Injection moulding vs CNC machining
Injection moulding front-loads the cost into a mould that runs thousands of parts for pennies each; CNC machining has almost no setup cost but charges full price for every part. For a typical desk accessory the crossover sits somewhere between 400 and 900 units.
We machine the first run and mould the second. The first batch pays for finding out whether anybody wants the product; the mould pays for the fact that they did.
| Criterion | Injection moulding | CNC machining |
|---|---|---|
| Tooling cost | €4,000–12,000 per cavity set | €120–350 of fixturing |
| Cost per part at 50 units | Uneconomic | Competitive |
| Cost per part at 5,000 units | Roughly a tenth of machining | Unchanged |
| Design freedom | Draft, uniform walls, no undercuts without side actions | Almost anything a tool can reach |
| Achievable tolerance | IT11–IT13 | IT7–IT9 |
| Lead time to first part | 5–8 weeks for the mould | 3–10 days |
| Surface finish | Mould texture, repeatable across the run | Tool marks unless post-processed |
Computing your own crossover
The arithmetic is simple enough to do on the back of a quote. Take the tooling cost, divide by the difference in per-part price between the two processes, and you have the break-even quantity. A €4,800 mould against a €9 per-part saving breaks even at 533 units.
What people get wrong is the denominator. The moulded part is not just cheaper to make, it is also faster to finish and less likely to need deburring — differences that widen the gap and pull the crossover down.
The design consequences are the real difference
A machined part can have sharp internal corners, non-uniform walls and undercuts wherever a five-axis tool can reach. A moulded part needs draft on every vertical face, walls within a narrow band of each other, and ribs thinner than the walls they stiffen — or it sinks, warps and shows every one of those errors on the visible surface.
This is why our generator checks the design against the process before it quotes: the same geometry can be perfectly machinable and completely unmouldable, and that is worth knowing before the mould is cut.