CNC is the “subtractive 3D printer”. Just imagine three-axes of motion, software, and a spindle with a cutter in the place of an extruder, and you have a CNC router. CNC stands for computer numerical control, a term that goes back to when a computer was the size of a refrigerator. CNC’s range from desktop hobby machines to four-foot furniture-making machines and metal working behemoths.
CNC starts with a block or plate of clamped material. Then, using a g-code motion recipe (like a 3D printer), CNC moves the cutter in paths to cut pockets, outlines, and through-holes as well as face off surfaces.
CNC offers these advantages over 3D printing:
CNC has these downsides:
But the next question is, assuming you have a machine and earplugs, what kind of material should you feed into it? Let’s take a tour of the basic CNC material choices for the hobbyist maker.
First stop: baltic birch plywood. This is a great prototyping material for many CNC projects. It’s low-cost, high-quality, and paintable. Just be careful you don’t need any of the following:
Next up is polycarbonate. If your part can be clear and doesn’t need to serve as a bearing or slippery surface, PC is often the way to go. If you need more strength or rigidity, consider an assembly, and remember that polycarbonate can be cold-bent on a bending brake, an excellent way to add structure and rigidity after machining.
Now we come to a fork in the road:
Last stop on our short tour is acetal, for when you need a precise, slippery material available in black or white.
Getting confused between the different plastic options? Check out this chart comparing plastic properties.
For more detail, we take a more in-depth look at the five recommended materials for CNC.
Baltic birch plywood is great for CNC: It’s consistent, void-free, stable cabinet-grade plywood. It also has an attractive exposed edge. For more, see all about Baltic birch plywood.
Polycarbonate, also known as Lexan or Makrolon, is a strong, impact-resistant engineering-grade plastic that mates very well with CNC. Thicker material does get very pricey. If you can work with 1/4″ clear sheet, this is a versatile material that is a pleasure to cut.
Aluminum is what they used to make airplanes of (until carbon fiber came along). Aluminum has an excellent strength-to-weight ratio, and is much stiffer than plastic. Working with aluminum has its challenges but opens the door to strong, high-tech parts coming right off your CNC machine.
Ultra-high-molecular-weight polyethylene (UHMW) is like a poor man’s Teflon. Apart from having the same ultra-low coefficient of friction, UHMW is TOUGH. UHMW has a good bit of flex, so it isn’t a precision material. But if you need a bulky, slick, indestructible part with no moisture absorption, this is a good material to try.
Alternatively known as POM or Delrin, acetal is a terrific engineering-grade material with very similar properties to nylon. It absorbs no water and cuts like butter.
The following are some other popular options for CNC milling:
License: The text of "How to Choose the Correct CNC Material" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.
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