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Terminology & Tool Build


 Useful Terminology


Abrasion- The gradual wearing away of the cutting edge by the friction created between the end mill and the work piece material.


Adapter- A devise for fitting a tool to, and driving it from, the spindle nose of a machine.


Angular Flute- The space between two flutes which forms a cutting edge, thus forming an angle with the cutter axis. It is unlike a helical flute since a cutting edge which lies in a single plane.


Axial Rake – Applies to angular (not Helical) flutes. The axial rake at any given point on the face of the flute is the angle between the tool axis and a tangent plane at the given point.


Axial Relief- The relief measured in the axial direction between a plane perpendicular to the axis and the relieved surface. It can be measured by the amount of indicator drop at a given radius in a given amount of angulation rotation.


Axial Runout- The total variation of an indicator reading taken at the face of a cutter near the outer diameter.


Axis- The line about which the end mill rotates (the centerline of the cutter).


Back-Off- Also referred to as relief. It is the result of the removal of tool material behind or adjacent to the cutting edge to provide clearance and prevent hell drag.


Ball End-


Built- up Edge- The adhering of work piece material on the tooth face of an end mill.


CAM Relief- The relief from the cutting edge to the back of the tooth face of an end mill.


Chamfer- The beveled corner on an end mills tooth design to eliminate a sharp corner and/or to strengthen an otherwise weak corner.


Chatter- (1) An irregularity in cutting action that will result in an undesirable finish. (2) The undesirable sound created by an irregularity in the cutting action.


Chips- The pieces of material removed from the work piece by the cutting action.


Chipping- What happens when fragments of the cutting edge break away during the cutting action.


Chip Breaker-  a shoulder in a machine tool made by grinding a groove parallel to the cutting edge or by attaching a plate to the top to form a wall against which the chip produced in turning or other machining will be broken up.


Chip Thickness- The thickness of a chip removed by the cutting edge.


Clearance- The space behind the relieved land of an end mill tooth designed to eliminate the undesirable contact between the end mill and the work piece (heel drag).


Clearance Angles- Angular or curved surfaces behind the relieved land. (see Heel in image)C:\Users\Steve\Desktop\my images\effects\examples\fig. 2.jpg


Climb Milling- The rotation of an end mill in the same direction as the feed at the point of contact, thus relieving feed force requirement. It produces the thickness part of the chip first.


Clogging- The packing of chips in the flutes of the end mil.


Concave- (1) The deviation from a plane where the middle segment is below the outer edges, or (2) The deviation from parallelism on an end mill where the diameter is less in the middle than at the ends.


Concave Relief- A concave relieved surface behind the cutting edge.


Contour Milling- Milling of a specified shape, primarily with the periphery of an end mill, without the axial movement of the end mill in relationship to the work piece.


Convectional Milling- Rotation of an end mill in the opposite direction to the feed at the point of contact, thus increasing the feed force requirements. This type of milling produces the thinnest part of the chip first.


Convex- (1) The deviation from a plane where the central segment is above the outer edges, or (2) the deviation from parallelism on an end mill where the diameter is greater at the middle than at the ends.


Core Diameter- The diameter of a circle tangent to the bottom of the flutes.


Corner Radius-


Crater- A depression in the tooth face caused by the erosion of tool material from chip contact.


Cutting Edge- The leading edge of the end mill tooth, formed by the intersection of the two finely finished surfaces, generally having an included angle of less than 90 degrees.


Cutting Edge Angle- The angle formed by the cutting edge and the tool axis. A constant lead will produce a constant cutting edge angle on a cylindrical end mill, and a varying cutting edge angle on a tapered end mill.


Cutting Speed- The number of feet per minute that a given point on the circumference of an end mill travels, usually expressed as sfm.


Depth of Cut- The thickness of the work piece material being removed, measured from the cutting edge to the shoulder of the material being cut. May be axial or radial depth of cut. C:\Users\Steve\Desktop\my images\effects\examples\fig. 3.jpg

DIA-Diameter = Larger tools can remove material faster than small ones, therefore the largest possible cutter that will fit in the job is usually chosen. When milling an internal contour, or concave external contours, the diameter is limited by the size of internal curves. The radius of the cutter must be less than or equal to the radius of the smallest arc.


Down Milling – Preferred term: Climb Milling


Eccentric Relief- A convex relieved surface behind the cutting edge.

Effective Rake- The complement of the angle between the direction of the motion of any point on the cutting edge and the direction of chip flow from the same point. Effective rake is the result of three factors: (1) cutter Geometry, (2) the actual path of the cutting edge, (3) the actual direction of chip flow.


End Mill- A cutting tool intended to cut primarily on the circumference of the tool, while being held by an adapter or collet.


