CNC Programming: Definition, Process, And Types

If you are just getting started with computer numerical control (CNC) milling or any other form of CNC machining, it might first appear confusing and challenging.

The use of computer technology in the manufacturing industry has grown tremendously over the decades. Advanced technologies are controlling how machinery operates, adding many benefits to the manufacturing processes.

The best manufacturers use CNC machines or services to produce intricate parts with repeatable results. CNC milling is one of the most prominent processes in these businesses. Others include CNC drilling, CNC turning, and CNC routing. In this comprehensive guide, we delve into the world of CNC milling. We hope that the milling machine insights offered here will help you undertake your next CNC milling project satisfactorily.

What Is CNC Programming?

CNC programming refers to the process of using software to develop CNC machine instructions. These instructions control how the CNC machine moves while interacting with the work piece. Popular CNC machines that work with CNC programming are CNC lathes and CNC milling machines.

Since its inception, CNC programming has enabled people to make incredible carvings and many other things, from code. The CNC program make the machine tools and the CNC machines to interact with the work piece to create amazing things.

A lot of mastery is needed to execute the programming effectively. Machines and tools are involved, so there is some level of delicacy involved. However, one can master this skill with exercise.

Most CNC machines control their processes using G-codes and M-codes. G-codes are used for instructing the position of the work piece or cutting tool. M-codes have several functions, including activating the tool rotations.

There are also alphanumeric codes used in CNC programming. These codes direct specific functions such as speed of rotation, feed rate, tool number, and so on.  The alphanumeric codes include S, T, D and F.

How Does CNC Programming Work?

Even the best CNC operators and programmers started with the basics. These basics concern how CNC programming works. There are several steps in CNC programming. Each step is a continuation of the preceding one.

Every CNC programming project starts with the use of Computer-Aided Design (CAD) software to design a part. Next, the design is taken to Computer-Aided Manufacturing (CAM) software. The CAM software converts the previous instructions to others that are understandable by the CNC machine.

There are several programming languages for CNC machining, but the most popular is G-Code. This language is based on alphanumeric codes. These codes control particular actions, for instance, turning on the coolant and changing the position of the cutting tool.

These programs are arranged in lines, with a line carrying a command. The CNC machine activates the commands in the order that they are written.

Now, to create a CNC program, here are the steps:

Step 1: Part design

A 3D model of the part needs to be designed. The software to use at this point is CAD software. The 3D model outlines all the basic details about the part – details, features, and dimensions. It is a visual version of the part aimed at guiding the CNC programmer.

Step 2: Produce the Tool paths

The CAM software comes in handy in this step. It helps generate these paths, which are simply definitions of the operations and movements the tool needs to make to generate the part defined earlier.  For optimum results, the software will define the tool paths having considered factors such as tool rotation speed and properties of the work piece material.

Step 3: Produce the CNC programming

This is the next step in the CNC programming process. The programmer typically uses the G-code to come up with commands for the CNC machine. Some element that the program needs to highlight in the CNC program are the cutting depth and the starting position.

Step 4: CNC machine preparation

The CNC program may be ready, but there is still one thing that needs preparation – the CNC machine. This is where the CNC program will be executed. Therefore, the CNC machine must be set up correctly.

Some areas to countercheck and set up are the system safety, coolant, work piece holding mechanism, feed rate, and cutting speed. In short, everything in the machine should be in accordance to the requirements of the CNC program.

Step 5: Program execution

As in any other program, the last step in the CNC programming process is running the program. With the CNC machine ready and the program already loaded to the machine, it is time to run everything.

The CNC machine is designed to read and execute the CNC program one line after the other. This might be an automated process, but the operator should remain vigilant as the machining process continues. Sometimes there is a need for adjustments, so the operator will be there to do the necessary.

Types of CNC Programming

There are three types of CNC programming. These are manual CNC programming, computer aided manufacturing (CAM), and conversational programming. Here is a more detailed look at these types of CNC programming:

Manual CNC Programming

Manual CNC programming has been around for a long time so it is very popular. The operator can do the programming manually and transfer the file to the machine. Alternatively, the CNC programmer can punch the program on the CNC machine controller directly.

Manual CNC programming entails the CNC programmer using his or her knowledge to manually write the CNC program. The programmer combines the knowledge with information about CNC machine accessories and tools as well as the available coding instructions.

With this set of information and knowledge, the actualize the the CNC machine programming from scratch. There are specific steps that every professional CNC programmer must follow:

  1. Definition of tooling paths and processing using the CNC coordinate system

  2. Generating a workshop drawing from provided geometric information

  3. Arranging the tools in according the process steps

  4. Writing the CNC program in G code programming language

  5. Feeding the program to the control unit

Pros of Manual CNC programming

The unlimited nature of this type of CNC programming is the biggest advantage to the user. The CNC programmers can go to the finest details when setting up the CNC program. It doesn’t matter whether it is the feed rate, number of cycles, or speed of rotation; you can do virtually every form of tweaking with the manual version of CNC programming.

