First Article Inspection Guide for Deep Hole Drilled Parts

First article inspection (FAI) is the formal verification that a manufacturing process produces parts meeting all engineering requirements. For deep hole drilled components — where a 0.05 mm diameter error at depth can scrap a part worth thousands of dollars — a thorough FAI is both a customer requirement and a process validation tool.

What Is First Article Inspection? ​

First article inspection is the complete dimensional and material verification of the first production part from a new or changed manufacturing process. It answers a single question: does the process produce conforming parts?

The FAI is governed by AS9102 in aerospace and by customer-specific requirements in other industries. It applies when:

• A new part is introduced to production
• A design change affects form, fit, or function
• A material or source changes
• Manufacturing process, tooling, or location changes
• Production has been stopped for more than two years

For deep hole drilling, the FAI is particularly critical because the bore is invisible during the cutting process. Defects are only discovered after the part is complete, making process validation before full production essential.

AS9102 Documentation Requirements ​

The AS9102 standard defines three forms that constitute the First Article Inspection Report (FAIR).

Form 1: Part Number Accountability ​

Form 1 identifies the part, its revision level, the manufacturing location, and the reason for the FAI.

Form 2: Product Accountability ​

Form 2 documents all materials, special processes, and functional testing requirements.

For deep hole drilled parts, special processes may include:

• Material certification and traceability
• Hardness verification
• Non-destructive testing (ultrasonic, magnetic particle, penetrant inspection)
• Surface treatment (if specified)

Form 3: Characteristic Accountability ​

Form 3 is the dimensional inspection record. Each characteristic on the engineering drawing is assigned a numbered balloon, and the corresponding measurement is recorded in Form 3.

For a deep hole drilled part, typical characteristics include:

Step-by-Step FAI Process ​

Step 1: Pre-Planning ​

Before any cutting begins:

1. Review the engineering drawing. Identify all dimensions, tolerances, notes, and specifications.
2. Balloon the drawing. Assign a unique numbered balloon to each characteristic. Use a consistent system — typically clockwise from the top-left view.
3. Identify critical-to-quality (CTQ) characteristics. These require special attention and sometimes 100% inspection.
4. Select measurement methods. Verify that your inspection equipment can reach and measure each characteristic.
5. Prepare Form 1 with part number, BOM, and supplier information.
6. Prepare Form 2 with material and special process requirements.

For deep hole drilled parts, pay special attention to characteristics that are difficult to measure at depth — particularly straightness and diameter at full depth. Ensure your inspection plan addresses these before production begins.

Step 2: Setup Verification ​

Before cutting the first article:

• [ ] Machine warm-up cycle completed and verified
• [ ] Spindle runout measured: ____ mm TIR (max ____ mm)
• [ ] Guide bushing ID verified: ____ mm
• [ ] Tool diameter measured: ____ mm
• [ ] Coolant pressure and flow at specification
• [ ] Workpiece material verified against print
• [ ] Workpiece hardness verified
• [ ] All inspection equipment calibrated and within date
• [ ] Inspection method for each characteristic confirmed

Step 3: Machine the First Article ​

The first article must be produced under production conditions:

• Use production-intent tooling (not prototype tooling)
• Use production parameters (speed, feed, coolant pressure)
• Use the same machine that will run production
• Use the same operator skill level

This is not the setup trial. If you are still dialing in parameters, those parts do not qualify as first articles. The FAI part is the first part produced after the process is confirmed ready.

Step 4: Dimensional Inspection ​

Perform complete dimensional inspection per the ballooned drawing.

Bore Diameter Measurement ​

For deep holes, measure diameter at three locations:

• Entry: within 1× diameter of the opening
• Mid-depth: at approximately 50% of hole depth
• Full depth: within 1× diameter of the bottom (blind hole) or exit (through hole)

At each location, measure in two axes (0° and 90°) to capture ovality.

Surface Finish Measurement ​

For deep holes where a profilometer cannot reach full depth, replica methods are commonly used. Apply a two-part silicone impression compound to the bore surface, allow it to cure, and measure the replica with a standard profilometer.

Straightness Measurement ​

For holes exceeding 1 m depth, laser-based methods are the only practical option. The laser autocollimation method uses a laser source aligned to the bore axis, a probe with feelers that contact the bore wall, and a CCD camera that detects the probe position. The system scans the full bore length and calculates straightness as the diameter of the smallest cylinder enclosing the measured axis center points.

Step 5: Material and Process Verification ​

Collect and attach:

• Material certificate of conformance (COC) with heat lot traceability
• Hardness test report
• Special process certifications (if applicable)
• NDT reports (if required)

Step 6: Compile the FAIR ​

Assemble the complete first article inspection report:

1. AS9102 Form 1 — Part Number Accountability (signed and approved)
2. AS9102 Form 2 — Product Accountability (materials and processes)
3. AS9102 Form 3 — Characteristic Accountability (measurement results)
4. Ballooned drawing or CAD model
5. Supporting documentation (material certs, process reports, calibration certs)

Step 7: Review and Submit ​

• Verify all characteristics are recorded with actual measured values (not just "pass" or "OK")
• Confirm non-conformances are documented with NCR numbers
• Have the reviewer and approver sign Form 1 (must be different individuals)
• Submit to the customer or prime contractor per their requirements

Deep-Hole-Specific Inspection Challenges ​

Challenge 1: Access at Depth ​

Standard inspection tools have limited reach. Bore gauges require extension rods that flex under their own weight in deep holes, introducing measurement error.

