adjacent

In a triangle, a side that touches an angle. The adjacent sides form the angle.

approach distance

A short distance added to the beginning of a toolpath. Approach distance helps to prevent damage to the machine and the workpiece.

arc center method

A method for programming circular tool movements that indicates the location of the arc's center along the X and Y axes using I and J codes. The arc center method is usually used for full-arc motions.

arc-in motion

A partial-arc motion that leads into a larger-arc motion. Arc-in and arc-out motions leave a smooth surface finish.

arc-out motion

A partial-arc motion that exits from a larger-arc motion. Arc-out and arc-in motions leave a smooth surface finish.

axes

An imaginary line that passes through the center of a point or object. Axes are used to describe the positions of objects in the Cartesian coordinate system.

block

A single line of a part program. A block is composed of words and is written in code.

bolt-hole pattern

A series of equally spaced holes around the circumference of a larger imaginary circle. Bolt-hole patterns are calculated with trigonometry.

boring

The process of enlarging an existing hole with a single-point tool. Boring can be performed on a mill using either the canned cycle G85 or G86.

boxing routine

A series of toolpaths used to machine a rectangular pocket. A boxing routine starts in the center of the pocket and moves outward in a rectangular pattern.

CAD/CAM

Computer-aided design/computer-aided manufacturing. The use of computers to aid in the design and manufacturing of a part. CAD/CAM makes it comparatively easy to machine complex surfaces, especially parts with three-dimensional contour features.

calculator

A small, handheld device used to solve mathematical problems. Calculators can be useful for finding the sine, cosine, or tangent of an angle.

canned cycles

A predetermined machining sequence used to simplify programming. A canned cycle sequence is initiated by a single G code.

Cartesian coordinate system

The system that describes the position of any point or object in three-dimensional space by expressing its distance from a fixed position along linear axes. The Cartesian coordinate system is used to describe measurements in CNC milling and turning.

chamfer

An angled surface added to an edge of a workpiece. Chamfers replace a sharp edge with a 45° angle.

chatter

The development of surface imperfections on the workpiece caused by vibrations of the cutting tool. Chatter can occur if step-over is either too little or too much.

chips

An unwanted piece of metal that is removed from a workpiece. Chips are formed when a tool cuts or grinds metal.

circular pocket

An interior recess shaped like a circle that is cut into the surface of a workpiece. Pockets generally are created using an end mill.

circumference

The distance around a curve or circle. The circumference is the circle's outer perimeter.

clearance

Any useful space that is intentionally maintained between components. Clearance is often necessary to prevent machine damage.

clearance plane

The distance specified by the R level. A clearance plane indicates the safe distance for rapid tool movement from one operation to the next.

CNC

Computer numerical control. A self-contained system of computers and precision motors that executes program instructions to guide machine tool components and manufacture parts. CNC machines use part programs to control the cutting operations required to create a part.

CNC mill

A machine tool that uses computer numerical data to control cutting operations on flat, square, or rectangular workpieces. On a CNC mill, the cutting tool rotates against a workpiece that is fixed to a worktable.

collet

A slitted device that expands or contracts to securely hold a cutting tool or workpiece. On the mill, collets hold tools in the spindle.

computer numerical control

CNC. A self-contained system of computers and precision motors that executes program instructions to guide machine tool components and manufacture parts. Computer numerical control machines use part programs to control the cutting operations required to create a part.

concentricity

A geometric tolerance that creates a tolerance zone for the median points of a cylindrical feature. Concentricity of a hole improves when the hole is reamed or bored with the G85 canned cycle.

contour features

A curved part of a workpiece. Contour features are complex and generally calculated using CAD/CAM software.

conversational programming

A programming method that allows an operator to machine a part by responding to a series of prompts. Conversational programming does not reveal the actual program codes.

coordinates

A series of numerical positions that describe any point of an object in three-dimensional space. Coordinates are usually described on CNC mills using the X, Y, and Z axes of the Cartesian coordinate system.

cosine

In a right triangle, the ratio of the length of the side adjacent to the angle and the hypotenuse. The cosine of a right triangle can be found by calculating the ratio as a division problem.

counterboring

A holemaking operation that enlarges one end of a previously drilled hole to a certain depth. Counterboring allows the enlarged end to provide room for the head of a screw or nut.

cutting fluid

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

cycle time

The full time it takes to manufacture a part. Lower cycle time can be achieved when using a peck drilling canned cycle with the G73 rapid peck drilling cycle.

deflection

The unintended movement or repositioning of a component due to a mechanical force. Deflection of a cutting tool can cause poor surface finish and inaccurate dimensions.

