Aerospace CNC machining isn't just machining with tighter tolerances. It's a different way of working — different materials, different documentation, different consequences for getting it wrong.
When a bracket fails on a bicycle, the rider pulls over. When a bracket fails on an aircraft, people die. That reality shapes every decision in aerospace machining: material selection, process control, inspection, and paperwork.
I've supplied machined parts to aerospace customers over the years, and here's what I've learned about what actually matters when you're sourcing aerospace CNC parts.
Materials that show up in aerospace machining
Aerospace parts use a narrower material palette than general industrial work. Here's what we see most often:
| Material | Typical Aerospace Application | Key Properties |
|---|---|---|
| 7075-T6 / 7075-T651 aluminum | Structural brackets, fuselage frames, wing ribs | 500+ MPa tensile, high strength-to-weight |
| 6061-T6 aluminum | Non-structural housings, enclosures, heat sinks | Good all-around, anodizes well, widely available |
| Ti-6Al-4V (Grade 5) titanium | Engine mounts, fasteners, landing gear components | 900 MPa tensile, ~40% lighter than steel |
| 17-4 PH stainless (H900/H1025) | Actuator shafts, valve bodies, high-strength fasteners | 1,100-1,300 MPa tensile after heat treat |
| 15-5 PH stainless | Structural components requiring higher toughness than 17-4 | Better transverse toughness than 17-4 PH |
| Inconel 718 | Hot-section brackets, exhaust components, turbine hardware | Maintains strength to 700°C |
| A286 stainless | High-temperature fasteners and fittings | Oxidation resistance to 700°C |
Aluminum 7075 and titanium do most of the structural heavy lifting. 17-4 PH covers high-strength steel applications. Inconel shows up when the part lives near the hot end.
What you don't see much of: plain carbon steel. Too heavy, rusts, doesn't earn its place in an aircraft. Even stainless is limited to specific applications where corrosion resistance justifies the weight penalty over aluminum or titanium.
Tolerances: tighter, but not tight everywhere
The most common mistake I see on aerospace drawings is the blanket tight tolerance. An engineer slaps ±0.05mm on every feature and calls it "aerospace grade."
Real aerospace tolerances are selective. Certain features — bearing bores, seal surfaces, fastener holes for interference-fit hardware — need ±0.012mm or better. But a cable pass-through or a lightening pocket wall thickness? ±0.25mm is fine.
Here's what I've found works in practice:
| Feature Type | Typical Tolerance | Notes |
|---|---|---|
| Bearing bore diameters | ±0.01mm or tighter | Often requires honing after machining |
| Seal surfaces | ±0.012mm, Ra 0.4-0.8 μm | Surface finish and geometry equally important |
| Interference-fit fastener holes | ±0.012mm | Reamed, not just drilled |
| Dowel pin locations (true position) | ±0.05mm | Relative to datums, measured at assembly |
| Clearance holes | ±0.13mm | Standard drill tolerance |
| Non-critical external surfaces | ±0.25mm | Lightening pockets, cosmetic surfaces |
| Threaded holes | Per spec (NASM/J-series) | Thread class matters more than hole position |
The tolerance stack that matters most in aerospace isn't any single dimension — it's the true position of mounting holes relative to each other. Three holes that are individually within ±0.05mm but 0.2mm off in position will misalign the entire assembly. This is why aerospace drawings specify datums carefully and why competent shops verify positional tolerances with CMM, not calipers.
AS9100 and what it actually means for machined parts
AS9100 is the aerospace quality management standard — essentially ISO 9001 with 100+ additional requirements specific to aviation, space, and defense. It covers everything from supplier management to process control to traceability.
For a buyer sourcing CNC aerospace parts, here's what AS9100 certification signals about a shop:
Material traceability is mandatory. Every piece of raw material has a mill certificate, a heat number, and a paper trail back to the pour. The shop maintains this traceability through the entire process — from incoming stock to final shipment. If there's a material defect discovered three years later, they can trace every part from that batch.
First article inspection (FAI) is non-negotiable. Before production, one part gets measured completely — every dimension on the drawing, not just the critical ones. The inspection report becomes part of the quality record. AS9102 is the standard form for aerospace FAI reports.
Process control is documented. Tool changes, machine settings, in-process measurements — all logged. If a dimension drifts during production, the shop can identify exactly which parts might be affected and isolate them.
Sub-tier supplier control. The shop verifies that its material suppliers, plating vendors, and heat treaters also meet quality requirements. You can't have an AS9100 shop sending parts to a non-certified anodizer.
