Aerospace CNC Machining Supplier Guide

Aerospace machining outsourcing rarely fails at the drawing stage. It fails later, when a shop that passed every commercial check turns out to have no approval for the heat treatment on the print, no certified nondestructive testing personnel, and no temperature-controlled inspection room for the tolerances it quoted. This guide sets out what to verify before a purchase order is issued, what to ask in a technical review, and which answers should stop a qualification.

What sets aerospace machining apart

A commercial job shop and an aerospace machine shop may run the same brands of five-axis mills. The difference lies in what the drawing asks them to prove, and how much evidence they must keep.

General tolerances on aerospace drawings sit around ±0.05 mm (±0.002 in), close to other precision industries. The gap opens on flight-critical features. Bearing bores are held to roughly ±0.005 mm with surface finishes of Ra 0.4 µm or better, sealing faces to Ra 0.2 µm, and hole patterns controlled by true position, occasionally to ±0.0127 mm (±0.0005 in). A single part can combine those micrometre-level features with clearance holes at ±0.127 mm, and the cost of the job follows the tight dimensions rather than the average. Geometry is defined through GD&T to ASME Y14.5, so position, profile and perpendicularity callouts carry the design intent.

Material choice shapes the process plan just as much. Aluminum 7075 machines quickly and holds tolerance without much fuss. Titanium Ti-6Al-4V and nickel alloys such as Inconel 718 generate heat at the cutting edge, work-harden, move under residual stress and wear tooling fast. Cutting data, fixturing and in-process probing all change with the alloy, and a shop that runs aluminum all week will not hold titanium tolerances at aluminum cycle times.

Certifications to verify before you release a drawing

AS9100D

AS9100D is the aerospace quality management standard published by the International Aerospace Quality Group. It contains every ISO 9001 requirement plus rules for risk management, configuration control, counterfeit part prevention and control of external providers.

The certificate proves less than buyers assume. The scope statement decides everything, because a company can hold AS9100D for assembly while a separate machine shop on the same site operates outside that scope. Check the IAQG OASIS database for three things: the certificate is current, the scope covers the processes you are buying, and the legal entity named matches the entity quoting your job.

NADCAP

NADCAP approvals are granted per process, not per company. The commodity list covers heat treatment, nondestructive testing, chemical processing, coatings, welding, sealing, elastomer bonding and non-traditional machining such as EDM. Each has its own audit criteria, so a shop approved for heat treatment may hold no approval at all for NDT.

The programme is administered by the Performance Review Institute, and it exists because special processes cannot be verified by inspecting a finished part. A heat-treat specification on the drawing means little if the parts travel to an unapproved subcontractor and return with a certificate of conformance. Related requirements usually travel in the same package: AS9102 governs first article inspection, AMS 2750 sets pyrometry rules for heat-treating equipment, and NAS 410 covers certification of NDT personnel.

ITAR and export controls

ITAR controls the export, re-export and transfer of defense articles and technical data. It is codified at 22 CFR Parts 120 through 130 and administered by the Directorate of Defense Trade Controls at the U.S. Department of State. Dual-use items fall under the Export Administration Regulations, administered by the Bureau of Industry and Security.

The practical test for a buyer is simple. If the drawing is export-controlled, the supplier must be registered and able to receive the technical data before you send it. Registration is legal eligibility rather than a quality credential, and the penalties for ignoring it are criminal, not commercial.

Prime contractors such as Boeing, Airbus and GE Aerospace generally require process approvals on top of a quality certificate, and that expectation flows down through every tier. A machined bracket from a distant tier-two shop still has to satisfy criteria written by the airframer.

How to assess real capability

Capability claims sound alike. Specific answers do not.

Which machine platforms will run this part, and does the geometry truly need five-axis work or can it be produced reliably with fewer axes? How is the part held during roughing and finishing, and where does the datum transfer happen between setups? Which titanium or nickel grades has the shop cut in the last twelve months, and can it show inspection reports from those jobs? How are tool wear and burr control managed on critical edges?

Inspection deserves its own conversation. Ask whether CMM inspection stays in-house, whether the room is temperature controlled, how surface finish is measured, and what data supports the critical characteristics. A process capability index above 1.33 on tight dimensions is a reasonable floor for production work; anything above 1.67 signals real margin. Gage R&R studies should exist for the gauges used on those features. Programming matters too: ask which CAM platform the shop runs, whether that means Mastercam, Siemens NX or an in-house system, and whether toolpath simulation happens before a new programme reaches the machine.

