Why Copper for CNC Machined Parts?
Copper offers two properties no other common metal matches simultaneously: exceptional electrical conductivity (~100% IACS for pure copper, vs ~26% for brass) and exceptional thermal conductivity (~400 W/m·K). These make copper the default choice for electrical contacts, bus bars, heat sinks, cooling blocks and any part where electrical or thermal performance is the primary requirement. The tradeoff is that pure copper is soft, prone to built-up edge in machining, and lacks the strength of steel or aluminium.
Copper Alloys We Machine
| Grade | Key property | Best for |
|---|---|---|
| C11000 (ETP Copper) | 99.9% Cu, ~100% IACS conductivity | Electrical bus bars, contacts, heat sinks, electrodes — highest conductivity |
| C10100 (OFE Copper) | Oxygen-free, ultra-high purity | Vacuum electronics, waveguides, high-frequency RF parts — no oxide inclusions |
| C17200 (Beryllium Copper) | High strength (~1,200 MPa UTS) | Springs, precision connectors, molds, non-sparking tools — premium alloy |
| C93200 (Bearing Bronze) | Cu-Sn-Pb, excellent wear | Bushings, plain bearings, wear plates |
ETP copper (C11000) is our default for electrical and thermal applications. OFE copper for vacuum/RF work. Beryllium copper on request for spring contact and tooling applications.
Mechanical Properties (C11000 ETP Copper)
| Property | Typical value |
|---|---|
| Electrical conductivity | ~100% IACS |
| Thermal conductivity | ~400 W/m·K |
| Ultimate tensile strength | ~220–250 MPa (annealed) |
| Yield strength | ~70 MPa (annealed) |
| Density | 8.94 g/cm³ |
| Melting point | 1,083 °C |
Copper is soft (Brinell hardness ~35–65 HB). It requires sharp, polished tooling and careful chip control to avoid galling and smearing. Machinability is ~20% relative to brass — it machines slower and tends to produce long stringy chips that require attention.
How We Machine Copper
- Tooling: Highly polished high-positive-rake carbide or HSS — copper galls on rough flutes. Sharp edges at all times.
- Coolant: Flood cooling with good lubricity reduces galling and helps chip removal.
- Chip control: Copper forms long stringy chips — we run chip-breaking geometry where available and clear regularly.
- Tolerances: ±0.025 mm achievable on critical features. Copper's softness means clamping force must be controlled to avoid distortion.
- Surface finish: Ra 0.8 µm achievable with sharp tooling; copper polishes to mirror with abrasive finishing.
Typical Copper CNC Parts
- Electrical bus bars and contacts — machined to shape from rod or plate
- Water-cooled heat sinks — channel-milled cooling blocks for high-power electronics
- Electrodes for EDM — graphite and copper electrodes machined to exact geometry
- RF and waveguide components — OFE copper for microwave applications
- Induction heating coils and susceptors — precision-machined coil shapes
- Ground straps and bonding hardware — machined connection blocks
- Replacement pump and valve parts — legacy copper and bronze fittings reproduced from worn samples
Copper vs Brass for thermal applications. Copper has ~3.5× the thermal conductivity of brass. For heat sinks and cooling blocks where heat transfer is critical, use copper. For fittings, connectors and structural parts, brass is easier to machine and often cheaper per part.
Frequently Asked Questions
What is the difference between ETP copper and OFE copper for machined parts?
ETP (Electrolytic Tough Pitch, C11000) contains a small amount of oxygen (~300 ppm) — it is 99.9% pure and suitable for most electrical and thermal applications. OFE (Oxygen-Free Electronic, C10100) is 99.99% pure with essentially no oxygen — it is required for vacuum electronics, waveguides, and high-frequency RF components where oxygen inclusions would degrade performance. OFE is also required where the part will be joined by hydrogen brazing. For most heat sink and bus bar work, ETP is fine and more readily available.
Can you machine copper to tight tolerances?
Yes. ±0.025 mm is routinely achievable. Copper's softness requires careful clamping and tooling selection to avoid distortion, but it machines cleanly with sharp, polished tooling. We specify correct clamping forces for soft-material parts in quoting.
Is beryllium copper (C17200) safe to machine?
Beryllium copper can be safely machined provided beryllium dust is controlled — fine airborne beryllium particles are a health hazard. We machine C17200 with appropriate wet machining (to suppress dust) and dust extraction. We are experienced with this alloy for spring contacts, precision molds and non-sparking tooling. Specify C17200 in your enquiry and we will confirm our process controls.
Can you reproduce old copper fittings or parts from a sample?
Yes. Old pump fittings, heat exchanger parts, or legacy copper hardware can be reproduced from a worn sample using the same process as our broader replacement parts service: we measure the worn part, rebuild CAD, and machine or cast the reproduction. For large copper castings we can arrange sand casting; for machined copper parts we machine directly from rod or plate.
Why does copper cost more to machine than brass?
Copper's 100% IACS conductivity comes with lower machinability (~20% vs 100% for brass). Slower speeds, more tool changes and more careful chip management increase machine time and tooling cost. The copper material itself is also typically more expensive per kilogram than brass. The electrical and thermal performance justifies the premium where those properties are needed.
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