Why Does Machining Copper Cost So Much More Than Brass (And When Should You Pay for EDM)?

1. The Conductivity vs. Machinability Trap: Why Pure Copper is a Headache

If you look at the raw material prices of copper and brass, they aren’t astronomically different. So why is a custom CNC-machined copper part often twice as expensive to buy as the exact same part made of brass? The answer has everything to do with how the metal behaves when a sharp spinning tool hits it.

Think of pure copper (like C10100 or C11000) as industrial chewing gum. It is highly ductile, meaning it likes to stretch and bend rather than snap. When a CNC milling cutter tries to slice through pure copper, the metal doesn’t break off into nice, clean little chips. Instead, it tears, smears, and generates massive amounts of friction. This friction causes the copper to literally melt and weld itself to the cutting tool. Once a tool is clogged with sticky copper, it snaps in half.

To stop their expensive tools from breaking, the machine shop has to drastically reduce the speed of the machine and take very tiny, shallow cuts. In the manufacturing world, time is money. If it takes the CNC machine three hours to slowly carve out a pure copper block that would normally take 45 minutes in aluminum, you are paying for those extra two hours of machine time.

2. The Brass Alternative: Saving Money at the Cost of Power

If pure copper is so terrible to cut, what is the alternative? Enter Brass (usually grade C36000, known as “Free-Machining Brass”). Brass is simply copper mixed with zinc and a tiny bit of lead. This chemical cocktail is a magic trick for manufacturing. The additives make the metal slightly brittle, meaning when the cutting tool hits it, the brass shatters into perfect, tiny chips that fly cleanly out of the way.

Brass is widely considered the easiest and fastest metal to machine on the planet. Machine shops love it. They can run their equipment at maximum speed, tools last forever, and the resulting parts come out with a gorgeous, shiny surface finish. Because it cuts so fast, the labor and machine-time costs are rock bottom.

3. When Traditional Milling Fails: Enter EDM (Electrical Discharge Machining)

Sometimes, the problem with pure copper isn’t just that it takes a long time to cut; sometimes, a standard CNC mill physically *cannot* cut your design. Let’s say you are designing a high-end copper heatsink for a computer processor. It features a dense forest of tiny, paper-thin cooling fins. If you try to cut those fins with a normal spinning metal end-mill, the physical pushing force of the cutter will just bend and crush the soft copper fins flat.

This is where the factory will tell you they need to use EDM (Electrical Discharge Machining). It sounds like science fiction, but it is a very common industrial process. Instead of cutting metal with a sharp blade, EDM uses electricity to erode the metal away.

In Wire EDM, a hair-thin wire charged with electricity is fed through the metal part while submerged in water. It never physically touches the metal. Instead, microscopic lightning bolts (sparks) jump from the wire to the copper, vaporizing the metal atom by atom. Because nothing is physically pushing against the part, you can cut incredibly delicate, microscopic features in dead-soft copper without bending it a single millimeter.

4. The True Cost of EDM: Why You Should Only Use It When Necessary

If EDM is so precise and doesn’t bend the metal, why don’t we use it for everything? The answer is speed. EDM is incredibly slow. While a CNC mill can aggressively hog out handfuls of metal in seconds, an EDM machine slowly burns its way through the material millimeter by millimeter.

Furthermore, EDM machines are expensive to buy, require a lot of electricity, and consume expensive brass wire that can only be used once before it is thrown away or recycled. Therefore, the hourly rate for an EDM machine is very high.

As a smart buyer, your goal is to design your parts so they can be made on a standard, cheaper CNC mill. Avoid designing razor-thin walls, ultra-deep square holes, or delicate webs in soft copper. If you design parts with sturdy, thick walls, the shop can mill them. You should only approve an EDM quote when your design features impossible internal sharp corners or delicate fins that absolutely cannot be achieved any other way.