additives

A substance that has been intentionally added to a metal to improve its properties. Additives often improve machinability.

aluminum alloys

A silvery white metal that is soft, light, and has a high strength-to-weight ratio. Aluminum alloys contain a blend of metals and have high machinability ratings.

American Iron and Steel Institute

AISI. An organization that issues general classification standards for irons and steels. The American Iron and Steel Institute assigns machinability ratings to a wide variety of materials.

B-1112

A particular grade of steel that acts as the standard for machinability ratings. B-1112 steels have a 1.00 machinability rating.

bismuth

A white, brittle metal with a pinkish tinge. Bismuth may be added to steel to improve machinability.

boring

The use of a single-point cutting tool to enlarge an existing hole. Boring operations, which are programmed in sfm (m/min), help to create a hole that is concentric and that meets tight tolerances.

carbide

A common cutting tool material used to make both indexable inserts and solid cutting tools. Carbide is very hard and difficult to machine by traditional methods.

carbon

A common, nonmetallic element found in all types of steel. Carbon is the main hardening element in steel.

case hardening

The heating of a metal within a carbon-rich environment to increase carbon levels on the metal surface. Case hardening creates a hardened exterior shell.

catastrophic tool failure

The sudden and complete loss of tool performance. Catastrophic tool failure can be the result of gradual degradation and intermittent failure.

centerline

An imaginary line that runs through the center of a cylindrical workpiece and around which the workpiece rotates. Centerlines are at a 90° angle to a lathe's headstock.

chip

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

chucks

A workholding component used to locate and clamp the workpiece as it rotates. Most chucks have three moveable jaws and are mounted in the spindle.

clamping force

The compressive force that holds a workpiece in place. Clamping forces resist secondary tool forces.

CNC machine

Computer Numerical Control machine. A sophisticated, precise machine tool run by a computer that requires a programmed speed and feed rate value. CNC machines are very rigid and are capable of fast cutting speeds.

cold working

The shaping of metal at temperatures much lower than the metal's molten state. Cold working of steel is done at room temperature.

collets

A device with a hole at its center through which the workpiece passes and that holds the rotating workpiece in place. Collets are designed to hold specific dimensions.

computer numerical control machines

CNC machines. A sophisticated, precise machine tool run by a computer that requires a programmed speed and feed rate value. Computer numerical control machines are very rigid and are capable of fast cutting speeds.

constant

A variable or number that does not change value. The English constant 3.82 or the metric constant 318.3 is used in lathe speed conversion formulas.

constant surface speed

CSS. A setting on a CNC lathe that adjusts the spindle rpm as the tool travels toward and away from the spindle's axis. Constant surface speed keeps surface feet per minute (m/min) consistent.

continuous chips

A chip that does not break apart and instead forms a long, curled string. Continuous chips are often created when machining ductile metals.

cutting

The use of single- or multi-point tools to separate metal from a workpiece in the form of chips. Cutting processes vary based on the requirements of a finished part.

cutting edge strength

The ability of an insert edge to resist deformation. Cutting edge strength is affected by rake and relief angles.

cutting forces

A force generated by the motion of the cutting tool and the resistance of a workpiece. Cutting forces are affected by rake and relief angles.

cycle time

The time it takes to perform a single task. Cycle time may refer to the time it takes to make one part or to perform one step in a process.

depth of cut

The distance to which the cutting tool plunges into the workpiece. Depth of cut indicates the amount of material that is removed by one pass of the cutting tool.

diameter

d. The distance from one edge of a circle to the opposite edge that passes through the center. Diameter measurements are required with round or cylindrical features.

drilling

Using a multi-point tool to machine a new round hole into the surface of a workpiece. Drilling operations, which require a constant rpm, can be done on a drill press, lathe, or mill.

ductility

A material's ability to be drawn, stretched, or formed without breaking. Ductility is more common in softer metals.

engine lathe

The original and most basic type of manual lathe. Engine lathes are often used for short production runs and customized work.

