Complete engineering guide to machining C110 copper — the highest-conductivity metal available for CNC machining
In One Sentence
C110 copper — also known as Electrolytic Tough Pitch (ETP) copper — delivers the highest electrical and thermal conductivity of any commercially machinable metal, rated at 101% IACS and approximately 391 W/(m·K) thermal conductivity; however, its soft, ductile, “gummy” material behaviour and low 20% machinability rating make it one of the trickiest metals for CNC work. Success depends on sharp polished tooling, sufficiently aggressive feeds to suppress built‑up edge, and flood coolant for heat dissipation and reliable chip control.
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1. What Is C110 Copper?
C110 copper — designated as UNS C11000, Electrolytic Tough Pitch (ETP) copper, or commercially pure copper — is the most common grade of copper used in electrical and thermal applications. It contains a minimum of 99.9% pure copper, with a small amount of oxygen (0.02–0.05%) added to improve manufacturing characteristics.
The “tough pitch” designation refers to the specific method of refining and deoxidizing the copper during production, which preserves its exceptional electrical conductivity while maintaining good workability.
What makes C110 special:
Highest electrical conductivity of any commercially machinable metal — 101% IACS (International Annealed Copper Standard)
Exceptional thermal conductivity — approximately 391 W/(m·K), roughly 2.5× better than aluminum and 24× better than stainless steel
Excellent corrosion resistance — naturally forms a protective oxide layer
Non-magnetic — suitable for sensitive electronic applications
Good formability — can be bent, drawn, and formed without cracking
Important note: C110 is specified for conductivity first, machinability last. If your application requires electrical or thermal performance — C110 is the answer. If you need easy machining, choose brass instead.
Global Equivalent Designations:
UNS: C11000
ASTM: C110 (ETP Copper)
Chinese: T2；TU0 (oxygen‑free copper, not equivalent to C110)
European: CW009A
Japanese: C1100
2. Key Material Properties
Understanding C110’s properties explains why it is specified for the most demanding electrical and thermal applications — and why it requires disciplined machining practices.
| Property | Value | Why It Matters |
|---|---|---|
| Purity | ≥ 99.9% Cu | Highest conductivity available; no alloying elements to reduce performance |
| Density | 8.89 – 8.96 g/cm³ | Heavier than aluminum (2.7 g/cm³); similar to steel |
| Tensile Strength (annealed) | 210 – 300 MPa (32 – 45 ksi) | Moderate strength — softer than brass and bronze |
| Yield Strength (0.2%) | 160 – 230 MPa (23 – 33 ksi) | Low yield strength — parts can deform under load |
| Elongation at Break | 35 – 50% | Excellent ductility — but this is what makes chips “gummy” |
| Hardness (annealed) | 40 – 80 HB / 10 – 65 HRB | Very soft — easy to mark; requires careful fixturing |
| Electrical Conductivity | 101% IACS | The highest of any CNC-machinable metal |
| Thermal Conductivity | ~391 W/(m·K) | ~2.5× better than aluminum; ~24× better than stainless steel |
| Melting Point | 1,083°C | Stable under all normal operating temperatures |
| Coefficient of Thermal Expansion | 16.5 – 17.6 µm/(m·°C) | Similar to aluminum; thermal drift during machining is a concern |
| Corrosion Resistance | Excellent | Naturally forms protective oxide layer |
| Magnetic Response | Non-magnetic | Suitable for sensitive electronic applications |
| Machinability Rating | 20% (vs free-cutting brass = 100%) | One of the most difficult metals to machine |
The key takeaway: C110’s electrical conductivity of 101% IACS and thermal conductivity of 391 W/(m·K) make it the undisputed champion for electrical and thermal applications — but its 20% machinability rating means it requires specialized tooling, disciplined parameters, and careful process control.
3. Why C110 Copper Is Challenging to Machine
C110 is one of the most challenging metals to machine. Three mechanisms combine to make it a machinist’s challenge.
3.1 Built-Up Edge (BUE)
Root cause: Copper is highly ductile and has a strong affinity for most tool materials (carbide, HSS). At the cutting zone, the workpiece material welds to the tool face under cutting temperature and pressure, forming a built-up edge.
The problem: The BUE changes the effective tool geometry — it increases the actual depth of cut relative to programmed depth and creates a rough, torn surface finish rather than a clean shear surface.
