness number (HSc or HSd)

Number related to the height of rebound of a diamond-tipped hammer dropped on the material to be tested. Hardness measured on the Model C Scleroscope is expressed as a 2-digit number followed by the letters HSc, and hardness measured on the Model D Scleroscope is expressed as a 2-digit number followed by the letters HSd.

Scleroscope hardness test

Dynamic hardness test using a calibrated instrument that drops a diamond-tipped hammer from a fixed height onto the surface of the material being tested. The height of rebound of the hammer is a measure of the hardness of the material. The result is expressed as the Scleroscope hardness number. See Brinell hardness test; Knoop hardness test; Rockwell standard hardness test; Rockwell superficial hardness test; Vickers hardness test.

semisynthetic cutting fluid

Water-based chemical solution that contains some oil. See synthetic cutting fluid.

sensitizing heat-treatment

Heat-treatment, whether accidental, intentional or incidental (as during welding), that causes precipitation of constituents at grain boundaries, often causing the alloy to become susceptible to intergranular corrosion or intergranular stress-corrosion cracking.


Refers to control of motion. Applied to the industrial robot, it describes automatic feedback, or “closed-loop,” operation in which sensing devices monitor movement and report any deviation between commands as issued and movement as monitored. Deviations trigger corrective action. Robots without servocontrol may be “open-loop” but most often are controlled by preset mechanical or electric stop-switches. Because they are not self-correcting, they have limited capabilities.


Control mechanism in a machine tool to feed the cutting tool into the part and slow or speed up the drive motors as required.


Main body of a tool; the portion of a drill or similar end-held tool that fits into a collet, chuck or similar mounting device.

shaper tool

Single-point tool that traverses the workpiece in a reciprocating fashion to machine a desired shape.


Using a shaper primarily to produce flat surfaces in horizontal, vertical or angular planes. It can also include the machining of curved surfaces, helixes, serrations and special work involving odd and irregular shapes. Often used for prototype or short-run manufacturing to eliminate the need for expensive special tooling or processes.

shear lip

Narrow, slanting ridge along the edge of a fracture surface. Term sometimes also denotes a narrow, often crescent-shaped, fibrous region at the edge of a fracture that is otherwise of the cleavage type, even though this fibrous region is in the same plane as the rest of the fracture surface.

shear plane

Plane along which the chip parts from the workpiece. In orthogonal cutting, most of the energy is used to create the shear plane.

shear strength

Stress required to produce fracture in the plane of cross section, the conditions of loading being such that the directions of force and of resistance are parallel and opposite although their paths are offset a specified minimum amount. The maximum load divided by the original cross-sectional area of a section separated by shear.

shock loading

Tool is subjected to sudden, heavy loads and/or impacts, as in interrupted cutting. See interrupted cut.

shop air

Pressurized air system that cools the workpiece and tool when machining dry. Also refers to central pneumatic system.

shot peening

Cold working a metal’s surface by metal-shot impingement.

shrink-fit toolholding

Method of holding a round-shank cutting tool in a toolholder. To shrink-fit, the toolholder is heated in order to expand its bore, allowing a tool to be inserted. As the holder cools, the bore contracts around the shank to firmly hold the tool in place.

shuttle mechanism

Mechanism typically used to feed parts into an assembly machine in a back-and-forth motion, inserting a part at the end of each stroke.

single-crystal diamond

Industrial-grade, natural diamond. Not recommended for cutting ferrous materials because it tends to react chemically with them and break down. Also not recommended for interrupted cuts in hard materials. Replaced by polycrystalline diamond in many applications. See diamond; PCD, polycrystalline diamond; superabrasive tools.


Bonding of adjacent surfaces in a mass of particles by molecular or atomic attraction on heating at high temperatures below the melting temperature of any constituent in the material. Sintering strengthens and increases the density of a powder mass and recrystallizes powder metals.

slack quenching

Incomplete hardening of steel due to quenching at a rate slower than the critical cooling rate for the particular steel, resulting in the formation of one or more transformation products in addition to martensite.


