WHAT IT PROVES · WHO PERFORMS IT · WHAT TRAVELS WITH THE PART
A first article is a question with a measured answer.
PROBED IN THE MACHINE · PROVEN OFF IT · EVERY CRITICAL FEATURE HAS A NUMBER
WHAT IS A FIRST ARTICLE INSPECTION, WHO PERFORMS IT, AND WHAT TRAVELS WITH THE PART?
A first article inspection is the proof that the first part made by a process matches the print, feature by feature, before any more are made to it. The shop that made the part performs it, on its own instruments, and the numbers travel with the part so the customer can check them again on theirs.
By Cyclone Machining Co.Updated
◆01·WHAT IT IS
A question with a measured answer.
The question is whether the program, the setup, the tooling and the instruments, working together for the first time, produced what the print asked for. The answer is a number for every critical feature, set beside the print's own requirement, with the instrument that took it named. That is the whole of it. A first article is not a sample looked over by an experienced eye, and it is not a certificate. It is a measured record of one part, taken at the moment the process was proven.
It proves the process as it ran. What it settles, before a second part is cut, is that the datum scheme was read correctly, that the fixture holds what the print assumes, that every tool is the length and diameter the program believes it is, and that the tolerances on the print are the tolerances in the metal.
It is not the same thing as a production part approval package. The inspection proves the first part matches the print; the package is the larger set of documents a customer's own quality system may ask for around it, and the inspection sits inside it as one of its parts. Here the first article is the job itself, whatever the quantity.
◆02·WHEN
When a first article is due.
A new part is the obvious case. The others matter as much: a new revision of a part already made, because the changed feature has never been cut on this setup; a move to a different machine or fixture, because the datum is now held by something new; a new material lot on a part where the material is on the print; and a long gap since the last run, because tooling and holders drift and nobody's setup notes are as good as they remember.
A revision is not a restart. The fixture, the datum scheme and the program from the last run stay with the job, so a revised feature is inspected as a change against a proven process rather than as a new job from nothing. The old part and the new print are read together, which is how a revision that quietly moved a datum gets caught before the cut.
When the quantity is one, the first article is the job. A one-off prototype, a development fixture, a replacement machined from the broken original: each is a first article by definition and is inspected as one. A single part leaves with the same numbers a first-of-fifty leaves with.
◆03·WHO
Who performs it, and why that is the right answer.
The shop that made the part performs the first article inspection, on the instruments it holds. The customer's receiving inspection then checks the part again on theirs. Two independent measurements that agree are the proof; one measurement, however careful, is a claim. That is why each number names its instrument: the customer can see what was used and choose what to repeat.
Which features count as critical is settled with the customer when the print arrives and before the setup is planned, so the probe cycle and the off-machine check are built around them instead of finding them at the end. Nothing ships until the part is inspected and approved.
No third party is involved unless the customer's own system requires one. If it does, say so with the order, and the part is held for it.
◆04·WHERE
Before the cut. In the cycle. Off the machine.
The first gate is before the cut. Every tool goes across the optical pre-setter before it touches material, so the length and diameter in the program are the length and diameter in the spindle. A tool set by hand and trusted is the fastest route to a first article that fails on a depth or a wall.
The second gate is in the cycle. The part is probed while it is still clamped, against the same datum it is being cut from. A feature that will carry other features is measured before those features are cut, so a tolerance stack is checked mid-operation rather than discovered at the end. While the part is still in its setup with stock left to take, a feature that reads out is corrected and cut again.
The third gate is off the machine. Size is taken at the bench with the micrometer and the caliper; location, flatness, hole pattern and step heights go to the CMM, where a touch probe is brought to the part by hand, point by point, and read against the print. An in-machine probe shares the machine's own axes and the bench instruments do not, so agreement between the two readings is what a first article stands on.
One setup makes all of it cleaner. When a part is clamped once and every face is reached from one datum, every feature is measured from the origin it was cut from. Each time a part is unclamped and re-clamped the datum can move and the error accumulates, and a first article on a part that visited four setups is an argument about which setup moved. Five-axis work exists here largely to end that argument.
◆The three gates a first article passes
BEFORE THE CUT
Every tool goes across the pre-setter, so the length and diameter in the program are the ones in the spindle.
IN THE CYCLE
The part is probed while it is still clamped, against the same datum it is being cut from.
OFF THE MACHINE
The bench and the CMM read it again on instruments that share nothing with the machine.
◆05·WHAT FAILS ONE
Decided before the cut, almost every time.
The usual causes of a failed first article are worth naming, because most of them are reading errors rather than machining errors. A feature measured from the wrong datum. A thread checked with a gauge of the wrong class. A surface finish nobody agreed in words. A part made to one revision and inspected to another. A tolerance read from the title block when the feature carried its own.
Each of those is caught by reading the print twice: once to quote it, once to plan the inspection before the program is written. The number written against a feature is the one that was measured, never the one that was expected, and a feature that cannot be brought to the print is raised with the customer before anything else happens rather than discovered in the box.
To prepare for one, send the print revision the part will be inspected to, the datum scheme if the print leaves it open, and a note on which features you consider critical. That is enough. The rest is the shop's job.
◆06·THE BOX
What arrives with the part.
The part, inspected and approved, and the print it was made to, with the revision noted. The measured numbers for the critical features, each set against its requirement, each with its instrument.
The setup and the program stay with the job. When part two is ordered, or a revision arrives, the process starts from what was proven rather than from zero, and the second first article is a comparison rather than a discovery: part two differs from part one where the drawing changed and nowhere else.
THE QUESTIONS PEOPLE ACTUALLY TYPE
Asked before the print is ever sent.
8 answers. Each one answered the way it is asked, before the print is sent anywhere.
What is a first article inspection?
The measured proof that the first part made by a process matches the print, feature by feature, before any more are made to it. Every critical feature gets a measured value and the instrument that took it.
Who performs the first article inspection?
The shop that made the part, on the instruments it holds; the customer's receiving inspection then checks it again on theirs. Two independent measurements that agree are the proof.
How is it different from a production part approval package?
The inspection proves the first part matches the print. The package is the larger document set a customer's quality system may ask for around it, and the inspection is one of its parts.
What is checked in the machine, and what after?
Critical features are probed in the cycle while the part is still clamped. Off the machine, size is checked at the bench and location, flatness and hole pattern go to the CMM, so the features that matter most are read twice.
Does an aerospace or medical quality system require one?
Most require one on a new part, a new revision and a change of process. Say what your system needs when you send the print, and the inspection is planned around it from the start.
What will fail a first article?
Usually a reading error made before the cut: the wrong datum, the wrong gauge class, a finish nobody agreed in words, or a part made to one revision and inspected to another.
How do I prepare for one?
Send the print revision the part will be inspected to, the datum scheme if the print leaves it open, and a note on the features you consider critical.
What arrives with the part?
The part, inspected and approved; the print it was made to, revision noted; and the measured numbers for the critical features. The setup and the program stay with the job for part two.
Sources
They support the general facts. The shop practice is its own.
- First article inspection, the general referenceHow the practice is defined and where it is used.
- The coordinate measuring machine, explainedThe instrument that turns a feature into a number.
Send the print, and say which features decide it.
A first article here is the job, not a stage at the end of it. Send the print with the revision it will be inspected to, mark what matters, and the probe cycle and the off-machine check are planned around those features before the program is written.