Acronyms and Term Definitions for Grinding Carbide Tools

Precision machining with carbide cutting tools is a world of exact language and acronyms. This list doesn’t cover everything you’ll run into, but many common terms are defined here.

A

ae: Radial depth of cut (RDOC), also known as “stepover.” Is often specified as a percent of tool diameter.

ap: Axial depth of cut (ADOC), also known as “stepdown.”

Acme thread: A screw thread with a 29-degree angle. Used mainly for feed and adjusting screws on machine tools.

Acute angle: An angle that is less than 90 degrees.

Allowance: The prescribed difference in dimensions of mating parts to provide a certain level of fit.

Alloy: A metal made with a mixture of two or more different metals.

AlTiN: Aluminum titanium nitride coating for a tool. It has high heat resistance properties, so it is well suited for hard machining applications like drilling. It is a good coating option for hardened steel, alloy steel, low carbon steel, carbon steel, martensitic stainless steel, PH stainless steel, and titanium.

Annealing: The controlled heating and cooling of a metal to remove stresses. This can make a metal softer and easier to work with.

Arbor: A shaft or spindle for holding cutting tools.

Axis: The line, real or imaginary, passing through the center of an object about which it could rotate; a point of reference.

B

Back rake: The angular surface ground back from the cutting edge of a tool.

Bevel: Any surface that is not at right angles to another surface. Also, a tool used for measuring, aligning, or checking the accuracy of work machined at an angle or bevel.

Blind hole: A hole made in a workpiece that does not pass through it.

Bore: To enlarge and finish the surface of a cylindrical hole by the action of a rotating boring bar (cutting tool) or by the action of a stationary tool pressed (fed) against the surface as the part is rotated.

Boring bar: A cutting tool where the tool bit, the boring bar, and, in some cases, the tool holder are incorporated into one solid piece.

Brass: A nonferrous alloy consisting essentially of copper and zinc.

Bronze: A nonferrous alloy consisting essentially of copper and tin.

Burr: The sharp edge left on metal after cutting. Also, a rotary cutting tool that can be attached to a drill.

C

CAD: Computer-aided design.

Caliper: A device used to measure inside or outside dimensions.

Cam: A device for converting regular rotary motion to irregular rotary or reciprocating motion. Sometimes it is the effect of off-center lathe operations.

CAM: Computer-aided manufacturing.

Carbide bit: A cutting tool created by grinding a cutting geometry into a tungsten carbide blank.

Carbon steel: A broad term applied to tool steel other than high-speed or alloy steel.

Center drill: A combined drill and countersink used to prepare work for mounting centers.

Chamfer: The angular or beveled surface cut on the corner or edge of a machined part or tool.

Chatter: Vibrations caused between the work and the cutting tool. Chatter may leave distinctive tool marks on the finished surface that are not intended.

Chips: Material cut or removed during a machining operation.

Chip breaker: A small groove or notch parallel to the cutting edge in a tool that helps keep chips short.

Chip load: The distance a bit moves forward as a single flute cuts into a material. The formula for chip load is CL = (feed rate / no. flutes) / RPM. The TOTAL chip load is the distance a bit moves forward during a single revolution (TCL = feed rate / RPM) and is given in inches (or millimeters) per revolution.

Clearance: The distance or angle by which one object’s surface clears another.

Clearance angle: The angle between the rear surface of a cutting tool and the surface of the work at the point of contact.

CMM: Coordinate measuring machine—a device that measures the geometry of physical objects by sensing exact points on the surface with a probe. The probe may be mechanical, laser, optical, or white light.

CNC: Computer numerical control.

Coolant: A common name for numerous cutting fluids or compounds used while machining to increase the tool life and to improve surface finish.

Counterbore: To enlarge the top of a hole, as for the head of a socket-head or cap screw. Also, the tool that is used.

Countersink: To enlarge the top part of a hole at an angle for a flat-head screw. Also, the tool that is used.

Cross feed: The feed that operates across the axis of the workpiece or at right angles to the main or principal feed on a machine.

Cutting speed (CS): The surface speed of the workpiece in a lathe or a rotating cutter. It is expressed in feet per minute (FPM) and converted to revolutions per minute (RPM) for setting up a machine.

D

D: Small diameter.

Deburr: To remove sharp edges.

E

Eccentric: A circle not having a geometric center.

End mill: A cutting tool used in industrial milling applications. It is distinguished from a drill bit by its application, geometry, and manufacturing. A drill bit can only cut in the axial direction, while most milling bits can cut in the radial direction. Not all mills can cut axially; those designed to cut axially are known as end mills.

End mills are used in milling applications such as profiling, facing, plunging, slotting, and side milling.

F

Fn: Feed per revolution.

Fz: Feed per tooth.

Face milling: Milling a large flat surface with a milling cutter that operates in a plane that is at right angles to its axis.

Facing: The process of making a flat or smooth surface (usually the end) on a material.

Feed: The rate of travel of a cutting tool across or into the work. In the U.S., expressed in inches per minute or in inches per revolution.

Feed mechanism: The mechanism, often automatic, that controls the advancing movement (feed) of the cutting tools.

Ferrous: A metal alloy in which iron is the major ingredient.

Flute: The groove in a cutting tool that provides a cutting edge and a space for the chips to escape and permits the cutting fluids to reach the cutting edges. Both straight and helical flutes are commonly encountered in modern cutters.

FPM: Feet per minute of workpiece.

Full plunge cut: Cutting with a milling cutter using the entire flute length in a single pass.

G

Gage: Any one of a large variety of devices for measuring or checking the dimensions of objects.

H

Hardening: A heat-treating process for steel that increases its hardness and tensile strength and reduces its ductility.