facing

A turning operation that removes material from the end of the rotating cylindrical part. Facing operations, which are programmed in sfm (m/min), are usually performed to establish a part's length.

feed

The rate that the cutting tool travels along the length of the workpiece. Feed measures a linear movement.

free-machining steels

A particular grade of steel that has small amounts of additional alloying elements to improve machinability. Free-machining steels may include added bismuth or sulfur.

hardness

The ability of a material to resist scratching, indentation, or penetration. Increased hardness in a material can generate more heat and make it more difficult to machine.

high-speed steel

HSS. An inexpensive cutting tool material that has a high toughness. High-speed steel is tougher than carbide but offers less hardness and wear resistance.

horsepower

hp. A unit of power used to describe machine strength. Increased horsepower allows a machine's spindle to exert a greater amount of force.

hydraulic-operated chucks

A workholding device with moveable jaws that uses pressurized liquid to increase its clamping force and rigidity. Hydraulic-operated chucks are safer to operate at higher speeds than traditional chucks.

inches per minute

ipm. The distance in inches that the entire tool advances in one minute. Inches per minute is a measurement of feed of a rotating cutting tool on the lathe.

inches per revolution

ipr. The distance in inches that the tool advances during one complete revolution of the workpiece. Inches per revolution is a measurement of feed on the lathe.

inclusions

A substance that is unintentionally present in a metal and often has undesirable properties. Inclusions tend to be harder than the metal itself and reduce machinability.

Inconel

A superalloy made of nickel and chromium that is designed to perform well in extreme environments. Inconel is very difficult to machine and resists both oxidation and corrosion.

ipr

Inch per revolution. The distance in inches that the tool advances during one complete revolution of the workpiece. Inch per revolution is a measurement of feed on the lathe.

lathe

A machine tool that is used to produce a range of cylindrical workpieces. On a basic lathe, the part rotates in a spindle while the cutting tool is guided along its exterior diameter or into the part to create a hole located on the part's centerline.

lead

A bluish white metal that is very soft and ductile. Lead can be added to steel to improve machinability, but it is less desirable because of the risk of lead poisoning.

live tooling

Rotating power-driven cutting tools, such as end mills and drills, that are held in the turret of a lathe. Live tooling can perform machining operations off the part centerline while the workpiece is held stationary in the spindle.

m/min

Surface meters per minute. The distance in meters that the workpiece surface travels in one minute. Surface meters per minute, which is a metric measurement for speed, depends on workpiece size and rpm.

machinability

The ability of a metal to be cut and shaped by machine processes such as cutting, grinding, turning, or drilling. Machinability indicates the relative ease with which a metal can be machined.

machinability rating

The ease with which a cutting process is able to machine a material as rated on a scale with 1.0 as the standard. A machinability rating that falls below 1.0 indicates a material is more difficult to machine, and a rating above 1.0 indicates a material is more easily machined.

millimeters per minute

mm/min. The distance in millimeters that the entire tool advances in one minute. Millimeters per minute is a metric measurement for feed of a rotating cutting tool on the lathe.

millimeters per revolution

mm/rev. The distance in millimeters that the tool advances during one complete revolution of the workpiece. Millimeters per revolution is a metric measurement for feed on the lathe.

milling

A cutting operation in which a rotating multi-point cutting tool is fed along a part's surface to remove material. Milling operations are very versatile and generally produce flat surfaces.

mm/rev

Millimeter per revolution. The distance in millimeters that the tool advances during one complete revolution of the workpiece. Millimeters per revolution is a metric measurement for feed on the lathe.

off-center drilling

A holemaking process that makes a round hole at any location on a part that deviates from the part's centerline. Off-center drilling can sometimes be performed a lathe with live tooling.

overcutting

Removing too much workpiece material during a machining process. Overcutting is a result of excessive feed rates.

part program

A series of digitized instructions used by a CNC machine. Part programs guide the machine tool to perform the necessary sequence of operations to machine a specific workpiece.

pi

A special constant value that relates the diameter of a circle to its circumference. Pi is roughly 3.14 and is used to find the circumference and area of a circle.

