Engineering · Machining guide
How to machine C110 (ETP) copper.
C110 electrolytic tough-pitch (ETP) copper looks easy on paper — soft, low strength, no abrasive carbides. In practice it’s one of the trickier materials to machine well because of its gumminess and tendency toward built-up edge. Sharp tools, the right rake angle, and careful chip control are essential. Used for bus bars, RF housings, grounding hardware, heat sinks, and high-conductivity electrical components.
01 · Why soft is hard
Gummy chips, built-up edge, no chip break.
C110 is electrolytic tough-pitch (ETP) copper — ≥99.9% Cu with a small controlled oxygen content (~0.02–0.04%), the workhorse grade wherever electrical and thermal conductivity matter. (The fully oxygen-free grades C101/C102 — the true “OFHC” — are reserved for service where dissolved oxygen would cause hydrogen embrittlement, such as UHV and brazed assemblies.) The combination of softness, ductility, and high thermal conductivity creates three machining problems: chips don’t break — they form long stringy ribbons that wrap around tools and parts; the soft chip welds to the cutting edge as built-up edge, ruining surface finish; and the high thermal conductivity carries cutting heat into the workpiece, so the part warms and grows during the cut (measure after it cools).
The fixes are sharp positive-rake tools (no honed edges — they create more pressure and worse BUE), high cutting speeds (heat goes into the chip), aggressive coolant flush, and chip-breaker insert geometry where available.
02 · Cutting parameters
Fast and sharp.
| Operation | Tool | SFM | IPT / IPR |
|---|---|---|---|
| Roughing turn | Uncoated polished carbide | 400–700 | 0.008–0.018 IPR |
| Finishing turn | Uncoated polished carbide | 600–900 | 0.005–0.012 IPR |
| Finishing turn | PCD | 1000–2000 | 0.003–0.008 IPR |
| End mill (rough) | Solid carbide 2-3FL | 300–500 | 0.003–0.008 IPT |
| End mill (finish) | Solid carbide 3FL | 500–700 | 0.002–0.005 IPT |
| Drilling | Solid carbide | 150–250 | 0.005–0.010 IPR |
| Tapping | HSS | 30–60 | — |
IPT (chip-load) values assume roughly ½–1″ end mills; scale down for smaller tools — see the chip-load chart.
03 · Practical notes
Vacuum-grade discipline.
- Tooling: uncoated polished carbide. Sharp positive-rake geometry — 12–20° rake. Avoid coatings (TiN, AlTiN) — they encourage chip welding on copper. PCD inserts give exceptional surface finish for finishing.
- Coolant: water-soluble flood with extreme-pressure additives. Through-tool coolant for deep features. Some shops use kerosene or light oil for ultra-clean vacuum applications.
- Vacuum-grade requirements: for SRF cavities, vacuum chambers, and cryogenic hardware, the surface must be free of organic contamination, embedded particles, and machining oils. Dedicated tooling, no leaded materials nearby, vapor-degrease cleaning post-machining.
- Chip control: long stringy chips are the norm. Use chip-breaker geometry on inserts, peck-cycle drilling, programmed retracts to break chips. Don’t leave parts running unattended without chip evacuation.
- Surface finish: 8 µin Ra is achievable with PCD finishing. For mirror-finish vacuum surfaces, follow with diamond-paste polishing.
- Common spec: ASTM B187 (rod, bar, and bus bar). For broader copper-alloy context, see our materials catalog.
Keep exploring
Related tools & references
ETP copper properties, conductivity, and temper data.
Push speeds to keep heat in the chip, not the tool.
Per-tooth chip loads for gummy copper alloys.
8.94 g/cc — bus bar and RF housing stock weights.
Compare C110 against OFHC C101/C102 grades.
Need C110 copper parts machined?
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