Brass selection and machining guide

Why brass is specified

Brass is a copper-zinc alloy, and it is chosen for a combination of properties that few metals offer together. It machines more freely than any other common metal, which means fast cycle times, low tool wear and a clean finish with very little effort. It conducts electricity and heat well. It is non-magnetic and non-sparking. It takes plating and polishing well, and it has a warm gold appearance that many products use as the finished look rather than a coating. It also solders and brazes easily, which matters for assemblies that are joined after machining.

Choosing an alloy type

Brass alloys differ in composition, and the choice that matters most for a machined part is usually the trade-off between machinability and lead content.

Free-cutting brass	Leaded — lead is added to break chips, which is what makes this family so fast and clean to machine. It gives the best surface finish and the longest tool life, and it is the default for connectors, fittings and turned parts that are not restricted on lead.
Lead-free brass	Restricted-lead — used where lead content is limited, for example by RoHS, ELV or a customer specification, or where the part contacts drinking water. These grades generally machine differently from leaded brass, typically with longer chips and more tool wear, so cycle times and tooling need to be planned for the change.
Higher-strength brass	Alloyed — additional alloying elements raise strength and wear resistance where a plain free-cutting grade would be too soft, at some cost to machinability and conductivity.

Tell us the alloy designation on your drawing. If the drawing only says "brass", the lead requirement and the conductivity requirement are the two questions that usually decide which alloy is appropriate.

How brass behaves in the machine

Brass is the material machinists reach for when a part has to be made quickly and cleanly. Chips break short instead of stringing, which makes chip evacuation straightforward and allows deep pockets and drilled holes without the chip problems stainless and POM present. It cuts at high speed without building up on the cutting edge, tool wear is low, and the surface finish comes off the tool rather than needing a finishing pass. Threads cut cleanly, small features hold their shape, and thin sections are less troublesome than in most metals.

That ease is why brass is a good material for very small, high-feature-count parts, and why it is often run on sliding-headstock machines where the part is turned from bar. It is also why a brass part frequently costs less than the same geometry in stainless, despite the higher stock price. The same properties are why so many connector and pogo-pin components are brass: small, high-feature-count parts turned from bar in volume.

Two behaviours are worth knowing about. Brass work-hardens when it is cold-formed, so parts that have been heavily formed before machining can carry internal stress and may need a stress-relief step. And brass is susceptible to stress corrosion cracking in ammonia and amine environments, so a part that will be exposed to those, or to certain cleaning agents, needs the alloy and the stress state considered rather than assumed.

Design details worth deciding early

• The lead requirement, if the part is subject to RoHS, ELV, drinking-water rules or a customer specification. This is the single detail that most often changes the alloy.
• Whether the part carries current or transfers heat, because the conductivity requirement narrows the alloy choice.
• The service environment, particularly any ammonia or amine exposure, which affects both alloy selection and whether stress relief is needed.
• Threads and knurling, both of which brass handles well and which are often the reason the part is brass in the first place.
• Whether the appearance is functional or decorative, because it decides whether polishing and plating are needed at all.
• Assembly method, since brass solders and brazes easily and the joint may influence the finish sequence.

Finishing

Brass tarnishes over time, so appearance is a design decision rather than a default. Polishing produces a bright reflective surface and is common on visible parts. Plating is used where a specific appearance or additional wear and corrosion resistance is needed, and the options include nickel, zinc, chrome and electroless nickel. Where the warm gold colour is the point, the part is often left unplated and polished, and the customer accepts the tarnish as part of the material's character.

A note on identifying brass in a photograph: colour alone does not establish the alloy. Several copper alloys share a similar appearance, and different brass grades look the same in a finished part. The alloy is determined from the material certificate and the drawing specification, not from how the part looks.

When another material is the better choice

• If maximum electrical or thermal conductivity is the requirement rather than a good compromise, copper outperforms any brass.
• If the part is a bearing or a wear surface in a wet environment, bronze is generally the more suitable copper alloy.
• If the part needs corrosion resistance without regular maintenance, stainless steel is the more durable route.
• If weight and cost matter more than conductivity or appearance, aluminum is the usual substitute.
• If the part is a non-conductive mechanical component, a machined plastic such as POM will be lighter and cheaper.