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Evolving from the numerical control (NC) machining process which utilized punched tape

cards, CNC machiningis a manufacturing process which

utilizes computerized controls to operate and manipulate machine and cutting tools to shape

stock material—e.g., metal, plastic, wood, foam, composite, etc.—into custom parts and

designs. While the CNC machining process offers various capabilities and operations, the

fundamental principles of the process remain largely the same throughout all of them. The

basic CNC machining process includes the following stages:
    Designing the CAD model
    Converting the CAD file to a CNC program
    Preparing the CNC machine
    Executing the machining operation
    CAD Model Design
    The CNC machining process begins with the creation of a 2D vector or 3D solid part CAD

design either in-house or by a CAD/CAM design service company. Computer-aided design (CAD)

software allows designers and manufacturers to produce a model or rendering of their parts

and products along with the necessary technical specifications, such as dimensions and

geometries, for producing the part or product.
    Designs for CNC machined parts are restricted by the capabilities (or inabilities) of

the CNC machine and tooling. For example, most custom CNC machine parts tooling is cylindrical therefore the part

geometries possible via the CNC machining process are limited as the tooling creates curved

corner sections. Additionally, the properties of the material being machined, tooling

design, and workholding capabilities of the machine further restrict the design

possibilities, such as the minimum part thicknesses, maximum part size, and inclusion and

complexity of internal cavities and features.
    Once the CAD design is completed, the designer exports it to a CNC-compatible file

format, such as STEP or IGES.
    CNC Machining Tolerances Tables
    When specifying parts to a machine shop, it's important to include any necessary

tolerances. Though CNC machines are very accurate, they still leave some slight variation

between duplicates of the same part, generally around + or - .005 in (.127 mm), which is

roughly twice the width of a human hair. To save on costs, buyers should only specify

tolerances in areas of the part that will need to be especially accurate because they will

come into contact with other parts. While there are standard tolerances for different

levels of machining (as shown in the tables below), not all tolerances are equal.
    CAD File Conversion
    The formatted CAD design file runs through a program, typically computer-aided

manufacturing (CAM) software, to extract the part geometry and generates the digital

programming code which will control the CNC machine and manipulate the tooling to produce

the custom-designed part.
    CNC machines used several programming languages, including G-code and M-code. The most

well-known of the CNC programming languages, general or geometric code, referred to as G-

code, controls when, where, and how the machine tools move—e.g., when to turn on or off,

how fast to travel to a particular location, what paths to take, etc.—across the

workpiece. Miscellaneous function code, referred to as M-code, controls the auxiliary

functions of the machine, such as automating the removal and replacement of the machine

cover at the start and end of production, respectively.
    Once the CNC program is generated, the operator loads it to the CNC machine.
    Machine Setup
    Before the operator runs the CNC program, they must prepare the CNC machine for

operation. These preparations include affixing the workpiece directly into the machine,

onto machinery spindles, or into machine vises or similar workholding devices, and

attaching the required tooling, such as drill bits and end mills, to the proper machine

    Once the machine is fully set up, the operator can run the CNC program.
    Machining Operation Execution
    The CNC program acts as instructions for the CNC machine; it submits machine commands

dictating the tooling’s actions and movements to the machine’s integrated computer, which

operates and manipulates the machine tooling. Initiating the program prompts the CNC

machine to begin the CNC machining process, and the program guides the machine throughout

the process as it executes the necessary machine operations to produce a custom-designed

part or product.
    CNC machining processes can be performed in-house—if the company invests in obtaining

and maintaining their own CNC equipment—or out-sourced to dedicated CNC machining service

    Types of CNC Machining Operations
    CNC machining is a manufacturing process suitable for a wide variety of industries,

including automotive, aerospace, construction, and agriculture, and able to produce a range

of products, such as automobile frames, surgical equipment, airplane engines, gears, and

hand and garden tools. The process encompasses several different computer-controlled

machining operations—including mechanical, chemical, electrical, and thermal processes—

which remove the necessary material from the workpiece to produce a custom-designed part or

product. While chemical, electrical, and thermal machining processes are covered in a later

section, this section explores some of the most common mechanical CNC machining operations

    CNC Drilling
    Drilling is a machining process which employs multi-point drill bits to produce

cylindrical holes in the workpiece. In CNC drilling, typically the CNC machine feeds the

rotating drill bit perpendicularly to the plane of the workpiece’s surface, which produces

vertically-aligned holes with diameters equal to the diameter of the drill bit employed for

the drilling operation. However, angular drilling operations can also be performed through

the use of specialized machine configurations and workholding devices. Operational

capabilities of the drilling process include counterboring, countersinking, reaming, and

