CNC Drawings and Tolerances: What to Send to China

What should you send a Chinese machine shop?

Prepare one controlled request for quotation, or RFQ, that defines both the part and how you will accept it. Adapt the package to your replacement component, product development or repeat-production order.

Use a STEP model to communicate geometry and a PDF drawing to record manufacturing and inspection requirements. Give both files the same part number and revision. Ask the supplier to confirm that the files open correctly and identify any conflicts before quoting.

The checklist below is a recommended purchasing package. Agree which documents your order requires.

Which tolerance standard should the drawing name?

Avoid writing only “ISO 2768”. Identify the applicable part, edition and tolerance class where applicable. Have the designer select requirements that suit the part's function.

ISO's catalogue, checked on 2026-10-18, lists ISO 2768-1:1989 as published. It covers general tolerances for linear and angular dimensions without individually indicated tolerances. If selected, state the class and scope on the drawing.

The catalogue lists ISO 2768-2:1989 as withdrawn and identifies ISO 22081:2021 as its replacement. ISO 22081 addresses general geometrical and size specifications. Ask the designer to review an inherited reference; do not simply replace the standard number.

ISO 1101:2017 defines symbols for geometrical specifications and their interpretation. Ask the designer to specify the datums and individual controls needed for functional features.

These references identify standards, not reproduced tolerance tables. Select actual limits from the applicable standard and the part's functional requirements, then obtain the shop's written acceptance.

Make units, projection and document precedence explicit

For a millimetre-based package, state that dimensions are in millimetres and identify the units used for surface texture and other measured properties. Ask the shop to confirm the STEP import units. If you use inch dimensions, identify them clearly and agree any conversion before manufacture.

Show the first-angle or third-angle projection symbol on the drawing and make the view arrangement consistent with it. ISO 5456-2:1996 addresses orthographic representations. Specify the method you use rather than expecting the factory to infer it from your country.

Agree what governs if the model, drawing or purchase order disagrees. One arrangement to consider is to use the model for geometry and the drawing for stated requirements, with discrepancies referred back for written resolution before machining. Record your actual agreement.

Keep reference dimensions clearly identified. Ask for clarification of missing acceptance dimensions rather than asking the shop to measure a PDF image.

Remove ambiguities before they become scrap

Material: replace descriptions such as “aluminium” or “stainless steel” with the required grade and condition. If the supplier offers a local alternative, request its designation and supporting specification for approval. Assess equivalence from the specifications rather than a translated trade name.

Threads and holes: specify the thread system, size, pitch, tolerance and usable depth where relevant. Distinguish a blind hole's drilling depth from its full thread depth, and identify through holes, countersinks and counterbores.

Finish: separate surface texture from appearance and coating. Replace descriptions such as “smooth”, “black” and “same as the sample” with identified faces, measurable requirements and any approved appearance sample.

Treatment and dimensions: state whether acceptance dimensions apply before or after coating or heat treatment. Identify areas that must remain uncoated and features whose fit needs checking after treatment.

Edges and machining access: define functional edge requirements, permitted radii and any areas where tool marks are unacceptable. Ask the shop to flag inaccessible features or proposed geometry changes before quoting.

Cost: ask the designer which features need tighter control. For quotation comparisons, use the separate guide to CNC machining cost drivers in China.

How to add Chinese-language notes safely

Use Chinese notes to repeat the approved technical meaning. Keep dimensions, symbols, material designations and standard references consistent across languages. Have technical translations checked and agree which language governs if wording conflicts.

Suggested notes to adapt and approve include: “尺寸单位为毫米。” meaning dimensions are in millimetres; “材料代用须经买方书面批准。” meaning material substitutions require the buyer's written approval; and “图纸与模型不一致时，须先取得书面澄清，再进行加工。” meaning drawing and model discrepancies require written clarification before machining.

Where your design requires dimensions and tolerances to apply after surface treatment, consider “尺寸及公差适用于表面处理后的成品。” Have the designer confirm that this is correct for the part before adding it.

Keep translated notes within the controlled drawing revision. If an email or message changes a requirement, update the released package and obtain acknowledgement.

Agree inspection before accepting the quote

Identify the dimensions and geometrical controls that determine fit, assembly or safety. Ask the supplier how it will verify them and whether suitable measurement equipment is available. Request both manufacturing and measurement capability confirmation.

Agree whether inspection covers every part or an agreed sample, which features are reported and when reports are delivered. State whether a first article requires approval before the remaining batch is produced.

Request reports tied to the part number, revision and identifiable batch or sample. Where required, agree material traceability and treatment records. Request evidence of material composition and applicable product compliance separately from dimensional results.

Require written approval for deviations. Record the affected feature, proposed change and quantity covered before the supplier proceeds.

If you sell in the US or EU

US entry — CBP's Tips for New Importers and Exporters, checked on 2026-10-18, states that the importer of record remains responsible for correct entry documentation and applicable duties, taxes and fees even when using a broker. Give your broker the part's material, function and intended use alongside its commercial description.

US tariffs — USTR's Section 301 tariff search page, checked on 2026-10-18, provides HTS-based information on China Section 301 coverage and additional duty rates. Check the classification and applicable measures for the actual part before ordering; this guide does not assign a tariff rate.

US food-contact applications — FDA's Inventory of Food Contact Substances Listed in 21 CFR, checked on 2026-10-18, identifies substances and regulatory references for specific intended uses and conditions of use. If a part or coating will contact food, specify the application and request evidence relevant to those conditions rather than accepting an unsupported “FDA approved” description.

EU — the European Commission's CE marking guidance, checked on 2026-10-18, explains that CE marking is required only for products covered by the relevant legislation. Assess the part's intended use and applicable product rules before requesting marking or compliance documents.

UK example: keep the machining quote separate from import VAT

For a buyer importing parts into the UK, HMRC's import VAT valuation guidance, checked on 2026-10-18, requires valuation to start with the customs value even where no duty is payable. Add applicable import duties and other charges, excluding import VAT itself, and the specified incidental expenses.

For example, a Cambridge buyer should ask the clearing agent to account for relevant packing, transport and insurance costs to the first UK destination, without double counting. Include relevant incidental expenses resulting from transport to a further UK destination if that destination is known at importation. This illustrates valuation, not a tax rate.

Getting an incomplete drawing package ready

If you have a sketch, a sample or an unfinished model, identify the unresolved design decisions before requesting a production commitment. Ask for proposed changes separately from the quote against your released specification.

Discuss help preparing the package through product development, or describe your prototype and limited-quantity needs through small-order sourcing. Agree the design, documentation and inspection deliverables before commissioning work.

Cambridge China Bridge's website states that factory audits and goods inspections are usually included in the quote for an order placed with the company; complex checks requiring a third party are charged separately by prior agreement. Confirm the scope in your quotation.

Sources

The official sources listed below support the standard references and market-specific statements. They were checked on 2026-10-18. The service-scope statement was checked against Cambridge China Bridge's website. The RFQ checklist and suggested drawing notes are practical recommendations to adapt and approve for your design.