Lathe Tool Geometry 351

alloys

A metal with purposefully added elements to enhance its mechanical and physical properties. Alloys can also refer to elements added to metal.

alphanumeric

Containing both letters and numbers. Both ANSI and ISO use alphanumeric symbols to categorize carbide cutting tools.

aluminum

A silver-white metal that is light and thermally conductive. Aluminum is a ductile metal that is prone to forming long, stringy continuous chips.

American National Standards Institute

ANSI. A private, nonprofit organization that administers and coordinates voluntary standards and systems. The American National Standards Institute provides a classification system for carbide cutting tools using a detailed alphanumeric label for tool geometry and for cutting inserts that details characteristics such as size, shape, and tolerance.

back rake angle

The angle formed by the face of the tool and a line parallel to the floor, if viewed from the side facing the end of the workpiece. A positive back rake angle tilts the tool face back and away from the workpiece, and a negative angle tilts it forward and toward the workpiece.

brittle

A material's resistance to being stretched, formed, or drawn. Brittle materials fracture easily but produce discontinuous chips.

BUE

Built-up edge. The unwanted rough edge on a cutting tool created when pieces of the workpiece pressure weld on the tool edge during cutting. BUE can reduce the quality of the finished cut.

built-up edge

BUE. The unwanted rough edge on a cutting tool created when pieces of the workpiece pressure weld on the tool edge during cutting. A built-up edge can reduce the quality of the finished cut.

carbide

A common cutting-tool material used to make both indexable inserts and solid cutting tools. Carbide tools are very hard and wear resistant.

cast iron

An alloy of iron, carbon, and silicon that contains at least 2.0% carbon. Cast iron is a hard, brittle material that is usually turned on the lathe with tools set at negative rake angles.

centerline

An imaginary line that divides a shape into two equal halves or that runs through the center of a cylindrical object. A centerline can bisect a workpiece along its length or along its width.

chatter

Vibrations of the cutting tool that cause surface imperfections on the workpiece. Chatter is more common when using cutting tools at negative rake angles.

chipbreaker

An insert feature designed to prevent chips from forming into long pieces. A chipbreaker is either an indentation in the surface of a cutting insert or a wafer clamped above the insert in the toolholder.

chips

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

clearance angle

The angle that determines how much of the bottom edge of an insert's flank is in contact with the surface of a workpiece. A clearance angle, also known as a relief angle, helps determine the strength of a cutting edge.

continuous chips

A chip that does not break apart and continues to fold in on itself. Ductile materials tend to create continuous chips.

corners

A part feature where two or more sides come together, often at 90° angles. Corners are often cut using negative lead angles.

cratering

Tool wear characterized by depressions in the face of the cutting tool adjacent to the cutting edge. Cratering can be caused by machining with an excessively large end cutting edge angle.

cubic boron nitride

CBN. A type of cutting-tool material offering a hardness that is second only to diamond. Cubic boron nitride tools are very effective at machining hard materials, such as cast iron, but they are also very expensive.

cutoff

A shearing operation that creates a single cut to separate a piece of metal from the original stock. Cutoff operations can be performed on a lathe using the end flank of a rectangular insert.

cutting edge

The leading edge of a cutting tool that is in direct contact with the workpiece and performs metal removal. A cutting edge must be positioned carefully using tool geometry to create an efficient machining operation.

cutting forces

The various stresses involved in a machining process. Cutting forces are determined by a combination of speed and feed rate, tool angle, workpiece material, and other factors.

cutting tool

Devices made of hard, tough material that are used to remove metal by creating chips. A cutting tool can be protected from premature wear through the use of proper tool geometry.

depth of cut

The measurement of how far a cutting tool penetrates the workpiece. Depth of cut is the distance from the uncut surface to the machined surface.

diamond

A naturally occurring or manufactured stone made of crystalline carbon that is used as a cutting-tool material because of its extreme hardness. Diamond cutting tools should be used at negative rake angles because of their hardness.

discontinuous chips

A chip that easily fractures from the workpiece into a small, separate piece. Brittle materials tend to create discontinuous chips.

ductile

The measure of a material's ability to be stretched, drawn, or formed without fracturing. Ductile metals are easier to cut but produce continuous chips.

end cutting edge angle

The angle formed by the end flank of the tool and a line parallel to the workpiece centerline, if viewed from above looking down on the cutting tool. Increasing the end cutting edge angle tilts the far end of the end flank away from the workpiece.

end flank

The flat surface of the tool pointing away from the toolholder. The end flank is used to cut when the tool is plunged into the workpiece, particularly during grooving and parting operations.

