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In the last decade or so, 3D printing is one of the bold new technologies that has been dominating headlines and it’s easy to see why. It offers some serious advantages over conventional manufacturing methods and is an incredibly flexible and potentially powerful platform.

However, there are still significant drawbacks when it comes to mass production due to slow speeds and a lack of accessibility.

One technique that has been around for far longer and is still a valid alternative to 3D printing is CNC (computer numerical control) machining, which has been used in manufacturing for decades. But when it comes to prototyping and model building, which process is the best route to take?

What’s the difference?

The major difference between the two techniques is that 3D printing is an additive process whereas CNC is a subtractive process. The meaning behind these terms are quite literal, additive manufacturing is a layered process, whereby lots and lots of individual layers are printed on top of one another using plastic filaments or resins. Subtractive, meanwhile, is the opposite process – starting with a block of material and cutting away at it until the desired object is left.

For building smaller models (highly detailed model ships, for example) 3D printing is perhaps the most obvious process because it is able to replicate minor details with greater accuracy. CNC machines meanwhile, are more dimensionally accurate, but struggle with finer details and the process leaves significantly more waste.

Materials – Both processes can use a variety of different materials but 3D printing more commonly uses plastics – thermoplastics like ABS and nylon. CNC also uses plastics but also commonly uses metal (particularly aluminium due to its recyclable nature) and can even use wood in some circumstances. It is possible to 3D print with metal, but the metal resins used as a basis for these designs are incredibly expensive.

Approachability – Generally speaking, 3D printing is a simpler process because as long as the printer is functioning properly you can effectively set it up and then let it do its job completely unsupervised (though there might be post-processing work required). Using a CNC machine, meanwhile, is a much more complicated process that requires a skilled operator to control.

Cost – This will depend on quantity. For low quantity models and prototypes, 3D printing will comfortably be the more cost-effective option.

However, if you require any more than 100 units to be manufactured, then 3D printing will get exponentially more expensive. CNC is more suitable for larger jobs – car manufacturing, for example.

Eco-friendliness – As we’ve already established, as 3D printing is an additive, rather than subtractive process, the waste is minimal, whereas subtractive manufacturing, by its very nature, will always result in more to be cleaned away and disposed of after the job is done.

Accuracy – When it comes to geometric complexity, 3D printing will always come out on top. Indeed, it is possible for 3D printers to manufacture physical objects that no other method could possibly replicate. When it comes to size and overall accuracy, however, CNC is superior to all 3D printing processes.

Ultimately, there is no right or wrong answer here, it will always be a decision based on volume, budget and the complexity of the model. However, both are incredibly useful and powerful and have been used to create some truly exceptional models.

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