How to Prepare CAD Files for Chinese Manufacturers

To prepare CAD files for Chinese manufacturers, send a neutral STEP file of the 3D model plus a dimensioned 2D drawing in PDF or DWG format, with materials, tolerances, finishes, quantities, and a revision identifier clearly marked on both. This combination removes most of the ambiguity that causes wrong quotes, delayed production, and parts that don't fit.

That sounds simple, and most of the failures in this process come from skipping one of those elements. A lone STEP file with an email saying "quote 500 pieces" leaves the factory guessing about alloy grade, surface treatment, critical tolerances, and which version is current. The file package is the technical definition of what you're buying.

Sourcing agents like CN Ally routinely step in at exactly this point: reviewing file packages before they go out, flagging missing tolerances or ambiguous callouts, and coordinating the design-for-manufacturability (DFM) feedback round with the factory. If you want that review on your files, send them to us before you start requesting quotes.

What should a quote-ready file package contain?

A quote-ready package lets an engineer on the supplier side understand the complete job without reconstructing it from scattered messages. At minimum:

1. The 3D CAD model — geometry in a neutral exchange format, with the current revision.
2. The 2D technical drawing — dimensions, tolerances, and critical notes the 3D model doesn't carry.
3. Material and finish specifications — exact alloy or grade, surface treatment, cosmetic requirements.
4. Production details — quantities (prototype, first batch, full run), target timeline, inspection expectations.
5. Revision and contact information — file version, date, and who to ask when something is unclear.

Pack everything into one ZIP with a short cover note or spec sheet. Factories in China routinely receive requirements split across Alibaba chat, WeChat, emails, and PDFs; a single self-contained package with a version number prevents the classic failure where the factory builds to the wrong message. Ask the supplier to confirm in writing that they're quoting your stated revision.

Which CAD file format should you send?

The format question matters because your CAD software and the factory's CAM system are rarely the same. The table below covers what Chinese manufacturers actually accept, and what each format is good and bad at.

Format · What it is · When to use it · Limitations

• **STEP (.step / .stp)**: Neutral exchange format (ISO 10303) for exact solid 3D geometry · Default choice for nearly all 3D handoffs: machining, molding, tooling · Requires the factory's CAM to import it; doesn't carry every piece of model metadata
• **IGES (.iges / .igs)**: Older neutral format (Initial Graphics Exchange Specification) · Legacy data, older toolchains, surface-heavy models · Can import as separate unstitched surfaces instead of a closed solid; generally superseded by STEP
• **STL (.stl)**: Triangulated mesh format · 3D printing and rapid prototyping · Approximation of the surface, not exact geometry; tight tolerances and exact curves don't survive translation to mesh — weak choice for CNC
• **DWG (.dwg)**: AutoCAD native 2D format · 2D engineering drawings, sheet metal, laser-cut profiles · 2D only in practice for handoffs; geometry isn't a machinable solid
• **DXF (.dxf)**: Drawing exchange format · Laser cutting, waterjet, router work from 2D profiles · Flat profiles only; no 3D information
• **PDF (.pdf)**: Universal document format · The 2D drawing as a read-only reference alongside STEP · Not editable, not machinable — a communication document, not a model
• **Native files (.sldprt, .prt, .f3d, etc.)**: Your CAD program's own format · When the factory uses the same software, or when you want them to modify features · Compatibility risk if they use a different system; always pair with a STEP file

STEP is the practical default. Most CAM software reads it cleanly, it preserves exact geometry instead of approximating it, and Chinese suppliers from rapid prototypers to CNC shops list it as their preferred input. A side-by-side comparison of the two neutral formats from HVH Designer reaches the same conclusion: STEP for nearly everything, IGES only for legacy situations.

One practical point: before zipping anything, re-import your own exported STEP into a fresh session and check it. Missing faces, shifted origins, or collapsed features are common export artifacts, and a factory quoting from a broken file will either price in risk or quote something you don't want.

Do you need both 2D drawings and 3D models?

Yes — send both. This is the single most repeated piece of advice from manufacturers who work with overseas buyers, and it's worth understanding why.

The 3D model defines the geometry. The 2D drawing communicates design intent: which dimensions are critical, what the tolerances are, how holes and threads are specified, which surfaces get which finish, and how parts fit together. A machinist can open a STEP file and see the shape, but they can't see which of the two hundred dimensions you actually care about. The drawing is where that judgment lives.

