For a single prototype, CNC machining is the right choice when you need production-grade material properties and tight tolerances (down to ±0.005 mm); 3D printing wins on speed-to-first-part, geometric complexity and cost for visual or form-fit models. Most hardware teams use both — printing for looks and ergonomics, machining for functional testing.
The short answer by scenario
- Visual/appearance model, organic shapes: SLA 3D printing — smooth surfaces straight off the build plate
- Functional snap-fits, living hinges, ducts impossible to machine: SLS nylon or MJF
- Load-bearing parts, threads, sealing faces: CNC from real engineering stock (6061, 304, PEEK)
- 1–10 parts, metal, this week: CNC — material is stock, not a powder run
- 50+ identical parts: neither — compare vacuum casting or bridge injection molding instead
Accuracy and surface finish
CNC machining holds ±0.02–0.05 mm as standard and ±0.005 mm on precision features, with surface finishes from Ra 0.8 µm upward. SLA lands around ±0.1–0.2 % dimensional error (excellent for display), while SLS/MJF sit at ±0.3 % with a slightly grainy surface that takes bead blasting or dyeing well. If a dimension feeds a bearing or a gasket, machine it — or print oversized and machine the critical face.
Materials: real stock vs process-bound
CNC parts are the same 6061-T6, stainless 304, PEEK or ABS you'll production-mold, so test results carry over to production. Printed parts approximate properties: MJF PA12 is tough but isotropy and long-term creep differ from molded PA; SLA resins are brittle outdoors unless specifically formulated. For regulatory or fatigue testing, machined material wins.
Cost and lead time crossover
- 1 part, plastic, complex geometry: SLS/MJF often 30–50 % cheaper than 5-axis CNC
- 1 part, simple metal bracket: CNC usually cheaper than DMLS printing
- Setup-driven: CNC carries fixturing/programming cost that amortizes poorly below ~5 parts
- At SkillsProto both quotes come back together in 24 h, so you can compare landed cost directly
Hybrid workflows we run daily
A typical week at SkillsProto mixes both: SLS ducts for airflow studies, CNC-machined enclosures from 6061 for the same program, then vacuum-cast copies for marketing samples. We regularly print a near-net blank and machine critical interfaces — you get complex geometry without sacrificing tolerance where it counts.
How to decide in 60 seconds
Ask three questions: does any dimension feed a precision interface? (machine it) Does the geometry include internal channels or undercuts? (print it) Will the part see structural load or certification testing? (machine it). If answers conflict, split the part or print oversize and machine. Send us the STEP file and our DFM report will recommend a route with the trade-offs priced out.
Frequently Asked Questions
Is 3D printing cheaper than CNC machining for prototypes?
For single plastic parts with complex geometry, SLS or MJF printing is often 30–50 % cheaper because there is no fixturing or programming cost. For simple metal parts and precision interfaces, CNC is usually cheaper and delivers production-grade material. At SkillsProto both quotes arrive together within 24 hours so you can compare directly.
Which is more accurate: 3D printing or CNC machining?
CNC machining is significantly more accurate: ±0.02–0.05 mm standard and ±0.005 mm on precision features, versus roughly ±0.1–0.3 % dimensional deviation for SLA and SLS/MJF prints. For bearing bores, threads and sealing faces, machine the feature or print oversized and machine the critical surfaces.
Can I 3D print and then CNC machine the same part?
Yes — this hybrid workflow is common. A near-net part is printed (often SLA or SLS), then critical interfaces, threads or sealing faces are machined. It combines the geometric freedom of printing with ±0.01 mm-class accuracy exactly where the drawing demands it.
Related capabilities
Related guides
Have parts to quote?
Upload your files — DFM-checked quotation within 24 hours.