Machining, normally milling, that creates slots, grooves and similar recesses in workpieces, including T-slots and dovetails.

slotting attachment

Converts a milling machine’s rotary spindle motion into a reciprocating motion for machining keyways and slots.

slotting machine (shaper)

Vertical or horizontal machine that accommodates single-point, reciprocating cutting tools to shape or slot a workpiece. Normally used for special (unusual/intricate shapes), low-volume runs typically performed by broaching or milling machines. See broaching machine; mill, milling machine.


Prolonged holding of a metal at a selected temperature to homogenize its structure or composition.

solid model

3-D model created using “building blocks.” This is the most accurate way of representing real-world objects in CAD.

soluble-oil cutting fluid

Fluid in which oil is suspended in water. Because water is a superior heat-removal agent, this fluid is primarily used when lubrication is desirable but cooling is the key consideration. The ratio of oils and other additives to water varies with the application. For milling, the ratio of water to oil/additives runs 20:1 to 25:1. For sawing and other work, where a more confined tool/chip/workpiece condition is normal, a 10:1 ratio is used to improve lubricity. Additives include emulsifying agents that help keep the oil in suspension and substances that promote wetting, enhance lubricity, prevent chipwelding and inhibit rusting. Also known as emulsified oil. See cutting fluid.

spade drill

Flat end-cutting tool used to produce holes ranging from about 1" to 6" in diameter. Spade drills consist of an interchangeable cutting blade and a toolholder that has a slot into which the blade fits. In horizontal applications, universal spade drills can achieve extreme depth-to-diameter ratios, but, in vertical applications, the tools are limited by poor chip evacuation.

spade drilling

Drilling operation in which a machine powers a cutting tool consisting of a holder and flat, interchangeable end-cutting blades. Spade drilling takes over where twist drilling leaves off; requires more power and a larger machine but offers lower cost and greater rigidity. Large-diameter spade drills are used when trepanning is impractical or impossible. See drilling; trepanning.

spark-out (sparking out)

Grinding of a workpiece at the end of a grind cycle without engaging any further down feed. The grinding forces are allowed to subside with time, ensuring a precision surface.

specific power consumption

It is also called the unit power, or power constant, which is equal to the power required to cut a material at the rate of one cubic inch per minute or one cubic centimeter per minute. The units of measure are: hp/in.3/min. (customary U.S. system) and kW/cm3/min. (metric system).

spindle adapter

Bushing or toolholder that permits affixing a variety of taper- and straight-shank tools to a machine spindle.

spindle finishing

Mass finishing process in which workpieces are individually mounted on spindles then lowered into a rotating tub containing the finishing media. In most applications, the spindles rotate at 10 rpm to 3,000 rpm, but, in some cases, the spindles oscillate up and down instead of rotating. The process is sometimes automated for robotic loading and unloading. See finishing.

spiral milling

Milling while simultaneously rotating and feeding the workpiece to create a spiral form. Often used to mill flutes on endmill and twist-drill blanks.


Form of metal characterized by a porous condition that is the result of the decomposition or reduction of a compound without fusion. The term is applied to forms of iron, titanium, zirconium, uranium, plutonium and the platinum group metals.


Tool, guided by a pilot, used to machine a recess around a hole.


Similar to counterboring except that, in spotfacing, material around the original hole is cut. Application example: the recessed area into which a washer fits. See counterboring; countersinking.

stainless steels

Stainless steels possess high strength, heat resistance, excellent workability and erosion resistance. Four general classes have been developed to cover a range of mechanical and physical properties for particular applications. The four classes are: the austenitic types of the chromium-nickel-manganese 200 series and the chromium-nickel 300 series; the martensitic types of the chromium, hardenable 400 series; the chromium, nonhardenable 400-series ferritic types; and the precipitation-hardening type of chromium-nickel alloys with additional elements that are hardenable by solution treating and aging.