Solution: Use air gauges for small diameters (non-contact, compact) or laser-based systems for large diameters. Calibrate the measurement chain including extension rods.

Challenge 2: Thermal Effects ​

The part temperature may differ from the inspection laboratory temperature. A 1°C temperature change in a 1,000 mm steel part produces 0.012 mm of thermal expansion.

Solution: Allow the part to stabilize in the inspection environment for a minimum of 2 hours before final measurement. Record the temperature at the time of inspection.

Challenge 3: Surface Finish at Depth ​

Stylus profilometers have limited reach. Moving the part to a profilometer with sufficient reach may not be practical for large components.

Solution: Use replica compounds for deep bore surfaces. Validate the replica method against direct measurements on the first few parts.

Challenge 4: Straightness Quantification ​

Straightness is a 3D characteristic — the axis of the hole must be within a cylindrical tolerance zone. Simple two-point measurements cannot capture this.

Solution: Use a laser-based system that scans the full bore length and computes the 3D axis deviation. Report straightness as the maximum deviation from the reference axis.

Common FAI Mistakes ​

FAI for Different Deep Hole Drilling Processes ​

Gundrilled Parts (small diameter, high L/D) ​

BTA Drilled Parts (medium to large diameter) ​

Trepanned Parts (very large diameter) ​

FAI Equipment Checklist ​

Essential equipment for deep hole drilling first article inspection:

• [ ] Bore gauge set with appropriate range and extension rods
• [ ] Air gauge / air plug for small diameter bores (if applicable)
• [ ] Surface roughness profilometer (contact) with extension capability
• [ ] Replica compound for deep surface finish measurement
• [ ] Laser-based straightness measurement system (for holes > 500 mm depth)
• [ ] Depth gauge or height gauge
• [ ] Dial indicators and magnetic stand for runout measurement
• [ ] CMM access (for complex geometries or verification)
• [ } Hardness tester
• [ ] Temperature measurement (thermometer or thermocouple for part and environment)
• [ ] Drawing and ballooning supplies (marked-up print, colored pens for balloons)

FAQ ​

Q: Can a non-conforming part be used as a first article? Yes, if the non-conformance is documented with an NCR and the customer approves the deviation. However, the purpose of FAI is to demonstrate that the process produces conforming parts. A non-conforming FAI should trigger root cause analysis and process improvement before production release.

Q: How many parts are required for a first article inspection? AS9102 typically requires one part from the first production run. Some customers require multiple parts (3–5) for statistical capability assessment. Check your customer's specific requirements.

Q: Is a separate FAI required for each deep hole drilling machine? Yes. The FAI validates a specific process on a specific machine. If the same part runs on multiple machines, each machine requires its own FAI.

Q: Can I use on-machine measurement instead of removing the part for inspection? On-machine measurement (OMM) is increasingly accepted for deep hole inspection, particularly for straightness and diameter at depth. However, OMM must be correlated with off-machine measurement and the correlation verified. Many customers still require off-machine verification for critical characteristics.

Q: How long does a deep hole drilling FAI typically take? For a simple drilled hole (3–5 characteristics), allow 1–2 days including part cool-down, stabilization, and measurement. For complex parts with multiple features, extensive special processes, or long stabilization requirements, allow 3–5 business days.

Q: What is the difference between FAI and receiving inspection? Receiving inspection verifies that a received part meets purchase order requirements — typically a subset of characteristics. FAI is a complete verification of all engineering requirements. FAI is performed once per part-process combination; receiving inspection is performed on every shipment.

Q: Who can perform the FAI measurements? The measurements must be performed by a qualified inspector using calibrated equipment. The inspector should be independent of the production operator. Some customers require the inspector to have specific certifications (ASQ CQI, NADCAP, or customer-specific).

Q: What happens if the FAI reveals a non-conformance? Document the non-conformance on an NCR. Determine the root cause. Implement corrective action. Then produce a new first article incorporating the corrective action. The original non-conforming part cannot be resubmitted as the FAI part unless the customer specifically approves a use-as-is disposition.

Q: Is FAI required for rework or repair operations? Yes, if the rework or repair process is new or changed. An existing approved rework process does not require a new FAI unless a parameter changes.

Q: How should FAI records be stored? ASI recommend retaining FAIRs for the life of the product plus 10 years minimum. Store in a controlled digital repository with backup. Paper records must be scanned and indexed for retrieval. The FAIR must be retrievable within 24 hours during an audit.