Mill Tool Geometry 361

aluminum

A sliver-white metal that is light and thermally conductive. Aluminium is soft and therefore usually milled with double positive geometry.

angular land

A surface just behind the cutting edge that is angled toward or away from the direction of the cut. An angular land can be positive or negative.

axial rake angle

The angle formed by the tilt of the leading peripheral edge and a line parallel to the center axis. The axial rake angle describes how far the tooth face leans forward or backward.

axis

The center line of a circular or cylindrical object. The axis is used to help orient and measure the various aspects of tool geometry.

built-up edges

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

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 milled using double negative geometry.

chamfer

A beveled surface that eliminates a 90° sharp corner on the cutting edge. A chamfer is often created at a 45° angle.

chatter

Vibrations of the cutting tool that cause surface imperfections on the workpiece. Chatter can be reduced through proper usage of milling geometry, such as setting a large enough lead angle.

chip

An unwanted piece of metal that is removed from a workpiece. A chip is formed with a tool cuts or grinds metal.

chip load

The thickness of a chip that is removed by one cutting edge of the tool. Chip load is measured as feed per tooth.

clearance

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

clearance angle

The angle formed by the flank behind the land and a line tangent to the cutting edge. A clearance angle keeps the flank from rubbing against the workpiece.

clearance angles

The angle formed by the flank behind the land and a line tangent to the cutter periphery. A clearance angle keeps the flank from rubbing against the workpiece.

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.

cutting edges

The edge of a cutting tool that is in direct contact with the workpiece and performs metal removal. Cutting edge must be positioned carefully 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 points

The tip of the tool where the face and peripheral cutting edges meet. The cutting points are the first part of the tool to engage the workpiece when the tooth is set to a positive axial rake angle.

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.

diameter

The distance from one edge of a circle or circular object to the opposite edge, passing through the center. The diameter of a mill cutter is essential for measuring several aspects of milling geometry, such as the radial rake angle.

discontinuous chips

A chip that easily fractures from the workpiece into small, separate pieces. Brittle materials, such as cast iron, tend to create discontinuous chips.

double negative geometry

Milling tool orientation that uses negative axial and radial rake angles. Double negative geometry provides the greatest cutting edge strength but also generates the greatest cutting forces.

double positive geometry

Milling tool orientation that uses positive axial and radial rake angles. Mills with double positive geometry have low power requirements but weak cutting edges.

ductile

Able to be stretched, drawn, or formed without fracturing. Ductile metals tend to be soft and produce long, stringy chips.

end flank

The flat surface on the bottom edge of the cutting tool. The end flank passes over the newly machined workpiece to create the surface finish.

end milling

A milling operation that uses cuts with the bottom of side of the milling cutter. End milling is usually performed with a solid mill and can create features such as slots and grooves.

end mills

A milling cutter that performs a mix of peripheral and face milling. End mills have cutting surfaces on the bottom and sides of the tool.

face

The bottom surface of a mill or mill tooth. The face is the primary cutting surface used in face milling.

face cutting edge

The cutting edge on the end or bottom of a milling cutter. A face cutting edge passes over the newly formed surface of a workpiece.

face milling

A cutting operation in which the surface of the workpiece is perpendicular to the spindle axis. Face milling is primarily used to create flat surfaces on a workpiece.

face mills

A milling cutter that cuts metal with its face, or bottom, edge. Face mills often use inserts and are good for creating wide, flat surfaces.

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).

feed per revolution

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

fillet

The interior curved corner or radius of the flute. A fillet aids in efficient chip removal.

finishing

A final metal cutting pass that emphasizes tight tolerances and smooth surface finish. Finishing is often performed with teeth set at larger lead angles.

flute

A groove on the periphery of a cutter that provides room for chips to flow away from the cut. Flutes are present on cutting tools such as mills and drills.

flutes

A groove on the periphery of a cutter that provides room for chips to flow away from the cut. Flutes are present on cutting tools such as mills and drills.

free cutting

Cutting under ideal conditions. Free cutting indicates an operation with low cutting forces, optimal chip formation, and good chip removal.

