Thin Wall Stainless Machining: What Holds Size and What Does Not

Process / 17 Sept 2026

A thin wall is the most reliable way to turn a routine stainless part into a difficult one. It is also one of the most common features to arrive on a drawing without anybody having asked whether it needs to be that thin.

If a wall on your part is under about 1.5 mm, it is worth knowing what it costs and what would relieve it.

What counts as thin

There is no single number, because it depends on the span as much as the thickness. A useful way to think about it is the ratio of unsupported height to thickness.

Height to thickness ratio	Difficulty
Under 5:1	Routine
5:1 to 10:1	Needs attention, staged cuts, moderate cost increase
10:1 to 15:1	Difficult, specialist fixturing, steep cost
Over 15:1	Specialist work, expect scrap and a long first article

A 2 mm wall 10 mm high is comfortable. A 1 mm wall 15 mm high is a project.

In absolute terms for machined stainless: 2 mm and above is normal, 1 to 2 mm needs a shop that is paying attention, 0.5 to 1 mm is specialist, below 0.5 mm is a conversation, not a drawing note.

Why it is hard

Four things work against a thin wall in stainless, and they compound.

Deflection. The wall pushes away from the tool, so the cut gets shallower, and a shallow cut in stainless is a rubbing cut. The wall springs back after the tool passes and the dimension is wrong. Cutting forces in stainless are high, so deflection arrives earlier than it would in aluminium.

Work hardening. Because of the deflection above, the tool is constantly taking a lighter cut than programmed. That is the exact condition that creates a hardened surface layer, which makes the next pass worse. See work hardening in stainless machining for the mechanism.

Heat. SUS304 conducts at around 16 W per metre kelvin. A thin section has nowhere to send the heat, so it grows while it is being cut and shrinks afterwards. Measure it hot and it is in tolerance. Measure it cold and it is not.

Residual stress. This one catches everybody. Bar and plate arrive with internal stress from rolling, drawing and straightening. Machining removes material asymmetrically and unbalances that stress. The part moves, sometimes not immediately. A part that was flat coming off the machine can be out of flat the next morning.

What a good shop does

Recognising these in a quote conversation is a reasonable way to judge who is taking the part seriously.

Stress relieve between roughing and finishing. The single most effective measure on anything where a lot of material comes off one side. It costs an operation and it saves the part.

Leave stock and stage the cuts. Rough with material still supporting the wall, stress relieve, then finish. Never machine a thin wall to final size in one pass from solid.

Machine top down in steps. On a milled wall, take the full wall thickness for a few millimetres of depth at a time, rather than full depth at partial width. The uncut material below supports what is being cut.

Support the wall. Wax, low melting alloy, a machinable filler, or a fixture that clamps the inside of a thin ring rather than the outside.

Balance the removal. Taking material from both sides alternately unbalances the residual stress less than taking it all from one side.

Leave the thin feature last. Every operation after it will disturb it.

Let the part settle before final inspection. A part measured immediately after a heavy cut is measured warm.

What you can change on the drawing

This is where the money is. A shop can manage a thin wall. It cannot make it cheap.

Ask whether the wall needs to be that thin. Very often it was set by a weight target that has since moved, or copied from an aluminium design where 1 mm was free. Going from 1 mm to 1.5 mm can halve the cost of a part and change nothing about its function.

Add a sacrificial support. A tab, a web or a solid boss that holds the thin section rigid during machining and is cut off at the end. Design it in deliberately and note it on the drawing as removable. It is cheaper than the fixturing it replaces.

Relieve the tolerance on the thin feature specifically. A thin wall with a general medium class tolerance is a normal part. The same wall with ±0.02 mm is a different job. If the wall thickness itself is not functionally critical, say so on the drawing.

Do not put a tight flatness or profile call-out on a thin face. If you need it, expect stress relieving and a finishing operation, and price accordingly. See the general tolerance guide for what the geometrical class applies by default.

Consider a different grade. SUS303 cuts with much lower forces than SUS316L and deflects the wall less. If the service permits it, that is a real reduction in difficulty rather than a workaround. The comparison is in SUS303 vs SUS304 vs SUS316.

Consider a different process. A thin walled cylinder may be cheaper as a tube with machined ends than as a part hogged from bar. A thin walled box may be cheaper as a fabrication. Both change the drawing significantly, and both are worth asking about before the part goes into production.

Fixturing, and why it shows up in the quote

Thin wall parts often need a fixture that does not exist yet. Soft jaws machined to match the part, a mandrel that supports a bore from inside, a vacuum plate, a potting compound.

That fixture is a one off cost. On a run of five parts it dominates the price. On a run of five hundred it disappears into the unit price. This is why thin wall prototypes look disproportionately expensive and why the second order is often much cheaper than the first.

If you expect to reorder, say so at the enquiry. A shop that knows a fixture will be reused prices the first order differently.

What to tell the shop

Put these in the enquiry, not only on the drawing:

Which dimension on the thin feature is functionally critical, and which is not
Whether the wall thickness is negotiable and by how much
Whether a sacrificial feature is acceptable
Expected quantity and whether it repeats
Whether the part is inspected free or clamped, because a thin part measures differently in a fixture

That last point is regularly the cause of an argument. A thin ring measured in a chuck is round. The same ring free standing may not be. Specify which condition the drawing means.

Have a part with a wall you are not sure about? Get a quote. The quote shows where the cost sits before you commit to the geometry. Within 24 business hours.

Questions

What is the minimum wall thickness for machined stainless?

Around 0.5 mm is achievable on a small part with good fixturing and a shop that specialises in it. Below 1 mm the price rises steeply. Between 1 and 2 mm is routine on most parts. Treat 1 mm as the point where cost starts climbing.

Why do thin walls distort even when nothing touches them?

Residual stress. Bar and plate carry internal stress from rolling and drawing. Removing material unbalances it and the part moves. This happens after the cut, sometimes hours later.

Does stainless distort more than aluminium?

For the same geometry, yes on most counts. It work hardens, it holds heat in the cut and it has lower stiffness relative to its strength than people assume. The elastic modulus is higher than aluminium, but the cutting forces are far higher too.

What is the single best design change?

Adding a sacrificial feature that supports the thin section during machining and is removed at the end, or increasing the wall by a few tenths where the function permits.

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