CNC Machined Copper Parts & Suppliers

Karl Gillihan

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CNC Machining Copper: C101, C110 and Tellurium Copper Parts

Copper is bought for what it conducts, electricity and heat, not for how it machines, and there lies the tension. Pure copper is gummy, smears, builds up on the cutting edge and produces stringy chips that fight clean machining. The industry's answer is a fork in the road: accept the difficulty for maximum conductivity, or alloy in a trace element that transforms machinability at a tiny conductivity cost.

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The conductivity-versus-machinability tradeoff

C101 (oxygen-free electronic, OFE) and C110 (electrolytic tough pitch, ETP) are the high-conductivity coppers, both around 100 percent IACS. C101 is the purer, oxygen-free grade demanded where the slightest contamination or hydrogen embrittlement risk is unacceptable, vacuum and semiconductor applications, RF and high-reliability electronics. C110 is the everyday electrical-grade copper for busbars, terminals and grounding. Both are wonderful conductors and difficult, gummy machining materials. Tellurium copper (C145) is the elegant compromise. Adding roughly half a percent tellurium gives it free-machining behavior comparable to free-machining brass while retaining about 90-95 percent IACS conductivity. The tellurium forms tiny inclusions that break chips and reduce built-up edge, so it machines fast and clean. For any conductive part with significant machining content, C145 is usually the smart default unless the application specifically forbids the alloying element. The buyer decision is rarely about strength, since all these coppers are soft. It is about whether the application can tolerate C145's slight conductivity drop and tellurium content. If yes, machining cost and lead time drop substantially. If the part must be pure OFE for vacuum or ultra-high-purity reasons, you accept the harder machining of C101.

01

Taming gummy pure copper at the machine

Machining C101 and C110 well is about fighting built-up edge and managing stringy chips. Sharp tools with high positive rake and polished flutes are essential; a dull or negative-rake edge smears copper rather than shearing it. Many shops use uncoated or specially coated carbide and even keep dedicated tooling for copper to avoid contamination. High cutting speeds with generous feed help the chip form and break rather than smear, and copious coolant or cutting fluid keeps the edge clean. Chip control is the persistent headache: pure copper produces long, stringy chips that wrap around tools and parts. Chip breakers, peck cycles on drilling, and good evacuation matter. Tapping and threading pure copper is notoriously prone to galling and torn threads, so form taps, sharp tooling and proper lubricant are used, and tight thread tolerances are harder to guarantee than in tellurium copper. Surface finish on pure copper can be excellent once technique is right, copper polishes beautifully, but achieving a clean as-machined finish takes more care than in free-machining grades. This is why the labor premium on C101/C110 parts is real and why tellurium copper exists.

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Applications, finishing and what drives lead time

Copper parts are bought for performance in electrical and thermal roles: busbars and connectors, RF and microwave components and waveguides, heat sinks and thermal-management blocks, EDM electrodes (where copper and its alloys are themselves a tooling material), semiconductor and vacuum hardware, and induction-heating and high-current contacts. The grade follows the role: C101 for vacuum/RF/ultra-pure, C110 for general electrical, C145 where machining content is high. Finishing copper often centers on preventing oxidation and improving solderability or contact resistance. Bright copper tarnishes quickly, so parts are frequently plated, tin, nickel, silver or gold, depending on the electrical requirement, or passivated/treated to slow tarnish. Plating is a batched outside process adding days. For cosmetic or contact-critical parts, specify the plating clearly and identify masked areas. Lead-time drivers are dominated by the machining difficulty for pure grades and by plating turnaround. Material cost is significant too, since copper is a relatively expensive base metal whose price tracks commodity markets, so quotes can move with copper spot prices on larger parts.

Frequently Asked Questions

Pure copper, grades C101 and C110, is soft, ductile and gummy, which causes it to smear and weld to the cutting edge rather than shear cleanly. This built-up edge degrades finish and accelerates tool problems, and the metal produces long, stringy chips that wrap around tools and the workpiece and resist breaking. Tapping and threading are especially troublesome because copper tears and galls, making clean threads hard to guarantee. Shops manage all this with very sharp, high-positive-rake, polished tooling, high speeds with healthy feed so chips form and break instead of smearing, generous coolant, chip breakers and peck cycles. Even done well, pure copper machines slower and with more care than free-machining metals, so labor cost is higher. The common fix is tellurium copper (C145), which adds about half a percent tellurium to create chip-breaking inclusions, giving free-machining behavior while keeping roughly 90-95 percent IACS conductivity. Unless the application requires ultra-pure oxygen-free copper, C145 usually delivers the same part for less machining cost and shorter lead time.

