Copper and brass don't get the same attention as titanium or PEEK. They're not exotic. They're not aerospace glamour materials. But they show up everywhere — electrical connectors, fluid fittings, heat exchanger components, bearing cages, decorative hardware, plumbing parts, musical instruments — and they machine completely differently from steel or aluminum.
I've run thousands of copper and brass parts through the shop. Brass is one of the easiest materials to machine. Copper is one of the most annoying. Here's what I know about both.
The copper alloy family: what you'll actually encounter
"Copper" in a machining context can mean pure copper or any of several dozen alloys. The alloy matters more for machinability than the base metal. Here are the ones that show up in CNC work:
| Alloy | Common Name | Machinability Rating | Key Properties | Typical Applications |
|---|---|---|---|---|
| C110 (99.9% Cu) | ETP Copper | 20% | Max electrical conductivity (100% IACS), gummy to machine | Electrical bus bars, contacts, welding electrodes |
| C101 (99.99% Cu) | OFHC Copper | 20% | Oxygen-free, higher purity than C110, same machinability problems | Vacuum components, semiconductor parts |
| C145 | Tellurium Copper | 85% | Tellurium addition makes it machinable, conductivity ~93% IACS | Electrical connectors, machined contacts |
| C360 | Free-cutting Brass | 100% | The baseline for 100% machinability rating, lead content ~3% | Fittings, valve bodies, threaded components, decorative |
| C353 | Engravers Brass | 90% | Slightly less lead than C360, better for fine detail | Nameplates, decorative engraving |
| C260 | Cartridge Brass (70/30) | 30% | Good cold-working properties, fair machinability | Deep drawn parts, ammunition cases |
| C932 / C936 | Bearing Bronze | 70-80% | Good wear properties, moderate machinability | Bushings, bearings, wear plates |
| C510 | Phosphor Bronze | 20% | High strength and fatigue resistance, poor machinability | Springs, electrical contacts, bellows |
| C630 | Aluminum Bronze | 30% | High strength (comparable to steel), corrosion resistant | Marine hardware, pump shafts, landing gear bushings |
| C172 | Beryllium Copper | 20% | Highest strength of any copper alloy, heat-treatable, toxic dust | Springs, non-sparking tools, aerospace bushings |
The machinability rating uses C360 brass as the 100% baseline. Everything else is compared to it. Pure copper (C110, C101) at 20% means it machines at one-fifth the speed of brass with worse tool life and surface finish.
Why brass is a joy to machine
C360 free-cutting brass is the material I give to new operators for their first solo setup. It's forgiving to the point of being hard to scrap. Here's why:
The lead content (~3%) acts as a chip breaker. Where copper produces long stringy chips that wrap around the tool, the part, the chuck, and eventually the operator, brass produces small, brittle chips that snap off cleanly. They fall into the chip pan and stay there. No birds-nesting. No chip management drama.
Surface finish comes out bright and smooth with almost no effort. A standard finishing pass at moderate speed produces a mirror-like surface. You can hold ±0.01mm without sweating. Tool life is measured in days, not hours — inserts that machine stainless for 8 hours will cut brass for a week.
Brass doesn't work-harden. You can take a 0.05mm finish pass or a 4mm roughing pass and the material behavior is the same. No surprises when a light cut suddenly work-hardens the surface and kills the next insert.
Speed range: 400-1000 SFM with carbide. Feed 0.10-0.30 mm/rev for roughing, 0.05-0.10 for finishing. Depth of cut up to 4mm per pass with adequate horsepower. These are numbers that make aluminum look slow.
The tradeoffs: brass is soft (Rockwell B 40-70 for C360), so clamping pressure can mark the surface. Use soft jaws or protect finished surfaces. Threads in brass strip easily if over-torqued — brass threaded parts typically use coarser threads than steel equivalents. The lead in C360 means it can't be used for potable water applications in some jurisdictions (lead-free brass alloys like C46400 or C69300 exist for this).