depth

The distance of an object from top to bottom. Depth in a hole or pocket is measured from the surface of the part to the bottom of the hole or pocket.

depth of cut

The depth to which the cutting tool penetrates the surface of the workpiece. On a mill, depth of cut is dictated by the movement of either the spindle or the worktable.

diameter

The distance from edge to edge of the widest point of a circle. The diameter of a circle is always twice its radius.

drag line

A mark left along the length of a hole at the end of a G86 rough boring operation. Drag lines are the result of a boring tool retracting rapidly out of a hole.

drilling

The use of a multipoint tool to machine a new round hole into the surface of a workpiece. Drilling is a type of holemaking operation.

dwell

A pause built into the execution of a program in which the cutting tool remains in contact with the workpiece. A dwell can be used to improve the finish of a hole.

end mill

A long, thin milling cutter with a flat bottom and cutting edges that wind up the sides. End mills have helical flutes and relatively small diameters.

F code

A word in a part program that determines the feed rate during a cutting operation. F codes are usually given in inches per minute or inches per revolution.

face mill

A flat milling cutter with multiple cutting teeth on its periphery. Face mills rapidly remove metal from the top surface of a workpiece.

face milling

A milling operation in which the surface of the workpiece is perpendicular to the spindle axis. Face milling is primarily used to mill the top surface of the part.

features

A physical part attribute that naturally contains variation and imperfections. Features include corners, edges, flat surfaces, and holes.

feed

The rate at which the cutting tool and the workpiece move in relation to one another. Feed is typically a linear movement but can also be angular and circular.

feed rate

The rate at which the cutting tool and the workpiece move in relation to one another. Feed rate is typically a linear movement.

finishing pass

A cutting pass that refines the surface finish and brings a feature to its proper size. The finishing pass is typically the last operation in the part program.

G code

A word in a part program that determines the type of operation performed on the CNC machine. G codes apply to all blocks following their occurrence until a new G code occurs in the part program.

G code programming

A programming language that pairs address letters with numerical values to form commands. G code programming is used to direct CNC machine movements.

G73

A code in G code programming that generally activates the rapid peck drilling canned cycle. During the G73 canned cycle, the cutting tool backs up between pecks without fully exiting the hole.

G74

A code in G code programming that generally activates the left-hand tapping canned cycle. During the G74 canned cycle, the cutting tool rotates counterclockwise as it enters a hole to cut a thread.

G75

A code in G code programming that generally activates the clockwise rectangular pocket milling canned cycle. The G75 canned cycle begins machining over the pocket's center point and cuts outward in a clockwise direction.

G76

A code in G code programming that generally activates the counterclockwise rectangular pocket milling canned cycle. The G76 canned cycle begins machining over the pocket's center point and cuts outward in a counterclockwise direction.

G77

A code in G code programming that generally activates the clockwise internal circular milling canned cycle. The G77 canned cycle begins machining over the pocket's center point and cuts outward in a clockwise direction.

G78

A code in G code programming that generally activates the counterclockwise internal circular milling canned cycle. The G78 canned cycle begins machining over the pocket's center point and cuts outward in a counterclockwise direction.

G80

A code in G code programming that cancels a mode. G80 is used to end a canned cycle.

G81

A code in G code programming that typically activates the general drilling canned cycle. During the G81 canned cycle, the cutting tool positions to a hole location, drills a hole, and then exits out of the hole.

G82

A code in G code programming that generally activates the drilling with dwell canned cycle. During the G82 canned cycle, the cutting tool remains in position at the bottom of a hole before retracting out of it.

G83

A code in G code programming that generally activates the standard peck drilling canned cycle. During the G83 canned cycle, the cutting tool moves rapidly out of the hole between pecks.

G84

A code in G code programming that generally activates the right-hand tapping canned cycle. During the G84 canned cycle, the cutting tool rotates clockwise as it enters a hole to cut a thread.

G85

A code in G code programming that generally activates the boring/reaming canned cycle. The G85 canned cycle feeds a cutting tool into and then back out of a hole at the same feed rate without stopping at the bottom of the hole.

G86

A code in G code programming that generally activates the rough boring canned cycle. In the G86 canned cycle, a cutting tool feeds into a hole, stops at the bottom, and then moves rapidly back out of the hole.

G98

A code in G code programming that instructs the cutting tool to return to the initial level. G98 codes are often used at the end of canned cycles.

