Choose CNC machining when the part must be metal, hold tight tolerances, or take real heat and load. Choose 3D printing when the part is plastic, the shape is complex, you need it fast, or you only need a few.
How they differ
CNC machining cuts a part out of a solid block of metal or plastic with spinning tools. 3D printing builds a part up layer by layer. That one difference drives cost, speed and what each can make.
| CNC machining | 3D printing (FDM) | |
|---|---|---|
| Materials | Aluminum, steel, stainless, brass, and plastics like acetal (Delrin) and nylon | Plastics: PLA, PETG, TPU, ASA and more |
| Typical tolerance | About ±0.005 in (0.13 mm), tighter on request | About ±0.2 mm |
| Strength | Full strength of the solid material | Strong, weakest between layers |
| Complex shapes | Limited by tool reach | Internal channels, lattices and organic shapes are easy |
| Setup cost | Programming and fixturing for each new part | Almost none |
| One-off cost | Higher | Lower |
| Speed for one part | Usually days to weeks | Often next business day |
Pick CNC when
- The part has to be metal: shafts, brackets under load, heat sinks, engine-bay parts.
- A bearing bore or mating face needs a precise fit.
- The part runs hot or is safety critical.
Pick 3D printing when
- The part is plastic and you need it soon.
- You're still changing the design. A new version is just a new file.
- You need one or a few, where CNC setup costs would dominate.
- The shape is complex or organic.
The common combo
Many projects prototype in 3D printing until the design is right, then machine only the parts that truly need metal. That saves both money and machine time.
We print in-house in Olalla, WA, and we have access to CNC machines for customer orders. Not sure which process fits? Send the drawing and we'll tell you honestly. More: CNC machining for small runs · rapid prototyping