Brass CNC machining is the fastest way to produce precision metal parts that also have to look good, carry current or survive a threaded fitting. Brass is the reference material against which every other metal's machinability is rated: free-cutting brass C36000 is defined as 100% machinability, and everything else — aluminium, steel, titanium — is measured against it. That has a direct consequence for buyers: brass parts machine faster, hold finer detail, and often cost less per part than aluminium despite costing more per kilogram. This guide covers the grades you will actually be quoted, realistic tolerances, where brass genuinely outperforms aluminium and stainless, where it does not, and the finishing and compliance points that catch buyers out.
Why Brass Machines So Well
Brass is a copper-zinc alloy, and the grades used for machining contain a small amount of lead, which acts as a chip breaker and a lubricant at the cutting edge. The result is short, clean chips, low cutting forces, excellent surface finish straight off the tool and very long tool life.
Practically, that means:
- Cutting speeds roughly 1.3x those of aluminium and 4x those of stainless.
- Tool life around 1.5x aluminium and 4x stainless on comparable geometry.
- Machining cost per part typically 15% to 25% below aluminium, despite brass stock costing more per kilogram.
- Fine features — small threads, knurls, engraved detail, thin webs — hold their edges without the burr and tear-out you get in softer alloys.
Brass Grades You Will Actually Be Quoted
| Grade | Common name | Composition | Machinability | Typical use |
|---|---|---|---|---|
| C36000 / C3604 | Free-cutting brass | Cu 61.5%, Zn 35.5%, Pb 3% | 100% (reference) | Turned parts, fittings, inserts, fasteners |
| C37700 | Forging brass | Cu 59%, Zn 39%, Pb 2% | 90% | Hot-formed then machined components |
| C26000 | Cartridge brass | Cu 70%, Zn 30% | 30% | Deep-drawn parts, decorative trim |
| C46400 | Naval brass | Cu 59%, Zn 40%, Sn 1% | 30% | Marine hardware, seawater-exposed parts |
| C23000 / H62 | Red brass / common brass | Cu 62-85%, Zn balance | 30-40% | Plumbing, architectural, general hardware |
| C69300 / lead-free | EnviroBrass style | Cu-Zn-Si, Pb below 0.1% | 70-80% | Potable water and RoHS-tight applications |
If a drawing simply says "brass", ask which grade. The machinability spread between C360 and C260 is more than threefold, and it shows up directly in the quote.
Tolerances and Surface Finish
Brass is dimensionally stable and cuts cleanly, which makes it one of the easiest materials to hold tight tolerances in. Our standard capability is ±0.01 mm, and on brass turned and milled features that figure is comfortably repeatable across a production run rather than a first-article achievement. Fine threads, small-diameter bores and knurled surfaces are where brass shows the biggest advantage over aluminium.
As-machined surface finish lands around Ra 0.8 to 1.6 µm without a dedicated finishing pass, which is better than aluminium typically achieves in the same operation. Full tolerance guidance is in CNC machining tolerances.
Where Brass Genuinely Wins
Electrical contacts and terminals. Brass carries current reasonably well — around 26% IACS for C360 versus 100% for pure copper — while machining far more cleanly than copper. That combination is why connector bodies, terminal posts and contact carriers are so often brass. See electroacoustic components for the audio-side equivalents.
Threaded fittings, valves and plumbing. Brass threads machine crisply, gall less than stainless, and seal well. Valve bodies, hose fittings and compression components are classic brass work.
Decorative and audio trim. Polished or brushed brass has a warmth that anodised aluminium cannot imitate, which is why knobs, escutcheons, trim rings and badges are specified in brass when the brand wants a particular look. See audio knobs.
Small precision turned parts. Inserts, spacers, standoffs, custom nuts and studs and general precision fasteners run faster and cleaner in brass than in stainless, with less tool wear per thousand pieces.
Wear surfaces and low-load gears. Brass runs against steel with low friction and does not seize, which suits small gears, bushings and ratchet components.
Where Brass Loses
- Weight. At roughly 8.5 g/cm³, brass is about 3.1x heavier than aluminium. Any weight-constrained design — UAV structure, portable devices, moving robotics axes — should not be brass.
