3D printing vs CNC milling: All3DP compares these competing manufacturing technologies and explains which one to use for which purpose.
Note: We are talking about CNC mills and 3D printers in a price range between a few hundred to 3,500 dollars.
CNC milling machines take a block of solid material (e.g. aluminum or wood) and use sharp rotating tools or cutters to remove all parts that are not needed. So: Milling is a subtractive method – in contrast to additive manufacturing as in 3D printing.
CNC mills are computer-controlled. The computer feeds them machine-specific code that controls the cutting tools (just like the G-code used by 3D printers). The models for CNC mills are created using 3D modeling software, so-called CAM (computer-aided manufacturing) software applications. The CNC mills funded through Kickstarter in the last months also accept STL and OBJ files (just like 3D printers), some come with 1-year subscriptions for the CAM software Autocad Fusion 360.
Two examples of CNC mills successfully funded through Kickstarter:
3D printing: There are several types of 3D printers using different technologies and materials. All have in common that they start from scratch and build three-dimensional objects layer by layer (additive manufacturing).
CNC mills can work on a huge variety of materials: metal alloys (e.g. aluminum, steel alloys, brass, copper), softwoods and hardwoods, thermoplastics, acrylic, modeling foams, machining wax (for creating a positive model for casting). You may need different cutting tools for different materials, but the tool-to-machine interfaces are usually standardized – so the tools can easily be exchanged.
This way, you can utilize a CNC mill to manufacture prototypes in the same material that will be used for the final product – so you can immediately start testing.
Desktop 3D printers are usually restricted to a few materials, typically thermoplastics (PLA, ABS, sometimes nylon) or resins. Thermoplastics can be mixed with other materials such as ceramics, wood, metal, but the workpieces produced on a 3D printer will not be as robust as workpieces cut from a block of metal or wood.
As thermoplastics and resin 3D printers use completely different methods, a resin printer cannot handle thermoplastics – and vice versa.
CNC mills such as the Pocket NC and the Nomad 883 that were funded through Kickstarter, offer positioning accuracies of around 0.001 inch (0.025 mm) and tolerances of 0.005 inch (0.0127 mm). Of course, there are 3D printers such as the Zortrax M200 supporting resolutions of 0.025 mm and the CEL Robox with 0.02 mm. But the material worked on in a CNC mill (e.g. aluminum) allows much higher precision than the FDM used in many 3D printers that tends to deform when exposed to too much heat.
In practice, dull or damaged cutting tools, worn mills or faulty data delivered by the CAM software may result in inaccurate workpieces.
Some 3D printers (e.g. CEL Robox, Zortrax M200) promise very high precision but fail to deliver it from time to time. Just take a look at our “Common 3D Printing Problems” article, and you will find that high precision and FDM 3D printing not always go together. However, not always the technology is to blame: There is a lot a 3D printer user can misdo.
Comparing speed is difficult as CNC mills and 3D printers are typically used for different workpieces and materials. However, 3D printing jobs often take hours to complete, whereas CNC milling jobs with comparable size and complexity normally do not take more than an hour.
CNC mills are typically faster when chipping away material from a solid block than 3D printers that build objects layer by layer and occasionally have to slow down to avoid printing problems.
Noise: Depending on the material used, CNC milling can get extremely noisy. Cutting metal or wood using a large-diameter tool (to quickly remove large parts) can be ear-deafening. The rattling noise from a desktop 3D printer without casing is like a gentle waft in comparison. When cutting wax models, the noise from a CNC mill is hardly perceptible, however.
Vibrations: When working on a metal or wood block, a CNC mill also vibrates heavily – you wouldn’t want to have it on the desktop near you (even if you wore ear defenders to block of the noise). Vibration normally is no issue when 3D printing.
CNC milling means cutting away material using a rotating tool. The result: There is a lot of material spurting away, and that may be quite sharp (e.g., splinters of wood or metal). Not all CNC mills are fully enclosed when working on a block of material – so things can get quite messy. And with enclosed mills, you have to clean up the mess inside, once the workpiece is finished.
3D printing is not messy by design. When something goes wrong, however, you may need to remove thermoplastics from your printbed. But that is nothing compared to cleaning up after CNC milling.
Some postprocessing may be required both after 3D printing and CNC milling: Grinding and sanding. But we wouldn’t call that messy.
By design, there is less waste in 3D printing as this technology only requires the material needed for building the workpiece. In CNC milling you need a block of material that has at minimum the size of the workpiece – a lot of material has to be removed and often cannot be recycled.
There is a lot of overlap was far as the range of applications is concerned. Hence, we focus on the applications either technology supports while the other does not.
CNC milling is the better solution when manufacturing workpieces that need to be extremely robust and precise and/or heat-resistant.
3D printing has more exotic fields of application: It can be used for bioprinting, for printing food, for building purposes, and it can be used in space (e.g. on the ISS or in future space missions).
That’s difficult to compare. But getting started is less costly with 3D printing: You can get decent 3D printers for about $500 (e.g. the Prusa Steel or the Kossel ), while the CNC mills featured on Kickstarter recently start at $2,000.
Hm, that’s like asking: lead pencil or ballpoint pen? For some jobs you need a lead pencil while for others the ballpoint pen is the better tool. A 3D printer is the tool of choice for some applications, a CNC mill is the tool of choice for other applications. In an ideal world, an ambitious maker would purchase both a 3D printer and a CNC mill to be able to choose the right tool for the workpiece he intends to produce.
And if the space in your workshop is limited: You can get the best of both worlds.
In May, 630 backers on Kickstarter contributed almost $1.2 million to fund the development und production of a fascinating machine named BoXZY. BoXZY is a multifunctional machine combining 3D printer, CNC mill and laser cutter/engraver. This multitalent will be available in November.
BoXZY is a robust maker space in a compact aluminum cube that easily fits on a table. It can be turned from CNC mill to 3D printer to laser by simply exchanging tools. Additional tools and attachments can be added. The CNC mill operates at between 10,000 and 30,000rpm. It cuts aluminum, steel alloys, hardwoods, acrylic, thermoplastics (e.g. Delrin), modeling foams (such as Renshape), and machinable wax. The 3D printer uses various kinds of filaments: PLA, ABS, PVA and Nylon.
The BoXZY Loaded will cost $2,900, it combines CNC mill, 3D printer and laser engraver; there is also a BoXZY Pick 2 edition for $1,999 that combines two of the tools (depending on the buyer’s choice). $3,500 will buy you a BoXZY Supreme, including all 3 tools plus enclosure panels (for trapping heat and debris and blocking laser beams) plus heavy-duty mill and engraving sets and more. All BoXZY boxes come with Autodesk Fusion 360 Ultimate.
We expect more multi-purpose devices in the next future. There had been a Kickstarter project comparable to BoXZY a few weeks ago but it had been withdrawn recently.
Lead image by Michael Schwarzenberger through Pixabay
License: The text of "3D Printing vs CNC: Explained and Compared" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.
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