End Mill Selection 385

abrasive

Consisting of hard particles that can wear away other materials. Abrasive workpiece materials can shorten tool life.

aluminum

A silver-white metal that is ductile, light, and thermally conductive. Aluminum is a soft metal that tends to form chips that stretch rather than cut away cleanly.

aluminum chromium nitride

AlCrN. A compound of aluminum, chromium, and nitrogen used as a coating for cutting tools. Aluminum chromium nitride coatings improve wear resistance and are commonly used on cutting tools that cut stainless steel and steel alloys.

axial coolant holes

Holes in an end mill that deliver cutting fluid directly to the cutting area. Axial coolant holes can be found on the centerline of an end mill’s end face.

axial depth of cut

AP. The amount of an end mill’s peripheral cutting edges that are engaged with the workpiece in a single pass. Axial depth of cut measures how far beneath the workpiece surface the peripheral cutting edges penetrate.

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, also known as ball nose end mills, cut rounded edges and complex three-dimensional shapes into workpieces.

ball nose end mill

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

beveling

A metal removal process that produces an angled surface on the edge of an object. Beveling can be completed by a chamfer mill.

brittle

More likely to break instead of bend when subjected to force or pressure. Brittle tool materials and coatings are often also very hard.

carbide

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

carbide-tipped

A tool material made mostly of high-speed steel with an outer layer of carbide on the cutting edges. Carbide-tipped end mills offer the toughness of high-speed steel with added hardness from the carbide layer.

cast iron

A metal consisting of iron, more than 2% carbon, 1 to 3% silicon, and trace amounts of other elements. Cast irons are hard, brittle metals that should be cut with a lower rake angle.

centerline

An imaginary line that runs through the center of a cylindrical object. An end mill rotates around its centerline, also called its axis.

chamfer

An angled edge that eliminates a sharp corner. A chamfer on an end mill creates an angled surface between the peripheral cutting edges and end face.

chamfer mill

A type of milling cutter that has a specialized angled surface on its end face. Chamfer mills can complete a variety of operations including chamfering and countersinking.

chamfering

Machining a small, angled feature along a part edge to remove sharp edges or corners. Chamfering can be completed by a chamfer mill.

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 breakers

A device located on the cutting tool or toolholder that is designed to separate chips into smaller pieces for more effective chip evacuation. Chip breakers are often built into the surface of an end mill.

chip evacuation

The clearance of chips from the cutting area during a metal cutting process. Proper chip evacuation is important for making accurate parts and minimizing tool wear.

clearance

The space behind the cutting edge that eliminates interference between the cutting tool and the workpiece. Clearance prevents parts of the tool, other than the cutting edge, from touching the workpiece and provides space for chip flow.

clearance angle

The angle formed by the area behind the land and the workpiece. Clearance angles, sometimes called secondary relief angles, affect tool wear rates and cutting tool strength.

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 high-speed steel

HSS-E. A hard, gray, brittle metal often used to create cutting tools. Cobalt high-speed steel 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. CNC machines are much more precise than their manual counterparts.

concave

Curving inwards. Corner rounding end mills have cutting edges that are concave.

continuous chips

A chip that does not break apart, forming a long thin strip of unwanted metal. Continuous chips can snag and damage the tool and machinery.

contouring

A milling process that moves the tool in three linear axes simultaneously. Contouring, sometimes called three-dimensional profile milling, can create complex and rounded features in a workpiece.

conventional relief

Two flat surfaces behind the cutting edge of an end mill that provide clearance between the tool and the workpiece. End mills with conventional relief are generally more versatile and cost-effective than end mills with eccentric relief.

convex

Curving outward like the exterior of a circle or sphere. Eccentric relief end mills have a convex shape behind the cutting edge.

coolant-through end mill

An end mill with a cavity in its center that allows cutting fluid to pass through. A coolant-through end mill can deliver cutting fluid directly into the cutting area.

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 and make the corner of the tool less likely to chip.

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 and make the corner of the tool less likely to chip.

corner rounding end mill

An end mill cutter with distinct concave cutting edges on the end face. Corner rounding end mills create rounded surfaces on the edge of a workpiece.

countersinking

The process of cutting a cone-shaped recess into the opening of a hole. Countersinking allows screws to sit flush with a workpiece surface.

