CNC machining vs 3D printing — subtractive vs additive.
CNC machining and 3D printing solve the same problem — turning a CAD file into a physical part — from opposite directions. CNC removes material from a solid billet (subtractive). 3D printing adds material layer by layer (additive). Each has geometry it handles better and a cost curve that favors it at specific volumes. Choosing between them is usually less about the technology and more about the part. Makelab does not run CNC in-house — we run FDM, SLA, Industrial SLA, MJF, and FGF. This guide helps you decide which process is right for your project, honestly.
Detailed comparison
Property-by-property breakdown
| Factor | 3D Printing | CNC Machining |
|---|---|---|
| Best tolerance | ±0.1–0.2mm (SLA) | ±0.025mm |
| Surface finish (as-built) | 5–20 Ra μm (SLA smoothest) | 0.8–3.2 Ra μm |
| Complex internal geometry | Free — prints in one piece | Often impossible or multi-part setup |
| Undercuts and overhangs | Free | Requires multi-axis machine or fixturing |
| Material waste (polymer) | ~20% (unfused powder recovered) | 30–70% (chips and offcuts) |
| Setup time | Minutes (file to build) | Hours (fixturing, tool paths, tool changes) |
| Typical lead time | 2–5 days | 5–10 days |
| Cost at 1 part | Lower (no setup to amortize) | Higher (setup dominates) |
| Cost at 1,000 parts | Linear scaling | Setup amortized — can beat 3D printing |
| Best for | Complex geometry, low volume, rapid iteration | Tight tolerances, prismatic shapes, hard polymers |
Our recommendation
Choose CNC when tolerances are tight (under ±0.05mm), when the geometry is prismatic (blocks, plates, shafts that a mill can easily reach), or when you need a polymer grade like polyacetal, PEEK, or Ultem that is not available in 3D printing. Choose 3D printing when geometry is complex (undercuts, lattices, organic curves, internal channels), when part volume is low, or when turnaround matters more than absolute tolerance.
FAQ
Frequently asked questions
What tolerances can CNC vs 3D printing achieve?
CNC machining holds ±0.025mm tolerance, significantly tighter than 3D printing. SLA holds ±0.2mm (best in our 3D printing catalog), FDM holds ±0.5mm, and MJF holds ±0.3mm. Choose CNC when sub-0.1mm precision is required.
Is 3D printing faster than CNC machining?
Yes, for most parts. 3D printing requires minutes of setup (file to build) vs hours for CNC (fixturing, tool paths, tool changes). Typical 3D printing lead time is 2–5 days vs 5–10 days for CNC.
When should I use CNC instead of 3D printing?
Use CNC when tolerances must be tighter than ±0.1mm, when the material must be PEEK, Ultem, or another polymer not available in 3D printing, or when surface finish must be machined-smooth (0.8–3.2 Ra μm).
Is 3D printing cheaper than CNC for prototypes?
At 1–10 parts, 3D printing is almost always cheaper because there is no setup cost to amortize. CNC setup (fixturing, programming) costs $100–$500+ per part. At 100+ parts, CNC can become competitive.
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Choose MJF when volume is under 2,000-5,000 parts, when you need parts in days instead of months, when geometry is complex (undercuts, internal channels), or when your design is still evolving. Choose injection molding when volume exceeds 5,000+ parts of the same geometry and your design is frozen.
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