static stiffness

Relates to the machine tool and is measured in pounds per inch. Static stiffness indicates how many pounds of force it takes to deflect the spindle a linear distance of 1" in a given direction. See dynamic stiffness; stiffness.

statistical process control (SPC)

Statistical techniques to measure and analyze the extent to which a process deviates from a set standard.

statistical quality control (SQC)

Statistical techniques to measure and improve the quality of a given process.

steady rest

Supports long, thin or flexible work being turned on a lathe. Mounts on the bed’s ways and, unlike a follower rest, remains at the point where mounted. See follower rest.


Basically, iron in combination with carbon and other elements. There are five major groups of steels: carbon steel, alloy steel, stainless steel, tool steel and maraging steel.

steel-specification number

System of numbers developed by the American Iron and Steel Institute and Society of Automotive Engineers to identify steel. The first two digits in the code indicate the family and basic alloying elements. The final two digits indicate the approximate carbon content in hundredths of a percent. For steels with a carbon content above 1.00 percent, five digits are used. Numbers with L or S added indicate alloys incorporating lead or sulfur for improved machinability. A number of steels and alloys are identified under different codes, including tool steel, carbon tool steel, high-speed steel, die steel, stainless steel, strain-hardenable or workhardening steel and nickel-base superalloys.

steep-taper toolholder

Common method of securing the cutting tool body to the spindle in a machine tool. Comes in various styles, including CAT V-flange, British Taper (BT) and ISO.


Distance between the passes of the toolpath; the path spacing. The distance the tool will move horizontally when making the next pass. Too great of a step-over will cause difficulty machining because there will be too much pressure on the tool as it is trying to cut with too much of its surface area.


1. Ability of a material or part to resist elastic deflection. 2. The rate of stress with respect to strain; the greater the stress required to produce a given strain, the stiffer the material is said to be. See dynamic stiffness; static stiffness.

straight oil

Cutting fluid that contains no water. Produced from mineral, vegetable, marine or petroleum oils, or combinations of these oils.

straight-cut system

NC system wherein tools move at either 45° or 90° angles to the coordinate axes. Used in turning shoulders or milling rectangular shapes; normally is combined with point-to-point system for greater efficiency and flexibility.


Measure of the relative change in the size or shape of a body. Linear strain is the change per unit length of a linear dimension. True strain (or natural strain) is the natural logarithm of the ratio of the length at the moment of observation to the original gage length. Conventional strain is the linear strain over the original gage length. Shearing strain (or shear strain) is the change in angle (expressed in radians) between two lines originally at right angles. When the term “strain” is used alone it usually refers to the linear strain in the direction of applied stress.

strain hardening

Increase in hardness and strength caused by plastic deformation at temperatures below the recrystallization range.


Force per unit area, often thought of as force acting through a small area within a plane. It can be divided into components, normal and parallel to the plane, called normal stress and shear stress, respectively. True stress denotes the stress where force and area are measured at the same time. Conventional stress, as applied to tension and compression tests, is force divided by original area. Nominal stress is the stress computed by simple elasticity formulas, ignoring stress raisers and disregarding plastic flow; in a notch bend test, for example, it is bending moment divided by minimum section modulus.

stress relieving

Annealing designed to relieve internal stresses caused by machining, welding, casting, cold working, quenching or normalizing.

stress-rupture test, creep-rupture test

Method of evaluating elevated-temperature durability in which a tension-test specimen is stressed under constant load until it breaks. Data recorded commonly include initial stress, time to rupture, initial extension, creep extension and reduction of area at fracture.


Fatigue fracture feature, often observed in electron micrographs, that indicates the position of the crack front after each succeeding cycle of stress. The distance between striations indicates the advance of the crack front across that crystal during one stress cycle, and a line normal to the striations indicates the direction of local crack propagation.

superabrasive tools

Abrasive tools made from diamond or cubic boron nitride, the hardest materials known. See CBN, cubic boron nitride; diamond; PCD, polycrystalline diamond; single-crystal diamond.


