Copper CNC
Machining

C110 (also known as Electrolytic Tough Pitch copper, or ETP copper) is the most widely used commercial copper grade, with a minimum purity of 99.90% copper. In CNC machining, C110 is used wherever high electrical conductivity, high thermal conductivity, and corrosion resistance are required simultaneously. Typical applications include electrical bus bars, grounding components, heat sinks, thermal spreaders, electrical contact components, induction coil bodies, RF shielding enclosures, and plumbing fittings. C110 is the standard copper for most industrial and electrical applications that do not require welding or hydrogen-atmosphere brazing.

C101 (Oxygen-Free High Conductivity copper, OFHC) is a premium copper grade with copper purity of 99.99% or higher and oxygen content below 0.001%. The key difference from C110 is the near-zero oxygen content. C110 contains 0.02–0.04% oxygen as cuprous oxide inclusions — these cause hydrogen embrittlement when C110 is heated in hydrogen-containing atmospheres. C101 eliminates this problem entirely. Additionally, C101's higher purity gives it slightly better electrical conductivity (101% IACS vs 100% IACS) and is preferred for high-vacuum, semiconductor, scientific, and cryogenic applications where contamination or outgassing must be minimized.

T2 is the Chinese GB/T standard designation for electrolytic tough pitch copper equivalent to ASTM C110. T2 has a minimum copper content of 99.90% — functionally equivalent to C110 for all CNC machining applications. When sourcing from Chinese manufacturers or supplying to Chinese customers, T2 is the standard specification; ASTM C110 is the international equivalent. We stock and machine both designations and can provide mill certs to either standard.

Pure copper (C110, C101, T2) is more challenging to machine than brass due to its high ductility and tendency to produce long, stringy, gummy chips that cling to cutting tools. Unlike brass which has lead as a built-in chip breaker, pure copper requires careful tool selection (sharp, positive-rake geometry), controlled cutting parameters, adequate coolant, and chip management. However, copper machines significantly faster and easier than stainless steel. With proper tooling and parameters, tight tolerances and excellent surface finish are routinely achievable on C110 and C101.

C110 (ETP copper) has an electrical conductivity of 100% IACS — it is the reference material against which all other metals are measured for conductivity. C101 (oxygen-free copper) achieves 101% IACS due to its higher purity. For comparison: brass C360 is approximately 26% IACS, 6061 aluminium is approximately 43% IACS, and 304 stainless is approximately 2% IACS. Copper's unmatched conductivity makes it the first choice for any application where electrical or thermal conductivity is the primary engineering requirement.

Standard CNC machining tolerance for C110 and C101 copper is ±0.01 mm. Tighter tolerances of ±0.005 mm are achievable on precision features. Copper's high ductility means it can deform under clamping pressure if not properly supported — fixturing design is important for thin-walled or delicate copper parts. For C101 vacuum components and semiconductor parts, surface cleanliness and contamination control during machining are as important as dimensional tolerance.

Specify C101 instead of C110 when: (1) the part will be brazed or annealed in a hydrogen-containing atmosphere — C110 is susceptible to hydrogen embrittlement, C101 is not; (2) the application is in vacuum environments where low outgassing is required, such as semiconductor equipment or vacuum furnace components; (3) maximum electrical conductivity is required (101% IACS vs 100%); (4) the application is cryogenic; (5) the part will be used in high-purity environments where trace oxygen must be minimized. For all other applications, C110/T2 is adequate and less expensive.

Common surface treatments for machined copper parts include: silver plating (highest electrical conductivity at contact surfaces, standard for bus bars and connectors), electroless nickel (corrosion protection, wear resistance, uniform coverage on internal geometry), tin plating (solderable, RoHS-safe alternative to silver for electrical parts), and chemical cleaning with BTA passivation for C101 vacuum parts. Copper cannot be anodized — anodizing is specific to aluminium alloys.