Introduction to End Mills 255

additives

A substance added in small amounts to another substance or material. Additives change or improve a cutting fluid’s abilities to reduce friction and prolong tool life.

AE

The amount of the cutter diameter that is engaged with the workpiece. AE, also known as radial depth of cut or step-over, is generally 75% or less of the cutter diameter.

AP

The amount of peripheral cutting edges that are engaged with the workpiece in a single pass. AP, also known as axial depth of cut, measures how far the peripheral cutting edges cut into the workpiece surface.

axial depth of cut

The amount of peripheral cutting edges that are engaged with the workpiece in a single pass. Axial depth of cut, sometimes called AP, measures how far beneath the workpiece surface the peripheral cutting edges penetrate.

axial forces

The amount of stress the tool experiences along the tool’s axis. Axial forces can pull the tool out of the toolholder if they become excessive.

axis

An imaginary straight line that runs through the center of an object. An end mill rotates around its axis.

ball end mill

An end mill with a fully rounded end. Ball end mills cut rounded edges and complex three-dimensional shapes into workpieces.

body

The portion of the tool that enters the workpiece. The body includes the length of cut, end face, and flutes.

brittle

Hard and more likely to break instead of bend when subjected to force or pressure. Brittle tool materials include powdered metal and carbide.

carbide

A common cutting tool material developed by combining carbon with materials like chromium, tungsten, or titanium. Carbide is used in metal cutting tools for its hardness and wear resistance.

chip

A piece of metal that is removed from a workpiece during a machining operation. Chips are tiny curls, shards, fragments, shavings, or particles of metal.

chip load

The linear distance traveled by the cutter during the engagement of a single cutting tooth. Chip load, which is also known as feed per tooth, determines how much material a single cutting tooth removes in one rotation of the tool.

CNC

Computer Numerical Control. A combination of software and hardware that directs the operation of a machine tool. CNC machines are much more precise than their manual counterparts.

coatings

A thin layer of material added to the surface of a cutting tool. Coatings have a range of beneficial attributes, such as reducing friction and adding hardness on cutting edges.

cobalt

HSS-E. A hard, gray, brittle metal often used to create cutting tools. Cobalt is harder but less tough than high-speed steel and tougher but less hard than carbide.

collet

A slotted device that grips a cylindrical object. Collets used for toolholding are designed to hold tools with specific dimensions.

computer numerical control

CNC. A combination of software and hardware that directs the operation of a machine tool. Computer numerical control machines are much more precise than their manual counterparts.

contours

A curved surface or dimension that is cut into a workpiece. Contours are often created with end mills.

coolant

Any fluid used to cool, lubricate, and clear chips during metal cutting. Coolant, usually known as cutting fluid, can be made of oil, water, synthetic fluids, or a combination of these.

corner chamfer end mill

An end mill with an angled face between the peripheral cutting edges and the end face. Chamfer end mills cut angled edges into workpieces.

corner radius end mill

An end mill with a rounded face between the peripheral cutting edges and the end face. Corner radius end mills cut features with rounded edges into workpieces.

cutter diameter

The maximum width of an end mill’s cutting edges. Cutter diameter determines how wide of a cut an end mill can make in a single pass.

cutting edges

The leading face of a cutting tool that is sharp and comes into direct contact with the workpiece. The cutting edge performs the actual metal removal during a cutting operation.

cutting fluid

Any fluid used to cool, lubricate, and clear chips during metal cutting. Cutting fluid, sometimes known as coolant, can be made of oil, water, synthetic fluids, or a combination of these.

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 speed

The amount of workpiece material a cutting edge contacts in one minute. Cutting speed, sometimes called surface speed, is measured in surface feet per minute (SFM) or meters per minute (m/min).

cutting variables

Adjustable factors that affect how a cutting tool removes material during a machining operation. Cutting variables include speed, feed, and depth of cut.

deflection

The unintended movement or deviation of a tool due to the application of mechanical force. Deflection of a tool can cause inaccurate dimensions.

depth of cut

DOC. The amount of an end mill’s cutting edges that are engaged with the workpiece in a single pass. Depth of cut can be measured both axially and radially on an end mill.

emergency stop

E-stop. A button that machine operators can press to immediately shut off a machine in case of emergency. Emergency stop buttons are large, red, and generally placed on a yellow background for quick and easy location and identification.

end face

The cutting edges on the bottom of an end mill. The end face is important in a variety of end milling operations, including creating contours.

end mill

A cylindrical, fluted milling cutting tool that cuts with its bottom and side cutting edges. End mills can be used to machine complex features like grooves, slots, circular slots, pockets, and contours.