Helix: A path formed as a point advances uniformly around a cylinder, as the thread on a screw or the flutes on a drill.

Helix angle: The angle between the direction of the threads around a screw and a line running at a right angle to the shank.

High-speed steel: An alloy steel often used for cutting tools because of its ability to remove metal at a much faster rate than carbon steel tools.

Hogging: Cutting with a large chip load to quickly remove a lot of material.

I

ID: Inside diameter.

IPM: Feed rate in inches per minute.

K

Kc: Specific cutting force.

KAPR: Entering angle.

Keyseat cutters: Multipurpose milling tools designed to cut keyseats and keyways into shafts. These woodruff-style cutters are designed with dished sides for clearance.

L

LD: Large diameter.

LH: Left hand.

Limits: The smallest and largest dimensions that are tolerable (allowed).

M

Machinability: The degree of difficulty for machining metals; may be found in appropriate handbooks.

Mic/Mike: A term used for micrometer, or to measure with a micrometer.

Microtool: Generally considered as any rotary tool with a diameter less than 0.0313″ (0.8mm). May also refer to any rotary tool with a diameter less than 0.125″ (3.15mm).

Mill: A milling machine. Also, the act of performing an operation on the milling machine.

Minor diameter: The smallest diameter of a screw thread. Also known as the “root diameter.”

MRR: Material removal rate

N

nACo: An AlTiN-based nanocomposite coating for tools that stands up well to hard material machining and high heat. It’s a good choice for working with steels, hardened steels, stainless steels, and other superalloys.

nACRo: A coating for tools made up of an aluminum chrome nitride nanocomposite with silicon nitride added in. It is a step up from nACo in terms of its durability. It works well for nonferrous alloys, standard steel alloys, and superalloys. It is heat and scratch resistant and very good at extending tool life.

NC: Numerical control.

Nickel: An alloying element that increases the strength, toughness, and corrosion and wear resistance of steels.
Nonferrous metals: Any metal or alloy that does not contain iron. Examples include gold, silver, copper, aluminum, and brass.

O

OD: Outside diameter.

Overall length (OAL): The total length of a cutting tool.

P

Peck: Repetitive plunging of a bit into a material while gradually increasing the degree of penetration. Used to prevent breakage and minimize tip wander (deflection). Pecking is used when drilling small diameter holes in composite materials (like fiberglass) that tend to make the tip deflect. 

Pilot: A guide at the end of a counterbore to keep it aligned with the hole.

Pilot hole: A starting hole for large drills to serve as a guide, reduce the resistance, and help maintain the accuracy of the larger hole. Also called a “lead hole.”

Pitch: The distance from any point on a thread to the corresponding point on the adjacent thread measured parallel to the axis.

Pitch diameter: The diameter of a thread at an imaginary point where the width of the groove and the width of the thread are equal.

Pitch line: An imaginary line through threads at such points that the length of the part of the line between adjacent threads is equal to the length of the line within a thread.

Plain cutter: A milling cutter with cutting teeth on the periphery (circumference) exclusively.

R

Rake: The surface of a cutting tool against which the chips bear while being severed. If this surface is less than 90 degrees from the surface being cut, the rake is positive; if more, the rake is negative.

Reaming: A machining operation in which a rotary tool takes a light cut to improve the accuracy of the round hole and reduce the roughness of the hole surface.

Revolutions per minute (RPM): The rate of spin measured in inverse minutes.

RH: Right hand.

Roughing: The fast removal of stock to reduce a workpiece to approximate dimensions, leaving only enough material to finish the part to specifications.

S

SFPM: Surface feet per minute.

Shank: The part of a tool that connects the principal operating part to the handle, socket, or chuck by which it is held or moved.

Slotter: An attachment to operate a reciprocating motion. Used for machining internal slots and surfaces.

Spindle: A rotating shaft that serves as a support, a positioner, and a rotary drive for the tool or workpiece.

Spindle speed: The RPM at which a machine is set. See Cutting speed (CS).

Surface feet per minute (SFM): A measure (in feet per minute) of how fast a cutting edge passes through a material. From a practical point of view, it is equal to the tangential velocity of a point on the outermost surface of a cutting tool. The formula is the circumference of the cutter (in feet) multiplied by how fast the tool is turning (RPM): i.e., SFM = Tool diameter ✕ 3.14 ✕ RPM.

T

Taper: A uniform increase or decrease in the size or diameter of a workpiece.

Tenth: A unit of measurement in machining equaling 0.0001″, or one ten-thousandths of an inch (not to be mistaken for a tenth of an inch).

Thou: A machinist’s term for a unit of measurement equaling 0.001″, or a thousandth of an inch.

Thread angle: The angle formed by the two sides of the thread (or their projections) with each other.

Thread axis: A line running lengthwise through the center of the screw.

Thread depth: The distance between the crest and the root of a thread.

Thread mill: A cutting tool designed to cut threads by milling. Thread mills are used on numerically controlled machining centers that have simultaneous, triaxial control and helical interpolation functions.

Thread pitch: The distance from a point on one screw thread to a corresponding point on the next thread.

Thread pitch diameter: The diameter of a screw thread measured from the thread pitch line on one side to the thread pitch line on the opposite side.

Thread root: The bottom surface joining the sides of two adjacent threads.

TiCN: Titanium carbon nitride. A tool coating that works well on nonferrous materials, including aluminum. It can be used in some steel cutting applications. It is slightly harder than TiN and offers better lubricity because of its lower coefficient of friction. TiCN is good for milling and tapping cuts or any time a tool has particularly sharp edges or corners.

TiN: Titanium nitride; a good universal tool coating for working with ferrous materials like iron, steel, alloy steel, and low carbon steel. It can reduce overall tool wear.

Tolerance: The allowable deviation from a standard size.