Copper vs Brass: Properties, Machinability & How to Choose

Copper and brass look similar, share a metallic family, and both appear in CNC machined parts — but they differ dramatically in machinability, conductivity, strength, and cost. Choosing the wrong one can mean a part that overheats in service, a machining cycle that takes five times longer than expected, or a component that fails regulatory compliance.

This guide compares copper and brass at the alloy-grade level — not just “copper” vs “brass” in vague terms — using verified data from the Copper Development Association (CDA), ASTM specifications, and in-house CNC production records. Every property value is traceable to a specific UNS designation, so the data is useful for actual engineering decisions rather than generic overviews.

What Is Copper?

Copper (Cu) is a pure elemental metal — atomic number 29 — valued for its unmatched electrical and thermal conductivity among non-precious metals. Industrial-grade copper typically contains 99.5% Cu or higher, while electrolytic tough pitch (ETP) copper reaches 99.95%+ purity. This purity is what gives copper its position as the global reference standard for electrical conductivity: 100% IACS (International Annealed Copper Standard).

The reddish-brown color of fresh copper is distinctive and easy to identify. Over time, exposure to air and moisture produces a patina — first darkening to brown, then eventually developing the characteristic green verdigris seen on architectural elements like the Statue of Liberty’s exterior.

Key Copper Grades for CNC Machining

• C11000 (ETP — Electrolytic Tough Pitch) — 99.9% Cu, the most common commercial copper. Excellent conductivity (101% IACS) but poor machinability (rating: 20%). Produces long, stringy chips that wrap around tooling.
• C10100 (OFHC — Oxygen-Free High Conductivity) — 99.99% Cu, used in high-vacuum and cryogenic applications where even trace oxygen content matters. Machinability similar to C11000.
• C14500 (Tellurium Copper) — 99.5% Cu + 0.5% Te, developed specifically to solve copper’s machining problems. The tellurium additions create chip-breaking inclusions, boosting machinability to 85% while retaining 93% IACS conductivity. This is the recommended copper grade when both conductivity and machinability matter.

What Is Brass?

Brass is a copper-zinc alloy, not a pure metal. By adjusting the copper-to-zinc ratio (typically 55–95% Cu, 5–45% Zn) and adding small amounts of lead, tin, aluminum, or silicon, manufacturers produce brass grades optimized for specific applications — from deep-drawn cartridge cases to high-speed CNC screw machine parts.

The zinc content is what separates brass from copper in practical terms. Zinc increases hardness and tensile strength, improves machinability (especially when combined with lead additions), lowers the melting point, and shifts the color from copper’s reddish-brown toward a brighter gold or yellow. The trade-off is a significant reduction in electrical and thermal conductivity — common brass grades conduct only 25–28% as efficiently as pure copper.

Key Brass Grades for CNC Machining

• C26000 (Cartridge Brass, 70/30) — 70% Cu / 30% Zn, the most common structural brass. Excellent cold-forming behavior, but machinability is only 30% due to long, stringy alpha-phase chips. Named “cartridge brass” because it was the original alloy for drawn ammunition cases.
• C36000 (Free-Cutting Brass) — 61.5% Cu / 35.5% Zn / 3% Pb, the single most widely machined brass alloy. The lead particles act as microscopic chip-breakers and internal lubricants, giving C36000 a machinability rating of 100% — the benchmark against which all copper alloys are measured. The go-to grade for high-volume CNC turned parts like fittings, connectors, and valve components.
• C46400 (Naval Brass) — 60% Cu / 39.25% Zn / 0.75% Sn, where the tin addition inhibits dezincification in seawater. Used for marine hardware, pump shafts, and propeller shafts.
• C69300 (Eco Brass) — 76% Cu / remainder Zn + Si, a lead-free alternative to C36000 that achieves ~80% machinability through silicon-based chip-breaking. Compliant with NSF/ANSI 372 and RoHS for potable water and consumer electronics applications.

