Quick answer: A CNC first article inspection (FAI) should confirm that the intended material, drawing revision, machining route, tooling, setup, finishing, and inspection plan can produce a conforming part before the remaining batch is released. Buyers should define the FAI scope, report format, approval gate, and reinspection triggers in the RFQ and purchase order, not after production has started.
A first article can be one of the most valuable controls in a custom CNC machining order, but only when the buyer and supplier agree on what it must prove. The phrase “first article approved” is too vague by itself. It may refer to a machinist checking a few dimensions at the machine, a customer reviewing a physical sample, or a fully documented inspection package covering every drawing characteristic.
This guide explains how engineering and purchasing teams can define a useful CNC first article inspection without buying unnecessary paperwork or leaving critical requirements unverified.
What is a CNC first article inspection?
First article inspection is the planned verification of an initial part made from a new or changed production process. Its purpose is to provide objective evidence that the supplier has interpreted the controlled product definition correctly and that the planned process can produce the required result.
For CNC machined parts, the first article should be representative of the intended production method. That normally means using the approved material, current CNC program, planned tooling, workholding, setup sequence, finishing route, and inspection method. A hand-finished demonstration sample made by an exceptional route may prove that the geometry is possible, but it may not validate the process intended for the batch.
First piece, FAI, sample approval, and PPAP are different
| Control | Primary purpose | Typical output |
|---|---|---|
| Machine first-piece check | Verify setup and tool offsets before continuing the run | Internal measurement record or operator sign-off |
| First article inspection | Verify that the planned production process meets defined product requirements | Ballooned drawing, measured results, certificates, and approval record as required |
| Physical sample approval | Allow the customer to evaluate fit, appearance, assembly, or function | Shipped sample plus written approval or change request |
| PPAP | Demonstrate broader production-process readiness for an applicable customer or industry system | Customer-defined PPAP submission level and supporting records |
These controls can support each other, but one does not automatically replace another. State exactly what the order requires. If your program needs a formal aerospace FAI, identify the governing requirement and revision. The IAQG 9102 guidance explains that the standard provides consistent FAI process and documentation requirements for aviation, space, and defense products. It may also be used elsewhere when a standardized FAI process is needed, but it should not be added casually to every commercial part.
When should a buyer request FAI?
Consider a first article inspection when:
- A supplier is producing a part number for the first time.
- A new or revised drawing changes geometry, tolerance, material, finish, or acceptance requirements.
- Production moves to a different factory, machine type, fixture, program, or major process route.
- A long production interruption makes process continuity uncertain.
- A nonconformance, corrective action, or process change could affect conformity.
- The part has high-cost material, critical interfaces, complex GD&T, special processes, or significant failure consequences.
- The buyer requires documented approval before the balance of the order is released.
Not every repeat order needs a complete FAI. The scope should reflect product risk, process change, contractual requirements, and prior performance.
Define the FAI before quotation
Inspection planning changes cost and lead time. A complete dimensional report, CMM program, ballooned drawing, material traceability package, or physical sample hold point requires work that the supplier must include in the quotation and schedule.
Add the following to your CNC machining RFQ package:
- The drawing, model, specification, and revision that control acceptance.
- Whether every drawing characteristic or only defined critical features must be reported.
- Required material, heat-treatment, coating, and special-process certificates.
- The report format and whether actual measured values are required.
- Whether a physical sample, photographs, or assembly test is required.
- Who approves the FAI and whether production must stop pending approval.
- The response required for nonconforming or unclear results.
- Conditions that require a partial or full repeat FAI.
What should a CNC FAI report contain?
| FAI element | Buyer check |
|---|---|
| Part identification | Part number, name, revision, serial or lot reference, quantity, and inspection date match the order |
| Product definition | The correct drawing, CAD model, specifications, and approved deviations are listed |
| Ballooned drawing | Every reportable characteristic has a unique number that maps to the results |
| Dimensional results | Nominal, tolerance limits, actual result, units, and disposition are clear |
| Material evidence | Grade, condition, heat or lot, certificate, and any required test results are traceable |
| Special processes | Heat treatment, anodizing, plating, passivation, or other required processes have applicable records |
| Measurement evidence | Inspection method and equipment are appropriate for the feature and tolerance |
| Nonconformance status | Any out-of-tolerance result is identified with an approved disposition; it is not silently marked acceptable |
| Approval | Supplier review and customer approval fields match the agreed release process |
Use a ballooned drawing to make the report auditable
A ballooned drawing assigns an identifier to each characteristic that must be verified. The same identifier appears in the results table. This allows the buyer to move from a dimension, note, thread, surface-finish requirement, or GD&T control on the drawing directly to its recorded result.
The ballooning method should cover applicable notes and specifications, not only visible linear dimensions. Material, hardness, coating, marking, deburring, cleanliness, and packaging requirements may be part of the controlled product definition.