A practical qualification sequence

Start with paperwork, before any drawing changes hands. Verify AS9100D status in OASIS and process approvals with the relevant certification body, then settle export control status and put an NDA in place.

Next comes a technical review. Send the drawing at a defined revision, ask for a manufacturability assessment, and compare itemized quotations rather than totals. A realistic quote separates material, programming, fixturing, machining time, inspection, finishing, and documents such as material certificates and certificates of conformance.

Then order a qualification part or a small pilot lot. Require a full first article inspection report to AS9102, with ballooned drawings, completed Forms 1, 2 and 3, actual versus nominal data, and material certificates traceable to the heat or lot used in the article. A shop that cannot produce a clean report on request will struggle with production documentation later.

Qualification does not end at first article approval. Track on-time delivery, nonconformance response time and escape rate once production is running. Two or three consecutive lots show whether the process, rather than the operator who tuned it, is holding the tolerance.

Red flags worth acting on

The clearest warning sign is reluctance to share evidence. A supplier that cannot send a redacted first article inspection report, or that describes inspection only in general terms, has probably never built one for a customer who asked.

Other signs carry the same weight. Certificates that cannot be located in a public database. A scope narrower than the work being quoted. Material certificates with no heat or lot traceability. Inspection outsourced to a lab with no evaluation records. Brokers who will not name the facility that cuts the part. None of these is automatically disqualifying, but each shifts risk onto the buyer, and aerospace risk is expensive to absorb downstream.

Cost, lead time and the briefing you should send

Tolerance is the largest single cost driver. Tightening a feature from ±0.1 mm to ±0.01 mm can multiply cycle time by three or more, because the process then depends on thermal stability, tool wear compensation and in-process measurement rather than machine accuracy alone. Reviewing every tight tolerance against its function is the cheapest engineering work available on a programme.

Material and lead time are linked. Aircraft-grade titanium plate, nickel bar and closed-die forgings can add weeks or months before the spindle turns, and first article inspection adds a separate step after machining. Buyers who need parts early should discuss raw material strategy and delivery milestones before the purchase order, not after.

A useful request for quotation states the drawing revision, the standards governing inspection and documentation, the required material certification, the delivery schedule and the special processes involved. Commercial space programmes, from SpaceX and Blue Origin to smaller launch developers, tend to apply the same logic with less tolerance for schedule slippage.

FAQ

‌Is ISO 9001 enough to machine aerospace parts?‌
No. ISO 9001 covers quality management in general. Aerospace buyers expect AS9100D as a minimum, plus NADCAP approvals where special processes appear on the drawing. An ISO 9001 certificate says the shop manages quality with discipline; it says nothing about aerospace traceability, counterfeit part control or first article requirements.

‌What is the difference between AS9100D and NADCAP?‌
AS9100D certifies a company's quality management system across its operations. NADCAP approves one specific process, such as heat treatment or nondestructive testing, against technical audit criteria. A supplier may hold both, one or neither. Where the drawing calls a special process, the NADCAP approval is the one that matters.

‌What tolerances can an aerospace CNC supplier realistically hold?‌
Production tolerances between ±0.005 mm and ±0.0127 mm are routine on flight-critical features such as bearing bores and hole locations, provided the supplier has the machine platforms, thermal control and metrology to support them. General features sit near ±0.05 mm. Cost rises steeply as tolerances tighten, so expect the supplier to ask which dimensions are genuinely functional.

‌Does my supplier need ITAR registration?‌
Only if the work involves defense articles or controlled technical data. ITAR registration is tied to the content of the drawing and to who can access it, not to the machining process. If the answer is unclear, take export control advice before the drawing leaves your building.

‌What should a first article inspection report contain?‌
A compliant AS9102 report includes a ballooned drawing with every dimension and note numbered, Forms 1 through 3, measured values against nominal and tolerance, material and finish certifications traceable to heat or lot, and identification of the process, tooling and inspection equipment used to make the article.

‌How long does aerospace supplier qualification take?‌
Evidence, not machining, sets the pace. Certificate verification and export control checks take days. A technical review and quotation take one to two weeks. Cutting a qualification part and closing out the first article package usually adds several weeks, longer if raw material is not on the shelf.