End Style-  is the shape the end of the end mill to create a different style cut.


Face or End Milling- Milling of a surface which is perpendicular to the end mill axis.


Feed- The number of lineal inches the milling cutter advances in relation to the work piece. Usually expressed in inches per minute (ipm).


Feed Per Revolution (fpr)- The feed in inches per revolution of the cutter.


Feed per Tooth(fpt)- The feed in inches per revolution divided by the number of active teeth in the cutter. The number of inches the work-piece advances toward the end mill between each tooth.


Fillet- The radius at the bottom surface of the flute from which the core diameter is found.


Flat Relief- A relieved surface behind the cutting edge which is flat.


Flute- The chip space between the back of one tooth and the face of the following tooth. More flutes allow a higher feed rate, because there is less material removed per flute.  




Flute Length- The effective axial length of the cutting edge.


Form Cutter- Any cutter shaped to produce a specified form on the work piece.


Gash- (1) Preferred term: NOTCH (2) A term applied to the supplementary grinding on the end of the end mill to provide chip space.


Gullet- Preferred term: FLUTE


Heel- (1) The back surface of the tooth trailing the cutting edge. (2) A term applied to the supplementary grinding on the end of the end mill to provide chip space.

Heel Drag- An Interference between the heel and the work piece, due to insufficient relief or clearance or excessive deflection.


Helical- The cutting edge or flute which progresses uniformly around a cylindrical surface in an axial direction.


Helical Rake- Applies to helical teeth only. The helical rake at a given point on the flute face is the angle between the end mill axis and a tangent plane at the given point.


Helix Angle- The angle which a helical cutting edge makes with a plane containing the axis of a cylindrical end mill.

Hook- See Radial Rake. A concave condition of a tooth face. The rake of a hooked tooth face must be determined at a given point.


Land- the narrow surface of a profile sharpened end mill tooth immediately behind the cutting edge.


Lip- The material included angle between a tooth face and a relieved land.


LOC- the length of cut of the end mill


Machinability Rating- A rating, expressed as a percentage, relating to the difficulty of machining a given material to a standard. Usually AISI B-1112 is the standard, given a rating of 100%. It determines the acceptability of a tool for the work piece to be machined. This rating indicates the materials hardness, chemical composition and qualities, micro structure, propensity to work harden, elasticity, and propensity to be worked cold. In general, the higher a material’s machinability rating the harder it is to machine.


Milling- Method of removing material in the form of chips by means of rotating cutter.


Neck- the section of reduced diameter between the flutes and shank of an end mill

Normal Plane- A plane perpendicular to a given surface or a line in a given surface.


Normal Rake- The angle between the normal to the milled surface and a tangent to the tooth face at the same point on the cutting edge at this same point. Normal rake is established by: (1) cutter geometry, and (2) the cutter path, but disregarding the actual chip flow direction.


Notch- The space forming the end cutting edge.


Offset- The distance that a tooth is positioned off center to obtain the desired rake.


over All Length (OAL)-  the over All Length of the end mill; from the cutting edge to the base of the shank.


Peripheral Milling- Milling of a surface which is parallel to the end mill axis.


Periphery- The outside circumference of a cutter.


Plastic Deformation- the permanent, inelastic distortion of metals under applied stress, such as in the cutting action of end mills, that strain the material beyond its elastic limits.


Plunge Cut- The movement between the cutter and the work piece directly in line with the center of the cutter when the cutter is fed directly into the work piece, axial feeding.



Primary Relief- The relief directly behind the cutting edge.



RAD- Radius - a straight line from the center to the circumference of a circle or sphere

Radial Rake- the angle between the tooth face and a radial line passing through the cutting edge in a plane perpendicular to the end mill axis.


Radial Relief- Relief in a radial direction measured in the plane of rotation. It can be measured by the amount of indicator drop at a given amount of angular rotation.


Radial Runout- the total variation in a radial direction of all cutting edges in a plane of rotation.


Rake- The angular relationship between the tooth face, or a tangent to the tooth face at a given point a given reference plane or line.


Ramping- Milling a slot into a work piece by entering into the part at an angle, usually 5 degrees. Once a predetermined depth is reached the end mill is fed straight back to take out the ramp which has been formed, if the slot is needed to be taken deeper this process is repeated. By ramping the wear land at the depth of the cut line will move up the flute thereby not staying in one location, this will increase tool life of the end mill.

Resultant Rake- The angle between a tangent to the tooth face at a given point on the cutting edge and a radial line to this point, measured in a perpendicular plane to the cutting edge. The resultant rake pertains to cutter geometry only without regard to operating factors and defines the resultant rake obtained on an end mill due to a combination of: (1) radial rake or hook, (2) axial or helical rake, and (3) a corner angle or corner radius.


