Guides / Process

Inspecting a 5-Axis Part: Probing, CMM and First Article

September 26, 2026

A 5-axis part earns its complexity in the geometry, which is exactly where an inspection can miss something a simple part would never hide. Knowing what a shop actually checks, and when, helps you ask for the right level of proof without paying for more than the part needs.

In-process probing

Most 5-axis machines carry a touch probe that checks a feature right after it is cut, before the part moves or is unclamped. This catches an out-of-tolerance feature while it can still be corrected on that setup, rather than after the part is off the machine and the fixture is gone. It is fast and built into the cycle, but it only checks what the program tells it to check.

CMM: the independent check

A coordinate measuring machine checks the finished part on a separate system, off the machine that made it. This catches errors the in-process probe would not, including anything affected by the part relaxing after it comes off the fixture. A CMM report gives a feature-by-feature list of measured values against the drawing, which is what most buyers mean when they ask for “dimensional data” on a quote.

First Article Inspection

A First Article Inspection, or FAI, is a complete dimensional check of the first part from a new job or a new setup, documented feature by feature against the drawing. Aerospace and defense buyers often require it in a specific format, most commonly AS9102. Outside those industries, an FAI report is still useful proof that a shop verified the part properly before running the rest of the order, and it is worth asking for on any first order from a new supplier.

What actually gets measured

A dimensional report does not check every dimension on the drawing by default. It typically covers critical features called out with tight tolerance or GD&T, mating and sealing surfaces, and anything the buyer specifically flags. General dimensions with a loose tolerance are usually spot-checked rather than measured on every part. State on the RFQ which features matter most if the standard set does not cover them.

What to put on your RFQ

Say plainly whether you need a CMM report, an FAI report or neither, and whether that applies to the first piece only or to the full order. If you need a specific format, AS9102 or otherwise, name it. Leaving this unstated usually means you get whatever the shop does by default, which may be less than what your program actually requires.

The short version

In-process probing catches problems while the part is still on the machine. A CMM report is the independent check most buyers actually want. An FAI is a full record of the first part, not a routine step on every job. State what you need on the RFQ rather than assuming it is included.

The full path from drawing to accepted parts is in our 5-axis quality checklist.

See also: 3D scanning, CMM and probing compared for complex surfaces.

Frequently asked questions

Keep reading

• Thermal Growth on 5-Axis Machines and How Shops Control It
• Collision Checking and Machine Simulation Before a 5-Axis Run