CNC Machining and 3D Printing – Friends or Foes?

By Damian Hennessey


CNC machining and 3D printing are two technologies making a big impact in many industries. But do they compete with or complement each other? Damian Hennessey, Director of Global Sales Operations - Protolabs, examines the evidence.

In simple terms, CNC machining is 3D printing in reverse. While 3D printing creates objects by building up layers in three dimensions, CNC machining cuts into them. It’s like the difference between making a sculpture out of clay (an additive process) and carving it from marble (a subtractive process).

Clearly, some items are best produced by just one of these processes. But there are many instances where they work well together. A good example of this is where a 3D-printed object is ‘finished’ by CNC machining, perhaps to refine the surface, or add holes, grooves or threads.


Playing to different strengths

So when is it wise to keep the two processes separate? What does each one do better than the other? If you’ve ever used 3D printing, you’ll know it’s particularly good for highly specialised designs. 

cnc vs 3dp

The way it starts from nothing and adds layers means it can create an almost infinite variety of outputs, limited only by the printer’s capability. Also, it’s a flexible process, so you can switch quickly between jobs. And the cost per unit of a given item is always the same, regardless of quantity. So 3D printing is ideal for producing personalised, even unique, objects. No wonder it’s becoming increasingly useful in many medical and dental applications, where you can use it to customise items to fit individual patients.

But this great strength can also be a weakness: 3D printing can be uneconomical for some large-scale manufacturing. There’s also a limit on output size. While the process is perfect for small, intricate items, it currently works to a maximum size close to that of a washing machine (produced using stereolithography in certain materials).

This is where CNC machining sometimes has the upper hand. It can produce considerable quantities of precision-crafted products efficiently, in a variety of materials. Parts for commercial and industrial equipment and machinery are particularly popular applications, especially those made from high-density metals. It can also be used for smaller batches of products, but usually at a higher unit cost.


Joining forces to meet design challenges

So the choice between 3D printing and CNC machining can often come down to the size of the production run and size of the outputs. But when these factors are neither too large nor too small to eliminate either process, the technologies can be combined to great effect.

And there’s an urgent need to explore and develop this combined approach. As manufacturers have to meet increasing demands from customers, so technology has to develop to keep pace. It’s all about producing more effective products and services, faster and more efficiently. This is where combining 3D printing with CNC machining can bring major benefits.

In particular, the two technologies together can help meet the tough design challenges today’s manufacturers are facing – especially the demand for lighter weight components and products, and for items with increasingly complex geometries. Here’s where 3D printing, combined with CNC machining, can achieve more than any other process. The flexibility of 3D printing is enhanced by the precision of CNC machining to produce ever more intricate objects.

And because CNC machining can work as a fine-tuning add-on to 3D printing, it doesn’t have to be confined to larger production runs. At Protolabs, we have the equipment for both 3D printing and CNC machining, so we often combine technologies to produce prototypes and models, or for medium-run outputs required for performance testing. This dual approach is also ideally suited to making replacement parts for obsolete products.

The trick is to recognise the distinctive value of each technology, and apply them to design and production processes in the most appropriate way. Through the cycle of prototyping, testing and manufacturing, 3D printing and CNC machining can be used individually at different points or in combination. Working with a supplier that has both technologies under one roof means you can move more nimbly between them. The result? You make the most of both processes to meet the demands of today’s fast-changing markets.