Usinage CNC du laiton : guide 2026 des nuances, tolérances et conception (C360, C260, sans plomb)
Guide d’ingénieur pour l’usinage CNC du laiton : C360 vs C260 vs nuances navales et sans plomb, usinabilité, paramètres de coupe, tolérances réelles, finitions, dézincification et coût.
Le laiton est le matériau que les usineurs adorent en secret : les nuances de décolletage tournent 2 à 3× plus vite que l’aluminium et laissent une finition brillante directement sortie de l’outil. Mais le « laiton » est une famille de deux douzaines d’alliages dont l’usinabilité va de 100 à 30 — le mauvais choix de nuance se manifeste plus tard par des outils qui accrochent, des raccords dézincifiés ou des pièces qui se fissurent sur l’étagère. Ce guide est ce que nos ingénieurs utilisent réellement pour spécifier et chiffrer les pièces en laiton.
Brass at a glance
Brass is a copper–zinc alloy. Vary the zinc content (and add a pinch of lead, tin, or bismuth) and you shift the balance between machinability, strength, corrosion resistance and colour. That tunability is why brass covers everything from a free-spinning gas fitting to a deep-drawn ammunition case to a marine propeller shaft — but it also means the grade on your drawing matters more than the word "brass".
Why engineers choose brass
- Best machinability of any common metal. Free-cutting C360 is the reference standard the whole CDA machinability scale is built around. Chips break clean, tool wear is low, and cycle times are short.
- Corrosion resistance in water, steam, and many chemicals — the reason brass owns the plumbing, valve and fitting market.
- Electrical & thermal conductivity high enough for connectors, terminals and heat-transfer parts (though below pure copper).
- Low friction and self-lubricity against steel — ideal for bushings, gears, valve stems and lock components.
- Non-sparking and non-magnetic grades for explosive-atmosphere tools and instrument parts.
- Aesthetics. The warm gold colour and its ability to take a mirror polish or antique patina make brass a default for hardware, instruments and décor.
Where brass loses is weight (roughly 3× aluminium) and raw-material cost per kilo. For a fuller trade-off across metals and plastics, see our CNC material selection guide.
Brass grades you can order
Ninety percent of machined brass is one of the grades below. Specify by UNS number (C360, C260…) rather than "brass" — the machinability and corrosion behaviour differ enough that a substitution can wreck a part. The reference data below broadly follows the Copper Development Association (opens in new tab) alloy database.
| Grade (UNS) | Nominal composition | Machinability | Tensile (MPa) | Best for |
|---|---|---|---|---|
| C360 — Free-cutting | 61.5Cu / 35.5Zn / 3Pb | 100 | 340–470 | Screw-machine parts, fittings, valves, fasteners, gears |
| C260 — Cartridge | 70Cu / 30Zn | 30 | 300–540 | Deep-drawn & cold-formed parts, ammunition cases, terminals |
| C385 — Architectural | 57Cu / 40Zn / 3Pb | 90 | 360–480 | Extrusions, architectural hardware, forgings |
| C464 — Naval brass | 60Cu / 39.2Zn / 0.75Sn | 30 | 380–610 | Marine hardware, shafts — added tin resists dezincification |
| C230 — Red brass | 85Cu / 15Zn | 30 | 270–390 | Potable-water fittings, condenser tubes, corrosion service |
| C693 — Lead-free (EnviroBrass) | Cu/Zn + Bi/Se | 85 | 340–470 | RoHS / drinking-water parts needing near-C360 machinability |
Lead-free brass & RoHS / potable-water rules
The lead in C360 is what makes it machine so beautifully — it acts as a built-in chip-breaker and lubricant. But lead is now restricted in two big markets: drinking-water components and RoHS/REACH electronics. If your part touches potable water or ships into the EU electronics market, C360 may be off the table.
Potable water (US)
- The US Safe Drinking Water Act (opens in new tab) caps wetted-surface lead at a 0.25% weighted average.
- Rules out standard C360 (3% Pb) for wetted parts.
- Use low-lead / lead-free brass: C693 (EnviroBrass), C875xx silicon brass, or bismuth grades.
RoHS / REACH (EU electronics)
- RoHS allows up to 4% Pb in copper alloys as an exemption — so C360 often still qualifies for electronic hardware.
- REACH SVHC reporting still applies above 0.1%.
- When in doubt for consumer electronics, spec a low-lead grade and remove the ambiguity.