pneumatic-operated chucks

A workholding device with moveable jaws that uses air pressure to increase its clamping force and rigidity. Pneumatic-operated chucks are safe at higher speeds than traditional chucks.

rake angles

An angle formed by the face of the tool and a line parallel to the floor when viewed from the side facing the end of the workpiece. Rake angles affect cutting forces and contact between the tool and workpiece.

relief angles

An angle formed by the surface of the workpiece and the bottom end of the cutting tool. Relief angles influence tool wear rates and cutting edge strength.

revolutions per minute

rpm. The number of revolutions that a spindle or cutting tool completes in one minute. Revolutions per minute is a measurement of speed in both English and metric systems.

rigidity

The quality of a workpiece, machine, or machine setup characterized by being stiff and inflexible. Improved rigidity reduces vibration.

rpm

Revolutions per minute. The number of revolutions that a spindle or cutting tool completes in one minute. Revolutions per minute is a measurement of speed in both English and metric systems.

sfm

Surface feet per minute. The distance in feet that the workpiece surface travels in one minute. Surface feet per minute, which is an English measurement for speed, depends on workpiece size and rpm.

shear region

The area on a workpiece where a cutting tool cuts and separates the workpiece into smaller sections. Shear regions are sometimes created during workhardening processes.

single-point tool

A machining tool that has one cutting edge. Single-point tools are often used in turning and boring operations.

softness

The ability of a material to be scratched, indented, or penetrated by another material. Softness will affect a material's machinability rating.

speed

The rate that the workpiece surface and cutting tool pass each other at the point of contact. Speed on a lathe refers to the rotation of the workpiece in the spindle.

spindle

The part of the machine tool that spins. Spindles hold the workpiece on lathes.

standard

A unit of measurement to which other units are compared. The standard for a material's machinability rating is 1.0, which corresponds with the rating for steel grade B-1112.

strength

The ability of a material to resist forces that attempt to break or deform it. Increased strength in materials can make them more difficult to machine.

sulfur

A pale, yellow, brittle element. Sulfur is often added to steel in order to improve machinability.

superalloy

An alloy consisting of numerous alloying elements that is very expensive and designed to perform well at elevated temperatures. Superalloys have very high hardness and low machinability ratings.

surface feet per minute

sfm. The distance in feet that the workpiece surface travels in one minute. Surface feet per minute, which is an English measurement for speed, depends on workpiece size and rpm.

surface finish

The degree of smoothness of a part's surface after it has been manufactured. Surface finish is the result of the surface roughness, waviness, and flaws remaining on the part.

surface meters per minute

m/min. The distance in meters that the workpiece surface travels in one minute. Surface meters per minute, which is a metric measurement for speed, depends on workpiece size and rpm.

threading

The process of cutting a long, spiraling groove into a workpiece with a single-point tool. Threading operations, which require a constant rpm, are essential for the creation of fasteners.

tolerances

An unwanted but acceptable deviation from a given dimension. Tolerances indicate the allowable difference between a physical feature and its intended design.

tool life

The length of time that a cutting tool can function properly before it begins to fail. Tool life is affected by several different cutting variables.

tool wear

The rate at which the cutting edge of a tool wears away during machining. Tool wear greatly affects manufacturing costs.

turning

A machining operation that rotates a cylindrical workpiece while a single-point tool is guided along the length of the part. Turning operations are performed on a lathe and are programmed in sfm (m/min).

turning

A machining operation that rotates a cylindrical workpiece while a single-point tool is guided along the length of the part. Turning operations are performed on a lathe and programmed in surface feet per minute (sfm) or meters per minute (m/min).

undercutting

Removing an insufficient amount of workpiece material during a machining process. Undercutting is a result of excessive feed rates.

work hardening

Increasing the hardness of a metal by bending or shaping. Work hardening includes cold working and case hardening processes.

workholding device

A device used to support, locate, and hold a workpiece during machining. Workholding devices accurately reference the tool performing the operation on the part being held.