Brass CNC Machining: C360 Free-Cutting Brass vs C110 Copper

Two connectors arrive on the same drawing set. One is a terminal block that must carry 200 A without warming up. The other is a decorative bezel that must polish to a mirror and hold a 0.05 mm profile. Quoting both in "brass" is how a shop ends up with a batch of parts that either cannot pass a voltage drop test or cannot be machined at a sensible cycle time.

Copper alloys are not interchangeable. C360 free-cutting brass and C110 electrolytic tough pitch copper sit at opposite ends of the family on almost every property that matters: conductivity, machinability, galling behavior and price.

Here is how to pick between them, and where the newer lead-free brasses fit.

Two different jobs in one metal family

C36000 is roughly 61.5 percent copper, 3 percent lead and the balance zinc. The lead is not decorative: it acts as an internal lubricant and chip breaker, which is why C360 carries a machinability rating of 100 in the standard scale and why it produces short, clean chips at almost any feed rate. It comes as extruded bar, not plate.

C11000 is 99.9 percent copper with a controlled oxygen content. It exists because pure copper conducts electricity and heat better than any affordable metal except silver. It is soft, gummy, and about one fifth as machinable as C360.

Between them sit the alloys most buyers actually need: tellurium copper for connectors that must be both conductive and machinable, and lead-free silicon brasses for anything sold into markets that restrict lead.

Conductivity and thermal numbers

The conductivity gap is the decision point. C110 carries roughly 3.6 times the current of C360 for the same cross section, so a brass busbar has to be much larger to do the same job. Once the section grows, so does the material cost and the space claim.

Where conductivity is secondary, C360 wins on everything else: it machines three to five times faster, holds a better finish, and costs less per kilogram.

What 28% IACS actually rules out

A common mistake is specifying brass for RF shielding or grounding hardware and then wondering why the contact resistance is marginal. At 28% IACS, C360 is fine for a mechanical bracket or a decorative part; it is not fine for a current-carrying path that was sized around copper.

The same applies to heat: at 115 W/m·K, C360 spreads heat poorly next to C110 at 391 W/m·K. A heat sink or cold plate should not be brass, however nicely it machines.

For connectors, C14500 is often the right compromise: 93% IACS and a machinability rating near 90.

Why C360 machines so easily

The lead particles in C360 act as stress concentrators ahead of the cutting edge, so the chip fractures instead of stretching. That produces three benefits at once: lower cutting force, less heat, and chips that clear the flutes instead of wrapping around the tool.

The practical result is that C360 tolerates aggressive parameters. Carbide turning speeds of 200 to 400 m/min are normal, feeds of 0.1 to 0.25 mm per revolution are comfortable, and high-speed steel tooling remains viable for small lots. Surface finishes of Ra 0.4 to 0.8 µm come off the tool without polishing.

C360 also holds tolerance well because it does not spring back much and does not work harden. A ±0.02 mm turned diameter is routine, and ±0.01 mm is achievable on a stable setup.

Two limits are worth knowing. C360 is not recommended for potable water because of dezincification and lead leaching; dezincification-resistant brass such as CW602N exists for that service. And it is an extruded bar product, so a wide flat part with a thin section may be cheaper in plate of another alloy than in C360 bar with a lot of waste.

Copper: galling, built-up edge and different tooling

Pure copper is where machining experience earns its money.

Copper galls against steel tooling. The metal adheres to the rake face, tears away, and takes carbide particles with it, so a tool that would run for hours in brass fails in minutes. The countermeasures are specific: high positive rake angles of 15 to 20 degrees, sharp uncoated carbide with polished flutes, generous clearance, and never a worn edge. Coatings designed for steel often make copper worse, because a rougher coating surface gives the copper something to grip.

Chip control is the second problem. C110 produces long stringy chips that wrap around the workpiece and bury the coolant nozzle. Pecking routines, high-pressure coolant and chip breakers sized for soft materials help.

C110 also moves. Its thermal conductivity pulls heat into the part, so the workpiece grows during roughing and shrinks as it cools. On a 100 mm dimension, a 20 °C rise is worth about 34 µm of growth at 17 ppm/K. Rough, let it stabilize, then finish.

Burrs, plating and finish

C360 breaks small, brittle burrs that come off with a light tumble or a hand pass. C110 smears instead of breaking, especially on cross holes and thread exits, and those smeared burrs are tough to remove without damaging the surface.

Plating behavior differs too. Brass takes nickel and chrome readily and polishes to a bright decorative finish. Copper plates well but is soft enough that handling marks appear before plating, so parts need careful packaging between operations.

For electrical contacts, specify the surface treatment explicitly: bare copper oxidises within days in humid air, and a thin tarnish inhibitor or a nickel underplate with a gold flash is often required to keep contact resistance stable.

Selecting an alloy

When we quote brass and copper parts at JSHS, the alloy usually accounts for more of the price difference than the machining does, so it is worth settling before the model is released. Send the drawing with the current, the environment and the target market noted and we will price the sensible alternatives in the quote.

Frequently asked questions

Is brass a good electrical conductor?

It is adequate, not good. C360 conducts about 28% IACS against 101% IACS for C110 copper, so a brass conductor needs roughly 3.6 times the cross section for the same resistance. Use brass for mechanical parts and copper for current paths.

Why does copper machining cost more than brass?

Pure copper is gummy, galls on the tool and forms long chips, so it runs at roughly one fifth the cutting speed of C360 and needs more operator attention. The material also costs more per kilogram.

Can lead-free brass be substituted directly for C360?

Usually, with a re-check on speed and finish. Lead-free grades machine at 75 to 85 percent of C360's rate and can produce longer chips. Expect a small cycle-time increase and confirm the alloy meets the applicable lead limit for your market.

Does brass need a surface finish after machining?

For appearance, often yes: polishing, nickel plating or a clear lacquer. For function, C360's as-machined finish is usually adequate. Copper parts benefit from a tarnish inhibitor if they will be stored before assembly.