Thin-Wall CNC Machining: Plan Stress Relief Before Finishing

Thin-wall CNC machining is less about the final cut than the sequence that gets you there. On a 1 mm wall in 6061-T6 or 304 stainless, roughing removes most material and leaves residual stress that can move the part after unclamping. If you finish in the same setup without allowing that movement, a ±0.025 mm tolerance or flatness callout may fail even when the machine is capable.

Plan a stress-relief pause between roughing and finishing. Leave 0.5–1.0 mm of stock, unclamp or use soft jaws with light pressure, and let the part normalize; for 7075 or POM/Delrin, rough, wait, then take a light semi-finish. Re-fixture on a stable datum, verify the wall with an in-process check, and only then take the finish pass at reduced radial engagement. This sequencing often costs one extra setup but prevents scrap and rework.

Keep finish requirements realistic. A Ra 0.8 µm finish on a flexible wall can force extra spring passes; Ra 1.6 µm may be sufficient for many covers and housings. Specify tight tolerance only on functional features, not every surface. On thin-wall machined parts, profile tolerance and wall thickness should be tied to the same datum scheme used for inspection.

Use CMM or vision checks after finishing, not only at the machine, because clamping can mask deflection. If lead time matters, discuss stress relief early: the extra operation is usually cheaper than a second machining cycle. A short process plan—rough, relax, re-fixture, verify, finish—is the practical route to repeatable thin-wall parts.

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For more guidance on related work, see: Hybrid CNC Machining: Turning and Milling in One Setup.