Now the honest part: not every aerospace part requires an AS9100-certified shop. Non-flight-critical ground support equipment, tooling fixtures, and R&D prototypes often don't need full certification. But if the part goes on an aircraft and the drawing says "AS9100 required," there's no shortcut.
Finishes and treatments for aerospace parts
Aerospace parts typically need more than an as-machined surface:
| Treatment | Typical Application | Notes |
|---|---|---|
| Type III hard anodize | Aluminum structural parts | 25-50 μm thickness, grey/dark grey, masks threaded holes |
| Type II anodize (clear or black) | Aluminum housings, covers | Thinner (5-15 μm), more color options |
| Alodine / chem film | Aluminum electrical enclosures | Conductive, good primer for paint |
| Passivation (AMS 2700) | Stainless steel parts | Removes free iron, restores corrosion resistance |
| Cadmium plating | Steel fasteners and fittings | Excellent corrosion resistance, lubricity; restricted in some applications |
| Zinc-nickel plating | Steel parts (cadmium replacement) | Good corrosion resistance without cadmium's environmental concerns |
| Dry film lubricant | Titanium and stainless fasteners | Prevents galling on threaded surfaces |
The biggest gotcha for aerospace parts is masking. Anodize changes hole diameters — a 6.00mm hole becomes roughly 5.98mm after Type III hard anodize. Threaded holes, bearing bores, and tight-tolerance bores must be masked before anodize, or machined oversize to compensate. The drawing needs to state which holes get masked. If it doesn't, the shop has to guess — and a wrong guess means scrapped parts.
We can't do AS9100-certified work, but we machine the parts that don't need it
Full disclosure: we don't hold AS9100 certification. We're not set up for it, and we tell every aerospace customer this upfront.
But here's what we do well: we machine aerospace-grade materials to aerospace-grade tolerances for the parts that don't carry flight-critical certification requirements. Ground support equipment. Test fixtures. R&D prototypes. Drone components. Satellite brackets for non-human-rated launches. Tooling and jigs. Parts where the material, tolerance, and surface finish requirements are aerospace-level but the regulatory paperwork isn't.
For customers who eventually need AS9100-certified production, we serve as the bridge: prototype in aluminum, validate the design, prove the process parameters, then transition to a certified shop for production quantities. We've done this handoff multiple times, and we know how to document our process so the next shop can pick it up cleanly.
DFM for aerospace CNC parts
Aerospace parts have specific design challenges that general DFM rules don't fully cover:
Thin ribs and webs are everywhere in aerospace. Structural brackets are designed with FEA-optimized topology — thin webs connecting thicker bosses. These thin sections (sometimes 1.5mm or less) vibrate during machining. The fix is usually staged roughing: remove 80% of the material, let the part stress-relieve overnight, then semi-finish the thin features with light cuts at low radial engagement. It adds a day to the schedule but prevents scrapped parts.
Large monolithic parts are common. Instead of assembling 20 small brackets, aerospace designers specify one large machined plate with all features integrated. These parts can be 400mm x 300mm x 50mm with hundreds of features. They're expensive because they tie up a machine for hours and carry high material cost (removing 80%+ of the stock). The DFM lever here is: does it really need to be one piece, or can it be three smaller parts bolted together? The answer depends on stiffness requirements, but it's a conversation worth having.
Edge distance for fastener holes. Aerospace joints use closely spaced fasteners, and the rule of thumb is 2x hole diameter minimum edge distance (center of hole to edge of part). Violate this and the material between the hole and the edge can crack under load. This is a design constraint, not a machining constraint — but if the edge distance is too small, the shop should flag it before cutting metal.
Radius everything. Sharp internal corners are stress concentrations. Aerospace parts live with cyclic loading and vibration, so fatigue life matters. Minimum 1.5mm internal corner radius is standard; larger is better. This also makes machining easier — a 6mm radius can use a 12mm end mill, which is faster and more rigid than the smaller tool a 1.5mm radius requires.
Bottom line
Aerospace CNC machining is demanding but not mysterious. The materials are specific. The tolerances are selective. The documentation is thorough. The shops that do it well are methodical about process control and honest about what they can and can't certify.
If you're sourcing aerospace CNC parts, start with clarity: is this flight-critical or not? Does it need AS9100, or will ISO 9001 quality standards with documented inspection suffice? Getting this answer right saves you from overpaying for certification you don't need — or dangerously skipping certification you do.
Send us your drawing with the application requirements. If your part needs AS9100, we'll tell you and recommend shops that can help. If it doesn't, we can machine it for you at aerospace-grade quality without the aerospace-certification premium.