Second, this programming method instills proficiency and discipline in the CNC programmers. Anyone writing the code must understand the part and the machining process in detail. There is no room for error.

The letters, spaces, dots, and any other detail must be perfectly placed for the CNC program to work. For someone facing competition for employment or clients, having this edge can make a difference.

Plus it is better to know what is happening in the back-end. Computer numerical control programming software is becoming more complex every day. As a machinist overseeing a machining tools and processes, you are tasked with understanding everything.

Cons of Manual Programming

There are a couple of disadvantages associated with manual machines. You see, manual programming can take forever to complete. This is the biggest drawback of manual programming, from the perspective of the user and CNC programmers.

CNC programmers saved a lot of time when they could no longer need to make tool paths manually. The CAM software takes much shorter time compared to the manual process.

We can all agree that any manual process is bound to have errors. This challenge is serious when it comes to manual programming. For this CNC programming type, a simple omission of a digit is enough to render the entire CNC software code useless.

Computer-Aided Manufacturing (CAM)

Computer aided manufacturing software is instrumental in the programming of CNC machines for part production. The CAM software is the way of communication from the designed part to the CNC machining tools.

It does not matter whether you are using a CNC lathe, CNC milling machine, or CNC laser; you need the CAM generated code for these tasks to be executed.

CAM programming is extremely powerful, yet very simple to execute. The machinist need not have knowledge on G code programming language.

In this programming approach, the user prepares a CAD design using software. This design carries a lot of details about the final part. CAM software works with the 3D model of the part.

The next step would be the transfer of the design to the CAM software. Here, the machining information such as the tool paths are input. With this data, the CAM software generates the G codes for the design.

Nowhere in this process does the expert knowledge of G-codes feature. The user cans still perform CNC programming using this method, with scanty G-code conversance.

Steps of using CAM CNC programming

There are various ways of undertaking CAM CNC programming. Here is the rundown of these steps:

#1. Source and buy the CAM CNC PROGRAMMING software

Both commercial and free CNC programming software options are available in the market. Whichever one you choose, ensure that is supports all the features related to the project. The best CNC programming software should also be compatible with your machining processes.

#2. cnc programming Software Installation

The supplier of the CNC programming software should provide all the necessary information concerning installation and configuration. In relation to that, you want to check your computer for its capability to handle the best CNC programming software.

#3. Part Design

The CAD software comes in handy at this stage. This is where you create the part design as you want it manufactured. That means that the CAD and CAM software are now already in your system. Ensure that the CAD design bears all the important details regarding the part.

Remember that the CAD software has room for modifications. In other words, you can revisit the design and make any desired changes. This is an important step before you can embark on the machining process. The CAD models help in assessing the suitability of the part before it is produced on the CNC machine.

Skills and experience in handling the CAD model concept and other issues related to part design are paramount at this stage. If you are not experienced in this area, you may want to hire an expert in CNC programming software.

#4. Setup of CAM

Here is where you express what exactly you want the CAM software to do. In other words, you need to determine machining elements such as feed rate, rotational speed, and so forth.

The software will then create tool paths for the same. A tool path is the movement that the CNC machine tool will make. It defines the machining process.

After setting up the CAM, the machine is now ready for the process. But you need to conduct a test run. Despite how the perfect the CNC program appears, there is always a potential for errors. The simulation process helps identify such errors for a chance to rectify them.

#5. G Code Generation

Once the settings are all good, it is time to create the G codes. The G codes should automatically come from the CAM software, but the settings matter. The CNC machine needs the G codes to control the movement of the machining tool.

#6. Preparing the Work Piece

Attention now turns to the work piece, which must be prepared for the machining process. Modern CAM software have means of helping the user set up the work piece properly. This helps in preventing human errors.

#7. CNC Machine Programming

All is now set for the feeding of the G codes to the CNC machine. The CNC machine has a controller which must not be programmed appropriately. Examples of data that is transferred to the controller of the CNC machine are G codes and tool paths. The work production process is now ready for activation.

#8. Supervision of the Process

After CNC programming using CAM software and all the related activities, human input is not entirely unnecessary. Errors still happen, so human intervention may be needed. Again, modern CAM software comes with features to help the user monitor the progress of the process.

Pros of CAM Programs

  • It takes less time to program compared to manual CNC programming

  • The need for the programmer to perform computations is eliminated

  • It removes the need for expert programmers

  • Programming language errors are unlikely due to the availability of simulation features

  • It allows for the effortless programming of intricate shapes

Cons of CAM Programs

  • The efficiency of the tool paths is less compared to the manual cnc programming option

  • Some basic knowledge or learning cnc programming is necessary

  • The operator does not have complete control of the process

Computer-Aided Manufacturing (CAM)

You can opt to use the easiest form of CNC programming – conversational programming. This type of programming is the best choice for entry-level programmers or machine operators who are yet to learn CNC programming. The user does not need any special knowledge or skills to implement this CNC programming.