Why pure copper makes machinists angry
Copper (C110, C101) machines like frozen gum. It's soft but abrasive. The chip doesn't break — it forms a continuous ribbon that wraps around everything. If a copper chip starts wrapping, you stop the machine and clear it. If you let it go, the chip builds up into a solid mass that can push the part out of the chuck or snap a tool.
The thermal conductivity that makes copper great for heat exchangers makes it terrible for machining. Copper conducts heat away from the cutting zone so fast that the chip doesn't get hot enough to become brittle. The chip stays ductile and stringy. Cooling doesn't help much — the problem isn't heat, it's the material's inherent ductility at any temperature.
Solutions that help:
- Sharp carbide inserts with high positive rake (15-20°) and polished flute faces to reduce chip adhesion
- Aggressive feed rates — 0.15-0.25 mm/rev minimum. Light feeds make the chip thinner and more likely to wrap
- Peck drilling cycles with short peck depth (1-2× diameter) to break chips in deep holes
- High-pressure coolant aimed directly at the chip to push it away from the cutting zone
- Chip breakers on turning inserts — and even then, expect inconsistent results
Surface finish on pure copper is rarely better than Ra 0.8 μm from turning alone. For electrical contact surfaces where finish matters, a quick polishing step is standard practice. Tolerances: ±0.025mm is practical, ±0.01mm requires sharp tooling and close attention.
The saving grace: copper cuts with low cutting forces. You don't need a heavy machine. A benchtop CNC can cut copper adequately for small parts. The challenge is chip management and surface finish, not power or rigidity.
Tellurium copper: the compromise
If you need copper's electrical conductivity but can't deal with pure copper's machinability, C145 tellurium copper is the answer. The tellurium addition (~0.5%) makes the chips break like brass while retaining ~93% of pure copper's conductivity.
It machines like a dream compared to pure copper. Chips break. Surface finish is clean. Tolerances are easy to hold. Tool life is reasonable. The cost premium over pure copper is about 20-30%, and for any part where machining time is significant, the premium pays for itself in reduced cycle time and scrap rate.
For electrical connectors, bus bars, and welding electrodes — applications where conductivity matters but pure copper's machinability drives up cost — C145 is what I recommend. The slight conductivity loss (7%) is almost never the limiting factor in the application.
Copper-nickel and other oddballs
A few other copper alloys deserve mention because they show up in specific industries:
Aluminum bronze (C630) is one of the strongest copper alloys, with tensile strength approaching 700 MPa — comparable to some steels. It machines more like stainless than brass: moderate speeds, sharp tools, good coolant, expect tool wear. The chips are manageable. It's used for marine hardware because it resists seawater corrosion, and for aircraft landing gear bushings because it handles high loads without galling.
Beryllium copper (C172) is the strongest copper alloy in the heat-treated condition (up to 1,400 MPa tensile). It machines like tool steel in the annealed condition, then gets heat-treated to full hardness after machining. The beryllium content (~2%) makes the dust toxic — machining produces airborne beryllium particles that can cause chronic beryllium disease. We don't machine it in our shop. If you need beryllium copper parts, go to a shop that has the dust collection and worker monitoring protocols for it. Don't machine it dry in a general-purpose shop.
Phosphor bronze (C510) is springy and tough. Machinability is poor (20%). It work-hardens if you baby it. Aggressive cuts with sharp tools, similar to 304 stainless in approach. Used for electrical contacts and springs where the combination of conductivity and fatigue resistance justifies its cost.
