Basic Cutting Theory 201

aluminum

A nonferrous, silvery-white metal that is lightweight, highly conductive, and non-magnetic. Aluminum is very soft, so aluminum workpieces may produce continuous chips during cutting operations.

axis

An imaginary straight line that passes through the rotating cylindrical workpiece. The axis, or centerline, divides a shape into two equal halves.

brittle

Difficult to bend, stretch, or form without breaking. Brittle metals tend to produce discontinuous chips.

built-up edge

BUE. Deformed metal that adheres to the cutting edge of the tool under high pressures and temperatures. Ductile metals tend to produce built-up edges.

carbide

A common cutting tool material developed by the combination of carbon with usually chromium, tungsten, or titanium. Carbide, which is used to make both indexable inserts and solid cutting tools, balances hardness and toughness.

cast iron

A metal consisting of iron, over 2.11% carbon, and 1 to 3% silicon. Cast irons are brittle metals that offer heat resistance and compressive strength.

casting

A manufacturing process that involves pouring liquid material into a hollow mold until the material cools into a solidified shape. Casting is one of three general methods used in manufacturing to create metal parts.

centerline

An imaginary line that passes through the center of the rotating cylindrical workpiece. The centerline, or axis, divides a shape into two equal halves.

chip control

The efficient breaking and effective removal of chips. Chip control produces short, curled chips.

chipbreakers

A device that is designed to cause chips to curl and break off. Chipbreakers are often built into cutting tools.

chipping

Tool wear resulting in the loss of small fragments from the cutting edge of the tool. Chipping is often caused by an excessive feed.

chips

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

continuous chips

A chip that does not break apart and instead forms a long, curled string. Ductile metals tend to create continuous chips.

contours

A curved, non-linear dimension created by a cutting process. Contours can be created by precise tool movements in milling.

copper

A reddish-brown metal that is thermally and electrically conductive as well as corrosion resistant. Copper is very ductile, so copper workpieces may produce continuous chips during cutting operations.

crater wear

Tool wear that creates a concave depression in the face of the cutting tool above the cutting edge. Crater wear is named for its shape and appearance.

cutting

A type of machining that removes material from a workpiece in the form of chips. Cutting uses single- or multi-point tools, generally via a machine tool.

deformation boundary

A boundary line where the deformed workpiece separates from the intact workpiece as a cutting tool applies force to the workpiece material. Deformation boundaries on workpieces are where the cutting action takes place.

deforms

Changes shape permanently. Deformed metal has lost its original shape.

depth of cut

The distance that the cutting tool is plunged into the workpiece. Depth of cut indicates the amount of material removed by the cutting tool.

discontinuous chips

A chip that easily fractures from the workpiece into small, separate pieces. Brittle metals tend to create discontinuous chips.

drill bit

A multi-point cutting tool used to machine round holes into workpieces. Drill bits have spiral cutting edges and are usually mounted in drill presses.

drill press

A machining tool that rotates a multi-point cutting tool to make a hole in a workpiece. Drill presses can hold drill bits and other holemaking tools.

drilling

The use of a multi-point tool to machine a new round hole into the surface of a workpiece. Drilling is often performed on a drill press.

ductile

Able to bend, stretch, or form without breaking. Ductile metals tend to produce long, continuous chips.

ductility

The ability of a material to be drawn, stretched, or formed without breaking. Ductility is more common in softer materials.

face mill

A flat mill cutter with multiple cutting teeth surrounding the outside edge. Face mills are used to create flat surfaces.

feed rate

The rate at which the cutting tool and the workpiece move in relation to one another. Feed is typically a linear movement.

fixtures

A customized workholding device used on machine tools to position and hold a part during various machining operations. Fixtures are built to hold a specific part design.

flank wear

Tool wear resulting in the gradual wearing away of the cutting edge. Flank wear is the least problematic and most predictable form of tool wear.

flutes

A spiraling groove on the periphery of a cutter. Flutes allow for chip flow away from the cut.

hard

The degree of a material's resistance to penetration. Hard metals often produce discontinuous chips during cutting operations.

hardness

The ability of a metal to resist scratching, indentation, and penetration. Hardness often indicates low machinability.

insert

A replaceable cutting bit that has multiple cutting edges. Inserts are held in a toolholder.

