CNC vs. 3D printing

It’s easy to compare CNC work and 3D printing, and while they do share some similarities primarily that they are both computer-controlled methods used to create a finished product they also have several key distinctions that make one better than the other depending on the unique needs of your application.

Here’s a breakdown of the most prominent differences between CNC machines and 3D printers to help determine which is best suited for the demands of your project.

Subtractive vs. Additive

The most significant difference between CNC work and 3D printing has to do with how the final product is formed or rather, how it starts.

CNC work makes use of subtractive manufacturing, in which the unneeded parts of a starting material are removed to achieve the desired result. The diameter of the cutting tool ultimately determines the smallest subtractive feature that can be created within the workpiece.

In 3D printing, additive manufacturing is leveraged. This means the product is created layer by layer until complete, and the nozzle diameter determines the smallest additive feature that can be produced by the machine.

This important distinction has an impact on many of the key features inherent in these two types of machines.

Materials

CNC work is known for its ability to utilize a wide variety of materials, including:

• Metals like aluminum, brass, and copper
• Hardwoods like birch, mahogany, and walnut
• Softwoods like cedar, pine, and redwood
• Foams and acrylics
• And more

This versatility often allows prototyping to take place using the same material that will be used to create the final product, which lends itself to increased accuracy in the early- to mid-project stages.

3D printing is a bit more limited in its material options, typically making use of thermoplastics or resins in most cases depending on the CNC machine. This can result in the final product not being as robust as one made from metal or wood.

Precision

CNC machines are also known for their immense precision, with many offering a repeatability of plus or minus .001 inches. This also helps achieve a superior finish and surface quality that in many cases means the product can be shipped directly to its destination once the project is complete.

With a 3D print job, some additional finishing steps are often required to prep the product for delivery. While these machines may advertise precision, they often fail to deliver on that promise when compared to CNC.

Efficiency

The job specifications between these two types of machines varies, of course, as CNC work is typically of a larger scale than that of 3D printing. However, the general efficiency can still be compared.

3D printing jobs, despite the smaller scale, often take hours to complete. This is one of the key reasons 3D printing is really not an option for larger-scale production. It simply takes too long.

CNC jobs of a similar scope take a fraction of the time, due largely to the fact that its quicker to remove material from an existing piece than it is to build a piece layer by layer. The efficiency of CNC work makes it one of the best options available for mid- to large-scale production, as you can quickly set and reset workpieces and cuts on an automated basis.

Waste

A key area where 3D printing has an edge over CNC is the amount of waste left over after a given project. As material is cut away from the workpiece during a CNC job, it must be disposed of and in certain cases is unable to be reused.

With 3D printing, the only material needed is that which will be included in the final product.

Applications

The characteristics of CNC and 3D printing make each one better-suited for specific applications than the other.

Given the efficiency and precision with which CNC routers and plasmas can complete projects, they are ideal for commercial and industrial equipment, furniture, signage, and machining aluminum and brass to name a few.

With 3D printing, the cost per unit on a project is always the same regardless of quantity, making them a better fit for creating one-of-a-kind products where timeline and repeatability are less critical factors.

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