Process choice
Milling and turning are not interchangeable. The geometry decides the process, and the setup count decides the price.
Key takeaways
- Round and symmetric → turning. Pockets, flats and off-axis holes → milling.
- Setup count usually matters more than cycle time.
- A turned part with cross-features may need mill-turn or a second setup.
- Tolerance type matters: diameters vs positions.
- Send the drawing and ask which route the shop would use — and why.
The geometry rule
| Feature | Process | Why |
|---|---|---|
| Cylindrical shaft, bushing, fitting | Turning | The part rotates; the tool moves along the axis |
| Plate, housing, bracket | Milling | Pockets, flats and holes in multiple directions |
| Turned body with cross-holes or flats | Mill-turn or two setups | The cross-features cannot be cut on the lathe alone |
| Deep pocket with square corners | Milling + EDM | The cutter cannot reach the corner |
| Thin-wall round shell | Turning, then support | Deflection and chatter decide the route |
Where the cost actually goes
Below is an illustrative comparison of a turned bushing and a milled housing. The numbers are relative, not a quote; they show which line dominates.
| Cost line | Turned bushing, 200 pcs | Milled housing, 50 pcs |
|---|---|---|
| Setups | 1 | 2–3 |
| Programming | Simple | More complex |
| Fixture | Collet or soft jaws | Custom fixture |
| Cycle time | Short, predictable | Longer, more variable |
| Inspection | Diameters, threads | Positions, flatness, profile |
| Main cost driver | Cycle time | Setup + fixture + inspection |
On the bushing, the cycle time repeats 200 times, so a small improvement matters. On the housing, the fixture and the second setup can cost more than the cutting. That is why “which process is cheaper” has no answer without the drawing.
When one part needs both
A turned body with milled flats or cross-holes is common. Options:
- Mill-turn: one machine, one setup, best for repeat parts.
- Two setups: turn first, then mill; cheaper for small quantities if the tolerance allows.
- Two suppliers: rarely worth it — the second setup re-introduces alignment error.
Design choices that change the route
- Cross-holes in a turned part: a mill-turn or second setup; moving the hole to a flat face may remove it.
- Square corners in a pocket: EDM; a larger radius may remove the operation.
- Thin wall in a turned shell: support and light cuts; a rib may be cheaper than a slower cycle.
- Tolerance on a milled position: CMM inspection; a turned diameter may be checked with a micrometer.
Tolerance: diameters vs positions
A turned diameter is measured across the axis; a milled position is measured from a datum. The inspection method and the achievable tolerance are different. Tell us which feature is critical, and we will quote the process that can prove it.
CNC milling · CNC turning · Custom CNC parts
FAQ
How do I know if my part is milled or turned?
If it is cylindrical and symmetric around an axis, it is usually turned. If it has pockets, flats, holes off-axis or complex contours, it is usually milled.
Can one part need both?
Yes. A turned body with milled flats, cross-holes or slots is common; it may need a mill-turn machine or two setups.
Which is cheaper?
For a simple round part, turning is usually faster. For a plate or housing, milling. The setup count matters more than the process name.
Does turning hold tighter tolerance?
A turned diameter is often easier to hold than a milled position because the tool stays on the axis. But the part, not the process, decides.
Can you quote both routes?
Yes. Send the drawing and we will say which route we would use, and where the cost is.