Both processes turn CAD into parts without tooling, so both are prototype workhorses. The right choice depends on what the prototype needs to prove.
Quick comparison
| Factor | CNC machining | 3D printing |
|---|---|---|
| Materials | Production metals and engineering plastics | Printable polymers and selected metals |
| Mechanical properties | Same as bulk material | Can be anisotropic (weaker between layers), technology-dependent |
| Accuracy | High — suitable for precision fits | Good; varies by technology, size and orientation |
| Geometry | Limited by tool access, internal corners need radii | Very complex shapes, internal channels, lattices |
| Surface finish | Smooth, can be anodized/plated | Layer lines or textured; needs post-processing for smooth cosmetics |
| Cost driver | Machining time, setups, tolerances | Part volume, build height, technology |
| Quantity sweet spot | 1 to hundreds (or more) | 1 to dozens; SLS/MJF can scale further |
Choose CNC machining when…
- The prototype must use the production material (e.g. 6061 aluminum, POM, stainless steel)
- You are testing loads, heat, wear or precise fits
- The part will be machined in production anyway
- You need cosmetic metal finishes such as anodizing
Choose 3D printing when…
- You are iterating form and ergonomics quickly
- The geometry is organic, hollow or has internal features
- The part will be injection molded later and you need a fast stand-in
- You need several design variants side by side
Combine both
Many robotics and electronics prototypes mix processes: machined structural parts for stiffness and accuracy, printed covers and brackets for speed. The goal is the fastest path to a prototype that answers your current question.
Design tips that reduce cost
- Machining: add internal corner radii, avoid deep narrow pockets, keep tight tolerances to critical features
- Printing: keep minimum wall thickness for the chosen technology, design for print orientation, avoid large flat areas that can warp
- Both: send STEP files and a drawing for critical dimensions
Learn more about CNC machining, 3D printing and rapid prototyping, or send your CAD files for a recommendation.