Properties Comparison by Grade

Most competitor guides compare “copper” vs “brass” using a single set of values for each. That approach is misleading — the property range within copper grades alone is enormous (machinability spans from 20% to 85%), and the same is true for brass (30% to 100%). The table below compares five specific grades that engineers are most likely to encounter when specifying CNC machined parts.

✅ Verified CDA alloy datasheets; ASTM B187 (C11000), ASTM B301 (C14500), ASTM B36 (C26000), ASTM B16 (C36000); MatWeb material database

CNC Machinability: Grade-by-Grade Breakdown

Machinability is the single most important practical difference between copper and brass for CNC manufacturing. It directly determines cycle time, tool life, achievable surface finish, and per-part cost — and the gap between copper and brass is wider than most engineers expect.

Why Pure Copper Is Difficult to Machine

C11000 ETP copper has a machinability rating of just 20% — the lowest of any commonly machined non-ferrous metal. The problem is copper’s combination of extreme softness and ductility. During cutting, the material deforms plastically rather than shearing cleanly, producing long, continuous “bird’s nest” chips that wrap around the tool, clog chip evacuation channels, and smear across the workpiece surface. The result is poor surface finish, unpredictable tolerances, and rapid tool buildup (BUE — built-up edge).

C14500 tellurium copper solves most of these problems. The 0.5% tellurium creates brittle inclusions throughout the copper matrix that act as internal chip-breakers — the same mechanism that lead provides in free-cutting brass. At a machinability rating of 85%, C14500 approaches brass-level machining performance while retaining 93% IACS conductivity. For any part that requires both conductivity and CNC machining, C14500 should be the default specification rather than C11000.

Why Brass Is the Benchmark

C36000 free-cutting brass defines 100% on the CDA machinability scale. Its 3% lead content creates discrete, evenly distributed particles throughout the alloy matrix. During cutting, these particles act as both chip-breakers (producing short, discontinuous chips) and internal lubricants (reducing friction between the tool face and chip). The practical result: C36000 runs at surface speeds up to 300 m/min, produces consistent sub-1.6 μm Ra surface finishes, and extends tool life 3–5× compared to pure copper.

Not all brass grades share this advantage. C26000 cartridge brass (machinability 30%) and C46400 naval brass (machinability 30%) contain no lead and behave more like copper during machining — long chips, higher cutting forces, and slower feed rates.

✅ Verified CDA machinability ratings; KUSLA in-house production data (cycle time ratios)

Recommended CNC Cutting Parameters

No competitor guide on “copper vs brass” provides actual cutting parameters — they stop at vague statements like “brass machines easier.” The table below gives starting-point recommendations for milling operations based on Sandvik Coromant and Kennametal published guidelines, adjusted against KUSLA Prototype’s in-house CNC production records.

✅ Verified Sandvik Coromant Copper Alloy Machining Guide; Kennametal Non-Ferrous Recommendations; KUSLA in-house data

Electrical & Thermal Conductivity by Grade

Conductivity is the primary reason engineers specify copper over brass. Pure copper (C11000) conducts electricity at 101% IACS — a value so high that modern refined copper actually exceeds the original 1913 standard. Adding zinc to create brass reduces conductivity dramatically: the zinc atoms disrupt the copper crystal lattice, increasing electrical resistance roughly proportional to zinc content.

✅ Verified CDA alloy datasheets; copper.org Industrial Design Guide; ASTM B301

The practical implication is significant: in a busbar application carrying 1,000 A, replacing copper with brass of equal cross-section would generate approximately 3.6× more resistive heat. Compensating for brass’s lower conductivity requires either increasing conductor cross-section (adding weight and material cost) or accepting higher thermal losses. For any application where electrical efficiency matters — power distribution, motor windings, heat exchangers, RF shielding — copper grades are the only viable choice.

The exception is C14500 tellurium copper, which retains 93% of pure copper’s conductivity while being far easier to machine. For CNC-produced electrical components like terminals, connectors, and contact pins, C14500 offers the best balance of conductivity and manufacturing cost. Competitor guides that compare generic “copper” at 100% IACS against generic “brass” at 25–28% IACS miss this critical middle-ground option entirely.