A useful 2D drawing for a Chinese manufacturer includes: all functional dimensions with tolerances; hole sizes, locations, and thread callouts; material designation with grade; surface finish per face or region; critical mating dimensions marked explicitly (datums, fit callouts); and a title block with part name, number, revision, scale, units, and date. China Importal's guidance on file formats makes the same recommendation from the buyer side: complement CAD files with 2D drawings showing the product from different angles.

If you're working in inches, state it loudly. China works in millimeters, and a unit mismatch is one of the dumbest and most expensive mistakes in this business. Put units in the title block, in the file name, and in the cover note.

How do you specify tolerances and GD&T?

Tolerances decide how expensive your part is to make and how likely it is to pass inspection. State them explicitly — never assume the factory will "figure it out" or apply a sensible default.

There are two layers. First, a general tolerance note on the drawing (e.g., "ISO 2768-m for linear dimensions" or "±0.25 mm unless otherwise specified") covers everything you didn't individually dimension. Without it, each unmarked dimension is negotiable, and the negotiation happens on the shop floor where you can't hear it. Second, tight tolerances only on the dimensions that need them. A ±0.02 mm callout on every hole multiplies inspection time and rejects parts that would have worked fine.

For features that genuinely need geometric control — flatness of a sealing face, concentricity of a bearing bore, perpendicularity of a mounting face — use GD&T symbols per ASME Y14.5 or ISO 1101, and reference the standard on the drawing. Two cautions matter specifically for Chinese suppliers: keep GD&T modest, because over-constraining every surface is the hallmark of a drawing never reviewed for manufacturability; and confirm the factory's GD&T fluency, adding plain-language notes alongside symbols until you've built a working relationship.

For a clear walkthrough of format and tolerance interplay in CNC work, JLC CNC's guide to CNC file formats covers which formats carry what kind of data through the CAM chain.

How do you call out materials and finishes?

Material callouts are where vague RFQs go to die. "Aluminum" on a drawing is not a specification — 6061-T6, 6063, and 7075 have different strength, machinability, and price. "Stainless steel" means nothing without the grade (304, 316L, 17-4PH) and, where it matters, the temper or hardness.

Write the material as a full designation: 6061-T6 aluminum per ASTM B221, not just "aluminum". For plastics, name the exact resin and grade (ABS, PC, PA6-GF30) plus any additive requirements like UV stabilizer or flame rating (UL 94 V-0). If you care about the raw material source or require RoHS/REACH compliance, say so in the package — compliance testing is cheap to specify up front and expensive to add after production.

Finishes need the same treatment: anodizing type and color (Type II, black, per MIL-A-8625), powder coat color and gloss level (a RAL code bridges the language barrier), bead-blast media and grade, or polish standard (e.g., SPI A-2). Where finishes differ across surfaces of the same part, mark the regions on the drawing rather than describing them in an email. Cosmetic requirements deserve a sentence of their own: are the visible faces cosmetic-critical, and what counts as an acceptable cosmetic defect? Factories judge by the written standard, not by what you pictured.

How should revision control work?

Every file that leaves your desk needs a revision identifier, and every revision needs to be traceable. The failure pattern here is painfully common: you send Rev B for quoting, Rev C with changes mid-negotiation, and the factory produces tooling from whichever file their engineer downloaded first.

A workable system is simple: name files as PartNumber_RevC_2026-10-02.step (never reuse a revision letter for a changed file), keep the revision in the drawing's title block with a small table noting what changed, and treat the dated ZIP package as the single channel of truth — changes go out as a new package, not a WeChat message.

How do you protect your IP when sharing CAD files?

Sending your design files to an overseas manufacturer means sending your IP to another legal jurisdiction. It's manageable with layered protection — no single measure is enough, and paranoia that prevents you from sharing anything costs as much as carelessness.

Split the package by stage. For initial quoting, many buyers send STEP files with sensitive internal features suppressed or simplified — enough geometry for an accurate quote, not the full production model. The complete model goes to the selected factory under contract.

Use a manufacturing NNN agreement, not a Western NDA. A standard US or EU non-disclosure agreement is difficult to enforce against a Chinese manufacturer. The widely used instrument for China is the NNN agreement — non-disclosure, non-use, non-circumvention — drafted under Chinese law, in Chinese, with jurisdiction in a Chinese court. Have it prepared by a lawyer who practices in China before you send full design files, not after.

