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A Machine Shop Primer on CNC Programming and Common Methods

April 3, 2023by Gerry Dillon

In our tireless and dedicated effort to manufacture high-quality precision parts, and maintain a reputation for accuracy and on-time reliability, Advanced Precision Machining (APM) Colorado machine shop relies on an assortment of Computer Numerical Control (CNC) machines in our facility. In today’s modern machine shop, CNC equipment typically consists of multi-axis milling machines, lathes, routers and grinders, but also newer technology such as robotic welders, laser marking machines, and 3D printers. With origins dating back to the 1950s, what was known first simply as “numerical control” lessened the need for constant operator attention and took the machine tools out of the hand of machinists, allowing for a first of its kind automation. Today, the punch tapes associated with numerical control have given rise to advanced computing technology, programming languages and computer-aided design (CAD) capabilities, making CNC technology an integral part of most manufacturing processes.

At its core, CNC involves the use of computers to control the various machine tools listed in the first paragraph, and they function through the use of numerically controlled computer programs, most often written in a CNC machining programming language called G-Code. G-code sends the signals, or directions, to a piece of machining equipment on the shop floor directing such essential functions as cutting tool speeds, spindle position, feed rates, and all other coordinated movements. Most modern CNC systems have become highly automated and quite complex, augmented by the addition of CAD and computer-aided manufacturing (CAM) programs. Due to the complexities involved with modern machining, CNC machinists have evolved to become skilled in all aspects of drawing and design, code writing, and equipment operation. When all’s said and done however, a precision machined part in the end is only going to be manufactured as well as the programming that was input to create it. Because of its importance, APM would like to provide a short primer on some common CNC programming methods.

As stated, CNC milling machines require a set of precise programming instructions to control nearly every aspect of the milling and machining process. After a CAD drawing is first drafted, the actual programming code (G-code) is created in a language that the CNC machine will understand. The program is then loaded into the microcomputer, or controller unit directly on the machine where it is stored in memory, then tested for accuracy. A CNC machinist next loads the required tools and material, then the computer directs the machine to perform the cutting operations according to the programmed instructions. Given the critical nature of CNC programming, let’s briefly examine three of the most commonly used methods: manual, conversational and CAM programming. 

  1.  Manual (non-conversational) CNC Programming

Perhaps thought of as the purest method, manual programming involves a CNC machinist preparing G-code commands without the assistance of a computer, thereby manually giving the CNC machine instructions on where to move, how fast, and on what path. Also known as non-conversational, it allows for complete control over a part program. This intimacy between programmer and machine brings out better machine performance when compared to more automated computerized methods. Because it’s done by hand, manual programming teaches strong discipline and is ideal for simple or high-volume work, although it’s time consuming and runs the risk of human error.

  1. Conversational (shop floor) CNC Programming

Conversational, or shop floor programming involves creating a set of programming instructions directly at the CNC machine using displays and menu-driven functions. The need to manually create G-code is either hidden or bypassed entirely, allowing a CNC machinist to step up to a machine and generate a CNC program quickly and easily. The program takes over and puts the machine in motion according to the commands given. It’s easy to learn and simple to use for small lots and short cycle times, but limited to more basic machine parts without complex tool paths.

  1.  Computer-aided Manufacturing (CAM system) CNC Programming

A computer-aided manufacturing system combines elements of both manual and conversational CNC programming by computer generating the G-code written in manual programming, then directly and automatically transferring it to the machine tool. The dimensions specific to a workpiece’s design are imported from a CAD system, the machinist directs the machining commands through a menu, the G-code program is generated, loaded into the machine, then it is left to run. Although it automates many processes and improves output, the total machine control associated with manual programming is limited. 

The description and methods shown for developing the CNC programs all have developed their own specific niche in the precision machining industry. They of course have a comprehensive list of additional pros and cons surrounding their use, and as any CNC machinist can tell you, their preferred use comes down not only to specific machining needs, but also personal preference. Be sure your machine shop chooses the optimal CNC programming method to deliver your parts accurately, on time and on-budget.

Need help with your next project requiring the precision and accuracy delivered by CNC, or want to learn more about the range of precision milling and machining options available to you, then contact our Colorado CNC machine shop. Advanced Precision Machining’s reputation for quality parts, on-time reliability and exceptional customer service cannot be matched! We’re happy to discuss any machining needs you have. Feel free to give us a call at 303.776.1910

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About the Author

Gerry Dillon is a co-founder, current owner and certified CNC machinist at Advanced Precision Machining (APM), a full-service machine shop located in Longmont, Colorado. Before making his home in the United States in 2000, Gerry was born and raised in Ireland and took an interest in milling and machining from an early age, ranking #1 in the Irish National Apprenticeship Program. In 2005, he began what’s grown into a leading Colorado machine shop. Gerry brings over 30 years of machining experience to the shop floor, and is certified in all aspects of geometric dimensioning and tolerancing.

by Gerry Dillon

Gerry Dillon is a co-founder, current owner and certified CNC machinist at Advanced Precision Machining (APM), a full-service machine shop located in Longmont, Colorado. Gerry has over 30 years of precision milling and machining experience under his belt.