What is G-code?
People talk about the “language” of computer programming, as if it was a single language. But as any seasoned programmer will tell you, that image is drastically over-simplified. There are literally hundreds of programming languages, each designed to make particular aspects of programming easier, or to operate particular systems. All of that variety means that programming languages aren’t unified, aren’t always remotely similar in their content, and certainly don’t do the same things. Some programming languages become obsolete and go extinct quite quickly, while others demonstrate a surprising resilience.
One of the programming languages to stand the test of time has been G-code. G-code is one of the languages used to operate Computer Numerical Control (CNC) machines. CNC machines rely on a computer to direct operations, rather than a human operator; G-code is the language used by those computers to perform operations. In this article, we’ll delve into what G-code is and how it works, giving you a better understanding of the importance of G-code to the fields of modern manufacturing and machining.
First off, a brief definition. Computer Numerical Control, or CNC, refers to machines which can be programmed to perform a series of cuts and maneuvers without an operator. CNC technology enables the automation of many steps in the manufacturing process. It also offers vastly improved quality control and uniformity of the parts produced. CNC technology has been around since the 1950s, but with the advent of computers and robotics, CNC machines can tackle increasingly complicated operations, moving on multiple axis and switching between different tools and cutting heads within the same machine.
Basic Characteristics of G-code
Maintenance tasks for CNC machines fall into three general categories: daily inspections, jobs that need to be performed every 500 hours or every six months, and additional inspections to be done every 1000 hours or every year. The daily checklist will of course be the longest one, and the one you’ll use most often. Don’t forget the other checks, however, especially if your machine is running around-the-clock or for extended shifts. Five 24-hour days is 121 hours, meaning that machines which are in nearly constant use could require a 500-hour inspection almost every month.
G-code originated in the 1950s. The letter “g” began commands in the code, often telling the machine to start operations, stop, etc. Thus, the entire language became known as g-code – even though not every command begins with “g.”
G-code began at a time when computers had limited capabilities and were not able to handle long, complex strings of commands: thus, g-code tends to be short and sweet. A sample string 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.)
While g-code doesn’t have to be terribly complex, it communicates all the necessary information to perform a variety of tasks. This succinctness makes it ideal for CNC routers, mills, lathes, electron discharge machines (EDMs), and any number of other factory and machine-shop machines. In the early days, programmers needed to enter g-code manually; today, CAD programs or wizards will often do so for you, making it easier for people without direct experience of g-code to operate CNC machinery.
How G-code is used
Every six months to a year, you should have your CNC machines thoroughly inspected by a trained technician, often one sent from the original manufacturer of the machine. That person can completely drain and replace the hydraulic fluid, clean the coolant tank itself, and perform an inspection of the chuck, jaws, and clamps of the machine heads.
G-code makes it possible to automate large industrial machines and manufacturing equipment. From its base form, established in the United States officially as RS-274-D, g-code has developed a number of flavors. Those flavors depend partly on the country of origin, and even more so on the particular machine using them.
G-codes generally initiate an operating or a series of operations, with other codes, often M-codes, forming the “body” of the code block. Some machines may use a g-code to initiate a particular part rotation, or even to follow an arc or curve in the tool’s path. Other machines won’t use those codes at all, and will employ completely different ones.
Each CNC program aims to produce parts quickly and efficiently, using G-code to keep commands as simple as possible. Nevertheless, certain codes pop up in CNC programs everywhere. These are some of the common ones:
- G0 – Move the tool to a set of coordinates as rapidly as possible. G0 can indicate a non-linear position: the tool may have to move along more than one axis.
- G1 – Move the tool to a new position in a straight line.
- G17, G18, G19 – Plane designation for an arc machining.
As mentioned, there are sets for common functions or common types of machinery
- G80-G89 – milling instructions
- G81-G88 – cylindrical grinding instructions
Whatever the machine and whatever the function, g-code has been instrumental in the development of modern industry. One of the most significant functions of g-code is its repeatability: a program can be written, entered into a machine, and then performed a limitless number of times. Rather than rely on a human operator to follow instructions correctly, industries can turn to operators to write programs (in g-code!) which command their machines to perform the same operation over and over again. Assuming the program is correct, this means parts can be made the same way, drilling done to the same depth, and machining done to the exact same standards across an entire run of parts.
In short, g-code made industrial automation possible. A good accomplishment for a nearly seventy-year-old programming language!
