CNC Programming: Intro for Beginners (Examples!)

CNC Programming: Intro for Beginners (Examples!)

CNC Programming: Intro for Beginners (Examples!)

Knowing how to do CNC programming can be a powerful skill whether you're a CNC professional or hobbyist.

This article introduces CNC programming for beginners through simple examples.

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What is CNC Programming?

Computer numerical control (CNC) programming is the process of writing or developing the code that controls the CNC machine to execute the desired machining process. It is the job of a CNC programmer to develop a program that perfectly replicates the given design.

NC, CNC, and DNC are the three types of programmable machining systems. NC systems were the initial programmable machines that are rarely used in the modern machining industry.

CNC machines use a computer system that replaced the traditional punch tape input method of NC machines.

Similarly, the DNC system consists of a network of CNC machines controlled by a single master computer system. This enhances the productivity by reducing the overall cycle time.

However, CNC machines are the most popularly used among the three and are readily available for different applications ranging from DIY projects to large-scale industrial manufacturing.

CNC machine generally works on the basis of the design prepared during the CAD phase of the process.

This CAD file is then imported into CAM software and converted into appropriate G-codes.

These G-codes control the various movements of the CNC machine to perform the required operation.

Although these codes are automatically generated by a computer system, it is important to understand the basics of programming a CNC machine by using the G-code programming language.

Almost every CNC machine uses combinations of G-codes and M-codes to perform the cutting operation and control various miscellaneous tasks of the machine.

Apart from these, CNC programming also uses codes such as S-codes, N-codes, T-codes, D-codes, and F-codes.

Where S-codes are used to manipulate the spindle speed of the CNC machine, T-codes are used for programming tool change commands, D-codes set the offset in the cutter diameter, and F-codes set the feed rate.

CNC Programming- Explained with an Example

Let us consider a milling example with the toolpath as shown in the image below.

Toolpath for the milling operation
Toolpath for the milling operation

To program a CNC router for executing the desired machining operation, the CNC programmer will prepare a G-code file with all the required machining instructions.

N01 G21 G90 G94
N02 G00 X20 Y00; POSITION 1
N03 G42 D15; TOOL COMPENSATION TOWARDS RIGHT
N04 S12000 F250 M03; SPINDLE SPEED AND FEED RATE
N05 G01 Z-15; LOWERING THE CUTTING TOOL
N06 G01 X80 Y00; POSITION 2
N07 G01 X80 Y75; POSITION 3
N08 G03 X75 Y80 R05; POSITION 4
N09 G01 X00 Y80; POSITION 5
N10 G01 X00 Y20; POSITION 6
N11 G01 X20 Y00; POSITION 7
N12 G40; CANCEL TOOL COMPENSATION
N13 G00 Z15 X00 Y00; DATUM POINT
N14 M03; STOP SPINDLE 

In this code, the N-code represents the block number and does not have any practical involvement in the machining operation. It is solely for the assistance of the programmer to keep a track of his code.

In block N01, G21 informs the machine that all the values are in the metric (mm) units, G90 is the selection of absolute machining and G94 sets the feed rate to mm per minute.

N02 block moves the cutting tool from datum point (O) to position 1. Here G00 signifies rapid linear motion without cutting operation.

In block N03, G42 signifies tool compensation towards the right and D15 signifies the required offset towards the right.

Tool compensation plays an important role in the accuracy of the part. Normally, the CNC machine follows the toolpath by placing the cutting tool center on the toolpath, resulting in dimensional accuracy.

Using G24 for tool compensation offsets the tool in such a way that the cutting edge of the tool is tangent to the toolpath, thereby eliminating the cause of dimensional accuracy.

N04 sets the machining parameters, where S12000 signifies the RPM of the cutter, F250 signifies the feed rate, and M03 signifies clockwise rotation of the cutting tool.

After setting the machining parameters, block N05 commands the machine to lower the cutting tool 15mm along the Z-axis. Here G01 signifies the feed of the cutting tool along a linear motion.

In block N06, the code specifies the linear movement of the cutting tool to position 2, where X and Y coordinates equal 80 and 00 respectively.

Similarly, block N07 moves the cutting tool to position 3 along a linear path.

Whereas in block N08, G03 signifies a circular interpolation of the cutting tool in the anti-clockwise direction from position 3 to position 4, and R05 signifies the radius of the curved path to be traced by the cutter.

After that, blocks N09, N10, and N11 signify linear interpolation of the cutting tool from position 4 to position 5, position 5 to position 6, and position 6 to position 1.

Block N12 cancels the tool compensation, N13 positions the cutting tool at the datum point, and N14 stops the spindle motion.

Therefore, in this example, block 1 to block 4 consist of commands to set up the machine for operation.

Block 5 to block 11 executes the desired cutting operation, and block 12 to block 13 wraps up the machining process by bringing the machine back to its initial state.

Types of CNC Programming

There are generally three types of CNC programming, and each type has its benefits and uses, making it important for a CNC programmer to have a basic understanding of all three.

Manual CNC Programming

Manual CNC programming, as the name suggests, involves manual coding of the program from scratch.

It requires a highly skilled individual capable of understanding each code and visualizing the outcome to ensure accurate results.

The programmer uses G-code editor software to write and edit his code to perform the desired machining operation.

Generally, when performing manual CNC programming, the CNC programmer interprets the 2D part drawing and determines the ideal toolpath to execute the desired machining operation.

This type of CNC programming is generally recommended for simple machining operations.

For example, manual programming of a CNC lathe to perform the following machining operation.

