On a CNC floor, the first part after a setup is a test. Until it is measured and approved, every part made after it is a gamble — so the machine waits.
When it happens
First-piece inspection is triggered by anything that could change the part:
- A new setup or changeover to a different part
- A tool change on a critical feature, or new inserts
- A program edit or offset correction
- The start of a shift, in many plants, even with no change
What gets checked
Usually the critical dimensions on the drawing, surface finish and any visible defects — enough to prove the setup is right, not a full report. If the part fails, the setup or offset is corrected and another first piece is made and checked; the batch starts only after one passes. A simple record keeps it traceable:
Part / program
- Example (illustrative)
- Flange 40-112, O1234
Reason for check
- Example (illustrative)
- New setup
Dimensions checked
- Example (illustrative)
- Bore Ø40 H7, OD Ø112, face runout
Result
- Example (illustrative)
- Bore +0.02 over — offset corrected, second piece OK
Approved by / time
- Example (illustrative)
- QC, 10:42
| Field | Example (illustrative) |
|---|---|
| Part / program | Flange 40-112, O1234 |
| Reason for check | New setup |
| Dimensions checked | Bore Ø40 H7, OD Ø112, face runout |
| Result | Bore +0.02 over — offset corrected, second piece OK |
| Approved by / time | QC, 10:42 |
First-piece vs first article inspection
The two are often mixed up. First-piece inspection is routine and repeats after every setup. First article inspection (FAI) is a formal, documented check of every drawing requirement, usually done once for a new part or a design change and often sent to the customer.
Counting the time it takes
The inspection itself may take five minutes; the wait for someone to do it can take much longer. If that time is lumped into “idle”, nobody sees it. If it is recorded as its own planned stop, the real cost of approval per setup becomes visible — and so do the shifts where the machine sat waiting for quality.
ThingConnect includes first-piece inspection as a default stop reason, treated as a planned stop, so operators can tag that wait at the machine. It then shows up as its own line in the downtime report, separate from breakdowns and from setup time.