NIMS Core Advanced Machining Skills 151

A axis

The rotational axis describing motion around the X axis. A axis movement can be in a clockwise or counterclockwise direction.

address

The letter used within a word that signals the essential function of the word. The address in a G code, for example, is the letter "G."

assembly

The process of joining objects. Assembly can include use of fasteners, adhesives, or welding.

B axis

The rotational axis describing motion around the Y axis. B axis movement can be in a clockwise or counterclockwise direction.

bill of materials

BOM. A report that lists the materials required to make a particular product and the cost of each individual component. A bill of materials includes all project materials, including any accessories and fasteners.

blocks

A single line of a part program. A block is composed of words.

bonded abrasive wheel

A grinding tool made of grits that are held together with chemical bonding and formed into a circular shape. A bonded abrasive wheel rotates along the surface of a part to remove material.

C axis

The rotational axis describing motion around the Z axis. The C axis describes the rotation of a machine spindle.

coatings

A finish used for protective and decorative purposes. Coatings like paint or varnish are applied to products at the end of the part creation process.

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.

computer-aided design

CAD. The use of a computer software program to aid in the automated design and technical-precision drawing of a part, product, process, or building. A computer-aided design model can be used like a part drawing.

computer-aided manufacturing

CAM. The use of a computer to assist in part manufacturing. Computer-aided manufacturing generates instructions for machining a part.

cutter radius compensation

CRC. An offset that accounts for variations in tool diameter. Cutter radius compensation is only necessary for tools that continuously cut along a horizontal plane.

datums

A point of reference for machine tools, programs, and fixtures from which measurements are taken. A datum can be a hole, a line, or any three-dimensional shape.

diameter

The distance from one side of an circle to the other side that passes through its center. Tool diameter measurement is usually included in a setup sheet.

English System

A standard system of measurements based on the inch, pound, and degrees Fahrenheit. The English System is known as the U.S. Customary System in the United States.

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.

fasteners

A device that holds objects together or locates them in relation to one another. Common fasteners include screws, bolts, and rivets.

feed

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

feeds

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

finishing

A cutting pass that emphasizes tight tolerances and smooth surface finish. Finishing is usually the last step in the machining process.

G code

A word in a part program that determines the type of operation a CNC machine performs. G codes can be either standardized or customized.

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.

grinding

The use of an abrasive tool to remove material from a workpiece. Grinding operations commonly use abrasive grains bonded into a wheel shape.

inches per minute

ipm. A unit of measurement that indicates how far in inches a tool advances in one minute. Inches per minute is used to measure feed.

inches per revolution

ipr. A unit of measurement that indicates how far in inches a tool advances in one rotation. Inches per revolution is used to measure feed.

knurling

A machining operation that displaces material rather than cutting it. Knurling embeds a textured, rough pattern into a part's surface.

linear interpolation

Machine tool movement along more than one axis at once. Linear interpolation is indicated in a part program by the word G01.

M code

A word in a part program used to signal an action from a miscellaneous group of commands. M codes change cutting tools or turn on or turn off coolant, spindle, or workpiece clamps, among other actions.

machine tool

A power-driven machine that uses a cutting tool to create chips and remove metal from a workpiece. Machine tools include lathes, mills, and drill presses.

machine zero

The default origin position on a CNC machine. Machine zero is set by the machine manufacturer.

machining

The process of removing material to form an object. Machining methods include milling, turning, and drilling.

manufacturer’s technical data references

Documents provided by a manufacturer that provide specific information about the products they manufacture. Machinists use manufacturer’s technical data references to help them select the proper cutting tool for a given operation.

meters per minute

m/min. The distance, in meters, that the cutting surface and workpiece move past one another at the point of contact in one minute. Meters per minute is also sometimes referred to as surface meters per minute.

millimeters per minute

mm/min. A unit of measurement that indicates how far in millimeters a tool advances in one minute. Millimeters per minute is used to measure feed.

millimeters per revolution

mm/rev. A unit of measurement that indicates how far in millimeters a tool advances in one rotation. Millimeters per revolution is used to measure feed.

N code

A word that acts as the name or title for a program block. N codes usually occur in increments of ten.

offset

A numerical value stored in the CNC control that repositions machine components. Offsets are used to adjust for differences in tool geometry, part size, tool wear, and any other changing variables that may affect the manufacturing of a part.

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.

program zero

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

revolutions per minute

rpm. The number of revolutions a spindle or cutting tool completes in one minute. Revolutions per minute is a measurement of speed in both English and metric systems.

roughing

A cutting pass that removes material without regard to surface finish. Roughing is often used to separate part pieces from a single sheet of material.

S code

A word in a part program that determines the spindle speed during a cutting operation. S codes are usually given in surface feet per minute or revolutions per minute.

sanding

A form of grinding that uses a fine grain abrasive to remove small amounts of material. Sanding improves the finish of a surface.

setup

The series of tasks necessary to prepare a product for processing. Setup includes the tasks involved when preparing a machine tool for the machining operations necessary to produce the product.

setup sheet

A document specification sheet for each machine and each batch of parts to be run. The setup sheet includes tool data, offsets, and operations, as well as identification information for the part, operator, and machine.

speed

The rate at which the spindle rotates. Speed indicates how fast the cutting tool or workpiece is spinning.

speeds

The rate at which the workpiece passes the cutting tool at the point of contact. Surface speed has the greatest effect on tool life.

stickout

The distance that the cutting tool extends past the toolholder. Increasing stickout reduces tool rigidity.

surface feet per minute

sfm. The distance, in feet, that the cutting surface and workpiece move past one another at the point of contact in one minute. Surface feet per minute depends on cutting diameter or cutting tool size and rpm.

surface finish

The degree of roughness and variation on the surface of a part after it has been manufactured. The surface finish of a part may need to be smooth or intentionally rough.

T code

A word in a part program used to indicate the specific cutting tool for a tool change. T code numbers indicate the position in the turret or toolchanger where the specified cutting tool is located.

tool length offset

A measurement used on a CNC mill to account for variations in tool length along the Z axis. Tool length offsets are required for each cutting tool.

toolchanger

A device on a milling machine that arranges multiple cutting tools in order and positions the tools for replacement. The toolchanger also stores the cutting tools between uses.

toolholder

A mechanism used to rigidly hold a cutting tool in place during machining. Multiple toolholders are held in the toolchanger.

toolpath

A series of program blocks that describes the movement of a single cutting tool. Toolpaths are typically generated by CAM software.

turret

A lathe component that holds a number of cutting tools. The turret rotates to place tools in the cutting position.

word

The pairing of an address letter and a numerical value in a part program. Words combine to make up a program block.

workholding

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

worktable

The component of a CNC mill that supports the workpiece and any workholding device during machining. The worktable moves on some CNC mills.

X code

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

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 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.