Need-to-Know Geometry: A CAD Release Protocol for Chinese CNC Suppliers

The file is a release, not an attachment

A CAD model sent to a Chinese machining supplier is not merely an email attachment. It is a controlled release of intellectual property, and it should be treated with the same discipline as a purchase order or a quality plan. The supplier needs enough geometry to make and inspect the part; it does not need the assembly context, the customer's name, the internal project code, or the next product's mounting holes.

The protocol below is deliberately modest. It assumes a UK buyer working with a Chinese CNC supplier under a purchase order, and it treats CAD transfer as a supply-chain control rather than a legal formality.

Define the manufacturing envelope first

Before exporting, ask what the supplier must see. For a turned part, that may be a single solid with threads, chamfers and datums. For a prismatic component, it may include the mating faces and clamping features. It rarely includes the full assembly.

Create a manufacturing model derived from the design master. Suppress or delete features that do not affect the supplied operation: cosmetic logos, unrelated pockets, assembly-only bosses, customer-specific markings. Do not suppress features that influence machining access, inspection or fit. The test is simple: if a feature changes how the part is held, cut or measured, it stays.

Record every suppression in a release note. A supplier should not have to guess whether a missing boss is intentional. The note should say what was removed, why, and which drawing view or model-based annotation governs the remaining geometry.

Use annotations the supplier can act on

A neutral format such as STEP is usually preferable to a native CAD file. It reduces the supplier's dependence on a particular software version and limits the amount of design history exposed. Where model-based definition is used, export the PMI with the model and confirm that the supplier's viewer reads it correctly. A clear 3D view is not a substitute for a readable tolerance.

If a 2D drawing accompanies the model, make the drawing the controlled document for tolerances, datums and surface finish. State clearly whether the model or the drawing prevails where they differ. Ambiguity here is more expensive than any NDA.

Watermark and identify every copy

Watermarking is often discussed as a deterrent. Its more useful role is attribution. Apply a visible identifier to drawings and PDFs: supplier name, release number, date and a unique document ID. For neutral CAD, add the same identifier to file metadata and, where practical, to a non-critical annotation layer.

Do not rely on a watermark to protect the design. It will not stop a determined recipient. It will help you answer a simpler question: which copy left the building, when, and to whom?

Treat the NDA as one control, not the control

An NDA with a Chinese supplier can be enforceable, but UK buyers should not treat it as a substitute for data minimisation. Jurisdiction, language, arbitration venue and the practical cost of enforcement all matter. Take Chinese legal advice on the governing law and dispute route before relying on a template.

The purchase order should also carry confidentiality and data-use clauses that flow down to any subcontractor. If the supplier intends to use a third-party CAD viewer, cloud storage or a programming bureau, that should be declared. The buyer's question is not whether the NDA is signed, but whether the data route is known.

Check the supplier's IT hygiene before release

A short supplier IT questionnaire is proportionate for most CNC work. Ask where CAD files are stored, who can access them, whether personal cloud accounts are used, how long files are retained, and how deletion is confirmed. Ask whether the supplier uses a viewer rather than native CAD for first review. A viewer reduces editing and re-use.

For higher-risk designs, ask for access logs and a named data owner. For lower-risk work, a signed acknowledgement and deletion undertaking may be enough. The level of scrutiny should follow the sensitivity of the geometry, not the size of the order.

Keep a release register

The audit trail should be simple enough to maintain. A release register with the following fields is usually sufficient: document ID, revision, hash, recipient, purpose, date sent, transfer method, acknowledgement and deletion date. The hash matters because it proves that the file received is the file sent.

Use a transfer method that creates a record. A shared link with an expiry date is better than an open attachment. A supplier portal is better still, provided the buyer can export the access log.

A six-step release sequence

1. Derive the manufacturing model and record suppressions.
2. Export STEP with PMI where required, plus a controlled 2D drawing.
3. Apply a unique watermark and metadata identifier.
4. Check the supplier's IT questionnaire and subcontractor declaration.
5. Send via an expiring link and obtain acknowledgement.
6. Log the release, hash and deletion date in the register.

None of this is exotic. It is the same discipline a UK buyer would apply to a sensitive drawing sent to a domestic supplier, adjusted for distance and jurisdiction. The aim is not to make collaboration difficult. It is to ensure that the file which leaves the building is the file the supplier needs, and that its journey can be reconstructed later.