Tough, difficult-to-machine alloys; includes Hastelloy, Inconel and Monel. Many are nickel-base metals.


Cooling below the temperature at which an equilibrium phase transformation can take place, without actually obtaining the transformation.


Heating above the temperature at which an equilibrium phase transformation should occur, without actually obtaining the transformation.


Ability of certain metals to undergo unusually large amounts of plastic deformation before local necking occurs.

surface grinding

Machining of a flat, angled or contoured surface by passing a workpiece beneath a grinding wheel in a plane parallel to the grinding wheel spindle. See grinding.

surface model

3-D model defined by surfaces. The surface consists of polygons.

surface texture

Repetitive or random deviations from the nominal surface, which form 3-D topography of the surface. See flows; lay; roughness; waviness.


Metal fines and grinding wheel particles generated during grinding.

Swiss-type machine tool

Type of turning center designed to turn small, complex, precision parts. It has an automatic lathe that has a sliding headstock and a guide bushing. The sliding headstock is the part of the machine that holds the bar stock and rotates it. The cutting tools move in and out of the material to create required diameters while the headstock moves the material forward to create required lengths. Swiss machines generate the features of the part by moving the material and the tool at the same time.

synchronous transfer

Part-transfer system in which all parts are progressively moved to the next workstation or tooling station at the same time.

synthetic cutting fluid

Water-based chemical solution that contains no oil. Normally contains additives that improve lubricity and prevent corrosion and rancidity. See semisynthetic cutting fluid.

T-slot cutter

Milling cutter for machining T-slots. Desired T-slot shape is reverse of cutter shape.

tailstock drill and tapholder

Accessory that mounts in a turning machine’s tailstock for center-drilling chucked work and tapping. See chuck.


Extended flat portion of tapered drill shank, endmill or other tool that allows maximum power transmission and proper positioning of the tool. Reverse shape of the machine-spindle slot into which it fits.


Cylindrical tool that cuts internal threads and has flutes to remove chips and carry tapping fluid to the point of cut. Normally used on a drill press or tapping machine but also may be operated manually. See tapping.

taper reamer

Reamer designed to produce a reamed hole with a specified taper. Principles of standard reamers apply. See reamer.

taper-turning attachment

Guide to which a cross slide is attached that permits the turning of tapers without disturbing the alignment of the tailstock. Also permits taper boring.


Machining operation in which a tap, with teeth on its periphery, cuts internal threads in a predrilled hole having a smaller diameter than the tap diameter. Threads are formed by a combined rotary and axial-relative motion between tap and workpiece. See tap.

tapping attachment

Fits in a drill-press spindle and automatically reverses the tap when the thread is completed, ensuring proper retraction of the tool.

tapping machine

Production machine used for high-volume tapping. Offers repeatability, high production rates and reduced tap breakage. Comes in a variety of configurations, including indexing units with multiple tapping spindles. Precise stroke-depth settings and automatic features generally make tapping machines cost-effective.

teaching pendant

Device used to “walk” a teachable robot through a new task.


1. In heat-treatment, reheating hardened steel or hardened cast iron to a given temperature below the eutectoid temperature to decrease hardness and increase toughness. The process also is sometimes applied to normalized steel. 2. In nonferrous alloys and in some ferrous alloys (steels that cannot be hardened by heat-treatment), the hardness and strength produced by mechanical or thermal treatment, or both, and characterized by a certain structure, mechanical properties or reduction in area during cold working.

tensile strength

In tensile testing, the ratio of maximum load to original cross-sectional area. Also called ultimate strength. Compare with yield strength.

thread chaser

Die-type external threading tool. Makes final threading pass.

thread grinder

Typically a form grinder as well as a thread grinder, this machine differs from other grinders in that precision gears and leadscrews ensure a precise traverse to impart the correct lead to a thread.

thread rolling

Chipless, cold-forming material-displacement process where a rolling head is pressed into the workpiece to create threads. The material is stressed beyond its yield point, which causes it to be deformed platically and permanently. There are three basic types of rolling heads: axial, radial and tangential.


