CNC Programming: A Master Guide

Modern factories are a far cry from the gritty, industrial, smoke-and-machinery dreams of steampunk enthusiasts. Modern factories boast a bewildering amount of technology; some of them are arguably far more high-tech than most offices when it comes to the variety of techniques on display.

Set foot into one of those factories and you’ll almost certainly encounter a number of CNC machines. Crucial to automation and high-end machining, Computer Numeric Control (CNC) has become an integral part of the modern factory. But without a background in engineering and programming you might be a bit confused – what is CNC, how does it work, and what is CNC programming?

In this guide we’ll break down CNC, detailing some of its history and how it is used, before we dive a bit deeper into the programming.

CNC Beginnings and Basics

When did CNC start?

CNC technology began in the 1950s, with mechanical punch cards that told certain machines which actions to take. By inputting the cards, operators could “program” a machine to perform a set of actions. However, while CNC began in the 1950s it didn’t really take off until the widespread adoption of computers and robotics. Computers allowed an operator to enter and save certain programs directly into a CNC machine, meaning that even inputting a program could be streamlined.

Main benefits of CNC

What’s the biggest appeal of CNC? There are several significant benefits

  • Quality control and consistency

In theory, a good CNC program should result in a good part every time. A CNC mill will remove the same amount of material, a lathe will turn a part at a given speed – with CNC, a given program is nearly infinitely repeatable. For a manufacturer, this means that an entire run of parts should be consistent. The first one and the last one should look identical – there’s no human error that results in flaws and errors.

At the same time, CNC makes quality control fairly easy. It’s the program that needs to be checked first, not the parts; as long as the program is correct, the parts should match.

  • Automation

CNC machinery doesn’t require an operator to run – only to input the program. A skilled operator could actually program and then run several machines simultaneously, allowing a high degree of automation. 

  • Ease of use

Not just anyone can operate a CNC machine; there is a level of technical skill and knowledge required. At the same time, it is generally far easier to learn how to program a CNC machine than it would be to actually operate one by hand. With the right training, most people can be trained to operate a CNC machine.

What is CNC programming?

All of the above tells us when CNC began and the benefits it offers; what about the technology itself? How is a CNC program executed – and how is it entered in the first place?

CNC programming relies on a special form of code, descended from the punch cards of the earliest CNC. Most lines of CNC programming consist of short sets of coordinates and instructions, and the majority of them start, or used to start, with the letter “G.”

The letter would be followed by a number – G76, for example – which indicated the starting position for the program. The G-code told the CNC machine where to move the tool to get ready for the rest of the program. Over time, the CNC programming language became known simply as g-code.

Different methods of CNC programming

  • G-code programming

G-code is the most basic form of CNC programming; it’s the programming language used by the other methods. But it can also be the hardest to learn; both other methods are ways to work around actually programming directly in g-code.

  • CAM software

Computer Assisted Manufacturing (CAM) software is a variant of Computer-Assisted Design (CAD) software. Both variants use a computer program to design, lay out, and program a set of instructions for a CNC machine. It’s the program itself that translates the design into the instructions for the CNC machine.

  • Conversational Software

Conversational software uses an interface to translate ordinary commands into g-code. It’s not as extensive or as versatile as g-code, but it works to make the interface much easier.

What is G-code?

Even after computers began to be used to control CNC machines, codes needed to be kept short and sweet; the earliest computer-controlled CNC machines weren’t equipped to handle long, complicated lines of code. So a simple line of g-code might look like this: 

G01 X1 Y1 F20 T01 M03 S500

The G command initiates the machine movement, and X and Y give the destination coordinates. F tells the machine how fast to move, in this case, at a rate of 20. T01 instructs the machine to use Tool 1 to perform the job, M03 starts the spindle moving, and S500 sets the spindle speed. (Example taken from here.) 

G-code developed as a highly succinct but powerful programming language, communicating all the vital information for a wide variety of operations. With g-code, CNC routers, metal lathes, and mills could perform an entire series of operations, even changing cutting tools mid-stream.

Computers gave CNC machines a dedicated language; other computers made programming in g-code even easier. Today’s CNC machines can be integrated with Computer Assisted Design (CAD) programs, allowing a design to be automatically translated into a g-code operation. 

Becoming a CNC programmer

If you’ve read this far and think that CNC operations might be the path for you, what’s next? What can you expect from a CNC career, and where should you turn for the necessary training?

What’s involved in learning CNC programming in g-code? 

By far the best way to learn how to program CNC operations is simply to learn from someone who already knows. You may be able to find internships, or simply start working at a machine shop under a trained CNC operator.

What to expect from a CNC career

Challenges

CNC programming involves far more than simply punching some coordinates into a computer, stepping back, and letting the machine run while you put your feet up. A CNC operator needs to have at least a passing acquaintance with three separate areas to really excel in the field.

  • General machining knowledge

You’ll need to know the difference between a lathe and a mill; understand which machines do best for different operations; be able to accurately measure and conceptualize the various cuts, movements, and turns the program calls for. 

  • Metallography

Not every part will react to the same program the same way. Metals differ widely in their properties; some are harder, some softer, some are conductive and some not. Each of those properties might require adjustment in a basic program, or at the very least might affect the speed at which your CNC machine completes the operation. A skilled CNC operator will know those characteristics and be able to adjust accordingly.

  • Programming

It’s one thing to run an existing CNC program; it’s entirely another to create a new one from scratch! You’ll probably need at least a passing familiarity with CAD programs, and the ability to conceptualize new programs based on designs or drawings.

Add all of these challenges together, and it becomes obvious that CNC isn’t an easy cruise in the park. It’s a challenging, but rewarding, career.

Financial Opportunities

Fortunately, there are some real upsides to learning CNC programming. First, as automation in the manufacturing industry grows, so does the demand for CNC programmers. New technology, such as 3D printing, relies on many of the same principles so that demand for experienced programmers is likely to continue to grow.

With high demand comes a correspondingly high wage. The median income for CNC programmers is around $40,000 per year in the US. That’s across all of the states – individual states have much higher averages. The median in Oregon, for instance, is over $60,000. Individual operators with skill and experience can command wages much higher than that.

Job Opportunities

Skill with CNC programming can lead to jobs in nearly any manufacturing sector. The automotive industry relies on CNC machines on assembly lines and shop floors, and even the power generation sector uses CNC machines to produce parts for turbines and other essential equipment. 

Aside from manufacturing, you’ll find CNC jobs in woodworking. A skilled CNC programmer could also find work in the production of other CNC machines or for a supplier of machine tools. There’s even CNC work in the scientific sector – producing, sectioning, and testing parts.

In short, job opportunities for CNC operators are plentiful. The more experience and skill you have with CNC, the more likely you’ll be to find a job at a large factory or a small machine shop.

Mastering CNC is a daunting task. Fortunately, gaining a basic grasp of CNC programming doesn’t require advanced degrees or an intuitive grasp of computer languages. G-code itself is conceptually simple; it’s simply a system of coordinates and basic commands used to tell a CNC machine what to do. 

Training in CNC programming also doesn’t require a massive investment. The best way to learn programming in g-code is simply to do it – hire on to work at a machine shop and learn from a more experienced CNC operator.

Job opportunities for CNC operators are fairly plentiful, and likely to increase as the technology becomes increasingly crucial to the rise in factory automation. Average pay for CNC operators is higher than the national average. Learning CNC programming can be a path to a profitable and fulfilling career.