helical

Shaped like a spiral that is wrapped around a cylinder. The teeth on some end and face mills are helical, which helps reduce cutting forces.

helical rake angle

The angle created by the center axis of the tool and the slope of the peripheral cutting edge. The helical rake angle, also known as the helix angle, can affect the strength of the cutting edge on a mill, among other properties.

helix angle

The angle created by the center axis of the tool and the slope of the peripheral cutting edge. The helix angle, also known as the helical rake angle, can affect the strength of the cutting edge on a mill, among other properties.

indexable cutters

A milling tool with inserts as its teeth. Indexable cutters have excellent flexibility because their teeth can be swapped, angled, and otherwise adjusted.

inserts

An indexable and replaceable cutting tool with a geometric shape that has multiple cutting surfaces. Inserts provide the cutting edges for many face mills.

intermittent cutting

A metal removal process in which one or more edges of the cutting tool repeatedly enter and exit the workpiece surface. Intermittent cutting, also called interrupted cutting, is often used in milling and leads to increased cutting forces.

interrupted cutting

A metal removal process in which one or more edges of the cutting tool repeatedly enter and exit the workpiece surface. Interrupted cutting, also called intermittent cutting, is often used in milling and leads to increased cutting forces.

land

An angled surface on a cutting tool just behind the cutting edge. The land's shape affects chip removal and surface finish.

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 tilt of the side flank of the insert and a line parallel to the center axis of the cutter. The lead angle helps determine depth of cut and the strength of the cutting forces generated during machining.

low-carbon steel

A plain carbon steel that contains less than 0.30% carbon. Low-carbon steel is prone to developing BUE, which can be reduced using double positive geometry.

metal removal rates

MRR. The volume of metal removed in a given amount of time. Metal removal rates are measured in cubic inches per minute or cubic centimeters per minute.

milling

A cutting operation in which a rotating multi-point cutting tool is fed along the surface of a part to remove material. Milling operations generally produce flat surfaces.

milling cutter

A multi-point cutting tool that has teeth around its cutting surface. Milling cutters include face mills and end mills.

milling geometry

The angles formed by the shape and positioning of a cutting tool. Milling geometry, or tool geometry, is a key factor in improving tool life, part surface finish, and machining efficiency.

MRR

Metal removal rates. The volume of metal removed in a given amount of time. MRR are measured in cubic inches per minute or cubic centimeters per minute.

multi-point tools

A cutting tool that has more than one cutting edge. Multi-point tools are used for metal cutting operations such as milling and drilling.

negative angular land

A milling tooth feature that tilts the surface behind the cutting edge toward the direction of the cut. A negative angular land increases cutting-edge strength.

negative axial rake angle

A measurement that indicates a tooth face that leans toward a line parallel to the center axis of a milling cutter. A negative axial rake angle allows for greater depth of cut but also requires more machine power.

negative inserts

An insert with two cutting faces and square edges. Negative inserts provide the greatest number of indexable cutting edges but limited chip clearance.

negative radial rake angle

A measurement that indicates a tooth face that tilts away from the center of the mill. A negative radial rake angle demands greater machine power but has improved cutting edge strength.

nose radius

The degree of roundness between two cutting edges of a tool. The size of the nose radius affects many aspects of cutting.

operators

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

parallel

Two lines that are equidistant from one another and do not intersect. A line parallel to the cutting axis is used to determine various aspects of mill geometry, including the lead angle.

parallel land

A surface just behind the cutting edge that is angled to exactly match the direction of the cut. A parallel land produces a high-quality surface finish.

peripheral cutting edge

The outside cutting edge of a milling cutter. A peripheral cutting edge is the primary cutting edge used in end or peripheral milling.

peripheral milling

A milling operation in which the cutting edge of the mill is parallel to the axis of the spindle. Peripheral milling is done with only the peripheral cutting edges of a mill.

periphery

The outer edge of an object. The periphery of a mill is the primary cutting surface in peripheral milling, though it is also used in face and end milling.

pitch

The relative quantity and spacing of teeth on a milling cutter. Pitch ranges from coarse, with few teeth, to fine, with many teeth.

