Quality control checks: a QC sheet is a decision

A QC sheet is worth the paper only if it can stop something. If a failed check leaves the batch moving, the sheet is a record of a decision nobody made, and the defect reaches the customer with a signature beside it. What separates a working control sheet from a form is not the number of fields but the ten minutes that follow somebody writing "fail".

What should a check actually measure?

Not everything that can be measured — the few characteristics where three conditions hold at once: the customer would notice the defect, the value can be read while the batch is still fixable, and the limit and the method are written down.

A check without a limit is an observation. "Check the seal" is not a check; "seal intact, no tear longer than the width of the tape, checked by hand at the end of the line" is. Two operators told to check the colour against nothing will disagree, and both will be right.

Is a check worth doing on every unit or every batch?

It depends on the cost of the defect that gets through. Full inspection belongs where a single bad unit is expensive or dangerous and the defect is invisible; sampling belongs where the process is stable and the fault shows up in the batch, not in one unit. Most lines need a third thing more than either: a check tied to a change — a new material lot, a tool change, a restart, the first unit of a shift. That first unit says more about the next hour than the tenth unit of the previous one.

What happens in the ten minutes after a fail?

A fail is only a decision if four things happen, and they happen in this order.

Stop or hold — the batch does not continue while somebody thinks about it. Quarantine physically: a marked area or a cage, not "over there by the wall", because a held batch that looks like stock will be picked. Mark the units and the batch in the system, so the hold travels with the record and not only with the pallet. Then dispose — scrap, rework, concession, return to supplier — with a reason and a name against it, and only then restart.

A held batch with no disposition is an open loop, and open loops close themselves in the direction of shipping.

Who signs, and what does a signature mean?

A signature means an identity and a statement: this person verified these values at this time. Anything that weakens either half weakens the sheet.

So a shared stamp is not a signature, a supervisor signing a stack at the end of the week is not a signature, and a sheet filled in before the work is done is a signature on a prediction. Signing in advance is rarely dishonesty — it is what a form invites when the only step within reach is the signature.

On a screen the equivalent is the user account, the timestamp and the values, stored on the record. A scanned signature image pasted into a template is decoration.

Should the check live on paper or on a screen?

On a screen where the value has to be compared with a limit, because the screen can refuse an impossible value and can stop the next step. On paper where the environment destroys devices — wet, dusty, hot, flour in the air — but then the paper enters the system during the same shift, already carrying the operator's identity.

Paper typed in a week later answers a question about the past, and the batch it describes left the building on Tuesday.

How do you know a check is really being done?

Three cheap tests. Look at the spread of the values: a real measurement varies, and a column of identical readings is a copied number. Ask for the same measurement twice on different days and compare. And keep a small physical sample — a retained unit, a photograph whose file name carries the time — because a number can be typed and a unit cannot be argued with. None of this proves a check was never skipped, but it makes skipping harder to hide.

The check	What it protects	Who signs it
Incoming material	A defect you cannot fix later	Receiving, against the delivery note
First unit of a run	The next few hours of output	The operator who set the machine
In-process	A drift before it becomes scrap	The line, once per shift
Final release	The customer, and the argument after	One named role, not the shift

How does the sheet connect to the batch?

The sheet carries the batch or lot, the machine, the operator, the shift and the material lot — before its first measurement field, not in a footer. Without the batch reference a complaint arrives with a date and a product, and the four hours of searching that follow are the real cost of a sheet designed as a diary.

The order to do this in

1. Start from the failures that reached a customer — complaints, returns, rework — and leave alone the failures you find interesting.
2. For each, name the characteristic, the limit, the method, and the point where the value is still fixable.
3. Write the fail path as a procedure: hold, quarantine, mark, dispose, restart.
4. Name one role allowed to release a held batch, and one person allowed to grant a concession.
5. Put the batch, machine, operator and material lot at the top of the sheet.
6. Delete every field nobody has used for a year, and every yes/no box with no value beside it.
7. Test it: put a failing unit into the flow and watch the next hour, without telling the supervisor.
8. Review the sheet against the complaints every quarter, and remove what the review cannot justify.

Where this goes wrong

• The sheet is complete at eight in the morning. The shift is signed for before it happened.
• Everything passes and the customer still complains. The checks measure what is easy to measure, not what fails.
• Rework with no reason. The unit returns to the flow and nobody knows what was wrong with it.
• The concession is the normal route. A concession granted every week is a specification that is wrong, written as an exception.
• The hold is on paper only. The pallet is still in the flow because the quarantine area is full of empty cartons.

What this does not cover

This is about the control step inside your own process, not about which standard, certification or customer requirement applies — those come from your customer or a regulator, and we implement what they state. It does not cover laboratory analysis or destructive testing. And a sheet cannot make an incapable process capable: it records what happened, and a process that fails half its checks needs engineering, not a longer form.

We build the check into the flow: a value against a limit, a hold that actually stops the batch, a signature that resolves to a person, and a history you can walk back from a complaint.