Relief- The result of the removal of end mill material behind or adjacent to the cutting edge to provide clearance and prevent rubbing (heel drag).


Relief Angle- The angle formed between a relieved surface and a given plane tangent to a cutting edge or to a point on a cutting edge.


Shank- the projecting portion of a cutter which locates and drives the end mill from the machine spindle o adaptor. The shank is the cylindrical (non-fluted) part of the tool which is used to hold and locate it in the tool holder. A shank may be perfectly round, and held by friction, or it may have a Weldon flat, where a set screw, makes contact for increased torque without the tool slipping. The diameter may be different from the diameter of the cutting part of the tool, so that it can be held by a standard tool holder.


Shear- (1) Action or stress which causes two adjoining parts of a work piece to slide relatively to each other in a direction parallel to their plane of contact. (2) The cutting action produced by axial or helical rake when the direction of chip flow is other than at right angles to the cutting edge.


Sparking- The creation of sparks during milling caused by the combustion of small chips.


Speed- The rate of rotation of a cutter. Usually expressed as revolutions per minute or (rpm) or in peripheral surface feet per minute(sfm).


Squealing- High pitched noise resulting from rubbing action of the cutter on the work piece.


Square End-

True Rake- See Effective Rake


Tangential Rake- The angle between a line tangent to a hook tooth face at the peripheral cutting edge and a radial line passing through this point of tangency.


Tooth- A projection on the end mill which carries a cutting edge.


Tooth Face- the surface of the tooth on which the chip encroaches.


Total Indicator Variation (tiv)/total indicator Runout (tir)- The difference between the maximum and minimum indicator readings during a checking cycle.


Tracer Milling- The duplication of a three dimensional form by means of an end mill controlled by a stylus that follows a template or may be program generated.


Up-milling- See Conventional Milling



Wear Land- The cylindrical or flat land worn on the relieved portion of the cutter tooth.


Weldon Shank-  A straight shank with special flats for driving and locating the tool.


Variable Helix- The variable helix end mill consists of unequal flute spacing at various points along the cutting length of the tool. Unequal flute spacing helps dampen vibration that is generated by the milling processes.  


Vertica Sheer Action-

Coating: Coatings prolongs the life of an end mill by acting as a chemical and thermal barrier between took and work piece.  Coatings protect the substrate’s (primary cobalt binder) from the heat generated during the milling process. Coatings reduce heat build-up on cutting edges, preventing galling and metal pick up.

All CGS coatings are PVD coatings.

PVD (Physical Vapor Deposition)- this type of coating is applied in a vacuum chamber at temperatures <750° F. Ions are transplanted by physical means (ion bombardment), the force of the ions bonds the coating to the tool surface. Because of the low temperature, the substrate (tool) does not lose hardness or undergo material distortion.

Bond: The bond between coating and tool is mechanical (chemical inert)

Uses: PVD coatings are preferred for cutting tools with “tight” tolerances. Additionally, it is the coating choice for precision steel, solid carbide, and brazed carbide tooling.



S- S after a product number means that item comes coated.


TiB2- TiB2 is the most stable of several titanium-boron compounds.  is resistant to sintering and is usually densified by hot pressing or hot isostatic pressing. resistant to oxidation in air up to 1000°C.


ZrN-  “Pale Yellow” Typically used on non-ferrous materials like aluminum, brass nickel alloys, etc. but can also handle some applications for certain iron and stainless steel grades. (Max. working temp. approximately 1110° F)



UN- (uncoated) no coating on the tool. the surface of the tool is the solid carbide that the tool is made from.


TiCN- This coating is recommended for non-ferrous materials like aluminum, brass and bronze. Has low heat resistance and good lubricity, hardness and smoothness. (MAX. working temperature is approximately 750° F)


TiN-“GOLD” Widely used general purpose tool coating used in most cutting operations. Medium heat resistance and good lubricity. Reduces wear and improves chip formation for extended tool life. Good adhesion and low friction.




AlTiN- Aluminium Titanium Nitride. Multil-layer coating, has excellent thermal stability, excels in high speed dry machining as well as wet machining. Excellent heat resistance surpassing all conventional coatings when machining cast iron and hardened steel. (Max. working temp. approximately 1470° F) This PVD coating has a gradually increasing percentage of aluminum added as it goes through the coating process. It gradually increases in the amount of Aluminum from the substrate interface until it reaches the outer surface of the coating, where there is a higher percentage (up to 65%) of aluminum in the film. As the tool heats up, the aluminum converts to aluminum oxide, staying in the film. This coating provides exceptional oxidation resistance and extreme hardness. AlTiN retains its hardness when the temperature is 800° to 930° C (1,470° to 1,700° F) This coating is ideal for dry machining environments.