Vet the factory before the files. Run basic due diligence — business license check, facility audit — on any manufacturer that will receive complete designs. A supplier you've audited and contracted with is a fundamentally different risk profile than a supplier who answered an Alibaba inquiry yesterday. Factory audits are a core part of our verification process for exactly this reason.

Practical measures help too: strip internal part numbers, customer names, and cost data from drawings; watermark them "property of [company], for quotation only"; and record exactly which files went to which supplier and when.

What mistakes cause the most factory rework?

Most failed handoffs are the same short list of avoidable errors. Check your package against these before sending:

1. Missing or mixed units. Inches in a millimeter shop. State units three times: title block, file name, cover note.
2. No tolerances on the drawing. The factory picks the loosest interpretation, and the parts don't fit yours.
3. Sending only a mesh file for machined parts. STL is for 3D printing; CNC needs exact geometry from STEP.
4. Unwatertight or corrupted 3D models. Small surface gaps stall CAM programming — re-import your exports and run a geometry check first.
5. Ambiguous material callouts. "Aluminum" without grade, temper, or standard number.
6. Cosmetic requirements left unsaid. "Looks good" is not a standard; define acceptable cosmetic defects in writing.
7. Changes sent through chat. The new revision lives in a WeChat message and never reaches the drawing.
8. DFM feedback requested too late. Ask at the quoting stage, not after tooling steel is cut.

Chinese factories will often suggest draft angles, wall thickness adjustments, or tolerance relaxations that cut your cost — but only if you ask before the design is frozen. A structured quality control plan that references the same drawings and tolerances closes the loop on the production side.

Frequently asked questions

What is the best CAD file format to send to a Chinese manufacturer?

STEP (.step or .stp) is the best default. It's a neutral, ISO-standardized format that preserves exact solid geometry and opens in virtually every CAD and CAM system Chinese factories use. Pair it with a dimensioned 2D drawing in PDF or DWG format that carries tolerances, materials, and finishes. Only fall back to IGES for legacy toolchains, and use STL only for 3D-printed parts.

Should I send 2D drawings or 3D models?

Both. The 3D model defines the geometry; the 2D drawing communicates what the 3D model can't — critical dimensions, tolerances, thread and hole callouts, material and finish specifications, and fitting requirements. Manufacturers and QC inspectors work primarily from the 2D drawing, so it should be complete enough to make and inspect the part.

How do I share CAD files without losing my IP?

Use a staged approach: simplified files for quoting, full files only under a China-enforceable NNN agreement (non-disclosure, non-use, non-circumvention) with jurisdiction in a Chinese court. Vet and ideally audit the factory before sending complete designs, strip internal identifiers from drawings, and log which files went to which supplier.

What tolerances should I put on drawings for Chinese factories?

Use a general tolerance note (such as ISO 2768-m or a stated ± value) to cover all unmarked dimensions, then apply tight tolerances only to dimensions that control function or fit. Over-tolerancing drives up cost and scrap; under-tolerancing creates ambiguity. Confirm the factory's GD&T fluency for complex callouts and add plain-language notes where symbols might be misread.

Can Chinese manufacturers work from native SolidWorks or Fusion files?

Sometimes, if they run the same software. But it's risky to rely on: version mismatches and missing licenses are common, and native files don't help the CAM programmer if their toolchain differs. Always include a STEP export alongside any native file, and treat the STEP plus 2D drawing as the authoritative package.

What should I include in the file name?

Part number, revision identifier, and date — for example, BRKT-0421_RevC_2026-10-02.step. The name should let anyone on either side identify the part and its currency without opening the file. Never send a changed file under an old revision name.

Run the pre-send checklist, then request quotes

Before any CAD package leaves your desk for a Chinese factory, run a simple gate: STEP model re-imported and checked; 2D drawing with units, tolerances, materials, and finishes; a revision identifier on every file; quantities and timeline stated; an NNN agreement in place for full designs; written confirmation of the revision from the supplier once quoting starts. Run that checklist once per product and most of the expensive failure modes disappear.

Then get a second pair of eyes on it. A sourcing agent who has seen hundreds of factory handoffs will spot the missing tolerance note or the ambiguous finish callout in minutes — the same gaps that turn into weeks of samples and rework. If you'd like that review before you start quoting, contact us or email hi@cnally.com and we'll look over your file package before it reaches any factory.