Understanding CNC Programming Basics: A Beginner’s Guide

Picture a symphony under the guidance of an orchestra conductor. The conductor interprets the musical score, dictating tempo and rhythm and ensuring seamless coordination among musicians to produce a flawless performance.

But wait!

That’s not all. In the background, there’s more than you realize. You have light and sound technicians, stage organizers, etc. All work together at different moments and different paces. Similarly, CNC programming orchestrates the intricate and precise movement of cutting tools and material manipulation.

With unparalleled accuracy, this transforms raw material into intricate designs, prototypes, and complex parts. The smartphone you use daily, the laptop you might be reading this from, and the watch you carry on your wrist all start with CNC programming.

And remember, all the other people working alongside the orchestra? With the modernization of CNC machining, we have multichannel programming. This allows the machine to work on several parts independently and synchronously, increasing efficiency. Just like the orchestra and everyone else working on the same function!

Milling machines:

With rotating cutting tools, milling machines sculpt and perfectly shape materials. CNC milling programming involves defining toolpaths in multiple planes, allowing for complex silhouettes and precise detailing.

Lathe Machines:

Lathes are fundamental CNC machines that shape cylindrical workpieces by rotating the part or raw material against cutting tools to achieve symmetry and high precision. CNC lathe programming revolves around specifying spindle speeds, tool movements, and feed rates.

Critical Concepts in CNC Programming

CNC programming encompasses various types of coding tailored to specific applications and machining processes.

Here are some types of CNC programming:


G-code, or “Geometric Code,” is a language used by CNC machines like mills, lathes, and routers. It is a set of instructions that tells the machine how and where to move.

G0 and G1:

  • G0: Rapid positioning. It tells the machine to move quickly to a specific point without cutting.
  • G1: Linear interpolation. It instructs the machine to move straight motion from one point to another, cutting material along the way.

Units (G20 and G21):

  • G20: Sets the units used to imperial (inch)
  • G21: Sets the units used to metric (mm)

Tool Change (T):

  • Specifies which tool to use.

Speed and Feed (F):

  • F: Sets the speed at which the tool advances through the material being cut.
  • S: Sets how fast the tool or material rotates.

Arcs (G2 and G3):

  • G2: Moves the tool in a curved path in a clockwise direction.
  • G3: Like G2 but in a counterclockwise direction.

Spindle Speed Control (G96 and G97):

  • G96: Constant surface cutting speed; the machine adjusts the spindle speed to maintain a constant cutting speed. This code is mainly used in Lathe.
  • G97: Maintains a constant speed independent of the movement of the tool.


M-Code, or “Machine Code,” deals with auxiliary functions and machine-specific operations.

  • M00 – Program Stop
    • Stops the running program; it is often used for manual intervention.
  • M01 – Option Stop
    • When option stop is turned on, the machine will stop at every M01.
  • M03 & M04 – Spindle On:
    • M03: Starts the spindle in a clockwise direction.
    • M04: Starts the spindle in a counterclockwise direction.
  • M08 & M09 – Coolant:
    • M08: Coolant on.
    • M09: Coolant off.
  • M30 – Program End:
    • This end of the current program.

Everyone has their own style when it comes to coding. Although there is no right or wrong way to do this, consistency is important, along with adding comments to your code. This will not only ease manual editing of your code but also ease understanding of what the code is doing.

The Importance of Learning CNC Programming

Programmers need to have an in-depth understanding of G and M codes. As mentioned earlier in the article, G and M codes can change from machine to machine. The programmer might need to modify the code manually, ensuring no crash, accident, or malfunction could pose a health risk or damage to the equipment.


CNC is a crucial part of modern manufacturing practices. Whether you plan on starting a career in machining or want to create intricate parts as a hobby, CNC programming is at the core of every machined part.

Although CNC programming might seem outdated, it is the language that machines speak. Nowadays, coding is done through CAM (Computer-Aided Manufacturing) software that eases the burden of coding, especially regarding very complex geometries.