Ask for actual values where the decision needs data
A pass/fail mark may be sufficient for some simple internal checks, but actual measured values are more useful for critical characteristics and formal approval. They show how much margin exists inside the tolerance and help identify drawing interpretation errors, measurement problems, or a process that is already near a limit.
Actual values do not prove long-term process capability by themselves. A single conforming first article is one observation. Repeat production may require in-process checks, sampling, capability data, dedicated gauges, or other controls depending on risk and volume.
Match the measurement method to the feature
Do not request a CMM report simply because the part is described as precision machined. Choose the method based on geometry, tolerance, surface, datum scheme, access, and uncertainty. Hand tools, height gauges, bore gauges, thread gauges, optical systems, surface-roughness instruments, CMMs, and functional fixtures each have suitable applications and limitations.
For complex GD&T, agree on datum establishment, alignment strategy, point density, filtering, and reporting convention where these choices could change the result. The drawing should communicate design intent; the inspection plan should explain how conformity will be demonstrated. See our tolerance and inspection guides for related planning questions.
Verify material and special processes
Dimensional conformity is only one part of FAI. Confirm the specified material grade, condition, and traceability. If the order requires a mill test report, certificate of conformity, hardness result, positive material identification, or independent test, state that before quoting.
Finishing can affect dimensions, threads, electrical contact, corrosion behavior, appearance, and masking zones. If the first article is inspected before finishing, define what will be rechecked afterward. If appearance is important, provide objective cosmetic criteria or an approved reference rather than relying on “looks good.”
Decide whether production waits for approval
This is one of the most important commercial decisions in the FAI plan. Possible release models include:
- Supplier internal release: Production continues after the supplier verifies the first piece.
- Report hold point: The supplier sends the FAI report and waits for written buyer approval.
- Physical sample hold point: The buyer receives and tests a sample before the remaining quantity begins.
- Limited-at-risk production: The supplier may proceed with a defined quantity while approval is pending.
Document the selected model, approval contact, response time, and responsibility for schedule impact. If the supplier machines the entire batch before a required customer approval, the FAI no longer protects the batch from a systematic interpretation or setup error.
What should trigger a repeat FAI?
Define reinspection triggers proportionally. A repeat or partial FAI may be appropriate after a design revision, material change, new supplier or manufacturing location, new machine or fixture, major CNC program change, altered sequence, special-process source change, long production gap, or corrective action that changes the process.
Not every administrative update requires every characteristic to be measured again. Review which features and records could be affected by the change and document the rationale.
Common FAI mistakes
- Writing only “FAI required” without defining scope or approval.
- Inspecting a sample made by a different method from the planned batch.
- Using the wrong drawing revision or mismatched 2D and 3D files.
- Reporting pass/fail without traceable actual values where data is required.
- Ignoring drawing notes, material, heat treatment, coating, or marking.
- Using measurement equipment that cannot meaningfully verify the feature.
- Approving a nonconformance informally without a documented disposition.
- Completing the full batch before a contractual approval hold point.
- Assuming one good part proves the process is capable indefinitely.
Copy-and-use FAI requirement for a CNC RFQ
First article inspection required: Yes Controlling part number / revision: Inspection scope: All drawing characteristics / listed CTQs only Ballooned drawing required: Yes / No Actual measured values required: Yes / No Material certificate required: Special-process certificates required: Physical sample required: Yes / No Photographs or assembly test required: Report format or customer template: Production release: Supplier approval / buyer written approval / sample approval Maximum quantity allowed before approval: Required report and sample date: Repeat FAI triggers: Nonconformance and deviation process:
Frequently asked questions
Does every CNC machined part need a formal FAI?
No. The requirement should reflect contract, industry, product risk, process change, and customer quality planning. A simple first-piece check may be sufficient for some low-risk work; other programs require full documented FAI.
Is a CMM report the same as an FAI report?
No. A CMM report is measurement output from one inspection method. An FAI package may also include product-definition references, ballooning, material and process records, other measurement methods, nonconformance status, and approvals.
Should the supplier inspect every dimension?
That depends on the agreed scope. Formal requirements may call for complete characteristic accountability. A commercial buyer may instead define critical and high-risk features. The decision must be explicit before quotation.
Can production start before customer FAI approval?
Only if the agreed release plan allows it. Production performed before a required approval is at risk. State the hold point and permitted quantity in the purchase order.
How does FAI help when choosing a supplier?
It tests drawing interpretation, process planning, inspection discipline, traceability, communication, and change control using the actual part. Combine it with the broader CNC supplier qualification checklist.
Next step: Review our custom CNC machining services and send your drawing package and FAI requirements for an RFQ review.
Scope note: This article provides general procurement and quality-planning guidance. Contractual, aerospace, automotive, medical, regulatory, and customer-specific requirements take precedence. Final inspection scope and feasibility depend on the controlled drawing and agreed quality plan.
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