The fix: Sharp, highly polished tooling with positive rake angle (8–12°).
3.2 Long, Continuous Chips
Root cause: Pure copper’s high ductility means chips do not fracture — they flow continuously from the cutting zone, forming long, stringy coils that wrap around the workpiece, chuck jaws, and tool holder.
The problem: In a production environment, this creates a chip management problem: the chips can damage the part surface, jam the tool path, and create a fire/entanglement hazard in the swarf collector.
The fix: Use chip-breaking insert geometry; increase feed rate to promote chip curl and break-off; program periodic retracts on deep turning passes.
3.3 Workholding Marking
Root cause: Copper in the half-hard condition is approximately HRB 40–50. Standard steel chuck jaws (serrated) will indent the OD of copper workpieces under clamping force.
The problem: For parts with tight OD tolerances or cosmetic finish requirements on clamped surfaces, this is a rejection cause.
The fix: Soft-jaw workholding (aluminum or brass-lined jaws bored to OD); collet chuck with split collet for round bar stock; never touch off a datum surface directly with steel workholding.
3.4 Work Hardening
C110 copper can work-harden during machining, leading to increased hardness and making subsequent passes more difficult. Work‑hardened surface will further promote built‑up edge in subsequent cutting passes.
The fix: Use sharp tools, apply cutting fluid, and avoid excessive heat generation.
3.5 “Gummy” Behavior
C110 is soft and ductile — it has been described as “gummy” to machine. The material tends to smear rather than shear cleanly, requiring positive rake angles and aggressive feeds to maintain cutting action rather than rubbing.
4. Machining C110 Copper: Parameters & Best Practices
4.1 Recommended Cutting Parameters
For milling C110 copper with polished carbide end mills:
| Parameter | Roughing | Finishing |
|---|---|---|
| Linear Cutting Speed | 90 – 150 m/min | 150 – 240 m/min |
| Cutting Speed (SFM) | 300 – 500 SFM | 500 – 800 SFM |
| Feed per Tooth | 0.08 – 0.12 mm/z | 0.04 – 0.06 mm/z |
| Depth of Cut | 1.0 – 1.5 mm | 0.2 – 0.3 mm |
Note: C110 requires lower speeds than brass but higher feed rates to prevent rubbing. Start conservative and increase gradually while monitoring tool wear.
For turning C110 copper with polished carbide inserts:
| Parameter | Roughing | Finishing |
|---|---|---|
| Cutting Speed | 90 – 150 m/min | 150 – 200 m/min |
| Feed Rate | 0.15 – 0.25 mm/rev | 0.05 – 0.10 mm/rev |
| Depth of Cut | 1.0 – 2.0 mm | 0.2 – 0.5 mm |
For drilling C110 copper:
Cutting speed: 30 – 60 m/min (for carbide drills) — for HSS drills, keep cutting speed 8 – 20 m/min.
Critical rules for C110 machining:
Feed must be aggressive — feeds that are too low cause rubbing, which generates heat, work hardening, and built-up edge. Feed rates should be higher than for steel.
Speed can be moderate — too fast generates heat that promotes BUE; too slow causes rubbing.
Never let the tool dwell — dwell causes work hardening and BUE formation (see note above).
For thin walls, use the “moderate speed + light depth of cut + high feed” combination.
4.2 Tool Selection
Recommended tooling:
Sharp, polished carbide tools — polished flutes reduce the material’s tendency to stick to the tool
Uncoated carbide with positive rake (8–12°) — coatings can actually increase friction with copper
PCD (polycrystalline diamond) — resists copper adhesion far better than coated carbide; ideal for production runs
Micro-grain carbide — provides the sharpest cutting edges
2-flute or 3-flute end mills for finishing — maximizes chip clearance
Left-hand spiral tools for deep slots — directs chips downward
Tools to avoid:
Dull tools — generate friction, heat, and built-up edge
Coated tools with thick coatings — the coating adds edge radius and increases cutting forces
High-speed steel (HSS) — acceptable for low-volume work but not production-efficient
4.3 Coolant Strategy
Coolant is essential for C110 — not optional.
Copper is prone to built-up edge, and heat accelerates this problem. Flood coolant is important because copper gets gummy when hot.
