Brass turning: the reference material in precision machining

TO REMEMBER

• Free-cutting brass (CuZn39Pb3, CW614N) serves as a reference for the machinability index of all other free-cutting metals, with a conventional value of 100%, compared to 20% for pure copper or 60 to 100% for steel depending on the grade.
• Several grades coexist: CW614N remains the reference for all applications, CW603N (richer in zinc) reduces material cost, and lead-free grades like EcoBrass (CW724R) meet the strictest regulatory requirements, particularly for drinking water.
• Brass machining dominates the taps, electrical connectors, automotive and watchmaking industries, the latter being at the very origin of machining in the Arve Valley.
• Jacquemoux Décolletage, a family business founded in 1960 in Marnaz, certified ISO 9001, IATF 16949 and ISO 14001, uses this heritage to produce your brass parts, from prototype to large series.

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Brass holds a special place in screw machining: it's the material that gave the technique its name. In the Arve Valley, the French cradle of screw machining, the first screw lathes were designed in the 18th century to mass-produce the brass screws and pinions for watch movements. Two and a half centuries later, brass remains the absolute benchmark for machinability: all other metals are compared to it to assess their own ease of machining.

At Jacquemoux Décolletage, located in Marnaz since 1960, we produce brass parts for industry, energy, automotive, and valve manufacturing. This article explains why this material remains essential in precision machining, details its composition, its main grades, and presents its industrial applications.

Why does brass remain the reference material for bar turning?

Unrivaled machinability, literally the industry benchmark

When a metallurgist assesses the machinability of steel , stainless steel , or a copper alloy, they express it as a percentage relative to free-cutting brass, conventionally set at 100%. This reference is not arbitrary: CuZn39Pb3 brass possesses all the qualities that facilitate cutting.

• A wood chip that naturally fragments The micro-inclusions of lead dispersed in the copper-zinc matrix act as points of failure. The chip breaks into short fragments, without requiring a specific chip breaker or complex tool geometry.
• Cutting effortsreduced : the two-phase structure (α+β) of brass offers significantly lower cutting resistance than steel or stainless steel, which limits heating, preserves cutting edges and allows high cutting speeds, often exceeding 200-300 m/min in carbide (well above the 80 to 200 m/min used on austenitic stainless steel).
• Limited tool wear : the low aggressiveness of brass on the cutting edge extends the life of the tools, which reduces machine downtime and tooling costs per part, a decisive advantage in high-volume production.
• A naturally neat surface finish : brass can be machined with fine surface finishes without additional operation, an advantage for parts that are visible or in direct contact with a fluid.

These complementary properties justify the choice of material.

Beyond its ease of machining, brass is chosen for a range of functional properties:

• It has good corrosion resistance, particularly in aqueous environments, making it a material of choice for taps and fluid circuits, provided that a suitable grade is chosen to mitigate the risk of dezincification (see below).
• Correct electrical and thermal conductivity, lower than that of pure copper but sufficient for many connector applications.
• An aesthetically pleasing golden appearance, sought after in hardware, decoration and precision instruments, without additional surface treatment.
• Good cold forming ability and a relatively low melting point (around 900 to 940 °C depending on the grade), which facilitate both machining and any rework operations.
• A non-magnetic material, useful in certain electrical, electronic or measurement applications.

What is free-cutting brass made of?

A formulation designed for machining

Brass is fundamentally a copper-zinc alloy. But "free-cutting brass" proper (designated CuZn39Pb3 or CW614N according to the European standard EN 12164) owes its performance to a precise proportion of three elements:

• Le copper (approximately 57 to 59%): provides the ductility, conductivity and corrosion resistance characteristic of copper alloys.
• Zinc (approximately 38 to 40%): mechanically strengthens the alloy and reduces its production cost compared to an alloy richer in copper. Zinc also determines the characteristic α+β two-phase structure of free-cutting brass, with the β phase being softer and more conducive to chip fragmentation.
• Lead (approximately 2,5 to 3,5%): the key element for machinability. Insoluble in the copper-zinc matrix, it is distributed in the form of micro-inclusions which act as an internal lubricant and natural chip breaker during cutting; without this, the brass would behave like a much stickier and stringier copper alloy.

This composition, standardized by EN 12164 for bars intended for high-speed machining, explains why machining brass is clearly distinct from forging or foundry brasses, which are formulated differently according to their use.

Towards unleaded: a regulatory evolution to watch

Lead, however effective it may be for machinability, poses a problem in applications involving contact with drinking water or food. Health regulations, in France as in the European Union, impose increasingly lower lead content limits for brass components intended for water networks, with sanitary certification requirements (such as ACS in France) for fittings and valves.

This evolution has led to the emergence of lead-free or very low-lead brass grades, notably silicon brasses (such as EcoBrass, CW724R), which retain good machinability, on the order of 80 to 90% of that of CW614N. The choice between a conventional grade and a lead-free grade depends directly on the final application of the brass part and the applicable health regulations.

