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Machining Thin Walls in Copper Without Losing Them

September 26, 2026

A thin copper wall does two things a steel wall does not. It bends away from the cutter, so it comes out thicker at the top than at the bottom. And it rings, so the finish chatters. Both are stiffness problems and copper has less of it than most metals a shop is used to.

What actually happens

The cutter pushes sideways on the wall. Steel pushes back. Copper moves, then springs back once the tool has passed, so the wall ends up thicker where it deflected most, which is at the top, farthest from the base.

At the same time the wall vibrates under the intermittent cutting load. The result is a wavy finish and, on very thin walls, a wall that can tear rather than cut.

What a shop does about it

Rough with support, finish in steps. Leave the wall thick during roughing, then finish in stages from the top down, so the section below the cut is still stiff.

Light radial depth, full axial depth. Take a thin slice down the full height rather than shaving the top.

Sharp tooling, real feed. The same rule as everywhere in copper. A rubbing tool pushes the wall harder than a shearing one. See tooling, feeds and speeds for copper.

Spring passes. A repeat of the finishing pass at zero extra depth to catch the material that deflected. They add time and they belong in the quote.

Alternate sides. On a free standing wall, cut one side, then the other, in steps, so the wall is never thin and unsupported on both faces at once.

Support the wall. Backing material, wax, a fixture that touches the far side. Costs setup, saves scrap.

Where the limit is

It is a ratio, not a number. A wall three millimetres thick and ten high is easy. Half a millimetre thick and thirty high is a different job entirely. Fin packs on heat sinks are the extreme case and the reason fin aspect ratio drives their price.

A shop will tell you what it can hold if you tell it the height, the thickness and what the wall does.

What to put on the drawing

• The wall thickness with a tolerance that reflects what the wall does. A thermal path or a cosmetic wall does not need what a sealing lip needs.
• Which walls are critical, and which the shop may leave alone.
• Whether the wall may be supported by a rib or boss. Often it can, and the designer never thought to allow it.
• Whether the top edge needs to be burr free. Thin copper edges burr badly and are hard to deburr without bending.

The grade question

Free-machining copper cuts cleaner and burrs less, which helps thin edges. It does not make the wall stiffer. If the part is a heat sink, stay on C11000 for the conductivity and manage the wall with strategy. If the part has thin features but no thermal or electrical requirement, C14500 is easier all round. See copper part design rules.

For estimators

Thin walls are spring passes and slow finishing. Neither is in a standard cycle estimate. Look for wall height to thickness ratios on the drawing before the number leaves the shop. The copper quoting checklist has it as item seven.

Frequently asked questions

Keep reading

• When a Machined Copper Part Needs Annealing and How to Ask for It
• How Copper EDM Electrodes Are Finished and Why It Matters