First Article Inspection for Deep Hole Drilling Processes

A deep hole drilling job for a new hydraulic cylinder application produces 50 bores that all pass diameter inspection — then the customer reports that the cylinders leak at 50 bar operating pressure. Investigation reveals that the first article inspection measured diameter at the bore entry and exit only, missing the 0.02 mm bell-mouth at mid-length caused by a worn guide bushing. The FAI was incomplete — it verified diameter at two positions but did not verify roundness, straightness, or surface finish along the full bore length. A proper FAI performed at setup with measurement at 5 positions along the bore, roundness measurement, and surface finish verification would have caught the guide bushing problem before the first 50 cylinders were produced.

FAI Requirements and Implementation ​

FAI Trigger Events for Deep Hole Drilling ​

FAI Measurement Points for Deep Hole Bores ​

FAQ ​

When is a full first article inspection required for deep hole drilling? ​

A full first article inspection is required when introducing a completely new deep hole drilling process that has not been previously qualified. Specific trigger events include: a new workpiece design (new bore size, new tolerance, new material, new surface finish requirement), a new drilling method (switching from gun drilling to BTA, or from BTA to ejector drilling), a new machine tool (new BTA drilling machine, new gun drilling machine, or a machine that has been relocated and re-installed), a new drill head design or tooling system, and a new workpiece material that requires different cutting parameters. A full FAI includes: dimensional verification of all drawing characteristics (diameter, roundness, straightness, surface finish, and any secondary features such as counterbores, chamfers, or threads), process parameter verification (coolant pressure, flow rate, feed rate, cutting speed, coolant concentration and temperature are documented for each setup), machine alignment verification (spindle runout, guide bushing alignment, tube support alignment, fixture alignment), material certification (workpiece material heat number and properties are verified against the drawing specifications), and capability study (initial process capability — Cp and Cpk — is calculated from the first 25–50 production parts). The full FAI must be completed and approved before production parts can be shipped to the customer.

How many parts should be included in an FAI for deep hole drilling? ​

The number of parts included in an FAI for deep hole drilling depends on the process maturity and the criticality of the application. For a new process FAI (no prior data on this specific setup), a minimum of 3 consecutive production parts should be fully measured — this provides initial data on part-to-part variation and confirms the process is stable enough to produce conforming parts. For the PPAP (Production Part Approval Process) used in automotive deep hole drilling, the standard requirement is 300 consecutive parts for initial capability studies, with the first 3 parts undergoing full dimensional layout. For aerospace FAI per AS9102, a minimum of 1 part must undergo full dimensional inspection, but 3 parts are recommended to establish variation baseline. For process change FAIs (tooling change, parameter change, or material change), a minimum of 3 parts should be measured — the results are compared to the original baseline FAI data to verify the change has not adversely affected bore quality. The measurement includes: every dimension on the drawing (for the full FAI), characteristics are measured at the specified frequency (every part for diameter, every 3rd part for roundness and surface finish, every 10th part for full geometry including straightness and cylindricity), and all measurement data is recorded with the specific measurement values, not just pass/fail.

What process parameters should be documented during FAI for deep hole drilling? ​

The process parameters documented during FAI for deep hole drilling provide the baseline for all future production and troubleshooting. Essential parameters to document: cutting parameters (spindle speed in RPM or cutting speed in m/min, feed rate in mm/rev or mm/min, depth of cut per pass or stock removal in mm), coolant system parameters (coolant pressure at pump in bar, coolant pressure at drill head in bar, coolant flow rate in L/min, coolant temperature at tank in °C, coolant concentration in % for water-miscible coolants, coolant type and manufacturer, and filtration rating in microns), tooling parameters (drill head type and serial number, insert grade and geometry, guide pad material and diameter, tool overhang in mm, guide bushing diameter and condition), machine parameters (spindle runout at collet nose in mm, guide bushing alignment relative to spindle axis, machine alignment — level and squareness of axes), and workpiece parameters (material grade and heat number, workpiece hardness (if applicable), workpiece length and starting diameter, and clamping method and location). These parameters form the baseline for the process — any future deviation from these parameters that occurs during production should trigger an investigation and possibly a new FAI. The FAI process parameter documentation should be maintained as a controlled document alongside the dimensional inspection report.

How does FAI for deep hole drilling differ from production inspection? ​

FAI and production inspection serve different purposes and have different scopes. FAI is a comprehensive, one-time verification performed when a new process is introduced or an existing process is changed — it verifies every dimension and characteristic on the drawing, documents all process parameters, and establishes the process baseline. Production inspection is the ongoing verification performed on every part or on a sampling basis during production — it typically measures only the critical-to-quality characteristics (usually diameter at one or two positions) rather than every drawing characteristic. For deep hole drilling, the differences are significant: FAI measures diameter at 3–5 positions along the bore (entry, mid-length, exit, and intermediate points) to detect taper and bell-mouth — production inspection typically measures at 1–2 positions. FAI includes roundness and straightness measurement — production inspection typically does not. FAI documents all process parameters (coolant pressure, flow, temperature, concentration, machine settings) — production inspection typically records only a subset. FAI includes destructive testing if required (metallurgical analysis, sectioning for bore condition verification) — production inspection is non-destructive. The FAI establishes the measurement plan for production inspection: the FAI results identify which characteristics are critical and which positions along the bore are the most sensitive to process variation, allowing production inspection to focus on the positions that best detect process drift.

What documentation is required for a deep hole drilling FAI? ​

The documentation required for a deep hole drilling FAI follows industry standards (AS9102 for aerospace, AIAG PPAP for automotive) with the addition of deep hole drilling-specific documentation. Core documentation: dimensional report (all drawing characteristics with measured values, measurement method, and pass/fail determination), material certification (workpiece material test report verifying chemical composition and mechanical properties), process parameter log (all machine settings, coolant parameters, and tooling parameters documented at the time of FAI production), tooling certification (drill head certification, insert grade verification, guide bushing diameter verification), machine alignment report (spindle runout, guide bushing alignment, machine level and squareness), capability study (for production FAIs — Cp, Cpk, and Ppk calculated from 25–50 parts — showing that the process is capable of meeting the tolerance), and inspection equipment certification (calibration certificates for all gauges and instruments used in the FAI). For deep hole drilling specifically, the FAI documentation should also include: chip morphology documentation (photographs of representative chips from the FAI run — chip size and shape confirms correct cutting parameters), coolant condition report (concentration, pH, temperature, tramp oil content, and bacterial count), and bore condition documentation (photographs of bore entry and exit if visible, surface finish traces from entry, mid-length, and exit positions). All FAI documentation must be reviewed and approved by quality engineering, recorded with a unique FAI number, and retained for the life of the production program or as specified by customer requirements.

Disclaimer: The FAI guidelines and documentation requirements provided in this article are general guidelines based on industry-standard practices (AS9102, AIAG PPAP). Specific FAI requirements vary by industry, customer, and application. FAI procedures must be developed in accordance with applicable quality system standards (ISO 9001, AS9100, IATF 16949) and customer-specific requirements. The authors and publisher assume no liability for any damages or losses arising from the use of this information — always follow applicable standards and customer-specific requirements. Content is for informational purposes only and does not constitute professional engineering advice. Verify all parameters with qualified personnel before implementation as of 2026.