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 in 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.

deburring

Removing sharp projections left on a workpiece after a machining operation. Deburring ensures that a workpiece has smooth, flat edges.

deflection

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

diamond coating

Natural or synthetic diamonds used as a coating for cutting tools. Tools with diamond coating have greatly increased hardness and wear resistance but cannot be used on ferrous workpieces.

dies

A component with specific dimensions used to shape metal that is forced through or against it. Dies are often created using tapered end mills.

drill mill

A type of milling cutter that has the cutting lips of a drill and the peripheral cutting edges of an end mill. Drill mills can complete both drilling and milling operations.

eccentric relief

A convex surface behind the cutting edge of an end mill that provides clearance between the tool and the workpiece. End mills with eccentric relief generally have stronger cutting edges than end mills with conventional relief.

end face

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

end mill

A type of milling cutter that cuts with its bottom and side cutting edges. End mills come in many variations and can be used to complete diverse applications.

failure

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

features

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

ferrous

A material in which iron is the main ingredient, such as steel. Ferrous metal workpieces should not be cut with tools that have diamond coatings.

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

The resistance between the contact surfaces of two objects. Friction generates heat and increases the wear between components.

grain structure

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

hardness

The ability of a material 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. Helix angles on end mills affect the strength of the cutting edges, the distribution of cutting forces, and chip evacuation.

high-speed steel

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

holemaking

A machining operation that creates, shapes, or finishes a hole. Holemaking operations include drilling, reaming, boring, countersinking, and counterboring.

HSS

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

hydraulic toolholder

A device used to hold a cutting tool in place using hydraulic pressure. Hydraulic toolholders create an even clamping force around the shank, which reduces vibrations.

indexable end mill

A type of milling cutter that uses indexable cutting inserts attached to a tool body. Indexable end mills are generally used on applications that require larger diameters.

indexable inserts

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

land

The surface on a cutting tool just behind the cutting edge. The land’s shape affects chip removal and cutting edge strength.

length of cut

The maximum amount of the peripheral cutting edges of an end mill that can engage with a workpiece. Length of cut determines how deeply the end mill can cut with its peripheral cutting edges in a single pass.

lips

The cutting edges of a drill that extend from the chisel edge to the periphery. The lips perform the actual metal removal during drilling.

lollipop end mill

A type of end mill with spherical cutting edges that are wider than the tool shank. Lollipop end mills, sometimes called undercutting end mills, are used to create highly precise tolerances and surface finishes.

long reach end mill

An end mill with an long neck that allows the cutting edges to reach into deep pockets and slots. Long reach end mills have a shorter length of cut, which makes the tool less likely to experience deflection.

machinability

The relative ease with which a machining operation can cut material from a workpiece. Machinability generally decreases with the hardness of the workpiece material.

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 tool

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

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.

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.

modular end mill

A type of milling cutter that has a cutting head that screws into a specialized shank. Modular end mills, also known as exchangeable head end mills, are generally used on operations that require cutter diameters between one half inch and one and a half inches (12.7-38.1 mm).

molds

A hollow cavity used to shape molten material. Molds are often created using tapered end mills.

neck

The portion of an end mill between the shank and the length of cut. The neck on a long reach end mill allows the tool to reach into deep slots and pockets.

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.

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 side milling and creating slots and pockets.

personal protective equipment

PPE. Safety equipment that personnel 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 shank with a smooth, cylindrical surface throughout. Plain shanks typically must use collets as toolholders.

pocket

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

powdered metal high-speed steel

HSS-PM. A tool material made by sintering high-speed steel powder with other metal powders to improve tool properties. Powdered metal high-speed steel tools are harder and more wear-resistant but less tough than high-speed steel.

primary relief angle

The angle formed by the land and the workpiece. Relief angles affect tool wear rates and cutting tool strength.

profile milling

The process of milling the overall shape or outline of a part. Profile milling often creates linear, angled, or contoured surfaces.

profiles

The overall shape of an end mill. Profiles affect a variety of cutting factors, such as the types of features that an end mill can cut and the strength of the cutting edges.

