Brass CNC Machining Service: Alloys, Tolerances and Finish

The brass family is wide, and zinc content decides how the chips break. Our copper and brass stock list covers C101, C103, C110, beryllium copper, C27400, C28000 and C36000. The first three are oxygen-free or high-conductivity copper grades, often chosen for busbars and RF housings where electrical resistance matters more than machinability.

C36000 is the free-cutting standard. Lead acts as an internal chip breaker, so tool life is long and surface finish comes off the insert at Ra 0.8–1.6 μm without extra work. If your part is a connector body, a valve stem or a fitting, this is usually the right starting point.

For potable water or food-contact parts, leaded grades are often restricted. C27400 and C28000 are lead-free options that machine acceptably but produce longer, stringier chips. Expect slower feeds and a higher scrap rate on deep bores. Tell us the compliance requirement at quote stage so we can pick the alloy before programming.

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  C36000Best machinability and finish; check lead restrictions first.
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  C27400 / C28000Lead-free choices for water and food contact.
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  C110High conductivity for electrical contacts and busbars.
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  Beryllium copperSpring properties and strength; requires dust control.

We work to ±0.005 mm (±0.0002 in) where the drawing calls for it. That level is realistic on brass, but not everywhere on the part. Diameters turned in one setup hold well because thermal expansion is small and the material cuts cleanly. Features that depend on a second op or a fixture shift are harder.

Deep small bores are the usual trouble spot. A Ø2 mm hole at 10× depth will drift, and no amount of machine accuracy fixes a tool that deflects. If the bore is functional, keep the depth ratio under 6× or accept a wider tolerance. We flag these in the DFM report rather than quoting a number we cannot hold.

Thin walls below 0.5 mm distort under clamping pressure. Brass is stiff, so it springs back, but the witness marks stay. For thin-wall bushings we often turn the OD and ID in one operation with a soft jaw, and leave a small stock allowance for a finish pass after stress relief.

Inspection is 100% before shipment. That covers incoming bar stock, in-process checks at each setup, and final dimensional review. Reports are available on request, and we keep the setup sheets tied to the lot so a repeat order runs the same way.

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  Best caseTurned diameters in a single setup hold ±0.005 mm.
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  Deep boresKeep depth under 6× diameter for tight tolerance.
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  Thin wallsBelow 0.5 mm, plan for a finish pass after roughing.

Our floor runs 127 high-precision CNC machines, including 16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. For brass, the mill-turn centers do most of the work. A part that needs a turned OD, a cross hole and a milled flat comes off one machine in one setup.

That matters because every re-clamp adds error. A valve body with four cross ports is a good example. On a three-axis mill with a rotary fixture, you re-index four times and stack up runout. On a mill-turn center with a Ø400 mm rotary table, the ports come in from one datum.

Chip control is the other daily issue. Brass makes small, hot chips that pack into pockets and recut the surface. We run high-pressure coolant and peck cycles on deep pockets, and we program a chip break into the toolpath rather than relying on the operator to stop the cycle. Stringy lead-free grades need more of this attention.

Maximum processing size is 4,000 mm, with travels from 4,000 × 400 × 150 mm down to 500 × 310 × 200 mm. Long brass bars for busbar work fit the large travel; small connector pins run on the compact machines where spindle speed is higher.

Brass comes off the machine with a burr on every edge that crossed a cutter. For electrical parts, a loose burr is a short waiting to happen. We deburr by hand on critical edges, then tumble or bead blast where the drawing allows. Tumbling rounds edges uniformly, which is fine for housings but not for a sealing face.

Plating is common on brass. Electroless nickel gives wear resistance and a uniform coating on complex geometry. Silver and gold plating go on RF and connector parts where contact resistance matters. Zinc plating is a lower-cost option for hardware that only needs corrosion protection.

Polished brass is a finish in itself. Brushing leaves a directional grain; polishing brings it to a mirror. If the part is decorative, decide the direction of the grain before we start, because it cannot be changed after plating.

Laser marking works on plated and bare brass, with a minimum character height of 1.5 mm. Below that, the mark fills in and becomes hard to read. For serial numbers and logos, send the artwork as vector and tell us the surface it lands on.

Quotation and a free DFM analysis come back within 12 hours. The DFM report is where we raise the issues that cost money later: a bore that is too deep for its diameter, a wall that will chatter, a tolerance that does not match the function. Fixing those at quote stage is cheaper than fixing them at inspection.

Production can start within 24 hours of a released order. Standard brass parts ship in 3–5 days. Our historical late-delivery probability is below 2%, which we track because repeat orders live or die on that number.

There is no minimum order quantity. One prototype and a 10,000+ part run go through the same setup and inspection process. Prototype work is often the fastest way to confirm an alloy choice before committing to a production lot.

Uploads are secure and confidential, and we sign an NDA on request. Drawings, models and any compliance documents stay tied to your project file.