extended length

The length that a tool extends from the toolholder. Extended length greatly influences the likelihood of deflection.

features

A distinguishing characteristic that performs a function on a part. Features created by end mills include profiles, contours, slots, and pockets.

feed

The rate at which the cutting tool travels along the length of the workpiece. Feed measures linear movement.

feed per revolution

fpr. The linear distance that a tool advances during one rotation of the workpiece or cutting tool. On the mill, fpr may be used to convert feed per tooth (fpt) to either inches per minute (ipm) or millimeters per minute (mm/min).

feed per tooth

fpt. The linear distance traveled by the cutter during the engagement of a single cutting tooth. Feed per tooth, which is also known as chip load, determines how much material a single cutting tooth removes in one rotation of the tool.

finishing

A cutting pass that emphasizes tight tolerances and smooth surface finish. Finishing removes only a small amount of material.

flutes

A set of recessed grooves on the periphery of an end mill. Flutes allow chips to evacuate the cutting area.

friction

A force that resists motion between two objects that are in contact with each other. Friction occurs when a tool cuts into a workpiece, which generates heat.

grain structure

The size, structure, and orientation of small, hard particles in a metal or alloy. Grain structure helps determine the properties of a metal.

hard

A material’s ability to resist indentation or scratching. Cutting tool materials must have higher hardness than workpiece materials, but high hardness generally means high brittleness and low toughness.

heat resistance

The ability to resist degradation when under extreme heat. Heat resistance is important for end mills, which are exposed to high levels of friction and heat during the milling process.

helix angle

The angle formed by the slant of a flute and the tool’s axis. The helix angle on an end mill determines the strength of the cutting edges as well as how effectively the tool can evacuate chips.

high-speed steel

HSS. A category of tool steels used for cutting tools. High-speed steel is an inexpensive material with high toughness.

impact resistance

The ability of a material to withstand sudden shock or impact. Impact resistance indicates the amount of impact a material can withstand without deforming or breaking.

inches per minute

ipm. An Imperial measurement that indicates how far in inches a tool advances in one minute. Inches per minute measures feed.

indexable inserts

A cutting tool with multiple edges that can be rotated into place as others wear down. Indexable inserts are often made of carbide.

length of cut

The length of the peripheral cutting edges. Length of cut determines how deeply the end mill can cut with its peripheral cutting edges in a single pass.

length-to-diameter ratio

L/D ratio. A numerical value comparing the length of a cylindrical tool or workpiece with its diameter. Higher length-to-diameter ratios offer less rigidity.

locked out

Isolated from power sources and de-energized of stored energy. OSHA requires employees to follow strict safety procedures for a machine to be locked out.

machine guards

A shield or cover over hazardous areas on a machine. Machine guards prevent accidental contact with body parts and prevent debris, such as chips, from exiting the machine.

machine tools

A power-driven piece of equipment for cutting or forming metal or other materials, such as lathes, mills, and presses. Machine tools can hold a variety of cutting and manufacturing tools.

machining

A manufacturing process that uses cutting tools to remove material to form an object. Machining includes methods like milling, turning, and drilling.

manual mills

A machine that uses a rotating, multi-point cutting tool to remove material from a workpiece. Manual mills require an operator to control machine movements and adjust settings.

mechanical forces

A stress that attempts to bend, stretch, break, or indent a material. Mechanical forces during milling operations can result in tool deflection.

meters per minute

m/min. A metric measurement of cutting speed that describes the distance that a cutting edge travels in one minute as it contacts the workpiece. Meters per minute depends on both the cutter diameter and RPM.

millimeters per minute

mm/min. A metric measurement that indicates how far in millimeters a tool advances in one minute. Millimeters per minute measures feed.

milling

A metal cutting operation that uses a rotating multi-point tool to remove metal from the surface of a workpiece. Milling is used to produce a variety of workpiece shapes and features, including contours, slots, and flat surfaces.

multi-point tools

A metal cutting tool that has two or more cutting edges. Multi-point tools include end mills and other milling tools.

optimize

To operate at rates that are simultaneously beneficial. Optimized cutting variables allow the machine to complete tool movements that create accurate parts and minimize tool wear.

overall length

The length from one end of an end mill to the other. Overall length is an important factor in selecting the correct end mill for a given operation.

part program

A series of alphanumerical instructions that the computer of a CNC machine interprets to guide the machine movements. Part programs direct a CNC machine to perform the necessary sequence of operations to machine a specific workpiece.

peripheral cutting edges

The cutting edges along the side of an end mill. Peripheral cutting edges are important in a variety of end milling operations, including creating slots and pockets.

