Eternal CNC shop-floor notes · a quick reference for designers and buyers
The "relative cost factor" below is benchmarked at 1× for aluminum 6061-T6, and already folds in tool wear, cycle time and scrap rate. These are long-run shop experience ranges, not absolute values.
| Material | Cutting speed (ref.) | Tool life | Surface finish | Relative cost |
|---|---|---|---|---|
| Aluminum 6061-T6 | Fast (300–500 m/min) | Long | Good (Ra 0.8 easy) | 1× |
| Aluminum 7075-T6 | Quite fast (250–400 m/min) | Medium | Good | 1.2× |
| Brass C360 | Very fast (400–600 m/min) | Very long | Excellent | 1.1× |
| Stainless 304 | Slow (80–150 m/min) | Short (work-hardens) | Poor (multi-pass) | 3–4× |
| Stainless 316L | Very slow (60–120 m/min) | Very short | Poor | 4–5× |
| Titanium Ti-6Al-4V | Very slow (30–60 m/min) | Very short (burns/chips) | Medium | 5–8× |
| PEEK (eng. plastic) | Medium (200–300 m/min) | Medium | Good | 1.5× |
Carbon steel (e.g. 45#, Q235) is also common — cheaper than stainless but it rusts. Avoid for outdoor or humid use unless you add a coating (see below).
For most structural parts, enclosures and brackets, 6061-T6 is enough. Cuts fast, easy on tools, nice surface — Ra 0.8 comes easy. If the function allows, this is our first recommendation. Don't second-guess it unless you need more strength or hardness.
7075 is far stronger than 6061, used in aerospace and load-bearing parts. But it's gummier, builds up edge buildup, and wears tools faster — the 1.2× is just the material delta; real cost is a bit higher once you count machining. Not unusable, just "expensive for a reason."
Cuts blazing fast, tools last forever, surface comes out bright. Great for precision small parts, fittings, decorative pieces. Only slightly above aluminum in cost, but the look is much better. First pick for brass connectors, gears, valve parts.
The real enemy of stainless isn't hardness, it's work hardening: a dull tool hardens it, and it gets harder the more you cut. You must run sharp fresh tools at high enough speed — no slow nudging. So short tool life and long cycle time are normal. Two notes: ① lead time runs 30–50% longer than aluminum, pad your schedule; ② loosen the tolerance one notch, and Ra 1.6 is the sane ceiling — don't insist on Ra 0.8. 316L resists chlorides better (coastal, chemical) than 304, but is slower and pricier.
Titanium's machining cost eats the margin: very slow, tools chip easily, and it burns (hot chips ignite). Reserved for biocompatible / high-temp parts (medical, aerospace). If 316L or 7075 can do the job functionally, switch — the savings are not small.
PEEK handles heat, insulates, self-lubricates — the go-to for semiconductor and medical. Around 1.5× in cost, not slow to cut, but watch workholding (it lets go and deflects). For non-high-temp / non-insulating needs, plain nylon or ABS is far cheaper.
| Your need | First pick | Note |
|---|---|---|
| General structure, enclosure, bracket | 6061-T6 | Best value |
| Load-bearing, aerospace / high strength | 7075-T6 | Accept slightly higher cost |
| Precision small parts, brass fittings, decorative | Brass C360 | Bright finish, easy cut |
| Food / medical / coastal / chemical corrosion | 304 / 316L | +30–50% lead time, looser tol. |
| Biocompatible / high temp | Titanium | Only if functionally required |
| High-temp insulation / semiconductor | PEEK | Use nylon/ABS if not needed |
| Indoor dry structure, want to save | Carbon steel + coating | Rusts; rely on plating |
6061-T6, 304 SS, 7075 — and we're done in one step.