How To Prepare Perfect RFQ Documents For Custom CNC Machining Projects

Sourcing custom CNC-machined metal parts from overseas manufacturers brings great cost advantages for product developers, mechanical engineers and procurement managers. However, many projects get delayed due to incomplete or unclear RFQ submissions. Missing dimensions, undefined tolerances, vague surface-treatment requirements and ambiguous material choices often lead to back-and-forth emails, incorrect quotations, sample rework and longer lead-times.

If you want accurate pricing, fast feedback and parts that match your design expectation, you need to build a complete RFQ package before sending your inquiry. This article walks you through practical rules for preparing CNC machining RFQ documents, common mistakes to avoid, and what information a reliable CNC manufacturer actually needs from you.

What Files Should You Provide For CNC Custom Machining

3D models and 2D engineering drawings serve different purposes, neither one should be skipped.

3D CAD Model

3D files help factories calculate machining time, recognize complex geometry and estimate raw-material consumption. Recommended formats：STEP, IGES. Avoid using STL files for formal CNC quotation, STL is mainly for 3D printing and lacks precise dimensional data.

2D Technical Drawing (PDF / DXF)

The 2D drawing is your legal technical standard. Mark all critical dimensions, geometric tolerances, thread specifications, chamfer and hole requirements on 2D drawings. Even if your 3D model looks complete, always attach a 2D drawing with tolerance notes.

Additional Attachment Notes

· Mark part number and revision version on every drawing file

· Compress multiple files into one zip package for easy download

· If you have existing sample photos, attach real-product photos for reference

Key Information You Must Include In Your RFQ

Complete information directly improves quotation accuracy. Check this list before sending inquiries：

1. Material selection Specify alloy grade clearly：Aluminum 6061 / 7075, Stainless Steel 304 / 316, 42CrMo, Carbon Steel, Copper, PTFE and other plastics. If you accept alternative materials, write down acceptable substitutes.

2. Quantity breakdown Separate sample quantity and mass-production quantity. Unit price changes significantly between prototype batch and bulk order.

3. Tolerance requirements Distinguish general tolerance and special tight tolerance. For non-critical features, you can follow standard ISO general tolerance rules. Only assign tight tolerance for functional mating surfaces, excessive tight tolerance will raise your production cost unnecessarily.

4. Surface finishing requirements Clarify surface treatment：Anodizing, black anodize, powder coating, sandblasting, polishing, passivation, deburring. Note color code for powder-coating or anodizing when required.

5. Special requirements Include thread standards, deburring rules, inspection demands, packaging requirements and target lead-time.

Common RFQ Mistakes That Cause Bad Quotation & Rework

Many customers suffer extra cost just because of simple document errors.

· Only sending 3D model without 2D tolerance drawing. Manufacturers can only guess tolerance standards, which may cause finished parts fail assembly.

· No material grade, just write “aluminum” or “steel”. Different alloys have big price and performance gaps.

· Over-specifying tight tolerance for non-functional surfaces, pushing up machining cost.

· Vague surface-finish description like “nice surface”. Always name exact finishing process.

· Missing revision number. When you update design files, old versions may still be used for production.

The Standard Workflow After You Submit RFQ

A qualified CNC custom machining supplier will follow this workflow：

1. Receive your RFQ package, engineering team carries out DFM review (Design for Manufacturability). They will point out hard-to-machine structures, risky thin walls or sharp inner corners and offer reasonable optimization suggestions.

2. Send formal quotation including unit price, tooling cost if applicable, sample lead-time and mass-production lead-time.

3. Once you confirm quotation, start prototype manufacturing.

4. Complete dimension inspection, surface-quality check before shipment.

5. Arrange delivery and provide inspection report upon request.

FAQ

Q: Can I send hand-drawn sketch for quotation?

A: Hand sketch works for preliminary rough estimate. For formal order, formal 2D drawing plus 3D model is still required.

Q: What if I do not know suitable material for my project?

A: Share your working environment, load condition and application scenario. Our engineering team can recommend proper material options for your reference.

Q: How fast can I get quotation after sending RFQ?

A: Complete RFQ package normally gets formal quote within 24-48 working hours. Incomplete documents will extend reply cycle.

Conclusion

Good RFQ preparation is half-way to successful custom CNC parts. Complete 3D files, standardized 2D drawings and clear technical specifications reduce miscommunication, cut rework risk and help you get fair and transparent pricing.

If you have CNC milling or turning parts to be manufactured, send your drawing package to us for professional DFM review and competitive quotation.