Guides / Process

Brass CNC Machining: Why It Is Cheap, and Where the Cost Hides

September 21, 2026

Brass has the best reputation of any metal on a shop floor. Free-cutting brass C360 is the benchmark that every other metal’s machinability is rated against, at 100. Steel sits near 50. Stainless sits near 25. Pure copper sits near 20.

So brass parts should be cheap, and most of them are. When a brass quote comes back higher than expected, the cutting is almost never the reason. This guide covers where the money actually goes.

Why brass cuts so well

Free-cutting brass carries about 3 percent lead. The lead does not alloy with the copper and zinc. It sits in the structure as tiny soft particles, and those particles do two things at once: they break the chip into short pieces instead of a long ribbon, and they lubricate the cutting edge.

The result is short chips that clear themselves, a bright finish straight off the tool, low cutting forces and tool life measured in thousands of parts rather than hundreds. A brass part on a well set up lathe is close to the cheapest machined part you can buy.

That is the whole trick, and it is also the reason the lead-free question matters so much. Take the lead out and you are machining a different metal.

The four places the cost actually sits

1. The bar price

Brass is roughly 60 to 70 percent copper by weight, so the bar price follows the copper market and moves week to week. On a heavy part the metal is the larger half of the quote, which is why brass quotes expire and why a repeat order is re-priced rather than repeated.

Two things reduce it: choosing a bar diameter close to the largest feature on the part, and asking whether the part could be hot forged to a near net shape before machining. Above roughly 5,000 pieces of a chunky fitting, forging in C377 and machining only the sealing features is often cheaper than turning the whole thing from solid.

2. The machine the part lands on

This is the biggest avoidable cost in brass work, and it never appears on the drawing.

A small round part with threads belongs on a Swiss type lathe or a bar-fed turret lathe. It comes off complete, one operation, no handling. The same part on a machining centre needs a fixture, two setups and an operator moving parts by hand.

The price gap between those two routes is usually larger than the gap between any two brass alloys. When you compare quotes and one is three times another, ask what machine it was quoted on before you assume somebody made a mistake.

3. Threads and cross holes

Almost every brass part is a fitting, and almost every fitting has a thread that has to seal rather than just hold.

A tapered pipe thread is a tool, a pass, a gauge check and a scrap risk. Cross holes that break into a bore leave a burr on the inside where nobody can reach it, and that burr is the most common reason a brass fitting fails a leak test after assembly.

Say on the drawing which threads are sealing threads, give the gauge class and say plainly that internal bores must be free of burrs. A shop that sees those notes quotes a deburring operation. A shop that does not see them quotes without one, wins the job, and comes back later.

4. Finishing

On a visible brass part the finishing is often larger than the machining. Tumbling, polishing, lacquering, nickel or chrome plating each add cost and a few days of calendar time.

Plating also shows every defect underneath it, so a part that is going to be plated needs a better machined surface than one that is not. Put the plating spec on the drawing and the machining spec underneath adjusts itself.

What to put on the drawing

• The alloy and why. Write C360 rather than “brass”. If the reason is a standard rather than a preference, write the standard too and leave the alloy open.
• Thread callouts in full, including class and whether the thread seals.
• Burr condition inside bores, not just on outside edges.
• Surface finish only where it matters. A polished sealing face is reasonable. A polished whole part is an expensive habit.
• Plating spec and thickness, if there is any.
• Quantity and whether it repeats. Setup on a bar-fed lathe is a fixed cost. A shop that knows the part repeats quarterly will quote the setup differently.

Where to go next

If your part is wetted by drinking water, the alloy question is decided for you before anything else. That is covered in leaded and lead-free brass compared. If you know the environment but not the grade, start from the brass alloys and what each one is for.

Frequently asked questions

Keep reading

• Swiss Turning Brass Parts and When It Is the Cheaper Route
• The Burr Inside the Bore Nobody Can See