First-Article Inspection and Part Disposition

What Is a First-Article Inspection?

A first-article inspection (FAI) is a structured, documented measurement of every print-specified feature on the very first part produced from a new or revised setup. Its purpose is simple: confirm that the machine, tooling, fixturing, and program together produce a part that matches the engineering drawing before a full production run begins. Scrapping one first-off part costs far less than scrapping a batch or, worse, shipping non-conforming parts to a customer.

The FAI is not a spot-check. Every feature called out on the drawing must be measured, recorded, and dispositioned. The result is a completed FAI form that becomes a permanent quality record.

Reading the Drawing Before You Pick Up a Gage

Start at the title block. Confirm part number, revision level, material, and any general tolerance notes. Then walk the drawing feature by feature. For each feature, ask two questions: What is the nominal dimension and its tolerance? Which gage is capable of resolving that tolerance?

A rule of thumb used throughout the trade is the 10:1 gage-to-tolerance ratio: your measuring instrument should have a resolution and accuracy at least ten times finer than the tolerance band. A ±0.010 in tolerance allows a caliper; a ±0.001 in tolerance demands a micrometer or bore gage.

Selecting the Right Gage for Each Feature Type

| Feature | Recommended Gage |

|---|---|

| Outside diameter | Outside micrometer |

| Bore (internal diameter) | Telescoping gage + micrometer, or bore gage |

| Length / step | Digital calipers or micrometer |

| Surface finish (Ra) | Surface roughness comparator |

| Angular chamfer | Protractor or angle gage |

| Thread | GO/NO-GO thread gage |

GO/NO-GO thread gages work on the Taylor Principle. The GO member checks that the full thread form fits (pitch diameter, lead, and flank angle all within limits). The NO-GO member checks that the pitch diameter is not beyond the maximum-material limit. A conforming thread accepts the GO ring and rejects the NO-GO ring. If the GO ring will not enter, the thread is undersize or damaged. If the NO-GO ring enters fully, the thread is oversized and the part is non-conforming.

Measuring Bores Safely and Accurately

A telescoping gage transfers the bore diameter to a micrometer for the actual reading. Compress the plungers, insert the gage at a slight angle, allow it to expand to the bore wall, then tilt it to the bore axis while locking the plunger. Remove and measure across the plunger heads with the matching outside micrometer. Take at least two readings 90° apart to detect out-of-round conditions. A bore gage with a dial or digital indicator is faster and reads directly but must be calibrated to a ring gage or micrometer setting before use.

Completing the FAI Form

For every feature, the form captures:

• Feature description (e.g., "Ø0.750 OD")
• Nominal dimension
• Upper and lower limits
• Actual measured value
• In tolerance (Y/N)
• Disposition

Write every number you read — do not round toward the tolerance limit to make a borderline value look good. Falsifying inspection records is a serious professional and legal violation in regulated industries.

Making the Disposition

Three outcomes are possible for each out-of-tolerance feature:

1. Accept as-is — only valid with written engineering disposition (a deviation or waiver). You cannot unilaterally accept a non-conforming feature.

2. Rework — material can be removed or a feature corrected and brought into tolerance. A diameter that is 0.002 in oversize on an OD can be taken to size; a diameter that is 0.002 in undersize on an OD cannot be built back up without a process such as welding, which requires separate engineering approval.

3. Scrap — the feature cannot be corrected. Record the specific reason (e.g., "bore 0.005 in undersize, no material to remove").

The disposition must be based on measured evidence recorded on the form — not on intuition, appearance, or what you expect the machine to have done.

Safety in the Inspection Area

• Deburr parts before handling. Sharp edges and chips cause lacerations; wear cut-resistant gloves when carrying freshly machined parts to the inspection station.
• Cleaning fluid and coolant residue on parts can be slippery and irritating; use a lint-free cloth and approved part-washing solvent in a ventilated area; consult the SDS for the solvent in use.
• Gage handling: Micrometers and bore gages are precision instruments; dropping them on the concrete floor alters calibration. Store in cases when not in use.
• Lockout/tagout is not required at the inspection bench, but if you must return to the machine to make an adjustment after the FAI reveals an out-of-tolerance feature, full LOTO procedures apply before touching any machine component.

Comparing to the CMM Report

A coordinate measuring machine (CMM) is a reference-grade instrument. Your hand-gage measurements will be compared to CMM values at the end of this lab. Differences larger than ±0.001 in on the same feature point to a technique error, a gage that needs calibration, or a gage that is under-qualified for that tolerance. Use the comparison as a learning tool, not a shortcut — the CMM report is instructor reference only during this exercise.