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Should I CNC machine or 3D print my part?
Choose CNC machining for tight tolerances, metal or fully dense material, and fine finishes: it holds ±0.005 in (±0.13 mm) standard and ±0.001 in (±0.025 mm) on critical features. Choose 3D printing for internal channels, lattices, organic shapes and nylon prototypes in 2–7 days, where machining would need many setups or cannot reach the geometry at all.
Which is cheaper at your quantity?
The same plate, each process in a suitable material (6061-T6 and 316 SS).
| Quantity | CNC machining | 3D printing |
|---|---|---|
| 10 | $86.80 | $229 |
| 50 | $43.90 | $197 |
| 100 | $37.20 | $187 |
| 500 | $26.70 | $176 |
| 1,000 | $23.70 | $176 |
| 5,000 | $21.90 | $176 |
| 10,000 | $21.80 | $176 |
| 50,000 | $21.80 | $176 |
| 100,000 | $21.80 | $176 |
Where each pays off
Production machining, turning, and sawing
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- First article
- 1–3 weeks
- Production
- 2–6 weeks per release
±0.005 in (±0.13 mm), or ISO 2768-m
Additive manufacturing
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- First article
- 2–7 days for plastic; 1–3 weeks for metal
- Production
- 1–3 weeks per release
SLS/MJF ±0.3% (±0.012 in / ±0.3 mm minimum); SLA about ±0.005 in (±0.13 mm) over the first inch; FDM about ±0.010 in (±0.25 mm)
Which should you pick?
Pick CNC machining when
- Features need ±0.001 in (±0.025 mm)
- The part is metal cut from wrought stock
- Surfaces need Ra 63–125 µin (1.6–3.2 µm) or better
- Geometry is prismatic and tool-accessible
Pick 3D printing when
- The part has internal channels, lattices or organic shapes
- Several parts can be consolidated into one print
- Nylon prototypes are needed in days
- Machining would need many setups or 5-axis work
Key differences
| CNC machining | 3D printing | |
|---|---|---|
| Tolerance | ±0.005 in (±0.13 mm) standard; ±0.001 in (±0.025 mm) critical | SLS/MJF ±0.3%, minimum ±0.012 in (±0.3 mm); SLA ±0.005 in (±0.13 mm) |
| Surface | Ra 63–125 µin (1.6–3.2 µm) as machined | SLS/MJF Ra 250–500 µin (6–13 µm); SLA under 63 µin (1.6 µm) |
| Geometry limits | Tool access; radiused inside corners; pockets up to about 4× width deep | Internal features possible; hollow parts need escape holes |
| Material behavior | Fully dense and isotropic | MJF near-isotropic; FDM weak between layers; metal LPBF over 99% dense |
| Cost driver | Machine time and setups | Build volume, height and post-processing |
| Lead time | 1–3 weeks to first article | 2–7 days plastic; 1–3 weeks metal |
Questions
Is 3D printing cheaper than CNC machining?
For complex plastic parts in low quantities, often yes. For simple metal parts, machining is usually far cheaper: metal printing runs hundreds to thousands of dollars per part, and printed metal still needs machining on critical features.
Can metal 3D printing replace machining?
For complex, topology-optimized or channeled parts, sometimes. Large, simple metal parts cost far less to machine. Printed metal parts usually keep 0.010–0.020 in (0.25–0.5 mm) of stock on critical features for finish machining.
Which is better for prototypes?
Print plastic prototypes for form and fit in days. Machine prototypes when the test needs production-grade metal, tight tolerances, or the same material the production part will use.
Try both on your part.
The builder prices the same geometry in every suitable process and material, with DFM for each.