First Article Inspection tolerances: what is realistic and what it costs
First Article Inspection is a full dimensional check of the first part from a new setup, reported against the drawing. It is used for proving that the process can make the part before the batch is committed. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.
It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, semiconductor is used as the example: cleanliness and surface condition that matter more than the nominal size.
What is realistic
The tolerance that can be held on First Article Inspection depends on the feature, the material and the batch size. A value held once on a first article is not the same as a value held across a thousand pieces.
| Aspect | Typical value |
|---|---|
| Process tolerance | measured, not assumed |
| Measurement | every drawing feature, on calibrated equipment |
| Surface finish | as specified on the drawing |
| Batch effect | capability, not a single measurement |
| Documentation | AS9102 or the customer's own format |
| Cost effect | the inspection time, which is small next to a scrapped batch |
What it costs to hold
Tolerance and cost are not proportional; they are closer to exponential once a process has to be controlled rather than simply performed. The inspection time, which is small next to a scrapped batch, which is why the drawing should say which features carry the function and which do not.
How it is verified
Every drawing feature, on calibrated equipment. Calibration dates and measurement uncertainty are recorded with the result, so a later order can be compared with the first instead of being measured from scratch.
Applications
First Article Inspection is used for proving that the process can make the part before the batch is committed, and in practice it appears most often in aerospace, medical, automotive launch, any new part number.
How it fits into a machining route
First Article Inspection applies to the whole drawing rather than to one operation. It sets how the part is measured as much as how it is made, which is why it belongs on the drawing from the first issue and not in a note added after a query.The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: the inspection time, which is small next to a scrapped batch. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.
Standards, documentation and what is issued
The documentation requirement is AS9102 or the customer's own format. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.
Every drawing feature, on calibrated equipment is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.
Frequently asked questions
What tolerance should be specified for First Article Inspection?
measured, not assumed is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.
Which material is usually used?
any is the usual choice, supplied against AS9102 or the customer's own format.
How is the result verified?
Every drawing feature, on calibrated equipment, with the results recorded so a repeat order can be compared with the first.
What is the most common mistake?
Measuring a part that is still warm from the machine.
How long does it take and what does it cost?
A realistic cycle is 1 to 3 hours for a complex part, and the cost driver is the inspection time, which is small next to a scrapped batch.
Related capability
If you are specifying First Article Inspection on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.
Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.
Related entries
These entries sit next to First Article Inspection in the encyclopedia: ISO 2768 General Tolerances, EN 10204 Material Certificates, Reaming and Boring. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