Process of both external (e.g., thread milling) and internal (e.g., tapping, thread milling) cutting, turning and rolling of threads into particular material. Standardized specifications are available to determine the desired results of the threading process. Numerous thread-series designations are written for specific applications. Threading often is performed on a lathe. Specifications such as thread height are critical in determining the strength of the threads. The material used is taken into consideration in determining the expected results of any particular application for that threaded piece. In external threading, a calculated depth is required as well as a particular angle to the cut. To perform internal threading, the exact diameter to bore the hole is critical before threading. The threads are distinguished from one another by the amount of tolerance and/or allowance that is specified. See turning.

threading machine

Typically takes the form of multispindle, universal threading machines that use dieheads and thread chasers to cut threads, often automatically or semiautomatically. Threading also is performed on lathes and automatic screw machines.


Hole or cavity cut in a solid shape that connects with other holes or extends all the way through the workpiece.

titanium aluminum nitride (TiAlN)

Often used as a tool coating. AlTiN indicates the aluminum content is greater than the titanium. See coated tools.

titanium carbide (TiC)

Extremely hard material added to tungsten carbide to reduce cratering and built-up edge. Also used as a tool coating. See coated tools.

titanium carbonitride (TiCN)

Often used as a tool coating. See coated tools.

titanium nitride (TiN)

Added to titanium-carbide tooling to permit machining of hard metals at high speeds. Also used as a tool coating. See coated tools.


Minimum and maximum amount a workpiece dimension is allowed to vary from a set standard and still be acceptable.

tool steels

Group of alloy steels which, after proper heat treatment, provide the combination of properties required for cutting tool and die applications. The American Iron and Steel Institute divides tool steels into six major categories: water hardening, shock resisting, cold work, hot work, special purpose and high speed.


Carriage or drum attached to a machining center that holds tools until needed; when a tool is needed, the toolchanger inserts the tool into the machine spindle. See automatic toolchanger.


Secures a cutting tool during a machining operation. Basic types include block, cartridge, chuck, collet, fixed, modular, quick-change and rotating.

toolpath, cutter path

2-D or 3-D path generated by program code or a CAM system and followed by tool when machining a part.

toolroom lathe

High-precision lathe built to hold tighter tolerances than regular, general-purpose lathes can hold. See lathe; turning machine.

tooth rest

Finger of metal that contacts a cutter edge during resharpening on a tool and cutter grinder, ensuring accurate location of edges so they are properly ground.

total indicator runout (TIR)

Combined variations of all dimensions of a workpiece, measured with an indicator, determined by rotating the part 360°.


Tool’s ability to resist breaking during cutting.

tracer attachment

Used to duplicate a workpiece. A stylus connected to a servo traces a template or sample workpiece. The attachment directs the movements of a machine tool that cuts a duplicate workpiece. For machining complex parts.

tramp oil

Oil that is present in a metalworking fluid mix that is not from the product concentrate. The usual sources are machine tool lubrication system leaks.

transformation range

Temperature range in which austenite forms as a tool is heated and disappears as the tool cools. This range is critical and must be known in order to heat-treat tooling.


Drilling deep holes that are too large to be drilled by high-pressure coolant drills or gundrills. Trepanning generates a solid core and normally requires a big, powerful machine. Shallow trepanning operations can be performed on modified engine or turret lathes or on boring machines. See boring; drilling; spade drilling.


Using a diamond or other dressing tool to ensure that a grinding wheel is round and concentric and will not vibrate at required speeds. Weights also are used to balance the wheel. Also performed to impart a contour to the wheel’s face. See dressing.

tungsten carbide (WC)

Intermetallic compound consisting of equal parts, by atomic weight, of tungsten and carbon. Sometimes tungsten carbide is used in reference to the cemented tungsten carbide material with cobalt added and/or with titanium carbide or tantalum carbide added. Thus, the tungsten carbide may be used to refer to pure tungsten carbide as well as co-bonded tungsten carbide, which may or may not contain added titanium carbide and/or tantalum carbide.


Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

turning machine

Any machine that rotates a workpiece while feeding a cutting tool into it. See lathe.

turret lathe

Differs from engine lathe in that the normal compound rest is replaced by pivoting, multitool turrets mounted on the cross slide and tailstock. See lathe.

turret ram mill

Variation of the vertical milling machine; has a movable ram mounted on a swivel base atop the column, providing positioning flexibility. See mill, milling machine.

twist drill

Most common type of drill, having two or more cutting edges, and having helical grooves adjacent thereto for the passage of chips and for admitting coolant to the cutting edges. Twist drills are used either for originating holes or for enlarging existing holes. Standard twist drills come in fractional sizes from 1¼16" to 11¼2", wire-gage sizes from 1 to 80, letter sizes A to Z and metric sizes.

ultimate strength

Maximum conventional stress (tensile, compressive or shear) that a material can withstand.

ultrasonic cleaning

Method of cleaning metal or plastic parts by immersing them in an aqueous or solvent-based cleaning solution and imposing ultrasound energy on the bath to enhance cleaning by creating cavitation conditions at the part surface, which imparts a strong scouring action to remove tenacious soils.

ultrasonic machining

Material-removal operation in which an abrasive slurry flows between a tool, vibrating at a high frequency, and a workpiece.

ultrasonic testing

Nonconductive test applied to sound-conductive materials having elastic properties for the purpose of locating inhomogeneities or structural discontinuities within a material by means of an ultrasonic beam.


In numerical-control applications, a cut shorter than the programmed cut resulting after a command change in direction. Also a condition in generated gear teeth when any part of the fillet curve lies inside of a line drawn tangent to the working profile at its point of juncture with the fillet. Undercut may be deliberately introduced to facilitate finishing operations, as in preshaving.


Tendency of a numerical-control/computer-numerical-control machine to round off the corners of a programmed path because of servo lag or backlash, or because mechanical systems cannot react quickly to programmed instructions, especially when the machine is cold.

undulations per revolution (UPR)

Undulations per revolution, or the number of waves on a workpiece, is a reference to the cutoff frequency of a workpiece.

universal head

Facilitates setups on a tool and cutter grinder by allowing the grinding head to rotate away from the work area, leaving table alignment undisturbed. Also called a swivel attachment.

universal milling attachment

Mounts on a horizontal mill, permitting the spindle to be set at almost any angle.

universal milling machine

Horizontal mill equipped with a table that swivels, with respect to the saddle, allowing angular surfaces to be cut without changing the workpiece’s position.

universal spiral-milling attachment.

On a universal mill, permits milling helixes with a helix angle greater than 45°. Mills gears, screw threads, worms, twist drills, spiral-milling cutters and other helical shapes. Mounted to a plain milling machine equipped with a dividing head, it permits the mill to handle work that otherwise would require a universal mill.


Workholding device with V-shaped slot for holding pipe and other round stock during machining or inspection.

vertical milling attachment

Permits a horizontal mill to perform vertical and angled milling.

vibratory bowl feeder

Hopper/conveyor mechanism utilizing a vibratory motion in conjunction with a spring suspension system designed to deliver parts to an assembly machine at a specified rate and with proper part orientation.

Vickers hardness number (HV)

Number related to the applied load and surface area of the permanent impression made by a square-based pyramidal diamond indenter having included face angles of 136º. The Vickers hardness number is a ratio of the applied load in kgf, multiplied by 1.8544, and divided by the length of diagonal squared.

