The Temporary Yes: How Informal Concessions Rewrite a Precision Baseline

A concession note is one of the most useful instruments in precision manufacturing. It allows a part that misses a stated requirement to be accepted for a defined reason, avoiding scrap and keeping a programme moving. The difficulty begins after the note is signed. What was intended as a single, bounded decision can become the working definition of acceptable quality on the shop floor. The drawing still says one thing; the accumulated practice says another. For UK buyers of machined components, that gap is a procurement risk long before it becomes a quality escape.

The Difference Between a Concession and a Change

A concession is an exception. A drawing change is a decision. The two are often confused because both can end with a part being accepted. In practice, a concession should answer a narrow question: may this specific batch, or this specific quantity, be used despite a known deviation? A drawing change answers a different question: should the requirement itself be different from now on?

When buyers accept a concession without distinguishing between those questions, the supplier is left to infer. Repeated use-as-is approvals begin to look like permission. Operators and inspectors learn that a feature outside the nominal tolerance can still pass. Planning teams may start to quote and schedule on the assumption that the deviation is available. By the time the next purchase order is placed, the original non-conformance may be forgotten, but its commercial effect is not.

The risk is not that concessions exist. Precision work involves variation, and a sensible buyer will not treat every deviation as a reason to stop supply. The risk is that concessions are allowed to accumulate without a controlled route back to the specification. A temporary yes becomes a permanent expectation by default rather than by design.

Why Recurrence Hides in the Part Number

Most purchasing systems record concessions against a part number. That is useful for traceability, but it is a poor way to see a pattern. A single part number may carry several unrelated features, and the same underlying problem may appear across a family of parts with different numbers. If the register only counts concessions by part, the buyer sees isolated events rather than a recurring drift.

A more revealing approach is to track recurrence by feature. Is the same bore diameter repeatedly accepted at the lower limit? Is the same edge condition repeatedly waived? Is the same surface finish repeatedly passed after a supplementary polish? These are not part-number problems. They are process signals. A feature-level view shows whether the supplier is holding capability or whether the concession route is quietly absorbing a weakness in the manufacturing method.

For procurement teams, this distinction matters commercially. A recurring feature concession can affect tooling life, inspection time, assembly fit and warranty exposure. It can also distort the price comparison between suppliers. One supplier may appear competitive because it is not actually meeting the stated requirement; it is meeting a looser practice that the buyer has approved informally. The comparison is no longer like for like.

Four Controls for the Purchasing File

A concession can be kept temporary without turning procurement into a bureaucratic obstacle. Four controls are particularly effective when written into the purchasing file and applied consistently.

Time-limit the permission

Every concession should carry an expiry date or a defined quantity limit. The approval should state whether it covers one delivery, one batch or a specified number of parts. An open-ended concession is not a concession; it is an uncontrolled change to the acceptance baseline. The expiry should be recorded in the purchasing system so that renewal is a deliberate act, not a background assumption.

Require named design-authority sign-off

A concession that affects form, fit or function should not be approved by a commercial contact alone. The buyer should require a named individual within the design authority to sign, with the scope of their authority stated. A generic approval from a quality inbox may satisfy an audit trail, but it does not establish that the right technical owner made the decision. Named sign-off also makes renewal harder to grant casually, because the same person must review the accumulated history.

Track recurrence by feature

Build the concession register so that it can be filtered by feature as well as part number. Record the characteristic, the deviation, the quantity affected and the reason given. Then review the register at intervals, not only when a non-conformance is raised. If the same feature appears repeatedly, the buyer has evidence that the process, the drawing or the inspection method needs attention rather than another short-term approval.

Demand root-cause evidence before renewal

A renewal request should not be treated as an administrative extension. The supplier should provide evidence of root cause and of the action taken to prevent recurrence. That evidence need not be elaborate, but it should be specific to the feature and the process. If the same deviation is presented again without a credible explanation, the buyer should consider whether renewal is simply formalising a capability gap. In some cases the correct answer is a drawing change; in others it is a supplier development action or a change of process. Renewal should follow a decision, not replace one.

What the Buyer Should See at Renewal

When a concession comes back for renewal, the purchasing file should answer a short set of questions. What was the original non-conformance? Which feature or features were affected? What quantity has been accepted under the existing concession? What has changed in the process since approval? Who within the design authority now accepts the deviation, and for how long? If those questions cannot be answered without searching through email, the concession was never under control.

A useful discipline is to treat every renewal as a fresh decision with the history attached. That prevents the supplier from assuming continuity and prevents the buyer from inheriting a decision made by someone who has since left the programme. It also creates a record that can be reviewed if the part later fails in service or causes difficulty at assembly.

Keeping the Baseline Visible

For Brimic Engineering, the purchasing lesson is straightforward: the drawing is the baseline, and a concession is a controlled departure from it. The departure should be visible, bounded and owned. It should not become the silent specification that a supplier works to because nobody closed the loop.

UK precision buyers operate in supply chains where technical authority is often distributed across design, quality and procurement. That makes informal approval routes easy to create and hard to unwind. The answer is not to refuse concessions, but to make them behave like decisions. Time limits, named sign-off, feature-level recurrence tracking and root-cause evidence before renewal are modest controls. Applied consistently, they stop a temporary yes from becoming the permanent drawing.