positive angular land

A milling tooth feature that tilts the surface behind the cutting edge away from the direction of the cut. A positive angular land increases surface finish quality.

positive axial rake angle

A measurement that indicates a tooth face that leans away from a line parallel to the center axis of a milling cutter. A positive axial rake angle has decreased edge strength but improves metal removal rates.

positive inserts

An insert with only one cutting face and angled edges that provide chip clearance. Positive inserts reduce the cutting forces produced in a cutting operation but also reduce edge strength.

positive radial rake angle

A measurement that indicates a tooth face that tilts toward the center of the mill. A positive radial rake angle has lower cutting edge strength but can be operated with less machine power.

positive/negative geometry

Milling tool orientation that uses a combination of positive axial rake and negative radial rake angles. Positive/negative geometry balances the benefits of double negative and double positive geometry and is, therefore, a good general-purpose milling geometry.

radial rake angle

The angle formed by the radius or diameter of the milling cuter and the face cutting edge. A radial rake angle describes how far the face cutting edge is twisted toward or away from the mill.

radius

A straight line extending from the center of a circle or circular object to its periphery. The radius of a mill cutter is essential for measuring several aspects of milling geometry, such as the radial rake angle.

relief angle

The angle formed by the slope of the land and a line tangent to the cutting edge. The relief angle directly follows the cutting edge and reduces flank wear while increasing chip flow.

rigid

Stiff and inflexible. Machines must be rigid in order to perform double negative milling operations.

roughing

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

runout

The accumulated position error and deviation from an axis as a mill rotates. Excessive runout can cause issues like reduced tool service life and poor surface finish.

screws

A threaded device used for fastening parts or transferring motion. Screws are used to hold indexable inserts in place on a milling cutter.

setup

All the necessary preparation of tooling and fixturing that occurs on a machine before a cutting operation begins. Setup includes the positioning of the tool, the milling machine, and the workpiece.

shearing action

The force created by downward movement of an angled blade to remove metal. Shearing action is determined, in part, by the helix angle.

shoulders

An angled surface similar to a chamfer created by milling. Ninety degree shoulders are milled using teeth with 0° lead angles.

side flank

The flat surface on the peripheral edge of the cutting tool. The side flank is responsible for the majority of material removal in metal cutting operations.

single-point tools

A cutting implement that mostly uses one cutting edge at a time. Single-point tools are often used for lathe metal cutting operations such as turning or threading.

soft

A material that deforms easily when subjected to stress. Soft metals include aluminum and copper.

speed

The rate at which the the edge of a cutting tool rotates past the surface of the workpiece 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 that work-harden may need to be milled using double positive geometry.

surface finish

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

tangent

A line or line segment that touches an object at exactly one point. Relief and clearance angles are determined by measuring the angle formed by the slope of certain insert components and straight lines tangent to the cutting edge of the insert.

teeth

The part of the milling cutter where the cutting edges are located. Teeth can either be molded into the tool, as in a solid mill, or they can be indexable cutting inserts.

tolerance

An unwanted but acceptable deviation from a given dimension defined by a blueprint. The required tolerance of a manufactured part affects insert selection and proper milling tool geometry.

tool failure

A form of wear that renders a tool unusable. Tool failure can occur over time or suddenly if the tool fractures.

tool geometry

The angles formed by the shape and positioning of a cutting tool. Tool geometry, sometimes called milling geometry when related to milling cutters, is a key factor in improving tool life, part surface finish, and machining efficiency.

tool life

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

tooth face

The flat surface of the cutting insert or tooth that is fed into the workpiece. The tooth face is not involved in the actual cutting but helps direct chips as they come off the workpiece.

wipers

A specialized milling insert with a long parallel land. Wipers provide optimal surface finish even at high feed rates.

work-harden

Increase the hardness of a metal by subjecting it to plastic deformation during a cold working or machining process. Work-hardening metals may need to be milled using double positive geometry.

workholding device

A manufacturing component used to support, locate, and hold a workpiece in place. A workholding device's strength and stability affect the type of cutting geometry used in a milling operation.

workpiece

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