At what quantity does injection molding become cheaper than CNC machining?

Roughly 5,000–10,000 identical parts, but it depends on size and complexity. Below that, CNC machining wins because there is no tooling to amortize. Above it, the per-part cost of molding drops far below machining. The crossover is earlier for small, simple parts and later for large or tightly-toleranced ones.

Can CNC machining match injection molding's tolerances?

For the machined features themselves, yes — often tighter. What molding does better is hold those tolerances across millions of identical pieces with near-zero per-part variation, once the tool is proven. CNC holds tolerance per part but the setup still varies slightly run to run, which matters less at low volume.

CNC vs Injection Molding: Which by Qty

The one number that decides it: quantity

Injection molding needs a steel tool that can cost thousands to tens of thousands of dollars. That cost is fixed, so it spreads across the run — and the per-part price collapses as volume rises. CNC machining has no tool: every part carries its own setup and machining time, so its per-part cost stays roughly flat. The two lines cross somewhere around 5,000–10,000 identical parts, earlier for small simple parts, later for large or tight-tolerance ones.

Factor	CNC Machining	Injection Molding
Tooling cost	None	High (steel mold, $k–$$k)
Best quantity	1 – ~10,000 pcs	10,000+ pcs
Lead time to first part	Days (program the model)	Weeks–months (design + cut + prove the mold)
Design changes	Cheap — edit the model, re-run	Expensive — modify the mold
Materials	Metal and plastic both	Thermoplastics only (plus some liquid silicone)
Geometry	Almost anything millable/turnable	Needs draft, no undercuts without side-actions
Per-part cost at volume	Flat, relatively high	Very low once tool is paid
Tolerance consistency	Holds per part; slight run-to-run variation	Near-identical across millions once proven

Factor

CNC Machining

Injection Molding

Tooling cost

None

High (steel mold, $k–$$k)

Best quantity

1 – ~10,000 pcs

10,000+ pcs

Lead time to first part

Days (program the model)

Weeks–months (design + cut + prove the mold)

Design changes

Cheap — edit the model, re-run

Expensive — modify the mold

Materials

Metal and plastic both

Thermoplastics only (plus some liquid silicone)

Geometry

Almost anything millable/turnable

Needs draft, no undercuts without side-actions

Per-part cost at volume

Flat, relatively high

Very low once tool is paid

Tolerance consistency

Holds per part; slight run-to-run variation

Near-identical across millions once proven

How to choose for your part

Choose CNC machining if…

You need under ~10,000 pieces, or you're not sure of the volume yet.
The part is metal (molding can't do aluminium or steel).
The design will change — CNC absorbs edits for almost nothing.
You need the first parts in days, not months.
The geometry has no draft or has internal features molding hates.

Choose injection molding if…

You're committed to 10,000+ identical plastic parts.
The part is a simple thermoplastic shape that molds cleanly.
Per-part cost dominates and you can wait for the tool.
Annual volume justifies the tooling investment.

The in-between case

Prototypes and bridge production almost always start in CNC even when the end game is molding — it proves the design fast and cheaply, then you commit to the tool once the part is settled. We do a lot of that bridge work; see prototyping and low-volume production. And if the part is metal or low-volume, molding isn't even an option — CNC vs 3D printing is the more relevant comparison.

A caveat on the numbers

The crossover isn't a fixed rule. A large, complex moulded part may never beat CNC at your volume; a tiny simple part may cross at 3,000. The only way to know is to price both for your actual drawing — our cost calculator gives a CNC range in seconds, and we'll quote molding-vs-machining honestly if you ask.

CNC Machining vs Injection Molding