Copper Machining and Fabrication in Appleton, WI: C101, C110, and Tellurium Copper

C101 (Oxygen-Free Electronic Copper, UNS C10100) is the highest-purity copper grade — 99.99% minimum copper content — specified when maximum electrical conductivity (101% IACS minimum) and minimal gas porosity during welding or brazing are required. C101 is the material of choice for high-vacuum electron tube components, waveguide bodies, and precision electrical connectors where conductivity cannot be compromised. It is slightly more expensive than C110 and is stocked primarily by specialty copper distributors rather than general metal service centers. C110 (Electrolytic Tough Pitch Copper, ETP, UNS C11000) is the commercial standard grade — 99.9% copper, 101.5% IACS typical conductivity, available in rod, bar, plate, sheet, and tube as widely stocked inventory. C110 is the correct specification for bus bars, electrical terminals, heat sink blocks, ground straps, and general electrical/thermal applications where the highest purity of C101 is not required. C110 is easy to solder and braze, soft enough to stamp and form readily, and machines acceptably though it requires sharp tooling to avoid built-up edge. Tellurium copper (C14500, UNS C14500) adds 0.4-0.7% tellurium to the copper matrix — a small addition that dramatically improves machinability (machinability rating 90% versus 20% for C110 on the standard scale where free-machining brass is 100%) while retaining approximately 93-95% of ETP copper's electrical conductivity. For precision-machined copper components — connector pins, switch contacts, screw machine parts, CNC turned terminals — Tellurium copper is the specification that makes production machining economically viable. Fox Valley CNC shops producing copper electrical components in significant volumes almost universally prefer C14500 over C110 for any turned or milled part.

Copper's machinability challenges stem from its softness (pure C110 is approximately 40 HRB), gumminess, and tendency to drag on the tool rather than shearing cleanly. Standard approach at Fox Valley shops: high-positive rake carbide inserts (or even polished HSS in some cases), cutting speeds above 500 SFM for turning, and cutting fluid that lubricates rather than just cools (soluble oil or straight oil rather than water-based coolant for the best finish and chip control). Sharp tooling changes frequently — even small amounts of tool wear on copper produce dramatic surface finish degradation. Tellurium copper (C14500) is the exception that proves the rule: it machines almost as freely as brass, produces short, chippy chips rather than long stringy ones, and holds tight tolerances (±0.001" on diameters is routinely achievable in production turning) with predictable tool life. Fox Valley screw machine and CNC turning operations running high volumes of copper electrical components specify C14500 bar stock as the standard material and reserve C110 for parts where the conductivity difference from tellurium addition matters. For milled copper components — bus bar work, custom heat sinks, and machined electrical housings — high-speed aluminum-geometry end mills with polished flutes run at 6,000-10,000 RPM with aggressive feeds produce good surface finish and chip evacuation. Flood coolant or air blast is used to prevent chip welding in deep pockets. Fox Valley shops with aluminum machining capability can typically transition to copper with tooling and parameter adjustments; the machine tool infrastructure is largely the same.

Copper sheet metal fabrication — shearing, punching, bending, and forming of C110 sheet in 0.032" to 0.250" gauge — is available from Fox Valley fabricators for electrical bus bars, ground planes, and heat exchanger plates. Copper work-hardens more slowly than aluminum but will crack on tight bend radii if the material is in a hard-drawn temper; annealed or half-hard temper (H01 or H02) is specified for formed parts. Fox Valley shops with press brake experience in copper understand the spring-back and bend allowance differences from steel and can hold formed dimensions to ±0.010" on production runs. Silver brazing of copper assemblies — joining copper-to-copper or copper-to-brass components with BAg series filler metals per AWS A5.8 — is available from Fox Valley shops with torch and induction brazing capability. Brazed copper assemblies are common in refrigeration and HVAC components, hydraulic fittings, and electrical buswork where a leak-free, high-conductivity joint is required. Furnace brazing of copper assemblies in a reducing atmosphere (hydrogen or exoatmosphere) produces very clean joints without flux residue, which is specified for high-vacuum or ultrapure-fluid handling applications. For copper tube and pipe bending — common in industrial refrigeration and compressed-air systems maintenance in Fox Valley industrial facilities — CNC tube bending to ±1° angular tolerance is available from regional fabricators. Copper tube in Type K, L, or M wall thickness can be bent to tight centerline radii without collapsing using mandrel bending setups.