China Brass CNC Processing Service

Brass is not one material. C36000 free-cutting brass contains 2.5–3.5% lead, which acts as an internal chip breaker. It machines faster than almost any metal we run, produces short chips, and holds a good surface off the cutter. For turned parts under Ø60 mm, C36000 is usually the cheapest route to a finished part. If your application restricts lead, C27400 and C28000 are the alternatives, and both demand more attention at the tool.

C27400 (63/37 brass) and C28000 (60/40 Muntz metal) are lead-free and stronger. They also gum up more. Cutting forces are higher, chips run long, and a tool that cut 10,000 C36000 parts may need changing after 2,000 on C28000. We adjust spindle speed down, feed per tooth up, and use sharper positive-rake inserts. The part still comes out accurate, but cycle time and tool cost rise. Worth knowing before you compare quotes on two different alloys.

Beryllium copper is a different animal again. It machines closer to a hard bronze, and the dust needs control. We machine it when the application needs high conductivity plus spring properties, typically in electrical contacts and RF housings. It is never the low-cost option.

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  C36000Free-cutting, best finish per minute, leaded. Default for valves, fittings and connectors.
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  C27400Lead-free, higher strength, longer chips. Common in potable-water and plumbing parts.
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  C28000Muntz metal, good hot working and corrosion resistance. Marine and architectural hardware.
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  Beryllium copperHigh strength with conductivity. Electrical contacts and spring members.

Brass is abrasive in a mild way. It does not tear like 304 stainless, but it does wear the flank of a tool steadily, and the wear shows up as a rising surface roughness before the dimension drifts. We run carbide almost exclusively on brass, with polished flutes and a high rake angle. For small-diameter holes under Ø3 mm, uncoated carbide with a 130–140° point works better than a coated tool, because the coating adds edge radius that the chip does not want.

Galling is the failure mode most people miss. Brass chips are soft and sticky. If a drill dwells in the hole, or a tap reverses without clearing the chip, the material welds to the edge and the next revolution tears the thread. We counter this with peck drilling, high-pressure coolant through the tool, and forming taps where the thread strength allows. Forming taps eliminate the chip entirely, which is why they hold better thread geometry in blind holes.

On the mill side, brass likes a climb cut and a light radial engagement. We keep radial depth of cut around 30–40% of the cutter diameter and push the feed per tooth up. Taking too light a chip work-hardens nothing (brass does not work-harden much), but it does rub the edge and shorten tool life. The sweet spot is a real chip you can see, not dust.

Five-axis work on brass is mostly about access, not about sculpted surfaces. Angled holes, undercuts and multi-face features on a valve body come off one setup instead of three. That removes the re-fixturing error and drops the tolerance stack. On our 16 simultaneous five-axis centers, a brass manifold with features on five faces can hold ±0.005 mm across those faces without a second op.

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  Rake angleHigh positive rake, polished flutes. Reduces built-up edge on soft brass.
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  CoolantThrough-tool high pressure for deep holes and tapping. Clears sticky chips.
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  TappingForming taps preferred in blind holes. No chip to jam the thread.
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  FixturingSoft jaws machined in place. Brass marks easily under hard clamping.

We quote ±0.005 mm (±0.0002 in) as our standard machining tolerance, and brass is one of the easier materials to hit it in. The metal is stable, it does not spring back much, and thermal growth during a short cycle is small. Where brass gets difficult is on thin walls. A wall under 0.8 mm on a Ø40 mm bushing will deflect under clamping and cutting pressure, and the roundness will move. If your design needs a 0.5 mm wall, say so on the drawing; we will plan the passes and the support differently.

Surface finish follows the alloy. C36000 turns to Ra 0.8–1.6 μm off the tool without extra work. Ask for Ra 0.2–0.8 μm and it becomes a finishing pass with a wiper insert or a light polish. C28000 will sit one band rougher for the same parameters. As-machined brass at Ra 1.6–3.2 μm is fine for most fluid-path and electrical parts, and it saves a finishing operation.

Bore geometry deserves its own note. A reamed Ø10 H7 bore in brass is routine. A bored Ø80 bore with a 0.02 mm total tolerance needs a warm machine and a finishing cut with a sharp boring bar, because brass will push away from a dull edge. We inspect bores with pin gauges and bore mics, and we log the readings against the drawing callout.

Brass is chosen partly for how it looks and how it conducts, so finishing matters. Bare machined brass will tarnish in weeks in a humid warehouse. A clear lacquer or a nickel plating stops that. Electroless nickel gives a uniform 5–25 μm layer, including inside bores, and keeps the part conductive if the layer is thin. Silver and gold plating are common on RF and contact parts where surface resistance must stay low.

For cosmetic parts, bead blasting produces a satin surface and hides tool marks. Brushing gives a directional grain that reads well on architectural hardware. Polishing to a mirror finish is possible but adds handling risk, because brass scratches easily and every subsequent touch needs gloves and soft tooling.

Laser marking works well on brass. We mark part numbers, date codes and logos down to a minimum character height of 1.5 mm. Below that, the mark gets fuzzy on a blasted surface. Engraving is deeper and survives plating, which is why we often engrave before nickel rather than after.

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  Electroless nickelUniform coverage inside bores. Good corrosion protection, stays solderable.
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  Clear lacquerCheapest way to stop tarnish. Cosmetic, not wear resistant.
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  Bead blastingSatin finish that hides machining marks. Common on visible hardware.
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  Laser markingPart numbers and traceability. Minimum character height 1.5 mm.

Ask for the mill certificate on the alloy, not just the grade name. C36000 from different mills can vary in lead content within the spec, and that changes chip behavior and finish. We check incoming bar stock against the certificate and keep the heat number on file. If your part is for potable water, the lead restriction is the first thing to confirm, because C36000 is not compliant and will not pass.

Second, ask how the shop handles thin walls and small features. Anyone can quote a brass turning job. The difference shows in how they fixture a 0.6 mm wall, whether they use forming taps in blind holes, and whether they inspect bores with the right gauges. Our inspection is 100% before shipment, with raw material checks, in-process monitoring and a final report on request.

Third, confirm the finishing chain. Plating and blasting are often subcontracted, and that adds a handoff where parts can be lost or damaged. We keep finishing under our own roof across three plants in Dongguan and Singapore, so the part goes from machine to finish without a shipping leg in between. For a brass part with a cosmetic requirement, that matters more than a few cents on the piece price.

On logistics, we quote and return a free DFM analysis within 12 hours, start production within 24 hours, and ship in 3–5 days. There is no minimum order quantity, so a single prototype and a 10,000-piece run go through the same process. Uploads are treated as confidential and we sign an NDA on request.