A Controlled Maybe: Making Chinese CNC Concessions Auditable

When a Chinese CNC supplier reports that a batch has missed a tolerance, the immediate question is commercial: can the parts be used? The more important question is procedural: if they can, how does the UK buyer record that decision so that it remains visible to design, quality, production and, eventually, service or liability functions? An out-of-tolerance part is not automatically scrap. A concession can be a legitimate engineering decision. But an informal acceptance — a line in an email, a verbal agreement on a call, a credit note without a drawing reference — creates a gap between what the drawing requires and what the business has installed.

That gap is the real risk. It is not that the parts will fail tomorrow. It is that nobody can later prove who accepted the deviation, against which drawing revision, for how many parts, and on what engineering basis. A concession note is not bureaucracy for its own sake. It is the mechanism that turns an awkward maybe into a controlled decision.

An Email Is Not an Acceptance

UK buyers often receive deviation news in the least formal channel available. A supplier’s sales engineer sends a photograph of a bore with a plug gauge, explains that the size is “only slightly over”, and asks whether the shipment should proceed. The buyer, under pressure to keep a production line running, replies that the parts can be shipped. That reply may feel like a practical solution. In quality terms, it is an unrecorded change to the acceptance criteria.

A formal process does not need to be slow. It does need to separate three questions: what exactly is nonconforming, whether the nonconformance matters for the intended use, and who is authorised to accept it. The first question belongs to inspection data. The second belongs to engineering. The third belongs to a defined signatory, not to whoever happens to be managing the purchase order.

Deviation Request, Concession and Non-Conformance

The terminology is worth fixing in the supply agreement. A deviation request is normally raised before production or before shipment, when the supplier proposes a departure from the drawing or specification. A concession is the buyer’s formal acceptance of nonconforming product that has already been produced. A non-conformance report records the fact of the failure; it does not, by itself, authorise use.

For Chinese CNC deliveries, the practical sequence is usually a supplier non-conformance report, a concession request from the supplier’s quality team, an internal engineering assessment by the UK buyer, and a signed concession note if the parts are to be accepted. The note should identify the part number, drawing revision, batch or serial range, quantity affected, the specific characteristic and measured result, the requirement it misses, the disposition, the approver and the date. If the concession is limited — for example, to a particular customer order or a temporary build — that limit must be stated on the document, not left in correspondence.

Assessing Fitness for Purpose

The engineering assessment should be proportionate to the characteristic. A cosmetic mark on a non-visible bracket is not the same as an out-of-tolerance bearing seat on a rotating assembly. A useful risk frame covers function, interface, assembly, safety, regulatory conformity, durability and appearance. For each, the question is not whether the deviation is acceptable in the abstract, but whether it is acceptable for the specific use and the specific quantity.

Where the deviation affects a mating part, the buyer should check the worst-case stack-up rather than the nominal fit. Where it affects a seal, a fastener or a load-bearing feature, the assessment should involve the engineer who owns the design, not only the quality inspector who found the issue. For safety-critical or regulated components, a concession may be the wrong tool altogether; the correct response may be rework, replacement or scrap. The concession note should record that reasoning, even when the decision is to reject.

Pricing the Decision

Accepting a deviation is not the same as accepting the original price. If the parts require sorting, additional inspection, rework at the UK end or a reduced service life, the commercial adjustment should reflect that. A credit note is appropriate, but it should reference the concession note and the affected quantity. It should not be used as a substitute for the engineering decision.

Equally, a supplier should not be allowed to treat a concession as a routine discount mechanism. If the same deviation recurs across batches, the issue is no longer a one-off concession; it is a capability or control problem. The buyer’s response should move from disposition to corrective action, with the concession history used as evidence in the supplier scorecard.

Records That Outlast the Batch

A concession that lives only in a quality inbox will disappear when staff change or when the batch is installed. The note should enter a concession register and be linked to the goods-in inspection record, the supplier’s non-conformance report and the relevant drawing revision. Where the buyer operates an MRP or PLM system, the concession should be visible against the item or batch, not buried in a shared drive.

This matters long after delivery. If a warranty claim, internal audit or customer query arises, the buyer needs to show that the deviation was known, assessed and accepted by an authorised person. The record should also show whether the concession was time-limited, quantity-limited or conditional on additional inspection. A note that says only “accepted by buyer” is not a controlled decision; it is a placeholder.

Keeping the Supplier in the Loop

Finally, the concession should close with a supplier response. The Chinese CNC supplier should confirm the root cause, the containment action for any remaining parts and the corrective action that prevents recurrence. If the concession was raised after shipment, the supplier should also confirm whether later batches are affected. This turns the note from a local acceptance into part of the quality relationship.

A concession is not a weakness in a purchasing process. It is a recognition that manufacturing produces variation and that engineering judgement has a role. The weakness is allowing that judgement to remain informal. For UK buyers sourcing CNC parts from China, the concession note is the difference between a decision that can be defended and a shrug that cannot.