Speeds and feeds that work
These are my shop numbers, verified through thousands of parts. They assume carbide tooling, adequate coolant, and reasonably rigid setup:
| Material | SFM Rough | SFM Finish | Feed (rough) | Feed (finish) | DOC max |
|---|---|---|---|---|---|
| C360 Brass | 600-1000 | 800-1200 | 0.15-0.30 | 0.05-0.10 | 4 mm |
| C353 Brass | 500-900 | 700-1000 | 0.12-0.25 | 0.05-0.10 | 3 mm |
| C110/C101 Copper | 200-400 | 300-500 | 0.15-0.25 | 0.05-0.08 | 2 mm |
| C145 Tellurium Copper | 400-700 | 600-900 | 0.12-0.25 | 0.05-0.10 | 3 mm |
| C932 Bearing Bronze | 300-500 | 400-600 | 0.10-0.20 | 0.04-0.08 | 2 mm |
| C630 Aluminum Bronze | 150-300 | 200-400 | 0.08-0.18 | 0.04-0.08 | 1.5 mm |
| C510 Phosphor Bronze | 120-200 | 150-300 | 0.08-0.15 | 0.03-0.06 | 1.5 mm |
For drilling brass: standard HSS drills at standard speeds work fine. For drilling copper: parabolic flute drills with polished flutes help chip evacuation. Peck depth for copper: 1× diameter for holes deeper than 3× diameter, otherwise chips pack the flutes and the drill seizes.
Tapping brass is straightforward — standard taps, standard speeds. Tapping copper is not. The tap wants to gall because copper has high friction against tool steel. Use a high-quality tap with a surface treatment (TiN or TiCN coating), plenty of tapping fluid, and lower RPM than you'd use for brass. Roll-form taps (which don't cut, but displace material) work well in copper because there are no chips to pack, but they require a different hole size than cutting taps.
Design rules specific to copper and brass parts
Thread engagement. Brass and copper threads strip at lower torque than steel threads of the same size. For load-bearing threaded connections in brass or copper, use thread inserts (helicoils or keyserts) or specify longer thread engagement — 1.5-2× the standard length of engagement for steel.
Wall thickness. Copper and brass are softer than steel. Thin walls that work in stainless or titanium may deform under clamping or in service in copper alloys. Minimum wall thickness of 1mm for features under 20mm, scaling up for larger features. C360 brass is more forgiving than pure copper.
Sharp edges. Copper burrs are stubborn. They fold over instead of cleanly separating from the edge. If your part needs sharp, clean edges (electrical contacts, for example), specify edge break requirements clearly and budget for deburring time. Brass burrs are minimal.
Corrosion considerations. Brass dezincifies in aggressive water — the zinc leaches out and leaves a porous copper structure. If your brass part contacts water (plumbing, marine), specify dezincification-resistant (DZR) brass or use bronze instead. Copper in contact with aluminum forms a galvanic couple — the aluminum corrodes sacrificially. If your assembly mixes copper and aluminum, you need isolation (gaskets, coatings) or accept the aluminum side will corrode.
Thermal expansion. Copper and brass expand more with temperature than steel. A 100mm copper part in an assembly grows about 0.17mm with a 100°C temperature rise. If the part mates with steel or aluminum parts that expand at different rates, the clearance at room temperature needs to account for this. I've seen assemblies seize because copper thermal expansion was overlooked at the design stage.
Cost comparison for a real part
A recent job: 50 pieces of a copper bus bar, 120mm x 25mm x 8mm with three mounting holes and a chamfered edge. We quoted it in three materials:
| Material | Material Cost/Part | Machine Time | Deburr Time | Total/Part |
|---|---|---|---|---|
| C110 Pure Copper | $3.20 | 14 min | 4 min | $24 |
| C145 Tellurium Copper | $4.00 | 9 min | 1 min | $18 |
| C360 Brass (if acceptable) | $2.80 | 7 min | 0.5 min | $12 |
The customer originally spec'd C110. We suggested C145. The conductivity difference (100% IACS vs 93% IACS) mattered less in their application than they thought — the bus bar cross-section was oversized for the current anyway. Switching to C145 saved $6/part and a week on delivery because the cycle was faster and deburring was minimal. The electrical engineer approved the substitution in one email.
Bottom line
If your part can be made from C360 brass, you win. It's the reference standard for machinability. Fast cycle times, clean surface finish, long tool life, minimal deburring. Costs less to machine than almost anything else.
If your part needs copper's conductivity, use C145 tellurium copper unless you have a very specific reason not to. The machinability improvement over pure copper pays for the material cost difference within a few parts.
If you're not sure which alloy fits your application, send us the requirements. We stock C360 brass and C145 copper in our shop, and we can help you pick the right alloy before you commit to a production run.