internal structure

The arrangement of particles or atoms within a material. A metal's internal structure deforms at the boundary line where cutting takes place.

lathe

A machine tool used to create cylindrical parts. A lathe holds a cylindrical workpiece on one or both ends while a single-point cutting tool is gradually passed along the surface of the rotating part.

low-carbon steel

A carbon steel that contains less than 0.30% carbon. Low-carbon steel, which is sometimes referred to as mild steel, is the most commonly welded metal.

machinability

The relative ease with which material can be removed from a workpiece by machining processes such as cutting or grinding. Machinability depends on the properties of the workpiece material.

machining

The process of removing material to form or finish a part. Machining includes processes such as metal cutting, water-jet cutting, and electrical discharge machining (EDM).

medium-carbon steels

A carbon steel that contains between 0.30% and 0.45% carbon. Medium-carbon steels are stronger and harder than low-carbon steels.

metal fabrication

A material manufacturing process that produces parts by mechanically deforming metal. Stamping and forging are two major types of metal fabrication processes.

milling

A machining operation that uses a rotating multi-point cutter to remove metal from the surface of a workpiece. Milling includes a wide range of versatile metal cutting operations.

milling machine

A machine that uses a multi-point milling cutter to perform various cutting operations. Milling machines are commonly used to machine slots, grooves, and flat surfaces in rectangular workpieces.

milling machine

A machine tool used to perform milling and other cutting operations. Milling machines utilize multi-point cutting tools.

molds

A hollow cavity used in metal casting to shape material. Molds are filled with liquid metal, which takes the shape of the mold as it solidifies.

multi-point cutting tools

A machining tool that has two or more cutting edges. Multi-point cutting tools include mills and drills.

negative rake angle

A rake angle producing a top surface of the cutting edge that slopes up and towards the centerline of the workpiece. Negative rake angles position the tool beyond a line perpendicular to the workpiece.

perpendicular

Two lines or axes that meet at right angles. Perpendicular lines are positioned at 90°, right angles to each other.

positive rake angle

A rake angle producing a top surface of the cutting edge that slopes down and away from the centerline of the workpiece. Positive rake angles position the tool behind a line perpendicular to the workpiece.

properties

The characteristics of a material that distinguish it from other materials. Properties include aspects such as hardness, toughness, and ductility.

rake angle

The angle between the front of the cutting tool and a line perpendicular to the workpiece surface. Rake angles measure how far the front of the tool is from the workpiece axis.

relief angle

The angle that is formed by the surface of the workpiece and the bottom end of the cutting tool. Relief angles measure how much space exists between the bottom of the tool and the workpiece surface.

shear forces

A force that attempts to cause the internal structure of a material to slide against itself. Enough shear force will cause the material to separate.

shear strain

The deformation that occurs due to forces that attempt to cause the internal structure of a material to slide against itself. Shear strain forms during metal cutting when a tool creates a chip.

single-point cutting tools

A machining tool that has one cutting edge. Single-point cutting tools are used primarily for operations on the lathe.

slab mill

A cylindrical milling cutter with multiple cutting edges spiraling down its sides. Slab mills often do not require carbide inserts to provide a cutting edge.

soft

Able to be easily scratched, indented, or penetrated. Softness can also be characterized as a lack of hardness.

speed

The rate that the cutting tool or workpiece moves at the point of contact. Speed generally measures a rotational movement.

strength

The ability of a material to resist forces that attempt to break or deform it. Strength generally indicates low machinability.

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.

tool chatter

Vibrations of the cutting tool on the workpiece surface. Tool chatter causes surface imperfections on the workpiece.

tool failure

The point at which a cutting tool can no longer be used for its intended application. Tool failure includes tool breakage.

tool life

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

tool wear

The rate at which the cutting edge of a tool wears away during machining. Tool wear rates increase with cutting materials that have low machinability.

toolholders

A mechanism used to rigidly hold a cutting tool in place during machining. Toolholders are available in standardized sizes and classified so they are paired with the correct style of cutting tool.

turning

The machining process used to make cylindrical parts. Turning is commonly performed on a lathe with a single-point cutting tool.

worktable

The part of a machine tool that supports the workpiece and any workholding devices. Worktables are an important component of mills.

zero rake angle

A rake angle producing a top surface of the cutting edge completely perpendicular to the centerline of the workpiece. Zero rake angles are 90° from the workpiece axis.