In CNC machining, stability and consistency of product quality are key to winning customer trust.
Whether in aerospace, medical devices, or semiconductors, even the smallest error in part precision is unacceptable.
FAI (First Article Inspection) and SPC (Statistical Process Control) are two critical methods to ensure machining accuracy and batch consistency.
FAI serves as the first gate before mass production, ensuring the process starts correctly and remains stable. SPC continuously monitors production to maintain that stability.
How can CNCFirst help you?
As a manufacturer with over 10 years of experience in high-precision CNC machining, we are equipped with advanced CNC machines and complete inspection instruments. We have also built long-term partnerships with customers in industries with strict standards.
This article will focus on FAI.
From its definition and importance to its implementation process, we will give a detailed explanation of this essential quality control step.
What is First Article Inspection (FAI) in CNC Machining?
You may wonder: isn’t FAI just about measuring part dimensions?
Actually, it is much more. FAI is like a full health check before production.
It not only confirms that part dimensions meet drawings, but also verifies machine status, tool offsets, program paths, fixture positioning, and every other step.
This ensures that mass production can run smoothly with qualified results.
FAI is required in cases such as
- New product is produced for the first time
- First-time production after major design or drawing changes
- Replacement of machines, tools, or fixtures
- Restarting production after long downtime
- Customer or industry standards explicitly require it
Why Perform FAI?
In one of our customer projects, a coordinate error occurred in a machining step of a complex copper part. If we had started mass production directly, we would have repeated the same mistake on over 100 parts and caused nearly 7,000 USD in losses.
FAI identifies and eliminates such risks at the very first part.
The value of FAI lies in:
- Preventing mass nonconformity
Detect and fix issues before they spread, reducing scrap and rework costs.
- Verifying manufacturability
Confirm CNC programs, tool offsets, and fixtures are stable and reliable.
- Building customer trust
Provide complete FAI reports as proof of quality commitment and professional capability.
- Supporting SPC
Use FAI data as the baseline for ongoing SPC monitoring.
The FAI Process: From Drawing to “Standard Sample”
FAI follows a standardized process, not just a one-time check.
Preparation
review drawings and 3D models, confirm technical requirements, create FAI plan, calibrate measuring tools.
First Part Machining
strictly follow process sheets and parameters; for complex parts, machining may involve multiple stages (rough, semi-finish, finish).
Comprehensive Inspection
full check of all dimensions, surface roughness, material certificates, heat treatment reports, functional tests (e.g., assembly, conductivity, air-tightness).
Evaluation & Correction
Customer Approval & Archiving
save full FAI reports, inspection data, and samples. Data also serves as SPC reference for mass production.
Tools & Equipment
A high-quality FAI relies on precise, traceable inspection equipment and standardized testing methods.
These tools not only verify part dimensions against drawings but also evaluate surface quality, geometric tolerances, and material conditions, ensuring the first article meets mass production standards.
Among all inspection equipment, the Coordinate Measuring Machine (CMM) is the most essential tool in FAI.
It can perform full 3D measurement of parts, covering key dimensions as well as form and position tolerances such as parallelism, perpendicularity, concentricity, and position.
During First Article Inspection, most critical measurement data comes from the CMM, making it the core data source for the FAI report.
The surface roughness tester is used to measure surface roughness parameters such as Ra and Rz.
Whether contact or non-contact type, it accurately reflects the impact of tool wear and cutting parameters on surface quality.
In industries like aerospace, medical, and semiconductors, surface roughness is a critical performance factor, which makes it an essential inspection item in FAI.
Height gauges, often used with granite surface plates, are applied to quickly measure part height, depth, and perpendicularity.
For parts with strict requirements on flatness or step height, the height gauge not only improves efficiency but also provides cross-checks against CMM results.
Calipers and micrometers, though basic, are also indispensable in FAI.
They are portable, fast, and cost-effective, suitable for preliminary checks during first article machining. This helps operators filter out obvious defects before formal inspection, saving time.
In certain FAI cases, additional tools are required, such as profilometers for complex contour accuracy, hardness testers for post-heat treatment hardness, and coating thickness gauges for surface coating or plating verification.
In practice, these devices are often used together.
This multi-device approach ensures accuracy while covering different dimensions of quality requirements, making FAI more reliable and comprehensive.
FAQ
1.Will FAI delay delivery?
It may add time at the beginning, but it reduces rework and makes the overall delivery schedule more reliable.
2. Does FAI require extra cost?
No. It is part of our standard quality system.
3. What if the first part fails?
We analyze the root cause, adjust the process, and redo FAI until it passes.
In CNC machining, FAI is not optional, but essential.
If you are looking for a partner who can guarantee both quality and delivery, we are ready to prove it with our experience, data, and real cases.
Send us your drawings or samples today. We will provide a free process evaluation and the best machining solution.
