Aviation CNC UK: What Engineers Need to Specify

Most aviation CNC work starts with aluminium because it machines fast and holds tolerance without much fighting. 7075 is the common choice for structural brackets and fittings where strength matters more than corrosion resistance. 6061-T6 is easier to cut and weld, so it suits housings, mounting plates and non-critical frames. 2024 machines well but is fussier about stress relief on thin walls.

Titanium is where the process changes. TC4 (Ti-6Al-4V) cuts at roughly a fifth of the feed rate you would use on aluminium, and the heat stays in the tool, not the chip. That means slower spindle speeds, more coolant, and a plan for tool wear. We keep separate tooling for titanium so contamination does not carry into aluminium jobs.

Stainless grades appear on fuel, hydraulic and actuator parts. 17-4PH holds strength after heat treatment and machines cleanly in the H1150 condition. 316L is the pick for corrosion resistance but galls easily, so thread milling beats tapping on anything below M4.

Inconel and magnesium are the two ends of the difficulty scale. Inconel 718 is slow and expensive to cut, so it only makes sense where the thermal requirement is real. Magnesium AZ31B and AZ91D machine quickly but need chip control and a strict no-ignition housekeeping routine. If your part can be redesigned in aluminium, it usually should be.

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  Aluminium6061, 7075, 2024, 5083, 6082 for frames, brackets and housings
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  TitaniumTA1, TA2, TC4; slow speeds, dedicated tooling, more coolant
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  Stainless303, 316L, 17-4PH for fuel, hydraulic and actuator parts
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  High tempInconel only where the thermal load justifies the cycle time

A ±0.005 mm callout is achievable on a machined feature when the feature is rigid, the material is stable, and the measurement is defined. It is a different story on a 300 mm thin-wall panel, where thermal expansion of the part during the day shift can move a bore more than the tolerance itself.

The practical rule is to keep tight tolerances on the features that control fit and function, and open the rest. A bolt hole pattern can sit at ±0.05 mm and still assemble. A bearing bore or a dowel location is where the tight number earns its cost. Over-tolerancing the whole drawing raises cycle time and inspection time without improving the assembly.

Finish follows the same logic. A sealing face or a sliding surface may need Ra 0.2–0.8 μm. A structural bracket is fine at Ra 1.6–3.2 μm as machined. We inspect 100% of parts before shipment, and reports are available on request, but the inspection plan should match the drawing callouts rather than defaulting to maximum scrutiny on every dimension.

Datum strategy matters as much as the number. If the drawing references a datum that cannot be reached in one setup, the shop has to re-fixture, and stacked error eats the tolerance you paid for. Calling out a machined datum face early usually saves both cost and argument.

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  Keep tightBearing bores, dowel holes, sealing faces, mating spigots
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  Open upClearance holes, non-critical profiles, cosmetic edges
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  WatchThin walls, long parts, and parts measured at a different temperature

Five-axis machining pays for itself when a part has features on four or five faces and the alternative is three or four separate setups. Every re-fixture adds locating error and queue time. On a bracket with angled pads and a compound bore, one 5-axis cycle usually beats a stack of 3-axis operations on both tolerance and lead time.

It does not pay when the part is flat. A cover plate or a simple profile runs faster on a 3-axis machine with a good vise. Moving that work to a 5-axis center burns spindle hours you do not need to spend. The decision should come from the feature map, not from the machine list.

Thin-wall parts need a different conversation. Aviation housings often have 1–2 mm walls, and the cutting force will deflect them. We rough with leave stock, let the part rest, then finish in light passes. Sometimes the answer is a soft jaw machined to the part profile, or a sacrificial tab that gets removed at the end.

For long parts, the 4000 × 400 × 150 mm envelope covers wing ribs, rails and stringer sections. Long parts also move after machining as internal stress releases, so we plan a stress-relief step or a finish pass after the part has settled.

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  Use 5-axisFeatures on multiple faces, compound angles, contoured surfaces
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  Use 3-axisFlat plates, covers, simple pockets, high-volume simple parts
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  Thin wallsRough, rest, light finish; soft jaws or tabs

Anodizing is the default for aluminium aviation parts. Clear anodize gives mild corrosion protection without changing dimensions much. Hardcoat builds a thicker oxide and improves wear resistance on sliding surfaces, but it grows the part, so mask the tight bores or allow for the build in the drawing. Conductive anodize exists for parts that need a ground path.

For steel and stainless, electroless nickel gives a uniform coating on complex geometry, which is useful when the part has internal passages. Zinc plating and black oxide are cheaper options for non-critical hardware. Silver and gold plating show up on electrical contacts and RF housings.

Cosmetic finishing is usually the last step and the easiest to get wrong. Bead blasting hides tool marks but changes the surface texture, so it should not be applied to a sealing face. Brushing and polishing give a directional or mirror look, and laser marking handles part numbers and traceability. Minimum character height for laser marking is 1.5 mm, so plan the marking field before the drawing is frozen.

Whichever finish you choose, tell us which dimensions must survive it. A coating that adds 20 μm to a bore can turn a press fit into a loose fit.

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  AluminiumClear, colour, hardcoat, conductive anodize
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  Steel and stainlessElectroless nickel, zinc, black oxide
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  CosmeticBead blast, tumbling, brushing, polishing
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  MarkingLaser marking and engraving, 1.5 mm minimum character height

Aviation buyers ask for paperwork as often as they ask for parts. Our inspection flow is raw material check, in-process monitoring, then final inspection before shipment. Reports are available on request, and 100% of parts are inspected before they leave. If your drawing calls for first article inspection, say so at quote stage, because it changes the time and the cost.

Material traceability is the other half. We work from certified stock and can pass material certificates with the shipment. If the part needs heat lot tracking or a specific mill certificate, that should be on the purchase order rather than discovered at goods-in.

Confidentiality is standard on aviation work. Uploads are secure, and an NDA is available on request. Many of the parts we machine are pre-release designs, so drawings and models stay inside the job folder and are not shared outside the people running the work.

Certifications cover the systems side: ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. ISO 27001 is the one that matters if you are sending controlled data, since it covers how information is handled, not just how parts are made.

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  InspectionRaw material check, in-process monitoring, final inspection
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  ReportsAvailable on request; FAI on request at quote stage
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  TraceabilityMaterial certificates and heat lot tracking on request
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  DataSecure uploads, NDA available on request

A UK engineering team often works with a mix of local machine shops and overseas suppliers. The decision usually comes down to three things: how tight the tolerance is, how fast the part is needed, and how much documentation the program requires.

Local shops win on proximity and on fast iteration during development. Overseas suppliers win on capacity and on cost for production volumes. The trade-off is shipping time and the need for clear inspection paperwork, because you cannot walk over to the machine to check a feature.

What makes the difference in practice is how the supplier handles a drawing review. A shop that flags an unreachable datum, a tolerance that will not survive anodizing, or a thread that is too small to tap is saving you a scrapped batch. We return a quotation and a free DFM analysis within 12 hours, and production can start within 24 hours of approval. Parts ship in 3–5 days, with no minimum order quantity, from one prototype to 10,000+ part runs.

For aviation programs, the sensible split is to keep the tight, high-documentation parts with a supplier you can audit, and to move the simpler, higher-volume parts where the process is proven. Either way, the drawing and the inspection plan should travel together.

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  QuoteQuotation and free DFM analysis within 12 hours
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  StartProduction can start within 24 hours
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  DeliveryParts ship in 3–5 days; historical late-delivery probability below 2%
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  VolumeNo MOQ; one prototype to 10,000+ part runs