Recommended:
Flood coolant (5–10% soluble oil) — standard approach; reduces friction, heat generation, and built-up edge
High-pressure coolant directed at the rake face — essential for chip control and BUE prevention
Water-soluble cutting fluids — effective for most copper machining
Mist or light oil — for light finishing cuts on small parts
Critical warning: Never let the tool dwell in the cut — copper work-hardens and forms BUE under sustained rubbing (see rule in 4.1).
Avoid:
Dry machining — built-up edge and tool failure are almost certain
Low-pressure coolant — will not penetrate the cutting zone effectively
5. Distortion Control in C110 Copper
For a detailed guide on thin‑wall distortion causes and prevention strategies, see our distortion control guide.
C110 copper presents unique distortion challenges due to its softness, high ductility, and relatively high coefficient of thermal expansion.
5.1 Thin-Wall Deflection
C110’s softness and low yield strength mean thin walls can deflect under cutting forces — especially with heavy depths of cut or dull tools.
Mitigation strategies:
Use the “moderate speed + light depth of cut + high feed” combination to minimize cutting forces
Increase wall thickness where possible — this improves rigidity
Support thin walls with backing plates or fixtures
Use climb milling to reduce cutting forces
For very thin sections, consider adhesive or wax fixturing to hold the part without distortion
5.2 Clamping Distortion and Workholding Marking
C110 is soft — hardness typically HRB 10–65. Over-clamping leaves permanent marks and can distort the part. Standard workholding also leaves marks, which is a common rejection cause for parts with cosmetic requirements.
Do this:
Soft jaws — machined to match your part shape (aluminum or brass-lined)
Collet chuck with split collet — for round bar stock
Vacuum fixtures — even pressure across the whole surface
Low clamping torque — just enough to hold, not enough to deform
Sacrificial toe clamps — for milled parts
Never clamp directly on finished surfaces with steel jaws
Avoid:
Over-tightening — copper marks easily
Point-load clamping — distributes force unevenly
Hard jaws without soft jaw covers — will indent the workpiece
5.3 Thermal Dimensional Drift
C110 has a coefficient of thermal expansion of approximately 16.5–17.6 µm/(m·°C). Heat generated during machining can cause dimensional drift.
Mitigation strategies:
Maintain consistent coolant flow to control temperature
Avoid prolonged cutting in any one area
Allow parts to stabilize to workshop temperature before final inspection
For high-precision work, use flood coolant to maintain thermal stability
5.4 Burr Formation Control
Copper’s ductility makes it prone to burr formation — especially at hole exits and part edges.
Mitigation strategies:
Program chamfer stops at hole exits
Use sharp tools with positive rake
Deburr immediately after machining to save time
For high-volume work, implement in-process deburring
6. C110 vs C360 Brass vs Bronze: When to Choose Which
This comparison helps you decide which copper alloy fits your application — balancing conductivity, machinability, strength, and cost.
| Property | C110 Copper | C360 Brass | Bronze | Practical Implication |
|---|---|---|---|---|
| Electrical Conductivity | 101% IACS | 26% IACS | ~7–15% IACS* | C110 is the only choice for maximum conductivity |
| Thermal Conductivity | ~391 W/(m·K) | 115 W/(m·K) | ~59 W/(m·K) | C110 is ~3.4× better than brass for heat transfer |
| Machinability Rating | 20% | 100% | 20–100% | Brass machines 5× faster than C110 |
| Tensile Strength | ~32 ksi | ~58 ksi | 35–100 ksi | Brass and bronze are stronger |
| Hardness | 10–65 HRB | 55–80 HRB | 40–95 HRB | C110 is softest — easiest to mark |
| Cost* | $$ | $ | $$$ | C110 costs more than brass; bronze is most expensive |
| Color | Reddish-orange | Gold | Brown-gold | Visual differentiation |
| Best For | Electrical, thermal, high-conductivity | Precision CNC, high-volume, cost-sensitive | Wear parts, marine, bearings | Match material to application |
*Note: Bronze electrical conductivity varies widely by alloy family. Cost varies heavily with raw metal market fluctuations and specific alloy composition.
When to choose C110: Electrical bus bars, connectors, heat sinks, RF components, grounding hardware, thermal management components, waveguides — any application requiring maximum electrical or thermal conductivity.
When to choose C360 brass: Precision CNC machined components, high-volume production, cost-sensitive projects, fittings, valves, connectors where conductivity is not critical.