Instead, the CNC machine is equipped with a set of presets. All the use needs to do is to use the machine’s control console for configuration.

One of the steps in conversational programming for CNC is to determine the machining parameters. These parameters include material type, machining type, and tool type.

Apart from being the best option for entry-level users, conversational programming is also recommended for simple machined parts. For complicated tool paths, you want to try the other types of CNC programming.

One notable characteristic of this programming approach is the ease and swiftness of the operation. It has become a big factor in rapid prototyping, because here focus is on quick turnover.

Example of Conversational Programming

If you were machining a shaft and wanted to use conversational programming, below is an example of how the interaction would be:

User: I want to machine a small shaft

Machine Interface: Enter the shaft diameter

User: Use two inches

Machine Interface: Enter the length

User: Use 10 inches

Machine Interface: Enter the shaft material

User: I want it to be mild steel

Machine Interface: Enter roughing tool

User: 3/4 inch facing mill

Machine Interface: What is the starting point?

User: Keys in the starting point parameters

Machine Interface: Confirmed parameters and ready for machining?

User: Yes.

Machine Interface: Choose the finishing tool

User: You can use an end mill

Machine Interface: Specify the depth of finishing pass

User: 0.10 inches is okay

Machine Interface: Confirm and machine

User: Confirmed

Machine Interface: Machined shaft ready

Pros of Conversational Programming

First, this CNC programming type is suitable for users at all skill levels. With software applications that have straightforward menus, any operator can perform this program. The best CNC programming software in this category even have training aids to help learn CNC programming. The operator can switch to G code programming at will.

CNC machine programming using the conversational technology is also preferable for shorter turnaround times. There are not many steps as you would expect with the programmer in CAM programming. No bureaucracies to deal with. Shorter lead times are always good for profitability in a business.

If you are looking for faster prototyping, conversational CNC machine programming would be the best bet. As long as you are not dealing with complex parts, this CNC programming type offers this advantage.

Talking of simplicity of part geometry, conversational CNC programming works where the part design is easy. It is fast and easy, so many shops dealing with simple designs would find it worthwhile.

Cons of Conversational Programming

The biggest undoing for this CNC programming type is that you cannot improve the cycle times. The system already has a set routine. Here are other disadvantages of this CNC programming version:

  • It does not support complex tool paths

  • It only works with simple part geometries

  • The flexibility is low, particularly in comparison to CAM programming

  • These programs are not interchangeable i.e. they are typically only relevant to the machines on which they are embedded

What Are the Codes Used for CNC Programming?

The CNC machine operates under the control of special letter addresses known as CNC code. Some of these addresses are used severally, with their meanings dependent on the accompanying G code.

The codes used for CNC programming are shown in letters. There are several of these letters, but they are generally referred to as G codes. We’ll now define these CNC coding methods as they are used to program CNC:


This class of G code defines the tool offset. The offset is either the amount of protrusion of the tool from the holder or the distance between a tool’s cutting edge and the centerline. This code is important in the compensation for deflections and tool diameter wear.


The F codes denote the feed rate of the CNC machine. The feed rate is the speed tool movements during the machining process. The feed rate can be accurate to the three decimal place level. An important point to note about these codes on tool movements is that they always come with a decimal point.


G codes, meaning geometric codes, are the most popular of the several types of instructions in CNC programs. Usually, these codes instruct the CNC machine control the type of motion that is required. CNC machines use a wide range of motions including circular feed, rapid positioning, and fixed cycle.


These are the miscellaneous commands. You could also call them non-geometric codes because they focus on non-geometric actions of the CNC machine. They define wait time, stop, process, and other related miscellaneous activities. A block of code may only contain one M code.


This type comes in when the user is generating the CNC coding manually. They are standard or notable blocks of CNC code in this respect.

You may not find the N codes in CAM-oriented code because they are not necessary in that instance. The main purpose of N codes is to simplify the understanding of the CNC program.


They are also called speed commands. They are for surface speed, spindle speed, increment speed, and so on. These speed codes define the speed in revolutions per minute (RPM). This code always appears alongside M03 and M04 for clockwise and and anticlockwise rotations respectively.


T codes are for identifying the different types of tools used in CNC machining. This CNC code helps select a tool. Note that this code is always placed alongside M6, a code that indicates tool change.


With this background on CNC programming, it is now easier to determine the right CNC programming type for your project. Your conversance with the programming type and how suitable the type is for your specific project are the leading criteria for this choice.

Aria Manufacturing Ltd. is a trailblazer in delivering the best CNC programming services and products. No matter the kind of CNC solutions you need, we have the resources to provide your kind of CNC parts. We serve a wide range of industries, so you can call us with all your CNC machining requirements.

Our team of experienced professionals will go beyond bringing CNC programming closer to you. They will help do your CNC machining project fast and with dependable results.

You can trust us to produce your parts to the highest precision and closest tolerances.

Contact us now for a free quote!


Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.