3D Printing vs. CNC Machining: What Is the Best Way to Make Your Part?

3D printing and CNC machining are two of the most popular manufacturing processes today. Both methods rely on digital control systems to enable the quick production of prototypes and are suitable for creating accurate, customized end-use parts.

However, they differ in almost every way – they are even direct competitors when it comes to producing solid parts. The biggest difference is that one method builds parts layer by layer, while the other works by removing material. If you find yourself at a crossroads choosing between CNC machining and 3D printing for your products, read on to find out more.

What Is 3D Printing?

3D Printing, also known as additive manufacturing, is a process that creates three-dimensional objects from a digital model by adding material layer by layer. The process begins with a digital model, which can be created using CAD (Computer-Aided Design) software, obtained from a 3D scanner, or downloaded from online repositories. Next, the model is imported into slicing software, which divides it into numerous two-dimensional cross-sectional layers that serve as a blueprint for the printer. The slicing software then converts these layers into a series of instructions—often in G-code—that the 3D printer can understand. Additionally, if the model contains overhanging parts, the software may generate support structures to ensure proper printing. Finally, the printer follows these instructions, depositing material layer by layer and bonding each new layer to the one beneath it, gradually building the complete object.

3D printing systems started entering the market in the late 1980s when Chuck Hull invented stereolithography (SLA), the first 3D printing technology. With ongoing research in new materials and technological advancements, more 3D printing techniques have emerged. Common types today include:

• FDM (Fused Deposition Modeling): Works by heating a thermoplastic filament, extruding it through a nozzle, and depositing it layer by layer. FDM is affordable, easy to use, and accessible for users of all skill levels. It supports large prints with the right machine setup and is suitable for architectural models, industrial design, and large-scale prototypes. However, it does not handle overhangs and fine details well and often requires support structures. FDM parts may have visible layer lines and weaker adhesion along the Z-axis, making them prone to delamination under stress.
• SLA (Stereolithography): Uses ultraviolet light to cure successive layers of liquid photopolymer resin. SLA prints have fewer visible layer lines compared to FDM and can produce ultra-smooth surfaces with fine details, making them popular for jewelry, dental models, and intricate prototypes.
• DLP (Digital Light Processing): Another resin-based 3D printing method, but instead of a laser, it uses a digital projector to cure an entire layer of resin at once. This makes DLP faster than SLA. DLP parts have sharp edges and crisp details and can be used in similar applications as SLA. However, they may sometimes show visible pixelation and typically have a smaller build area.
• SLS (Selective Laser Sintering): Uses a high-powered laser to sinter powdered materials, such as nylon and TPU, layer by layer. The unsintered powder acts as support, enabling interlocking, overhanging and other complex designs that are difficult to produce with other methods. SLS parts have good mechanical strength but tend to have a slightly grainy texture.
• DMLS (Direct Metal Laser Sintering): An extension of SLS, specifically designed for processing metal powders. It partially melts powder particles to fuse them together at a molecular level, resulting in slightly porous parts that may require post-processing, such as hot isostatic pressing, to achieve full density. Unlike SLS, DMLS needs support structures—which must be manually removed after printing—to counteract thermal stress and warping during the process.
• SLM (Selective Laser Melting): Also uses a high-power laser to produce metal parts, but unlike SLS, SLM fully melts the metal powder, creating 100% dense parts with superior mechanical strength, hardness, and durability, even comparable to cast or forged metal components. It works best with pure metals and select alloys. SLM generates higher thermal stress which can lead to warping and cracking. Stronger support structures are required to reduce these stresses.

What Is CNC Machining?

While 3D printing is a cutting-edge additive manufacturing process, CNC machining (Computer Numerical Control machining) represents a more traditional, subtractive manufacturing technique. Emerging in the 1950s from early NC (Numerical Control) systems, CNC machining has since evolved with digital automation, enabling high-precision manufacturing across industries.

To get a CNC part, you start by creating a digital model using CAD software. This model is then converted into machine-readable G-code through CAM programming, which specifies the precise movements, speeds, and operations. After that, the workpiece is securely mounted on the CNC machine, and the appropriate cutting tools are selected and installed. The CNC machine follows the G-code: beginning with rough machining to remove excess material and then moving on to fine machining to achieve the final dimensions and surface finish.

There are several common types of CNC machining widely used in the manufacturing industry:

• CNC Milling: A versatile machining process that uses rotating multi-point cutting tools to remove material from a workpiece. It can create flat surfaces, holes, angled cuts, and cavities with high precision. This process is widely used to manufacture engine components, molds, and structural parts in industries such as aerospace, automotive, and electronics.
• CNC Turning: Uses a single-point cutting tool to remove material from a rotational workpiece for creating cylindrical or conical shapes. It is highly effective in producing symmetrical parts like shafts, bolts, and bushings. This method is commonly applied in the production of automotive components, hydraulic fittings, and precision mechanical parts.
• WEDM (Wire Electrical Discharge Machining): A non-contact process that uses a thin, electrically charged wire to cut through conductive materials with extreme precision. It can shape hard materials, intricate geometries and fine details with minimal mechanical stress. WEDM is widely used in tool making, aerospace components, and medical device manufacturing.

