What is CNC?

An introduction to this automated manufacturing process

CNC stands for computer numerical control. It refers to the automated control of machinery and tools–such as drills, boring tools, lasers, and lathes–to generate physical parts from CAD (computer aided design) files. This manufacturing process is much faster, incredibly precise, requiring very little to no human assistance or interaction.

CNC machines have at least two axes, operating along an XYZ plane–X axis (vertical), Y axis (horizontal), and Z axis (depth)–following instructions from a computer. The number of axes usually determines the type of movement a CNC machine can perform. The instructions the machine receives are written in a programming language known as G-code. We can use CAM (computer aided manufacturing) software to automatically convert CAD files into G-code.

The first CNC machines

The first CNC machines were developed in the 1950s, and relied primarily on a data storage technique known as “punched tape”. This “G-code” would be manually punched into a data card and then be fed into a system that interpreted the data. These early machines were incredibly basic and limited. Learn more about the first CNC machines in the video below:

Subtractive manufacturing vs. additive manufacturing

CNC machining is a subtractive manufacturing process, unlike 3D printing, which is an additive manufacturing process. CNC machining is the process of removing material from a piece–whether that be a piece of wood, metal, or plastic–to create a part: essentially, it is the opposite of 3D printing. Additive manufacturing processes, on the other hand, build objects by adding material layer by layer.

Whereas, additive manufacturing can be likened to making a sculpture out of clay, subtractive manufacturing would be the equivalent to carving it from marble. While these processes are different, they are often used side by side. Choosing between them will depend on factors such as which material you are working with (you’re not going to print wood!), the complexity of the part (additive manufacturing is typically better suited for small parts and highly complex or intricate designs), quantity, and cost.

Uses

CNC machines can cut through nearly any material you can think of. Parts made with CNC machining are all around us. Aside from being used to create toys, molds, prototypes, and furniture, it is arguably the only way to produce high precision metal parts for engineering design; it is used to manufacture parts for cars as well as SpaceX rockets, insulation pieces, and even the tiniest and most delicate pieces in small electronics. This is because CNC machining can create parts with greater dimensional accuracy than most other common manufacturing technologies, achieving very tight tolerances.

Machining tolerances determine the limits between which the dimension of a part can vary. If a part falls between its maximum and minimum dimensional limit, it is considered to be within the tolerance. If the part's dimensions fall outside of these limits, however, these parts are outside the acceptable tolerance and considered unusable. The standard tolerance of any dimension in CNC machining is ± 0.125 mm, however, tighter tolerances of ± 0.050 mm or even tolerances of ± 0.025 mm are feasible–that is about a quarter the width of a human hair!

BUGA Wood Pavilion

The BUGA Wood Pavilion was designed by the Institute for Computational Design and Construction (ICD) and the Institute for Building Structures and Structural Design (ITKE) at the University of Stuttgart. It is made up of 376 bespoke hollow wood segments. Each of these segments was milled and assembled using CNC machinery. They fit together like a big three-dimensional puzzle. The structure, which spans 30 meters, is based on biological principles found in the plate skeleton of sea urchins.

Daniel Romero is an industrial designer and partner at TUUX, a studio based in Mexico, which specializes in product design, furniture design, interior design, and architecture. TUUX was awarded the Red Dot Design Award in 2019 and their work has been selected for three Ibero-American Design Biennials. If you have enjoyed this blog post, you can sign up for Daniel’s course, Introduction to CNC Router Furniture Design, and discover new ways to design and produce sustainable furniture using CNC machining.

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