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  • Writer's pictureRhys Andersen

5 Questions to Ask Yourself to Decide When to Machine Parts vs. When to 3D Print

Updated: Nov 10, 2023

3D printing has come a long way in recent years and is now seen as not just a fun oddity but a realistic manufacturing solution. There are several advantages to 3D printing and as the technology evolves these advantages will continue to become more apparent, while many of the current disadvantages will be resolved. So what are these advantages and when should you 3D print vs CNC machine a component?

two parts one silver cnc milled vs one black 3d printed by method mfg
Top: CNC machined metal part Below: black plastic 3D printed part

You might be surprised to find that some of the most enthusiastic adopters of 3D printing are in fact machine shops. Our shop in particular uses a 3D printer on a daily basis. One of the most common workflows for 3D printers in machine shops is creating fixtures to hold parts as they are being machined. This can often save time and money as a less expensive machine can free up more valuable on a CNC mill allowing it to continue to make end-use parts. Combine this with the almost click-to-print ease of creating any number of everyday shop organization tools, makes us very big fans. Not surprisingly many of our customers love 3D printing too, and most clients we work with have at least one 3D printer in their office to create prototypes and in some cases even end-use components.

So when should you 3D print vs. CNC mill a part?

How tight is the tolerance?

One of the best differentiators between 3D printing and CNC milling is tolerance. While the best 3D printers can hit common machinist level tolerances of +-0.005, these are best-case scenarios and are reserved for the highest-end machines available. For example, the most commonly used 3D print process is FDM extruder plastic through a hot nozzle. As the extruded plastic cools, it begins to shrink and in some cases can warp leading to variance in tolerance from the original CAD model and part to part. Higher-end machines tackle this issue by enclosing the printing process in a heated build chamber that slows the cooling process reducing this effect.

What features does your part have?

The second big deciding factor is what type of features your part has. Are there a lot of threaded holes? These features will need to be added after printing either by tapping or by adding threaded inserts as 3D-printed threads will not have the strength or accuracy to function effectively. This extra time and effort might lead you to opt for machining over 3D printing in specific cases.

How many parts do you need?

With a basic part in mind, 3D printing a single one-off plastic prototype is easily half the price of the same singular part machined in Aluminum due to the time involved in programming and set-up. However, this price advantage quickly disappears as the quantities increase due to the low per-part cycle time on machined components, which can be as low as a few minutes versus the hours it takes to 3D print the same part.

What is the part's end-use?

Another big factor is the end use of your part. Will your part live outdoors? The most common 3D printing materials, such as ABS, are not exceptionally UV stable and will discolor or, worse, break down under sun exposure. Machined parts also provide an easier-to-determine strength and safety factor as parts are machined from solid raw materials with known physical properties. 3D printing on the other hand has many more variables that you or your supplier will have to factor in to determine the overall strength of your part such as infill percentage and infill geometry. Because of these additional variables, 3D printing can be more of an art and can require more iterations to develop the perfect recipe to create reliable components for your given application.

So where does 3D printing shine?

There is no doubt that 3D printing is changing the manufacturing world, as well as the design of everyday objects. One area, in particular, is the geometry of producible parts. Some shapes just can't be machined or are just too expensive. New design and engineering tools employing AI are developing incredibly efficient forms that are both lighter and stronger than anything previously imaginable. Often these shapes have internal structures that simply can’t be reached by subtractive tools, making 3D printing the perfect process. Similarly, 3D printing can easily allow the integration of internal cooling channels or embedded sensors. Below are two incredible examples of how 3D printing is being used today.

Still confused? We're here to help.

The ever-evolving world of manufacturing offers a plethora of choices, with 3D printing and CNC machining at the forefront. Each method has its merits, driven by the specific requirements of a project. While 3D printing has dramatically transformed the way we envision and create parts, especially those with complex geometries, CNC machining remains an essential tool for high-tolerance and large-quantity tasks. Ultimately, the key lies in discerning which method aligns best with the goals of your project.

As the manufacturing landscape continues to evolve, we remain committed to guiding you in making the most informed decisions for your unique needs. The future is exciting, and we're here to navigate it with you. Reach out today to tell us about your next machining project!


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