    CNC Milling
    Milling is a machining process which employs rotating multi-point cutting tools to

remove material from the workpiece. In CNC milling, the CNC machine typically feeds the

workpiece to the cutting tool in the same direction as the cutting tool’s rotation,

whereas in manual milling the machine feeds the workpiece in the opposite direction to the

cutting tool’s rotation. Operational capabilities of the milling process include face

milling—cutting shallow, flat surfaces and flat-bottomed cavities into the workpiece—and

peripheral milling—cutting deep cavities, such as slots and threads, into the workpiece.
    CNC Turning
    Turning is a machining process which employs single-point cutting tools to remove

material from the rotating workpiece. In CNC turning, the machine—typically a CNC lathe

machine—feeds the cutting tool in a linear motion along the surface of the rotating

workpiece, removing material around the circumference until the desired diameter is

achieved, to produce cylindrical parts with external and internal features, such as slots,

tapers, and threads. Operational capabilities of the turning process include boring,

facing, grooving, and thread cutting. When it comes down to a CNC mill vs. lathe, milling,

with its rotating cutting tools, works better for more complex parts. However, lathes, with

rotating workpieces and stationary cutting tools, work best for faster, more accurate

creation of round parts.
    CNC Metal Spinning
    Close cousins to lathes, CNC spinning lathe machines involve a lathe set with a blank

(a metal sheet or tube) that rotates at high speeds while a metal spinning roller shapes

the workpiece into a desired shape. As a “cold” process, CNC metal spinning forms pre-

formed metal—the friction of the spinning lathe contacting the roller creates the force

necessary to shape the part.
    How Does a Swiss Machine Work?
    Swiss machining, also known as swiss screw machining, uses a specialized type of lathe

that allows the workpiece to move back and forth as well as rotate, to enable closer

tolerances and better stability while cutting. Workpieces are cut right next to the bushing

holding them instead of farther away. This allows for less stress on the part being made.

Swiss machining is best for small parts in large quantities, like watch screws, as well as

for applications with critical straightness or concentricity tolerances. You can find out

more about this topic in our guide on how swiss screw machines work.
    How Does a 5 Axis CNC Machine Work?
    5 axis CNC machining describes a numerically-controlled computerized manufacturing

system that adds to the traditional machine tool’s 3-axis linear motions (X, Y, Z) two

rotational axes to provide the machine tool access to five out of six part sides in a

single operation. By adding a tilting, rotating work holding fixture (or trunnion) to the

work table, the mill becomes what is called a 3+2, or an indexed or positional, machine,

enabling the milling cutter to approach five out of six sides of a prismatic workpiece at

90° without an operator having to reset the workpiece.
    It is not quite a 5-axis mill, however, because the fourth and fifth axes do not move

during machining operations. Adding servomotors to the additional axes, plus the

computerized control for them – the CNC part –would make it one. Such a machine- which is

capable of full simultaneous contouring- is sometimes called a “continuous” or

“simultaneous” 5-axis CNC mill. The two additional axes can also be incorporated at the

machining head, or split – one axis on the table and one on the head.
    CNC Lathe Operator Training
    To handle a CNC lathe, a machinist should have completed a set amount of coursework and

earned appropriate certification from an accredited industrial training organization. CNC

turning machining training programs will usually involve multiple classes or sessions,

offering a gradual instruction process broken up into several steps. The importance of

adhering to safety protocols is reinforced throughout the training process.
    Beginning CNC lathe classes might not include hands-on experience, but they may include

familiarizing students with the command codes, translating CAD files, tool selection,

cutting sequences, and other areas. A beginner CNC lathe course may include:
    Lubrication and scheduling lathe maintenance
    Translating instructions into a machine-readable format and loading them into the lathe
    Establishing criteria for tool selection
    Installing tools and parts for handling the material
    Producing sample parts, like die-

casting parts

    Later CNC lathe training typically involves actual lathe operation, as well as machine

adjustments, program editing, and the development of new command syntax. This type of lathe

machine training can include courses on。
    Figuring out where edits are needed from comparing sample parts to their specifications
    CNC programming edits
    Creating multiple cycles of test components to refine the results of edits
    Regulating coolant flow, cleaning the lathe, and repair and replacement of tools
    CNC Machining Equipment and Components
    As indicated above, there is a wide range of machining operations available. Depending

on the machining operation being performed, the CNC machining process employs a variety of

software applications, machines, and machine tools to produce the desired shape or design.
    Types of CNC Machining Support Software
    The CNC machining process employs software applications to ensure the optimization,

precision, and accuracy of the custom-designed part or product. Software applications used