The nuances and variations of free-cutting brass

The term "free-cutting brass" actually covers several nuances, each suited to a different compromise between machinability, cost, corrosion resistance and regulatory compliance:

• CW614N (CuZn39Pb3): the reference grade, used in the vast majority of brass machining applications. It offers the best balance between machinability, mechanical strength, and general corrosion resistance.
• CW603N (CuZn36Pb3): richer in zinc and therefore less expensive in terms of material, at the cost of slightly lower corrosion resistance. Used on less exposed parts or where material budgets are limited.
• CW602N / CW511L (dezincification-resistant brass, DZR): formulated with an inhibitor (usually arsenic) to limit the risk of dezincification. Essential for taps and potable water fittings in demanding conditions.
• CuZn40Pb2 (CW617N): reduced lead content compared to CW614N, an intermediate compromise between machinability and environmental requirements.
• EcoBrass and other lead-free silicon brasses (CW724R): the answer to the strictest lead regulations, with machinability that remains close to that of conventional free-cutting brass.

The choice of grade is therefore never limited to the ease of machining alone: ​​the final application of the part, its environment of use and the applicable health or environmental regulations guide the decision just as much.

Industrial applications of brass machining

The combination of machinability, corrosion resistance and conductivity makes brass a strategic material in several sectors:

• Taps and fittings : the first outlet for machined brass. Valves, plumbing fittings, tap bodies and nozzles exploit both the resistance to corrosion in aqueous environments and the sealing achieved through precision machining.
• Electrical connectors : Sockets, terminals, contacts and connectors take advantage of the electrical conductivity of brass, combined with its mechanical strength and ease of shaping.
• Automotive : sensors, fuel or air conditioning circuit fittings, inserts and on-board connector components, where dimensional reliability in large series is crucial.
• Hardware and decoration : locksmithing, handles, furniture components and decorative items, where the golden appearance of brass is sought for its own sake, without surface treatment.
• Industrial gases and fluids : fittings and components of gas circuits, where corrosion resistance and the sealing of machined parts are critical.
• Watchmaking and precision instruments A direct legacy of the Arve Valley, where brass machining was historically used to produce pinions, screws, and components for watch movements, before expanding to precision instrumentation. Jacquemoux Décolletage does not manufacture watch parts; however, this historical expertise remains the foundation upon which our brass machining expertise has been built.

Jacquemoux's expertise in brass machining

Since 1960, we have built our response to the requirements of brass machining around a few concrete advantages:

• A historical connection to the material: based in the Arve Valley, our company carries this technical heritage into its workshop culture.
• A complete machine park: 25 CNC lathes with fixed or moving headstock, 10 multi-spindle cam lathes and 24 single-spindle cam lathes, to handle both large series of simple parts and complex geometries, from Ø 2 to 60 mm in bar and up to Ø 150 mm in billet.
• Three quality certifications: ISO 9001, IATF 16949 (automotive) and ISO 14001 (environment), guaranteeing documented processes and reproducible quality batch after batch.
• A mastery of nuances: from classic CW614N to lead-free shades for the most regulated sanitary applications, we support the choice of shade according to your specifications.
• A prototyping and pre-production service : to validate a geometry or a nuance before mass production launch, and secure your project from the design phase.

Your questions about brass machining

Why is brass considered the reference material in bar turning?

Because its composition gives it exceptional machinability: short chips that naturally fragment, reduced cutting forces, high cutting speeds, and limited tool wear. This is why the machinability of all other free-cutting metals is traditionally expressed as a percentage relative to that of free-cutting brass.

Are there lead-free brasses for machining?

Yes. In response to regulatory requirements for applications involving contact with drinking water or food, lead-free or very low-lead grades have been developed, notably silicon brasses such as EcoBrass (CW724R). Their machinability remains close to that of conventional free-cutting brass, making it possible to meet health standards without sacrificing productivity.

Does machined brass resist corrosion in water circuits?

Generally yes, but with particular attention to dezincification, a selective corrosion that can affect certain brasses in aggressive or stagnant aqueous environments. For tap and drinking water fitting applications exposed to this risk, DZR (dezincification-resistant) grades, formulated with a specific inhibitor, should be preferred.

Which industrial sectors make the most use of brass machining?

Plumbing fixtures and fluid fittings are the leading applications, followed by electrical connectors, automotive components, and watchmaking components. Decorative hardware and gas fittings round out the main markets for machined brass.

Do you have a project involving machined brass parts?

From defining the grade to delivering your finished parts, the Jacquemoux Décolletage technical team studies your specifications and offers you a solution adapted to your dimensional requirements, volumes and regulatory constraints.

Contact Jacquemoux Décolletage for a precise quote and expert support for your brass parts.