Short answer
Print it if the shape is complex, the quantity is low, and plastic is acceptable. Machine it if you need metal, tolerances tighter than about ±0.1 mm, or a properly smooth surface. Cost usually favours printing for one-offs by a wide margin.
The fundamental difference
Machining removes material from a solid block. Printing adds material layer by layer. Almost every practical difference follows from that one fact.
Because machining cuts away, every internal cavity, undercut and pocket needs a tool that can physically reach it, and each new orientation means another setup. Because printing adds, internal channels and hollow shapes cost nothing extra — the machine simply does not fill that space.
Side by side
| 3D printing | CNC machining | |
|---|---|---|
| One-off cost | Low | High — setup dominates |
| Complex geometry | Free | Expensive |
| Tolerance | ~±0.3 mm | ±0.02 mm achievable |
| Surface finish | Layer lines visible | Smooth |
| Materials | Plastics | Metals and plastics |
| Strength | Directional — weaker across layers | Uniform through the part |
| Lead time | Days | Days to weeks |
Where printing clearly wins
One or a handful of parts, where a machine shop's setup cost would dwarf the material. Shapes with internal voids or organic curves that would need multiple fixtures to machine. Anything you expect to revise, because there is no tooling and no setup to redo. And anything where a few tenths of a millimetre either way genuinely does not matter.
Where machining clearly wins
Metal, obviously — if the part needs to be aluminium or steel, no amount of clever printing substitutes. Precision fits: bearing seats, sliding surfaces, anything mating to a tolerance a printer cannot hold. Surfaces that must be smooth as-made rather than sanded afterwards. And parts under sustained heavy load, where the layer weakness of a print is a genuine risk rather than a theoretical one.
The combination people forget
These are not mutually exclusive. A common and sensible approach is to print the bulk of a part and machine or insert only the features that need precision: a printed housing with a reamed bearing bore, or a printed bracket with threaded brass inserts pressed in. You pay machining prices only for the millimetres that need it.
A rough decision rule
Ask what would happen if the part were 0.3 mm out in every direction. If the answer is "nothing much", print it. If the answer is "it would not fit" or "it would leak", machine it — or print it deliberately oversize and have the critical feature finished afterwards.
Common questions
Is 3D printing cheaper than CNC machining?
For a one-off plastic part, almost always, because there is no setup, no fixturing and no tool paths to program. The gap narrows as quantities rise.
Is a machined part stronger than a printed one?
Yes. Machining cuts from solid stock so there are no layer interfaces at all. A printed part is strong along layers and weaker between them.
When should I choose machining instead?
When you need tight tolerances, a smooth sealing face, metal, or genuine isotropic strength. Those are the four things printing cannot match.
How accurate is printing compared to machining?
Printing holds roughly ±0.3 mm; machining holds an order of magnitude better. For a part that just has to fit and work, printing is usually enough.
Can a printed part be a prototype for a machined one?
Yes, and it is a good use of it. Prove the shape and the fit in plastic for a few pounds before committing to a machined part.
Do you do CNC machining as well?
No, we only print. If your part genuinely needs machining we will say so rather than sell you a printed part that will not do the job.
What this means when you order
If your part really wants machining, we would rather say so than take the job. Send the file with a note about the tolerances and loads and we will give you a straight answer.
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Published 7 September 2026 · last reviewed 5 October 2026.