G99

A code in G code programming that instructs the cutting tool to return to the R level or clearance plane. G99 codes are often used at the end of canned cycles.

gear

A round or cylindrical mechanical component with teeth that transmits power. Gears mesh with one another and can alter the speed, torque, or direction of mechanical energy.

geometry

A branch of mathematics that involves the measurements, properties, and relationships of dimensional objects. Geometry is used in CNC machining.

hypotenuse

In a right triangle, the side located opposite the right angle. The hypotenuse is the longest side of the triangle.

I code

The program code that indicates the location of an arc's center along the X axis. I and J codes are used for the arc center method.

initial level

The imaginary plane that indicates the tool position when a canned cycle is initiated. The initial level is typically located above the R level.

initial level return

A movement that positions the cutting tool at the initial level at the end of a canned cycle. Initial level return occurs when a G98 code is used in a part program.

internal circular milling

A milling operation during which a round interior recess, called a pocket, is cut into the surface of a workpiece. Internal circular milling operations are usually machined using an end mill.

isosceles right triangle

A triangle with one 90° angle and two 45° angles. The two 45° sides of an isosceles right triangle are always equal in length.

J code

The program code that indicates the location of an arc's center along the Y axis. J and I codes are used for the arc center method.

left-hand tap

A cutting tool that rotates counterclockwise as it enters a hole to cut a thread. Left-hand taps require the use of the tapping canned cycle G74.

length-to-diameter ratio

A ratio comparing the length of a cylindrical tool to its diameter. Higher length-to-diameter ratios offer less rigidity.

machine control unit

MCU. A small, powerful computer that controls and operates a CNC machine. Machine control units offer standard canned cycles as well as special canned cycles.

MCUs

Machine control unit. A small, powerful computer that controls and operates a CNC machine. MCUs offer standard canned cycles as well as special canned cycles.

milling cutter

A multipoint tool that removes metal from the surface of a workpiece. Milling cutters can create parts with complex shapes.

mode

A programmed function that stays in effect until it is either cancelled or substituted with another function. Most canned cycles function as modes on a CNC machine.

origin

The fixed center point of the Cartesian coordinate system. The origin has a numerical value of zero for any axis.

override

A control that adjusts a programmed element of part machining during operation of the part program. Speed and feed overrides allow an operator to adjust speed or feed rates.

P code

A word in the drilling with dwell G82 canned cycle that indicates how long the tool should dwell inside the hole. P codes are also used in multiple repetitive canned cycles to indicate the starting block number of the final toolpath.

part program

A series of alpha-numeric instructions that direct a CNC machine to perform the necessary sequence of operations to machine a specific workpiece. Multiple part programs can be stored in a CNC at one time.

peck drilling

A drilling operation that periodically retracts the tool to clear chips or flood the hole with coolant. Peck drilling is often used for holes that are deeper than the drill diameter.

pecks

A single pass of a peck drilling cycle. A complete peck drilling cycle is composed of a number of pecks.

pocket

An interior recess that is cut into the surface of a workpiece. Pockets can be circular, rectangular, or a combination of the two.

pocket milling

A milling operation during which an interior recess, called a pocket, is cut into the surface of a workpiece. Pockets can be either rectangular or round and generally are created using an end mill.

program zero

The position that acts as the origin for the part program of each particular workpiece. Program zero is selected by the part programmer.

Q code

A word in peck drilling and multiple repetitive canned cycles. Q codes indicate peck distance for peck drilling cycles and the ending block number of the final toolpath in a multiple repetitive cycle.

R level

The imaginary plane parallel to the X axis or Z axis indicating the cutting tool clearance plane. An R level indicates the safe distance for rapid tool movement from one operation to the next.

R level return

A movement that positions the cutting tool at the R level or clearance plane. R level return occurs when a G99 code is used in a part program.

radius

A straight line extending from the center point to the periphery of a circle. The radius of a circle is always one-half of its diameter.

radius method

A method for programming circular tool movements that indicates the size of the arc's radius using an R code. The radius method is best used for partial-arc motions.

rapid positions

The quick movement of a machine component to a certain location. Rapid positioning occurs when the cutting tool is a safe distance from the workpiece.

reaming

The process of enlarging or smoothing an existing hole with a multipoint tool. Reaming can be performed on a mill using the canned cycle G85.

rectangular pocket

An interior recess shaped like a rectangle that is cut into the surface of a workpiece. Pockets generally are created using an end mill.

right triangles

A triangle that includes a 90° angle as one of its three angles. Right triangles are often used in drilling calculations.

right-hand tap

A cutting tool that rotates clockwise as it enters a hole to cut a thread. Right-hand taps require the use of the tapping canned cycle G84.