end relief angle

The angle formed by the end flank of the tool and a vertical line down to the floor, if viewed from the side facing the end of the workpiece. Increasing the end relief angle tilts the end flank away from the workpiece.

face

The flat surface of a single-point tool into which the workpiece rotates during a turning operation. On a typical turning setup, the face of the tool is positioned upward.

facet angle

The angle created between the primary cutting edge and the workpiece in the direction of the feed. Facet angle is a feature described in an insert number.

facing

A lathe operation that feeds a single-point cutting tool across the end of a cylindrical workpiece to create a flat surface. Facing is often performed with tools set at a negative lead angle.

feed

The rate at which the cutting tool and/or the workpiece move in relationship to one another. Feed is often measured in inches per minute (ipm) or millimeters per minute (mm/min).

finishing

A final metal-cutting pass that emphasizes tight tolerances and smooth surface finish. Finishing is most often done with tools set at larger relief angles with positive rake angles.

flank wear

Tool degradation resulting from abrasion that occurs along the flank or flanks of the tool. Flank wear is the preferred form of tool degradation, but it can occur prematurely when a tool is operated at an excessively negative rake.

flanks

A flat surface of a single-point tool that is adjacent to the face of the tool. During turning, the side flank faces the direction that the tool is fed into the workpiece, and the end flank is the edge facing away from the toolholder.

fracture

The breaking of an object into two or more pieces as a result of prolonged stress or a sudden impact. Fracture is more common in hard, brittle cutting tools.

grooving

A machining operation performed on a lathe that cuts a narrow channel into a rotating cylindrical workpiece. Grooving is often performed with a rectangular cutting insert.

hard

A material's ability to resist penetration, indentation, and scratching. Hard metals require greater cutting forces but produce discontinuous chips when machined.

hardness

A material's ability to resist indentation or scratching. An increase in hardness generally lead to a decrease in toughness.

high-speed steel

HSS. A cutting-tool material made of iron alloyed with a large percentage of carbon and other metals. High-speed steel is tougher than carbide but offers less hardness and wear resistance.

HSS

High-speed steel. A cutting-tool material made of iron alloyed with a large percentage of carbon and other metals. HSS is tougher than carbide but offers less hardness and wear resistance.

inches per minute

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

indexable

A cutting tool with multiple edges that can be rotated into place. For indexable inserts, when one cutting edge wears out, an operator can turn the insert to expose a new cutting edge.

insert

An indexable and replaceable cutting tool with a geometric shape that has multiple cutting surfaces. Inserts for machining on a lathe are most commonly made of carbide.

insert numbers

A series of numbers and/or letters used to describe a cutting tool insert. Insert numbers usually refer to the ANSI insert identification number in the United States, but they can also refer to the ISO insert number.

internal threading

The process of cutting a long, spiraling groove into the interior of a cylindrical workpiece. Internal threading can be done on the lathe using a tool set at a negative lead angle.

International Organization for Standardization

ISO. An international organization that establishes standards and guidelines for various products and processes. The International Organization for Standardization provides an alphanumeric labeling system to describe tool geometry and a system to describe cutting inserts.

lathe

A machine tool that is used to produce a range of parts from a cylindrical workpieces. On a basic lathe, the workpiece is rotated in the spindle while the cutting tool is guided along the workpiece to create a finished part.

lead angle

The angle formed by the shank of the toolholder and a line perpendicular to the workpiece centerline, if viewed from above looking down on the cutting tool. The lead angle is always equal to the side cutting edge angle.

low-carbon steels

A plain carbon steel that contains less than 0.30% carbon. Low-carbon steels are prone to developing BUE, which can be reduced by turning them with tools set at positive rake angles.

metal cutting

A machining process that uses a tool to remove metal from a workpiece. Metal-cutting processes include turning, milling, and drilling.

metals

A naturally occurring material with high electric and thermal conductivity, luster, density, and strength. Metals include copper, iron, nickel, steel, and lead.