- Strength. C360 yield strength sits around 125 to 310 MPa depending on temper, well below 6061-T6 and far below 7075-T6 or alloy steel.
- Material cost. Brass stock typically costs 1.5x to 2.5x aluminium by weight, and copper price volatility feeds straight through.
- Dezincification. Alloys above about 15% zinc can leach zinc in certain water chemistries, leaving a porous copper structure. Naval brass or inhibited grades solve it; standard free-cutting brass does not.
- Stress corrosion cracking. Brass under sustained tensile stress in an ammoniacal environment will crack. If your part sees that, specify a resistant grade or a different alloy.
- Tarnish. Uncoated brass darkens. If the part is decorative and will be handled, it needs a lacquer or plating.
Finishing Brass
| Finish | What it does | Notes |
|---|---|---|
| Polishing / buffing | Mirror or satin appearance | Needs a lacquer afterwards or it will tarnish |
| Clear lacquer | Locks in the polished look | Adds a thin film — check it does not affect fits |
| Nickel or chrome plating | Wear resistance, brighter finish | Adds measurable thickness; mask critical threads |
| Tin plating | Solderability, food-contact friendly | Common on electrical parts |
| Passivation / anti-tarnish dip | Slows oxidation without changing dimensions | Good for parts that must stay bare |
| Brushing | Directional satin grain | Popular on audio trim |
If a finish adds thickness, say which features must be masked. The same rule that applies to anodizing aluminum applies here: dimensional responsibility has to sit with one party.
Brass vs Aluminium vs Stainless
| Factor | Brass C360 | Aluminium 6061 | Stainless 303/304 |
|---|---|---|---|
| Machinability rating | 100% (reference) | 90% | 45% |
| Relative machining cost | -15% to -25% vs Al | Baseline | +80% to +120% vs Al |
| Density | 8.5 g/cm³ | 2.7 g/cm³ | 8.0 g/cm³ |
| Electrical conductivity | ~26% IACS | ~40% IACS | ~2.5% IACS |
| Corrosion behaviour | Good, watch dezincification | Good, best anodised | Excellent |
| Lead content | 2.5-3.7% (C360) | None | None |
| Best for | Fittings, contacts, trim, fasteners | Structural, lightweight, enclosures | Medical, food, marine, high strength |
Compliance Note: Lead and RoHS
Free-cutting brass C360 contains roughly 2.5% to 3.7% lead. Copper alloys are covered by a RoHS exemption allowing up to 4% lead by weight, so C360 remains compliant for most EU electronic and electrical applications — but the exemption is reviewed periodically, and some customers impose their own internal limits regardless. If your product needs to be demonstrably lead-free, specify a lead-free grade such as C69300 or a silicon brass at the RFQ stage, not after the first article is approved.
Design and Sourcing Tips
- Specify the grade, not just "brass". The machinability and cost spread is too large to leave open.
- Exploit the machinability. Fine threads and small features that would be marginal in stainless are routine in brass — design to that capability.
- Watch the weight. If the part moves or is carried, run the mass calculation before committing.
- Decide the finish early. A lacquer or plating step changes both dimensions and lead time.
- Consider stamping for flat parts. Thin flat brass components are often cheaper as precision stampings once volume justifies a die.
- Ask for material certs. Copper alloy composition varies more between mills than aluminium does.
A brass CNC machining programme rewards early decisions, because grade, finish and lead-content requirements are all cheaper to settle before the first article than after it.
More on material selection generally is in CNC machining materials, with dedicated comparisons for aluminium and stainless steel. Our CNC milling service handles prismatic brass work and turning handles the rotational parts — see CNC turning service for the full turned-part capability.
Bottom Line
Choose brass CNC machining when the part needs fine machined detail, good electrical or thermal behaviour, a warm finished appearance, or clean threads in a fitting — and when weight and ultimate strength are not the binding constraints. Choose aluminium when mass matters and stainless when strength, corrosion or biocompatibility does.
We run brass CNC machining across turning and milling, with in-house polishing, plating and lacquer, at ±0.01 mm standard and 24-hour quotes on complete RFQ packages.
Send a STEP file and a drawing with the grade specified to gongtianbao@xhlmarketing.com or WhatsApp +86 17620300785.