Aviation CNC parts supplier: how to judge capability before you send an RFQ

Aviation parts are not one category. A bracket that holds a wiring loom has different demands from a hydraulic manifold or a rotor hub. What they share is that the drawing is the contract. Every dimension, callout and note is inspected against it, so the shop's job is to hit the numbers and to prove it with data.

Most of the parts we machine in this sector are non-flight-critical structural and system hardware: mounting plates, housings, bushings, fittings, spacers, and prototype airframe sections. These are still held to tight tolerances and full traceability, but they are the practical starting point for a new program because the geometry and inspection plans are simpler than primary structure.

CNC fits when the part has to be repeatable. A single hand-finished bracket can be made in a toolroom. A run of 200 identical brackets, all within ±0.005 mm on the bore pattern, needs a process. That is the difference a supplier brings: a defined setup, a defined toolpath, and a defined inspection routine that does not change between lots.

• 1
  Good fitPrismatic parts with pockets, bores, slots and hole patterns that can be reached from a few setups.
• 2
  WorkableThin-walled housings if wall thickness stays above roughly 1 mm and support ribs are allowed.
• 3
  Poor fitLarge single-piece skins and long stringers that are better formed or extruded.

Five-axis simultaneous machining is the reason many aviation parts are now cut in one setup. Instead of repositioning a part five times and stacking fixture error, the tool reaches the underside of a pocket, a compound-angle face, or a port on a curved surface without re-clamping. Fewer setups means fewer places for the part to move.

Our floor runs 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Maximum processing size is 4,000 mm, and the largest travel envelope is 4,000 × 400 × 150 mm. Medium and compact envelopes cover most housing and fitting work. Rotary tables of Ø400 mm handle parts that need continuous indexing.

Tolerance is a process statement, not a wish. We hold ±0.005 mm (±0.0002 in) on critical features when the material, geometry and fixturing allow it. A long, thin aluminum rib will not hold that number across its full length. Neither will a part that has to be clamped hard enough to distort. In those cases we say so before quoting, and we agree on which dimensions carry the tight callout and which can sit at a general tolerance.

Surface finish follows the same logic. As-machined faces land at Ra 1.6–3.2 μm. Where a sealing face or a bearing seat needs better, we target Ra 0.8–1.6 μm, and fine finishing reaches Ra 0.2–0.8 μm. Screening finish requirements to the faces that need them keeps cost and cycle time down.

Aluminum covers a large share of aviation hardware because it machines fast and holds a good finish. 6061 and 6061-T6 are the everyday choice for brackets and housings. 7075 gives higher strength for loaded fittings, though it machines slower and is less weldable. 2024 is common where fatigue resistance matters. 5052 and 5083 are used for formed and welded assemblies.

Stainless and steel take over when loads, wear or temperature rise. 303 is the free-machining grade for fittings and spacers. 304 and 316L are used for corrosion resistance. 17-4PH (SUS630) is a precipitation-hardening grade that holds strength after heat treatment, so it suits bushings and valve parts. On the steel side, 4130, 4140 and 4340 are standard for structural and shaft work.

Titanium is where the process gets slower. Ti-6Al-4V (TC4) and commercially pure TA1 and TA2 need low cutting speeds, rigid setups and plenty of coolant. Heat builds at the edge, and a tool that is fine in aluminum will fail quickly here. We machine titanium when the strength-to-weight ratio justifies it, and we quote it with the extra cycle time built in.

Nickel alloys such as Inconel, magnesium grades AZ31B and AZ91D, and copper alloys including beryllium copper round out the list. Plastics are also in scope: PEEK for high-temperature insulators, POM and PA for wear parts, PC and PMMA for transparent covers, and carbon fiber for stiff, light panels.

• 1
  Light and fast6061-T6, 6082, 7075 for brackets, plates and housings.
• 2
  Corrosion and wear303, 316L, 17-4PH for fittings, bushings and valve parts.
• 3
  High load4130, 4140, 4340 for shafts and structural hardware.
• 4
  Hot or lightTi-6Al-4V or Inconel when temperature or weight rules out steel.

The inspection plan is agreed before the first chip is cut. Raw material arrives with a certificate and is checked against the drawing before release to machining. During the run, in-process checks catch drift on critical dimensions before the lot is finished. Before shipment, every part is inspected. Reports are available on request.

For aviation work, that paper trail matters as much as the part. A supplier should be able to trace material back to the mill certificate, show which machine and setup produced a feature, and provide dimensional reports on the callouts you specify. If a shop cannot describe its inspection routine in plain terms, that is a signal.

Our quality system is certified to ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. The first three cover process control and traceability. ISO 27001 covers how customer drawings and models are stored and who can open them. Qualification rate across production runs is 99.99%.

Confidentiality is part of the process, not an add-on. Uploads are handled as confidential, access is limited to the people on the job, and an NDA is available on request. If your program needs one, sign it before you send the models.

Start with the drawing. Send the hardest features first: the tightest tolerance, the deepest pocket, the thinnest wall, the surface that has to seal. How a supplier responds to those tells you more than a general capability page. A useful answer names the setup, the machine and the inspection method.

Then ask about lead time in concrete terms. We return a quotation and a free DFM analysis within 12 hours, and production can start within 24 hours once the order is confirmed. Parts ship in 3–5 days for most work. Historical late-delivery probability is below 2%. Those are process numbers, not promises about your specific part.

Volume flexibility matters if the program is early. There is no minimum order quantity, so a single prototype and a 10,000+ part run go through the same shop. That matters when a design is still moving, because the first article and the production part come from the same process.

Finally, look at what happens after machining. If the supplier handles anodizing, plating, heat treatment and inspection in-house or through controlled partners, you avoid shipping parts between vendors and losing traceability at each handoff.

• 1
  Ask for the setup planA supplier who can describe fixturing has done the work.
• 2
  Check the tolerance claim±0.005 mm only holds on features that allow it.
• 3
  Request a sample reportSee how dimensions and material certs are documented.
• 4
  Confirm data handlingNDA and access control before models are shared.