rough boring

A holemaking operation that enlarges an existing hole with a single-point tool that rapidly retracts from the hole after machining. Rough boring often leaves a mark, known as a drag line, along the length of the hole.

sine

In a right triangle, the ratio of the length of the side opposite the angle and the hypotenuse. The sine of a right triangle can be found by calculating the ratio as a division problem.

speed

The rate at which the machine spindle rotates. The spindle speed affects how fast the cutting tool moves at the point of contact.

speed range

A limited set of possible speeds at which a machine is capable of running. Speed ranges for a manual mill include high and low range.

spindle

The part of the machine tool that rotates. On the mill, the spindle holds the cutting tool.

spot drill

A short, sturdy drill used to start a hole and accurately locate it. Most spot drills have a 90° tip.

spot drilling

A drilling operation that uses a shorter, sturdier drill to create a small hole that prevents the next drill from wandering off center. Spot drilling often uses a drill size slightly larger than the hole diameter to leave a chamfer after the hole is drilled.

step-over

The amount of the cutter's diameter that is engaged in a cut. Step-over is generally 75% or less of the cutter's diameter.

stress

A force that attempts to deform an object. The effects of stress are called strain.

surface finish

The degree of roughness and variation on the surface of a part after it has been manufactured. Surface finish on a part is never perfectly smooth, due to irregularities created during machining.

symmetrical parts

A part that can be divided into two equal halves with identical features that are equal distances from the centerline. Symmetrical parts typically have program zero placed in the center.

synchronizing

To operate at the same time or rate. Synchronizing allows feed and speed to work together to create tool movements.

tangent

In a right triangle, the ratio of the length of the side opposite the angle and the side adjacent to the angle. The tangent of a right triangle can be found by calculating the ratio as a division problem.

tap

A cylindrical cutting tool used to produce internal threads in a preexisting hole. A tap has thread forms on its outer surface that match the internal threads it is designed to produce.

tapping

The process of cutting internal threads in a hole with a rotating multipoint tool. Tapping can be performed on a mill using the canned cycle G84 or G74.

threads

A long, spiral ridge around the exterior or interior of a cylindrically shaped object. Threads can be machined in a hole using the tapping canned cycle.

three-dimensional

Having length, width, and depth. Three-dimensional parts can be machined with CNC machines.

through holes

A hole that passes completely through a workpiece. Through holes require that the depth of the hole, the length of the drill tip, and a small amount of additional clearance all be calculated.

tolerance

An unwanted but acceptable deviation from a given dimension. Tolerances indicate the allowable difference between a physical feature and its intended design.

toolpaths

A series of program blocks that describes the movement of a single cutting tool. Complex toolpaths are typically generated using computer-aided manufacturing.

trigonometry

A branch of mathematics that addresses the measurements and relationships of triangles and their components. Trigonometry is often used in milling calculations.

twist drill

A common drill characterized by helical flutes along its length and two cutting edges at the drill point. Twist drilling is usually preceded by spot drilling.

vise

A workholding device with two jaws that grip and hold a workpiece in place. Vises are commonly used for workholding on the mill.

vise jaw

A component on a vise that grips and holds the workpiece in place. A vise has one fixed jaw and one movable jaw.

workholding

A method or device for securing a workpiece for a machining operation. Workholding can include chucks, vises, and bolts.

workpiece

Any metal or other material that is being machined. Workpieces are usually held in a workholding device during milling.

X axis

The linear axis representing the longest distance of travel parallel to the worktable or left to right on a vertical mill. The X axis is perpendicular to the Y and Z axes.

X code

A word in a part program that describes a specific position along the X axis. X codes are usually used in conjunction with Y codes on a CNC mill.

Y axis

The linear axis representing the shortest distance parallel to the worktable, or towards and away on a vertical mill. The Y axis is perpendicular to the X and Z axes.

Y code

A word in a part program that describes a specific position along the Y axis. Y codes are usually used for CNC mills but not for CNC lathes.

Z axis

The linear axis that represents motion towards and away from the worktable, or up and down on a vertical mill. The Z axis is perpendicular to the X and Y axes.

Z code

A word in a part program that describes a specific position along the Z axis. Z codes are usually used for both CNC mills and CNC lathes.

Z depth

The Z axis position that marks the depth of a hole in a holemaking canned cycle. The Z depth is indicated by the Z code.

R code

The program code that indicates the length of an arc's radius. In certain canned cycles, an R code indicates the R level for tool return.

R code

A word in a canned cycle that describes the location of the R level or clearance plane. R codes are required for holemaking canned cycles to function.