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 cutting tool on the lathe.

negative back rake

An angle formed between the tool face and workpiece centerline when the face is tilted up and toward the workpiece. A negative back rake helps reduce the formation of continuous chips.

negative side rake

An angle formed between the tool face and the longitudinal centerline of the workpiece when the face is tilted up and toward the workpiece. A negative side rake offers greater cutting-edge strength when machining.

nose radius

The degree of roundness between two cutting edges of a tool. The nose radius is an important factor in the service life of a tool and surface finish quality.

operators

A person trained to run a specific machine. Operators are responsible for helping ensure that a machine runs properly, efficiently, and safely.

positive back rake

An angle formed between the tool face and workpiece centerline when the face is tilted away from the workpiece. A positive back rake helps limit the cutting forces generated between the tool and workpiece.

positive rake angles

The angle formed by the face of the tool and the centerline of the workpiece when the face of the tool is tilted away from the workpiece and down toward the floor. Positive rake angles reduce cutting forces but encourage the formation of long, stringy chips.

positive side rake

An angle formed between the tool face and the longitudinal centerline of the workpiece when the face is tilted down and away from the workpiece. A positive side rake can help improve surface finish.

relief angle

The angle that determines how much of the bottom edge of an insert's flank is in contact with the surface of a workpiece. A relief angle, also known as a clearance angle, helps determine the strength of a cutting edge.

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. Machines or workpieces with poor rigidity should be machined using negative lead angles.

roughing

A cutting pass that emphasizes high material removal rate over the quality of surface finish or accuracy. Roughing is often performed with tools set at negative rake angles.

service life

The length of time a cutting tool is expected to be operational before it must be replaced. Service life can be extended through the use of proper tool geometry.

setups

All the necessary preparation of tooling and fixturing that occurs on a machine before a cutting operation begins. Setups include consideration and implementation of tool geometry.

shank

The long, rectangular section of the toolholder that is clamped to the lathe turret. The shank helps determine the side cutting edge angle of the tool.

shoulders

An angled surface similar to a chamfer created by turning on a lathe. Shoulders are often machined using negative lead angles.

side cutting edge angle

The angle formed by the side flank of the tool and a line parallel to the shank of the toolholder, if viewed from above looking down on the cutting tool. A positive side cutting edge angle moves the side flank into the cut, and a negative angle moves the side flank out of the cut.

side flank

The flat surface of the cutting tool that faces the direction the cutting tool is fed against the workpiece. The side flank is responsible for the majority of material removal in metal-cutting operations.

side rake angle

The angle formed by the face of the tool and the centerline of the workpiece, if viewed from behind the tool down the length of the toolholder. A positive side rake angle tilts the tool face down toward the floor, and a negative angle tilts the face up and toward the workpiece.

side relief angle

The angle formed by the side flank of the tool and a vertical line down to the floor, if viewed from behind the tool down the length of the toolholder. Increasing the side relief angle tilts the side flank away from the workpiece.

single-point tooling

Machining with a tool that uses one cutting edge at a time. Single-point tooling is often used in turning and boring operations.

speed

The rate at which the surface of the workpiece rotates past the cutting edge of a tool at the point of contact. Speed is often measured in revolutions per minute (rpm).

stainless steels

A type of steel that contains more than 11% chromium and exhibits excellent corrosion resistance. Stainless steels should be cut on a lathe with tools at a positive rake angle to prevent work hardening.

strength

The ability of a material to resist outside forces that are trying to break or deform it. Strength is an important factor in determining the service life of a tool.

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 measured surface profile characteristics of a completed workpiece. Surface finish can be improved through tool geometry.

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 cylindrical workpiece. Threading can be either external or internal and is often performed using a single-point cutting tool on the lathe.

tolerance

An unwanted but acceptable deviation from a given dimension defined by a blueprint. Tolerance of an insert is one of the features described by an insert number.

tool geometry

The collective angles formed by the dimensions of the cutting tool and the positioning of the tool. Tool geometry is a key factor in tool service life, the surface finish of a part, and machining efficiency.

tool signature

The numerical code that describes all the key angles of a given cutting tool. A tool signature may be used for cutting inserts or tool bits.

toolholder

A device used to hold a cutting tool in place during machining. The position of a toolholder is key to ensuring an efficient cutting operation.

toughness

The ability of a material to absorb energy without breaking or fracturing. Tough cutting tools are able to withstand sudden stresses but are less hard.

tracing

A cutting operation that involves making very shallow cuts into a workpiece. Tracing is often done with cutting tools that have small or no nose radii.

turning

A machining operation where a cylindrical workpiece is rotated while a single-point tool is guided along the length of the part. Turning is a common machining operation performed on the lathe.

work hardening

An increase in the hardness of a metal due to plastic deformation during a cold working or machining process. Work hardening is less common when using positive rake angles because they generate lower temperatures and cutting forces.

workpiece

A part that is subjected to one or more manufacturing procedures such as welding, machining, or casting. Workpiece material is often a key consideration in determining tool geometry.