When to choose bronze: Bearings, bushings, marine hardware, wear-resistant components — tribological applications.
The decision rule: If it carries current or heat — choose C110. If it needs easy machining and moderate conductivity — choose brass. If it needs wear resistance — choose bronze.
7. Typical Applications for C110 Copper CNC Parts
C110 is specified when conductivity — not machinability or cost — is the primary driver.
Typical precision parts:
Electrical: Bus bars, electrical connectors, terminals, grounding components, RF connectors, waveguides
Power systems: Current-carrying components, motor terminals, switchgear parts, power transmission components
Thermal management: Heat sinks, cold plates, heat exchangers, thermal interface components
Electronics: Shielding structures, grounding conductors, signal shielding
Automotive: Spark plug electrodes, high-current connectors, EV components
Semiconductor: High-purity vacuum components, electrical contact parts (note: superconductors typically use oxygen‑free copper grades, not C110 ETP)
Applicable industries:
Electrical power distribution
Electronics and telecommunications
Automotive (especially EV and hybrid)
Thermal management and cooling systems
Semiconductor manufacturing
Aerospace and defense
8. Limitations and Design Considerations
C110’s exceptional conductivity comes with trade-offs that designers and engineers must consider.
| Limitation | Practical Impact | Design & Process Mitigation |
|---|---|---|
| Low machinability (20%) | Cycle times are 5× longer than brass; tool wear is higher | Quote with realistic cycle times and tooling costs |
| Softness / easy marking | Clamping marks, surface damage | Use soft jaws, collets, vacuum fixtures; low clamping torque |
| Gummy chips | Chips wrap around tools; cause BUE | Use polished carbide; aggressive feeds; flood coolant |
| Built-up edge (BUE) | Tool welding; poor surface finish | Sharp polished tools; positive rake; high feed |
| Low strength | Not suitable for structural applications | Design for electrical/thermal function only; use stronger alloys for load-bearing |
| Higher cost | C110 costs more than brass | Specify only where conductivity justifies the premium |
| Work hardening | Surface hardens during machining | Use sharp tools; maintain feed; avoid dwell |
Core design rule: C110 is specified for conductivity — not for machinability, strength, or cost. If your application requires electrical or thermal performance — C110 is the answer. If not, brass or bronze may be more cost-effective.
9. Common Machining Problems & Solutions
| Problem | Cause | Solution |
|---|---|---|
| Built-up edge (BUE) on tool | Insufficient feed; wrong speed; dull tool | Increase feed; use sharp polished carbide; use flood coolant |
| Long, stringy chips wrapping around tool | High ductility; insufficient feed | Increase feed; use chip-breaker geometry; program periodic retracts |
| Poor surface finish | Dull tool; rubbing; BUE | Replace tool; increase feed; use sharp polished tool |
| Clamping marks on part | Over-tightening; hard jaws | Use soft jaws or collets; reduce clamping torque |
| Work hardening of surface | Tool rubbing; insufficient feed | Increase feed; use sharp tool with positive rake; avoid dwell |
| Dimensional drift | Heat accumulation | Maintain consistent coolant flow; avoid prolonged cutting |
| Rapid tool wear | Wrong tool material; excessive speed | Use polished carbide; reduce speed slightly |
| Thin wall deflection | Cutting forces too high; insufficient support | Use “moderate speed + light DOC + high feed”; support walls |
| Tool chipping at entry | Interrupted cut; wrong geometry | Reduce feed at entry; use edge-honed tools |
Need support for your copper CNC machining project?
We produce tight‑tolerance copper custom parts including bus bars, electrical connectors, heat sinks, and other high-conductivity components. Contact us and submit your 2D drawings and STEP 3D files to our engineering team. We will conduct geometry review, offer optional DFM feedback, and propose a suitable machining solution for your requirements.
References
Copper C110 (ETP) material properties and conductivity data
CNC machining parameters for pure copper alloys
Copper vs brass vs bronze material selection guidelines
Editorial Note
This document is educational content built on industry‑standard practices for C110 copper CNC machining. All process data is for reference only. Always validate cutting parameters, tooling selection, and coolant strategy against your actual stock condition, machine tool capability, and tooling setup before formal production. Part performance also depends on post‑processing such as plating, passivation, and surface finishing.