Let conductivity requirements and machining content decide. C101 is oxygen-free electronic copper, the purest grade at about 100 percent IACS, required where contamination, outgassing or hydrogen embrittlement cannot be tolerated, such as vacuum systems, semiconductor hardware, and high-reliability RF and electronics. C110 is electrolytic tough pitch copper, also about 100 percent IACS, the standard for general electrical work like busbars, terminals and grounding where the trace oxygen content is acceptable. Both machine gummy and slow. Tellurium copper, C145, retains roughly 90-95 percent IACS but machines like free-machining brass, dramatically faster and cleaner, so for any conductive part with substantial machining it is usually the smart default. The deciding question is whether your application can tolerate the slight conductivity reduction and the presence of tellurium. If it can, choose C145 and save on machining cost and lead time. If the part must be ultra-pure oxygen-free copper for vacuum, ultra-high-purity, or specific electrical reasons, accept C101's harder machining. C110 sits in the middle for general electrical parts that do not need oxygen-free purity.

Often yes, because bare copper tarnishes and oxidizes quickly, which can raise contact resistance, hurt solderability and look poor. The right plating depends on the electrical and environmental requirement. Tin plating is common for solderability and corrosion protection on connectors and busbars. Nickel plating provides a durable barrier and is often an underlayer. Silver plating gives the lowest contact resistance and excellent solderability and is used on high-performance RF and high-current contacts. Gold plating, usually over nickel, is specified for the highest reliability and corrosion resistance in critical connectors. Some parts instead receive a passivation or anti-tarnish treatment to slow oxidation without full plating. Plating is a batched outside process that adds typically 3-7 days to lead time, so factor it into schedule. When ordering, specify the plating type and thickness, identify any masked or selectively plated areas, and note whether the part is contact-critical. For prototypes that only need to function briefly, an unplated copper part with anti-tarnish handling can suffice, but production conductive parts almost always carry a plating callout.

Copper can hold standard CNC tolerances, around +/-0.005 in (0.13 mm) generally and tighter on called-out features, but its softness and gumminess make tight-tolerance and threaded features harder to guarantee on pure C101 and C110 than on free-machining tellurium copper or brass. Soft material can deflect under cutting load and burr readily, and threads in pure copper are prone to tearing, so where tight threads or fine features matter, tellurium copper C145 is the more reliable choice. Surface finish, by contrast, can be excellent: copper polishes to a bright, smooth surface, and as-machined finishes of 32-63 microinch Ra are achievable with sharp polished tooling, though it takes more care on the pure grades to avoid smearing. Deburring soft copper needs attention because burrs are tenacious. For dimensionally critical conductive parts such as RF components or waveguides where both tolerance and conductivity matter, discuss the tradeoff with your shop early: you may machine C101 for conductivity and accept extra finishing labor, or switch to C145 if the slight conductivity loss is acceptable in exchange for tighter, cleaner features.

Copper machining serves applications where electrical or thermal performance is the whole point. Power and energy use copper for busbars, high-current connectors, terminals and grounding hardware. RF, microwave and telecom rely on machined copper for waveguides, cavities, antenna components and shielding where conductivity and finish drive performance. Thermal management across electronics, lasers and power systems uses copper heat sinks, cold plates and thermal blocks because of its high thermal conductivity. Semiconductor and vacuum equipment specify oxygen-free C101 for ultra-clean, outgassing-sensitive hardware. The EDM industry machines copper and copper alloys into electrodes, where copper is itself a tooling material. Induction heating, electric-motor and high-power contact applications round out demand. The grade tracks the application: C101 for vacuum, RF and ultra-pure needs, C110 for general electrical busbars and terminals, and tellurium copper C145 for parts with heavy machining content that can tolerate a slight conductivity reduction. Because copper is a relatively expensive, commodity-priced base metal, larger parts can see quotes move with copper spot prices, so material cost is a real factor alongside the machining difficulty of the pure grades.

Last updated: July 2026

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