Corrosion Resistance & Dezincification

Both copper and brass resist general atmospheric corrosion well — copper develops a protective oxide layer, and brass resists tarnishing in dry indoor environments for years. The critical failure modes are environment-specific, and understanding them is essential for material selection in anything beyond benign conditions.

Dezincification: Brass’s Achilles’ Heel

Dezincification is a corrosion mechanism unique to brass alloys containing more than ~15% zinc. In chloride-rich, acidic, or stagnant water environments, zinc atoms selectively dissolve out of the alloy matrix. What remains is a porous, spongy copper structure that retains the original part geometry but has lost virtually all mechanical strength. A dezincified fitting or valve body can fail catastrophically under pressure with no visible external warning.

The alloys most vulnerable are high-zinc brasses like C26000 (30% Zn) and C36000 (35.5% Zn). Mitigation strategies include specifying dezincification-resistant grades — C46400 naval brass (tin-inhibited) or arsenical brass for plumbing — or switching to copper, which is inherently immune since it contains no zinc to leach.

Stress Corrosion Cracking (SCC)

Brass is susceptible to stress corrosion cracking in ammonia-containing environments — a phenomenon sometimes called “season cracking” after its historical discovery in brass cartridge cases stored in tropical ammunition depots. Even trace ammonia concentrations in industrial atmospheres can cause spontaneous cracking in brass parts under residual machining stress. Stress-relief annealing (260–290°C for 1 hour per 25 mm thickness) after CNC machining eliminates this risk in most applications. Copper is significantly less susceptible to SCC than brass.

✅ Verified ASM Handbook Vol. 13B — Corrosion of Nonferrous Alloys; CDA Technical Guide

Cost Comparison: Raw Material + Machining

Competitor guides typically state that “copper is more expensive than brass” without quantifying the difference or accounting for machining cost — which often dominates total part cost for CNC-produced components.

⚠️ Estimates Based on KUSLA Prototype production quoting data, 2026. Actual costs vary by geometry, quantity, and commodity pricing.

The key insight: raw material cost for copper is only 30–50% higher than brass, but the total finished part cost for C11000 copper can be 4–6× higher because of the drastically longer machining cycle and higher tool consumption. C14500 tellurium copper brings total part cost down to just 1.5–2× brass — a far more reasonable premium for applications that demand high conductivity.

Lead-Free Brass: RoHS & NSF Compliance

C36000 free-cutting brass contains approximately 3% lead (Pb) by weight — a critical detail that most copper-vs-brass comparison guides ignore entirely. This lead content exceeds the thresholds set by multiple regulatory frameworks, making C36000 non-compliant for certain high-volume applications.

✅ Verified RoHS Directive 2011/65/EU Annex III; NSF/ANSI 372-2020; California Health & Safety Code §116875

For applications involving potable water contact, food processing, or consumer products sold into regulated markets, engineers must specify lead-free alternatives. C69300 (Eco Brass) uses silicon and bismuth as chip-breaking agents instead of lead, achieving approximately 80% of C36000’s machinability while meeting NSF 372 and RoHS requirements. C87850 (silicon brass) is another option, combining high strength with full lead-free compliance.

Pure copper grades (C11000, C14500) are inherently lead-free and fully compliant with all drinking water and electronics regulations — an advantage over brass that matters increasingly as global regulations tighten.

How to Choose: Decision Framework

Material selection between copper and brass depends on which performance attribute dominates the design requirement. The table below provides a structured decision path — start with the priority that matters most, and the recommended grade follows.

For projects where the optimal material is not immediately obvious, KUSLA Prototype offers free material consultation as part of the quoting process. The engineering team evaluates part geometry, operating environment, regulatory requirements, and production volume to recommend the best copper or brass grade for each application. Upload a CAD file to get a free quote with material recommendations included.

For a deeper comparison of brass against its other copper-alloy sibling, see the companion guide: Brass vs Bronze: Properties, Machinability & How to Choose.