When to Choose 3D Printing vs. CNC Machining

Both technologies offer unique advantages— CNC machining delivers high precision and material versatility, while 3D printing is preferred for creating complex geometries and rapid prototyping. The choice between them depends on various factors, including material requirements, design complexity, production speed, and budget consideration.

Quick reference table

The quick check table below provides a brief comparison to help you determine which process best suits your needs, or if a combination of both might produce optimal results.

Next, we can determine whether you should choose CNC machining, 3D printing, or both for your project by asking the following series of questions.

3D Printing vs. CNC Machining: What material do you plan to use?

3D printing and CNC machining both work with metals and plastics. CNC machining has a broader material adaptability. It is mainly used to produce parts from metal, though plastic has become increasingly popular. You may also use the CNC process to manufacture parts from woods, composites, even foams and wax.

The most common CNC materials:

• Metals: Aluminum, Stainless steel, Titanium, Brass
• Plastics: ABS, Nylon, Polycarbonate, PEEK

3D printing primarily works with thermoplastics, resins, and some metal powders. However, 3D-printed metal parts don’t come off the line cheap，though this is changing.

The common 3D printing materials：

• Plastics: Nylon, PLA, ABS, ULTEM, ASA, TPU
• Metals: Aluminum, Stainless steel, Titanium, Inconel

It is worth noting that very soft, flexible materials like TPU and silicone tend to deform under cutting forces, making precise machining difficult. Similarly, some superalloys are challenging to machine due to their high strength, work hardening, and heat resistance. For these materials, 3D printing may be a better choice.

3D Printing vs. CNC Machining: Which is better for complex parts?

Although 5-axis or more advanced machines can handle very complex geometries, it can still be difficult (or even impossible) to create hidden features and undercuts, as the tools can’t access all surfaces of the part. The geometry of the cutting tool itself also limits the ability to machine perfectly square corners. Additionally, custom fixtures or jigs are often demanded, which can be a significant limitation.

3D printers eliminate these geometry challenges in CNC machining. They can produce highly complex geometries with relative ease. While support structures may be needed for processes like SLM, the additional post-processing doesn't diminish the vast design freedom and complexity that 3D printing offers.

Does 3D printing or CNC machining offer better dimensional accuracy?

3D printing is generally less precise than CNC machining due to factors such as material shrinkage and the resolution limitations of the printing process. For example, precise 3D printing technologies like SLA typically achieve tolerances of around ±0.1mm under standard conditions. In contrast, precision CNC machines can hold tolerances as tight as ±0.025mm (0.001″) or even better.

When it comes to repeatability 3D printing— even high-precision methods like SLA or DLP— still lags behind CNC machining. CNC machines offer superior consistency due to their rigid mechanical setups, precise control systems, and the uniformity of the subtractive process. In contrast, 3D printing is more susceptible to variability caused by material shrinkage, layer adhesion, and environmental factors.

How does the surface finish compare between 3D printing and CNC machining?

3D printers like SLA can produce parts with fine, smooth, and textured layers, but CNC machining, with the right tools, can achieve even smoother surfaces.

Both methods can be further enhanced with a variety of surface finishing options to improve the functional and cosmetic qualities of the parts. For example, CNC machined parts can be anodized, powder-coated, bead-blasted, and passivated. Similarly, surface finishing options for 3D printed parts include plating, bead blasting, polishing, and heat treatments to strengthen the product.

How many parts are you manufacturing and is cost a primary concern?

For parts with typical geometries (ones that can be relatively easily achieved with CNC), the choice depends on both the material and the quantity of parts.

For plastic parts:

• If you're producing a low volume of parts (1-10 units), 3D printing is your best option due to its minimal setup requirements.
• When dealing with medium volumes (10-100 units), 3D printing is still a good choice, but you may also want to consider CNC machining.
• As the volume increases (100-1000 units), CNC machining becomes more efficient because of amortized setup costs, and injection molding could also be an option for certain designs.
• For very large volumes (1000+ units), injection molding typically becomes the best choice for plastic parts, rather than using 3D printing or CNC.

For metal parts, the situation is quite different:

• When producing low to medium volumes (1-100 units), CNC machining is often preferred, as metal 3D printing can be quite expensive.
• For higher volumes (100-1000 units), CNC machining is the most common method, but investment casting could also be an option
• For large volumes (1000+ units), investment or die casting is typically the best choice.

Chiggo’s Top Tips for Choosing Between 3D Printing & CNC Machining

Selecting the right manufacturing technology for your custom parts may seem like an insurmountable challenge, but it doesn’t have to be. As we always tell our customers at Chiggo, there is no perfect, one-size-fits-all manufacturing method. The best choice depends on a variety of factors. To help guide your decision, we've put together a few essential rules of thumb:

• Choose CNC machining if you're producing parts in medium to high quantities with relatively simple geometries.
• Choose CNC machining if precision and durability are key, especially for applications requiring long-term reliability, such as aerospace and medical components.
• Choose 3D printing for lower quantities of parts or rapid prototypes, particularly if your designs have complex geometries.
• When dealing with metal parts, CNC machining can be price-competitive even for low quantities, but geometry limitations still apply.

If you're still uncertain about the best manufacturing method for your part, contact our engineers and upload your design. Chiggo is a leading provider of CNC machining and 3D printing services in China, with an experienced team here to assist you!