Inspection instructions: writing a check somebody else can perform identically

The five things a reader needs and rarely gets

Which characteristic is being checked and where on the part it sits, shown on an image rather than described. Which gauge, identified specifically rather than by category. How the part is presented: which face down, in what fixture, cleaned or as-produced, at what temperature if it matters. How many pieces and drawn from where. And what to do with the result, including the failure route. Instructions typically cover the first and the fourth and leave the rest to the reader, which is why two stations checking the same feature produce different reject rates and nobody can explain it.

Ambiguity hides in presentation, not in the tolerance

Disagreements between inspectors are seldom about arithmetic. They arise because one person clamped the part and another let it rest, one wiped the surface and another did not, one measured at the end of the feature and another in the middle, one waited for the component to reach room temperature and another measured it warm off the machine. None of these feel like decisions to the person making them. Writing them down converts a tacit skill into something transferable, and it is the single change most likely to reduce variation attributable to the measurement rather than to the part.

Pictures beat prose at the machine

Documents read while standing, wearing gloves, under poor light and against a cycle time are not read the way an office document is. A photograph of the correct setup, an arrow to the feature, and an image of an acceptable and unacceptable example convey more than a page of careful wording. Keep the text to short imperative lines and put anything explanatory somewhere else. If the instruction has to be laminated and hung at the station, its length is constrained by that reality, which is a healthy discipline rather than a limitation.

Instructions age when equipment changes and nobody tells the author

The gauge named in the document gets replaced, a fixture is modified, the part moves to a different cell, a bench is reorganised and the reference samples end up in a drawer. Each change silently invalidates part of the instruction while the document continues to be followed, so the operator improvises and the improvisation becomes custom. Tie the document to the gauge register so that retiring a gauge flags every instruction that names it. That single link catches most of the decay, and it takes an afternoon to set up.

Test the instruction by watching somebody follow it

The simplest validation is to hand the document to a person who does not know the part and watch, without helping, where they hesitate. Every pause marks a gap. This takes half an hour, finds more than any review meeting, and has the additional benefit of producing a witness who can confirm the check was performable as written. Approving instructions from a desk, on the other hand, tends to produce documents that satisfy an auditor and confuse an operator, which is the wrong way round. Ask the volunteer afterwards what they were unsure about, since the hesitations they can articulate point straight at the wording to change.

Frequently asked questions

How detailed does an inspection instruction need to be for an experienced inspector?

Detailed enough for the person who covers when they are absent. Experience lets people fill gaps correctly, which is exactly why gaps survive undetected for years and then produce inconsistent results the moment somebody new arrives. The pragmatic test is whether the document specifies how the part is presented and which gauge is used, since those are the elements experienced inspectors supply from habit and newcomers supply from guesswork.

Should inspection instructions be separate from the operator work instruction?

For self-checked characteristics, combining them works better, because the operator reads one document at one station and the check appears in sequence where it belongs. Keep separate documents where an independent inspector performs the work at a different bench, or where the check applies to several parts. What matters more than the split is that both documents cite the same gauge and the same method, since a divergence between them produces two different answers to the same question.

How do we keep instructions matched to the gauges actually in use?

Reference gauges by their register identity rather than by description, and link the register to the documents that name them, so withdrawing an instrument produces a list of affected instructions automatically. Add a check of that list to the periodic review of the control plan. Without the link, gauge changes are handled by whoever is at the bench, and the document quietly describes equipment that has not existed for a couple of years.