Machinability & cutting parameters
Brass is unusual in that its biggest machining risk is the tool grabbing, not wearing. A sharp positive-rake tool — perfect for aluminium — will dig into free-cutting brass and cause chatter or a pulled thread. The fix is counter-intuitive: use a neutral or slightly negative rake so the tool scrapes rather than bites.
| Operation | Tool geometry | Surface speed (m/min) | Feed | Notes |
|---|---|---|---|---|
| Turning, rough | Carbide, 0° to −5° rake | 150–300 | 0.10–0.30 mm/rev | Brass can run faster; machine rigidity usually the limit |
| Turning, finish | Carbide, neutral rake, honed | 200–400 | 0.05–0.12 mm/rev | Leaves a bright finish; little benefit to coatings |
| Milling | Uncoated carbide, 2–3 flute | 150–300 | 0.05–0.15 mm/tooth | Climb-mill to reduce burrs on edges |
| Drilling | Slow-helix (brass) drill | 60–120 | 0.05–0.20 mm/rev | Standard 118° drills grab; use a brass-specific low-helix drill |
| Threading / tapping | Straight-flute tap | 15–30 | 1× pitch | Free-cutting brass taps cleanly; spiral flutes can over-cut |
Machining best practices
- Neutral/negative rake to stop grabbing. The single most common brass rookie mistake is running aluminium-geometry tooling and getting chatter or snatched threads.
- Climb-mill, and deburr by design. Free-cutting brass throws small burrs at edges. Climb milling and a light finishing pass minimise them; chamfer sharp edges in CAD so a deburr pass isn’t hand-work.
- Coolant is optional. Many brass jobs run dry or with a light mist. If you flood, a straight or lightly-emulsified oil keeps the finish bright; avoid aggressive alkaline coolants that stain brass.
- Support thin walls. Brass is denser and less stiff than steel; thin rings and tubes deflect under clamping. Use soft jaws or collets for round stock the same way you would for a soft metal.
- Manage the swarf. Brass chips are valuable and recyclable — segregate them from steel/aluminium swarf. On screw-machine runs the scrap value is a real line item.
1. Grade & temper check
Confirm UNS grade and temper against the print. Half-hard vs annealed changes both cutting behaviour and final spring-back.
2. Bar prep
For bar-fed screw work, verify stock straightness and diameter tolerance — brass bar can be oval enough to matter on tight OD parts.
3. Rough with negative rake
Remove bulk material fast; brass tolerates aggressive depths of cut.
4. Finish pass
Light, sharp finishing cut for the bright as-machined finish brass is known for.
5. Deburr & clean
Tumble, brush or hand-deburr edges; degrease to remove cutting oil before finishing or packing.
6. Inspect & protect
Measure at stabilised temperature; bag with anti-tarnish paper if parts ship bare.
Tolerances achievable in production
Brass’s excellent machinability means it holds tight tolerances more easily than most metals — the limits are usually your inspection budget and the part’s thermal stability, not the material. The bands below are what we deliver and stand behind. For the tightest work we route parts through our precision manufacturing line with full CMM verification.
| Feature | Standard | Tight (on request) | Notes |
|---|---|---|---|
| Outer diameter | ±0.02 mm | ±0.008 mm | Free-cutting grades hold tighter than red/naval brass |
| Bore diameter | ±0.025 mm | ±0.01 mm | Reamed or bored; drilled-only is ±0.05 mm |
| Linear dimensions | ±0.05 mm | ±0.02 mm | Stack-up matters on multi-feature parts |
| Threads | Class 2A/2B | Class 3A/3B | Brass taps and single-points cleanly |
| Surface roughness Ra | 0.4–0.8 µm | ≤0.2 µm | Achievable as-machined; polishing goes to mirror |
Finishing brass — and why you don’t anodize it
A frequent RFQ line is "anodized brass". Brass can’t be anodized — anodizing grows a protective oxide only on aluminium, titanium and a few other valve metals. Brass is finished by mechanical or plated methods instead. The right choice depends on whether you want the natural gold look, a different colour, or maximum tarnish protection.
- Bare / brushed: cheapest. Brass tarnishes to a warm patina over time — desirable on hardware, less so on precision surfaces.
- Polished + clear lacquer: mirror finish sealed against tarnish. The standard for decorative and instrument parts.
- Nickel / chrome plating: hard, corrosion-resistant, and hides the brass colour — common on plumbing trim and fasteners.
- Gold / tin / silver plating: for electrical contact resistance, solderability or appearance.
- Passivation / anti-tarnish (benzotriazole): a thin protective film for parts that must stay bright without a heavy coat.
For plated and coated finishes across metals, see our surface finishing services; for the broader finish-selection logic, our surface finishing guide maps finishes to substrates and requirements.
In-service failure modes (the part nobody warns you about)
Brass parts rarely fail at the machine — they fail months later in service, from two mechanisms that are entirely preventable at the design and grade stage.
Dezincification
- What: zinc leaches out of high-zinc brass in aggressive water, leaving a weak, porous copper sponge.