Vickers hardness test

Indentation hardness test employing a 136° diamond pyramid indenter (Vickers) and variable loads enabling the use of one hardness scale for all ranges of hardness from very soft lead to tungsten carbide. The result is expressed as Vickers hardness number. See Brinell hardness test; Knoop hardness test; Rockwell standard hardness test; Rockwell superficial hardness test; Scleroscope hardness test.


Measure of a fluid’s tendency to flow; varies with temperature.


Workholding device that mounts on various machining tables. Designs vary from plain to flanged to swiveling. Multiangle vises, such as the toolmaker’s universal vise, accurately hold work to allow machining at virtually any angle.

vision system

System in which information is extracted from visual sensors to allow machines to react to changes in the manufacturing process.

warm working

Plastically deforming metal above room temperature but below the temperature at which the material undergoes recrystallization.

waterjet cutting

Fine, high-pressure (up to 50,000 psi or greater), high-velocity jet of water directed by a small nozzle to cut material. Velocity of the stream can exceed twice the speed of sound. Nozzle opening ranges from between 0.004" to 0.016" (0.l0mm to 0.41mm), producing a very narrow kerf. See AWJ, abrasive waterjet.


The more widely spaced component of the surface texture. Includes all irregularities spaced more widely than the instrument cutoff setting. See flows; lay; roughness.


Frame elements that carry the workpiece table or spindles. There are three main types of ways: box, roller and hydrostatic. A box way is the oldest and simplest. It has high stiffness, good damping characteristics, a large surface contact area, and resistance to high cutting and shock load. A roller way consists of a rail and a slide, but has a rolling-element bearing between the two. A roller way has a lighter weight and operates with less friction than a box way, so it can be positioned faster and with less energy. With a hydrostatic way, the slide moves on a pressurized film of oil. Friction is almost zero, minimizing stick-slip and wear.

wear resistance

Ability of the tool to withstand stresses that cause it to wear during cutting; an attribute linked to alloy composition, base material, thermal conditions, type of tooling and operation and other variables.


On a rotating tool, the portion of the tool body that joins the lands. Web is thicker at the shank end, relative to the point end, providing maximum torsional strength.

wheel flange

Metal plate inside the grinding-wheel hole that allows the wheel to be mounted on a spindle.

wheel-balancing stand

Used to ensure that a grinding wheel is balanced before mounting it on the machine.

white cast iron

Cast iron that shows a white fracture. The material is free from graphite carbon because of its chemical composition.

width of cut

Width of the milled surface, reflecting a face milling cutter’s radial engagement, and a peripheral milling cutter’s axial engagement, in the cut.


Metal-removing edge on the face of a cutter that travels in a plane perpendicular to the axis. It is the edge that sweeps the machined surface. The flat should be as wide as the feed per revolution of the cutter. This allows any given insert to wipe the entire workpiece surface and impart a fine surface finish at a high feed rate.

wire EDM

Process similar to ram electrical-discharge machining except a small-diameter copper or brass wire is used as a traveling electrode. Usually used in conjunction with a CNC and only works when a part is to be cut completely through. A common analogy is wire electrical-discharge machining is like an ultraprecise, electrical, contour-sawing operation.

Woodruff cutter

Milling cutter used for cutting keyways.

work envelope

Cube, sphere, cylinder or other physical space within which the cutting tool is capable of reaching.

work-squaring bar

Mounts to the table of a contour band machine and automatically squares the work to the blade.


Tendency of all metals to become harder when they are machined or subjected to other stresses and strains. This trait is particularly pronounced in soft, low-carbon steel or alloys containing nickel and manganese—nonmagnetic stainless steel, high-manganese steel and the superalloys Inconel and Monel.

yield point

First stress in a material, usually less than the maximum attainable stress, at which an increase in strain occurs without an increase in stress. Only certain metals exhibit a yield point. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points.

yield strength

Stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2 percent is used for many metals. Compare with tensile strength.

zone melting

Highly localized melting, usually by induction heating, of a small volume of an otherwise solid piece, usually a rod. By moving the induction coil along the rod, the melted zone can be transferred from one end to the other.