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 such as hardness and toughness.

radial coolant holes

Holes in an end mill that deliver cutting fluid directly to the cutting area. Radial coolant holes can be found on an end mill’s flutes.

radial depth of cut

AE. The percentage of the end mill’s diameter that actively removes workpiece material in a single pass. Radial depth of cut, also known as stepover or AE, is generally 75% or less of the tool diameter.

rake angle

The angle between the front of the cutting tool and a line that passes through the center of the tool and the tip of the cutting edge. Rake angles affect cutting forces and surface finish.

right angle

An angle that measures exactly 90°. Right angles are formed by two lines that are perpendicular to one another.

roughing

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

roughing end mill

An end mill cutter that specializes in operations that prioritize quick material removal rates. Roughing end mills often have chip breakers and leave a rough surface finish.

safety glasses

A form of protective eyewear, usually made of thick plastic, that shields the eyes from flying debris and other potentially hazardous materials. Safety glasses protect machine operators from chips.

secondary relief angle

The angle formed by the portion of the tool immediately behind the land and the workpiece. Secondary relief angles, sometimes called clearance angles, affect tool wear rates and cutting tool strength.

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.

shrink fit toolholder

A device that holds a cutting tool in place using the thermal expansion and contraction of metal. Shrink fit toolholders result in a highly precise and rigid hold.

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.

silicon

A blue-gray, nonmetallic, crystalline material that is hard and brittle. Silicon content increases a material's abrasiveness.

sintering

Heating pressed powdered materials close to their melting point to fuse them into a solid product. Sintering often combines multiple metals to optimize their properties, such as combining hard, brittle carbide with tougher cobalt to create carbide cutting tools.

slots

A narrow channel cut into the surface of a workpiece. Slots made by end mills are typically shallow, curved, or angled.

solid end mill

A type of milling cutter with cutting edges and a tool body made of a solid piece of one material. Solid end mills are generally used on applications that require cutter diameters of one inch (25.4 mm) or smaller.

speeds

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.

spot drilling

A holemaking process that creates a preliminary hole in a workpiece in order to guide the drill used to finish the hole. Spot drilling can be completed by a drill mill.

square end mill

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

stainless steel

A grouping of steels that contain large percentages of chromium, as well as nickel, manganese, and/or nitrogen. Stainless steels have very high hardness.

steel alloys

Steel that contains intentionally added alloying elements to modify its characteristics. Steel alloys can be difficult to machine and should be milled using appropriate tool materials and coatings.

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 a higher rake angle.

tapered end mill

An end mill cutter where the end face is narrower than the shank diameter. Tapered end mills are generally less likely to deflect and can create angled surfaces in a workpiece.

titanium

A silver-gray, strong, but lightweight nonferrous metal. Titanium has high hardness and exceptional corrosion resistance.

titanium aluminum nitride

TiAIN. A compound of titanium, aluminum, and nitrogen used as a coating for cutting tools. Titanium aluminum nitride offers higher hardness and heat resistance than both TiN and TiCN.

titanium aluminum silicon nitride

TiAlSiN. A compound of titanium, aluminum, silicon, and nitrogen used as a coating for cutting tools. Titanium aluminum silicon nitride increases a tool’s hardness, heat resistance, and wear resistance.

titanium carbonitride

TiCN. A compound of titanium, carbon, and nitrogen often used as a coating for carbide cutting tools. Titanium carbonitride offers good wear resistance and higher hardness than TiN.

titanium nitride

TiN. A common coating element used to reduce friction on high-speed steel and carbide tools. Titanium nitride increases surface hardness, wear resistance, and insulation against heat.

tolerances

The allowable deviation from a given dimension. Tolerances indicate the allowable difference between a physical feature and its intended design.

tool geometries

The collective angles, edges, and shape 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 wear

The gradual erosion 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.

toughness

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.

T-slot

A type of slot where some workpiece material overhangs the recess in the workpiece. T-slots are common features used in machine worktables.

T-slot cutter

A specialized end mill with cutting edges on the periphery of a wide disc. T-slot cutters, sometimes called T-slot end mills, are used to create specialized T-shaped slots.

T-slot end mill

A specialized end mill with cutting edges on the periphery of a wide disc. T-slot end mills, sometimes called T-slot cutters, are used to create specialized T-shaped slots.

undercutting end mill

A type of end mill with spherical cutting edges that are wider than the tool shank. Undercutting end mills, sometimes called lollipop end mills, are used to create highly precise tolerances and surface finishes.

wear resistance

The ability of a material to resist the gradual wearing away that abrasion and friction causes. 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.

workholding

A device used to support, locate, and hold a workpiece. Workholding is specific to the machine tool and cutting operation.

workpiece

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

worktables

A component on a mill that supports the workpiece and any workholding device during machining. Worktables on the mill have T-slots that allow operators to attach a range of workholding devices.