Toolpath for the required lathe operation
Toolpath for the required lathe operation

N1 T0201              ; Tool number 2 with offset 1 
N2 G97 S450 M03       ; Spindle rotation clockwise with 450 RPM
N3 G01 X30 G95 F0.3   ; P1
N4 G01 Z-15           ; P2
N5 G01 X50 Z-30       ; P3
N6 G01 Z-60           ; P4
N7 G01 X80 Z-80       ; P5
N8 G01 X120	      ; P6	

The toolpath to be followed here follows a simple line diagram, making it easy to program by using the manual CNC programming technique.

Manual CNC programming eliminates the need for preparing a 3D CAD design and speeds up the machining process for simple operations.

CAM CNC Programming

Computer-aided machining (CAM) programming is one of the easiest, yet very powerful methods of programming a CNC machine.

In this method, CNC software is used to prepare a highly detailed CAD design with the exact dimensions of the final product.

Considering the similar example as mentioned above, CAM programming will require a 3D model of the workpiece, instead of the 2D tool path drawing.

3D CAD drawing of the required part
3D CAD drawing of the required part

This design is then imported into CAM software, where you can set the required toolpath and other related machining parameters.

The CAM software then automatically converts the design (SVG) into corresponding G-codes.

Unlike manual CNC programming, CAM programming does not require expert knowledge of G-code.

However, having basic G-code knowledge can help the programmer tweak the machining operation when needed.

Conversational CNC Programming

Conversational CNC programming is one of the easiest programming techniques, that does not require any special skills to operate the CNC.

In this technique, the programmer can configure the CNC machine directly from the control unit of the machine, by using a series of built-in presets.

The operator selects various parameters such as the desired machining operation, the kind of tool to be used, the type of material to be cut, and the types of cuts to be made in the material.

This type of programming is recommended for CNC manufacturing of simple parts without the need for complex toolpaths.

The quick and easy-to-perform operation of conversational programming makes it ideal for applications such as rapid prototyping and other manufacturing applications where quick turnover is of key importance.

Is CNC Programming Hard to Learn?

The answer to this question goes beyond a simple yes or no because basic CNC programming can be relatively easy for an individual with good math skills and an understanding of the working of a CNC machine.

Whereas programming a bit more complex CNC process will require a skillful programmer with around 1 year of experience as a CNC machinist.

Programming complex machines like multi-spindle lathes, 6-axis CNC machines, etc., requires an expert programmer with years of practice and thorough knowledge of different machining operations.

The difficulty of CNC programming also depends upon the type of programming being performed.

Manual programming is the most difficult one and needs an expert programmer with good knowledge of G-code.

CAM programming, on the other hand, requires comparatively less effort as most of the work is performed automatically by the computer system.

On the other hand, conventional programming does not even require a specialist programmer, as it requires the operator to select a series of preset settings to begin the machining operation.

How to Become a CNC Programmer?

Programming a CNC machine
Programming a CNC machine (Source: Universal Technical Insitute)

A CNC environment consists of various roles like CNC operator, machinist, and programmer.

CNC operator being an entry-level role does not require any specific experience. However, a high school diploma and an understanding of CNC machines are some of the basic requirements.

Similarly, a CNC machinist is the next level role which requires an experienced individual with a high school diploma and knowledge about the machining of different materials.

CNC programmer is the highest level role in a CNC environment that requires an extremely experienced individual with excellent CAD/CAM skills.

Unlike operator and machinist, CNC programmer is concerned with the computer phase of machining.

Although a CNC programmer does not necessarily require a graduation degree, some recruiters prefer candidates with a good educational background.

Therefore, a high-school diploma along with certain programming certifications will help you boost your opportunity to become a CNC programmer.

Apart from education, experience is another important factor that will help you become a CNC programmer.

An individual with over 5 years of experience in CNC environment will have enough knowledge about various CNC operations like CNC latheCNC mill, CNC routersCNC laser cutter, etc., and their axis system.

According to May 2021 report of the United States Bureau of Labor Statistics (BLS): Texas ranks highest in hiring CNC tool programmers, followed by California and Michigan, with an average annual salary of around $60,780.

Final Thoughts

CNC programming is an integral part of operating a CNC machine to perform the desired machining operation.

A skilled CNC programmer can enhance the quality of the process, whereas sub-par programming skills can result in improper machining output with poor quality.

Generally, manual CNC programming is recommended for expert programmers, whereas CAM programming is used for complex machining operations.

On the other hand, conversational programming is ideal for simple applications where quick cycle time is required.

Frequently Asked Questions (FAQ)

Is CNC programmer a good career choice?

Yes, CNC programmer is an excellent choice of career in the current manufacturing model. CNC machines can be found in almost every workshop and industry, thereby increasing the demand for a good CNC programmer.

Which language is commonly used for CNC programming?

G-codes is the most popularly used programming language for CNC machines.

Does CNC programmer need to have CAD skills?

No, a CNC programmer does not necessarily need to have CAD skills. However, he must be able to read and interpret blueprints and designs to program the CNC machine accordingly. Furthermore, certain organizations require a multi-skilled individual capable of preparing the design, setting the optimal parameters, and programming the CNC machine. This individual is generally known as a CNC machinist programmer.

About John

Hey I'm John. I talk about CNCs and Power Tools at Mellowpine. I'm a CNC hobbyist who has been making CNCs and writing about CNCs for a while. I currently also work as a consultant for business owners and hobbyists setting up their own CNCs. If you have any questions related to CNC, I'd be happy to answer them. Reach me at john@mellowpine.com

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John

Hey I'm John. I talk about CNCs and Power Tools at Mellowpine. I'm a CNC hobbyist who has been making CNCs and writing about CNCs for a while. I currently also work as a consultant for business owners and hobbyists setting up their own CNCs. If you have any questions related to CNC, I'd be happy to answer them. Reach me at john@mellowpine.com

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