    CAD: Computer-aided design (CAD) software are programs used to draft and produce 2D

vector or 3D solid part and surface renderings, as well as the necessary technical

documentation and specifications associated with the part. The designs and models generated

in a CAD program are typically used by a CAM program to create the necessary machine

program to produce the part via a CNC machining method. CAD software can also be used to

determine and define optimal part properties, evaluate and verify part designs, simulate

products without a prototype, and provide design data to manufacturers and job shops.
    CAM: Computer-aided manufacturing (CAM) software are programs used extract the

technical information from the CAD model and generate machine program necessary to run the

CNC machine and manipulate the tooling to produce the custom-designed part, such as

stamping parts,

custom plastic parts, etc. CAM

software enables the CNC machine to run without operator assistance and can help automate

finished product evaluation.
    CAE: Computer-aided engineering (CAE) software are programs used by engineers during

the pre-processing, analysis, and post-processing phases of the development process. CAE

software is used as assistive support tools in engineering analysis applications, such as

design, simulation, planning, manufacturing, diagnosis, and repair, to help with evaluating

and modifying product design. Types of CAE software available include finite element

analysis (FEA), computational fluid dynamics (CFD), and multibody dynamics (MDB) software.
    Some software applications have combined all of the aspects of CAD, CAM, and CAE

software. This integrated program, typically referred to as CAD/CAM/CAE software, allows a

single software program to manage the entire fabrication process from design to analysis to

    What is a CNC Machine? Types of CNC Machines and custom CNC precision machining parts
    Depending on the machining operation being performed, the CNC machining process employs

a variety of CNC machines and machine tools to produce the custom-designed part or product.

While the equipment may vary in other ways from operation to operation and application to

application, the integration of computer numerical control components and software (as

outlined above) remains consistent across all CNC machining equipment and processes.
    CNC Drilling Equipment
    Drilling employs rotating drill bits to produce the cylindrical holes in the workpiece.

The design of the drill bit allows for the waste metal—i.e., chips—to fall away from the

workpiece. There are several types of drill bits, each of which is used for a specific

application. Types of drill bits available include spotting drills (for producing shallow

or pilot holes), peck drills (for reducing the amount of chips on the workpiece), screw

machine drills (for producing holes without a pilot hole), and chucking reamers (for

enlarging previously produced holes).
    Typically the CNC drilling process also utilizes CNC-enabled drill presses, which are

specifically designed to perform the drilling operation. However, the operation can also be

performed by turning, tapping, or milling machines.
    CNC Milling Equipment
    Milling employs rotating multi-point cutting tools to shape the workpiece. Milling

tools are either horizontally or vertically oriented and include end mills, helical mills,

and chamfer mills.
    The CNC milling process also utilizes CNC-enabled milling machinery, referred to as

mill machines or mills, which can be horizontally or vertically oriented. Basic mills are

capable of three-axis movements, with more advanced models accommodating additional axes.

The types of mills available include hand milling, plain milling, universal milling, and

omniversal milling machines.
    CNC Turning Equipment
    Turning employs single-point cutting tools to remove material from the rotating

workpiece. The design of the turning tool varies based on the particular application, with

tools available for roughing, finishing, facing, threading, forming, undercutting, parting,

and grooving applications.
    The CNC turning process also utilizes CNC-enabled lathes or turning machines. The types

of lathes available include turret lathes, engine lathes, and special-purpose lathes.
    What is a Desktop CNC Machine?
    Companies that specialize in manufacturing CNC machines often offer a desktop series of

smaller, lightweight machines. Desktop CNC machines, although slower and less precise,

handle soft materials well, such as plastic and foam. They’re also better for smaller

parts and light to moderate production. Machines featured in a tabletop series resemble the

larger industry standard, but their size and weight make them better suited to small

applications. A desktop CNC lathe, for example, that features two axes and can handle parts

up to six inches in diameter, would be useful for jewelry and mold-making. Other common

desk CNC machines include plotter-sized laser cutters and milling machines.
    With smaller lathes, it’s important to differentiate between a benchtop CNC lathe

machine and a desktop lathe. Benchtop CNC lathes are generally more affordable, but also

smaller and somewhat limited in the applications they can handle. A standard CNC benchtop

lathe generally includes the motion controller, cables, and basic software. A standard CNC

desktop lathe, with a similar basic package, costs slightly more.



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