personal protective equipment

PPE. Safety equipment that workers wear or use to prevent injury in the workplace. Personal protective equipment includes safety glasses, steel-toed boots, and hardhats.

plain shank

A type of tool shank with a smooth, cylindrical surface throughout. Plain shanks typically must use collets as toolholders.

pockets

An interior recess that is cut into the surface of a part. Pockets can be circular, rectangular, or irregular.

powdered metal

HSS-PM. A type of tool material created by applying heat and pressure to metal powder. Powdered metal tools are harder and more wear resistant but less tough than high-speed steel.

profiles

The shape or outline of a part feature. Profiles can be linear, angled, or contoured depending on part specifications.

properties

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

radial depth of cut

The amount of the cutter diameter that is engaged with the workpiece in a single pass. Radial depth of cut, also known as stepover or AE, is generally 75% or less of the cutter diameter.

radius

A measurement of the distance between the outer edge of a cutting tool and its center. Knowing the radius of an end mill is essential for cutting accurate circular features in a workpiece.

revolutions per minute

RPM. A measurement of speed that tracks how many times a machine component rotates in one minute. Revolutions per minute measures the spindle speed on a milling machine.

rigidity

The quality of being stiff and inflexible. High rigidity is often required for end milling harder materials.

roughing

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

safety glasses

A form of protective eyewear, usually made of thick plastic, that shields the eyes. Safety glasses protect the eyes from flying debris and hazardous materials, such as metal chips and cutting fluid.

shank

The cylindrical part of an end mill above the cutting edges and flutes. Shanks fit into a toolholder that attaches the end mill to the machine tool.

shank diameter

The width of a tool’s shank. Shank diameter is important for fitting an end mill into a toolholder.

side lock toolholder

A device used to hold a cutting tool that includes a clamping screw to lock the tool in place. Side lock toolholders are compatible with Weldon shank tools.

slots

A narrow channel cut into the surface of a workpiece. Slots can be created with either a face or end mill.

solid tools

A cutting implement where the cutting edges and at least part of the shaft are made of one material. Solid tools can be made of a range of materials and include end mills, face mills, and drills.

speed

The rate at which the tool or workpiece rotates during a cutting operation. Speed in an end milling operation refers to how quickly the end mill rotates.

spindle

A rotating component of a machine tool. Spindles on mills hold and rotate cutting tools.

spindle speed

The rate at which the machine spindle rotates. Spindle speed is typically measured in revolutions per minute (RPM).

square end mill

An end mill with a 90-degree angle between the peripheral cutting edges and the end face. Square end mills cut features with right angles into workpieces.

step-over

The amount of the cutter diameter that is engaged with the workpiece. Step-over, also known as radial depth of cut or AE, is generally 75% or less of the cutter diameter.

surface feet per minute

SFM. An Imperial measurement of cutting speed that describes the distance that a cutting edge travels in one minute at its point of contact with the workpiece. Surface feet per minute depends on both the tool diameter and RPM.

surface finish

The degree of roughness and variation on the surface of a part after it has been manufactured. Surface finish is typically smoother when you use an end mill with more flutes.

surface speed

The amount of workpiece material a cutting edge contacts in one minute. Surface speed, sometimes called cutting speed, is measured in surface feet per minute (SFM) or meters per minute (m/min).

synthetic cutting fluids

A cutting fluid made from water and chemicals, such as nitrites and phosphates. Synthetic fluids, also known as chemical fluids, are primarily used for their ability to cool.

tagged out

Including a prominent visual warning that indicates the machine should not be turned on. Tagged out machines must not be operated until the tag is removed by an authorized employee.

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 life, production efficiency, and part quality.

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 gradual removal of material from the surface of a cutting tool due to contact and friction. Tool wear can affect part dimensions and part tolerance.

toolholder

A device used to hold a cutting tool in place. Toolholders come in a variety of shapes and sizes to fit different machine tools and cutting tools.

toolpath

The course followed by a cutting tool as it shapes a workpiece. Toolpaths are composed of a series of Cartesian coordinate positions.

tough

The ability of a material to absorb energy without breaking or fracturing. Toughness allows milling tools to withstand the sudden stresses of repeatedly impacting the workpiece, but higher toughness generally means less hardness.

variable helix

An end mill where the flutes have differing helix angles. Variable helix end mills reduce the vibrations that can occur in high efficiency milling operations.

wear resistance

A material’s ability to resist the gradual wearing away that abrasion and friction cause. Wear resistance can lengthen tool life.

Weldon shank

A type of end mill shank with one or two notches cut into the side. Weldon shank end mills fit into toolholders that grip the notches for a secure fit.

workpieces

A material being machined or undergoing another type of processing. Workpieces for milling operations are generally metals.