- Where: plumbing and marine parts in soft, chlorinated or brackish water.
- Fix: use dezincification-resistant grades — inhibited (arsenical) brass, naval brass C464, or red brass C230 for the harshest service.
Season (stress-corrosion) cracking
- What: residual machining/forming stress + ammonia or amine exposure cracks the part with no warning.
- Where: cold-worked C260 parts near fertiliser, cleaning agents or marine environments.
- Fix: stress-relieve anneal after heavy cold work (250–300 °C); avoid ammonia contact; prefer lower-zinc grades where possible.
Brass vs bronze, copper and aluminium
Brass competes with three neighbours. The deciding factors are usually conductivity, corrosion environment, strength-to-weight and cost.
| Property | Brass (C360) | Bronze (C932) | Copper (C110) | Aluminium (6061) |
|---|---|---|---|---|
| Machinability | 100 | ~70 | ~20 (gummy) | ~90 |
| Density (g/cm³) | 8.5 | 8.9 | 8.9 | 2.7 |
| Electrical conductivity | Medium | Low–medium | Highest | High |
| Corrosion resistance | Good | Excellent | Good | Good (anodized) |
| Wear / bearing | Good | Excellent | Poor | Fair |
| Relative material cost | Medium | Higher | Higher | Lower |
| Best for | Fittings, hardware, terminals | Bushings, bearings, marine | Busbars, conductors, heat | Lightweight structural |
Cost & sourcing tips
- Free-cutting grades save money twice — lower cycle time and lower scrap. On high-volume screw-machine parts, C360 often beats a "cheaper" grade on total cost because the machine spends less time per part.
- Design to standard bar diameters. Brass bar comes in set sizes; a part sized just under the next stock diameter avoids machining away expensive metal.
- Recover scrap value. Segregated brass swarf has real resale value — worth structuring into the quote on big runs.
- Match grade to requirement, not habit. Don’t pay the naval-brass or lead-free premium unless marine or potable-water service actually requires it.
- Qualify the supplier on a first article. A short FAI run flushes out grade, tolerance and finish issues cheaply — see our supplier selection guide.
DFM checklist for brass parts
Frequently asked questions
The questions we field most often from engineers and buyers speccing a brass part.
Foire aux questions
- For most machined parts, C360 free-cutting brass is the default — it machines faster than any other common metal and costs less to produce. Switch to C260 for deep-drawn or cold-formed parts, C464 naval brass for marine service, red brass C230 for potable water and corrosion resistance, or a lead-free grade (e.g. C693) when RoHS or drinking-water lead limits apply.
- No. Anodizing only works on aluminium, titanium and a handful of other valve metals that grow a protective oxide. Brass is finished by polishing and lacquering, or by electroplating (nickel, chrome, gold, tin). If a drawing says "anodized brass", it needs to be corrected to a plating or coating spec.
- That’s almost certainly season cracking — stress-corrosion cracking caused by residual stress from machining or cold-forming combined with exposure to ammonia or amines (cleaning products, fertiliser, some packaging). The fix is a stress-relief anneal after heavy cold work and keeping the parts away from ammonia. It’s a grade and process issue, not a machining defect.
- Because brass machines so cleanly, we hold ±0.02 mm on diameters as standard and ±0.008–0.01 mm on critical features on request, with surface finishes down to Ra 0.2 µm and mirror polishing beyond that. The practical limit is usually inspection cost and thermal stability, not the material.
- Only when a requirement demands it. Lead-free grades like C693 machine at roughly 85% of C360’s speed and cost a little more per kilo. If the part touches drinking water or must meet strict RoHS/REACH limits, it’s mandatory. Otherwise, standard C360 is faster and cheaper.
- Often not. Free-cutting brass generates little heat and many jobs run dry or with a light mist. If you use flood coolant, a straight or lightly-emulsified cutting oil keeps the finish bright — avoid aggressive alkaline coolants, which can stain brass.
- Free-cutting brass leaves fine burrs at edges. Climb milling, a sharp finishing pass, and designing chamfers/edge-breaks into the part all reduce them. For volume production we tumble or brush-deburr; hand deburring is reserved for features geometry can’t reach.
Which brass grade should I use for CNC machining?
Can brass be anodized?
Why is my brass part cracking on the shelf before it’s even used?
How tight a tolerance can you hold on brass?
Is lead-free brass worth the extra cost?
Does brass need coolant when machining?
What causes burrs on machined brass and how do you prevent them?
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À propos de l'auteur
JLYPT Engineering Team
Senior CNC Application Engineers
We turn and mill brass every day — plumbing and gas fittings, electrical terminals, watch and instrument components, decorative hardware. This guide distils what our application engineers check before quoting a brass part, from grade selection to the finishing and in-service failure modes that catch first-time buyers out.
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