A clear CNC machining RFQ helps a supplier review your part faster and quote with fewer assumptions. For custom metal or plastic parts, the quote is not based only on size. Material grade, tolerance, geometry, quantity, finishing, inspection and delivery expectations all affect machining time and cost.
This guide is written for engineers, buyers and sourcing teams preparing drawings for CNC milled parts, CNC turned parts, prototype parts or low-volume production components.
1. Send the Correct CAD and Drawing Files
The most useful RFQ package includes a 3D file and a 2D drawing. STEP and IGES files help the manufacturer inspect geometry, tool access, hole depth, undercuts and setup direction. A 2D drawing is still important when the part has critical tolerances, threads, fits, datum references, surface roughness or cosmetic requirements.
If you only send an STL file, the supplier may need clarification before quoting because mesh files do not always communicate design intent or precise editable features. For production-intent parts, send STEP whenever possible.
2. Define the Material Grade
Do not write only “aluminum” or “stainless steel” if a specific grade matters. Aluminum 6061 and 7075, stainless steel 304 and 316, brass, copper, titanium and PEEK behave differently during machining and finishing. Material choice affects tool wear, surface finish, tolerance stability, lead time and cost.
| Requirement | Typical Material Direction |
|---|---|
| General lightweight parts | Aluminum CNC machining, often 6061 |
| Higher strength lightweight parts | 7075 aluminum or titanium CNC machining |
| Corrosion resistance | Stainless steel CNC machining, often 304 or 316 |
| High-performance plastic | PEEK machining, Delrin, nylon or other engineering plastics |
3. Give Real Quantity Ranges
Quantity changes the best machining strategy. A single prototype may be quoted with flexible setup choices. A low-volume production order may need more stable workholding, inspection planning and finishing control. If you are still testing demand, give a range such as 5, 20, 100 and 500 pieces so the supplier can show how unit cost changes.
4. Mark Critical Tolerances Only Where Needed
One common RFQ mistake is applying tight tolerances to every surface. This raises cost without improving function. Mark the features that control fit, motion, sealing, alignment or assembly. For non-critical surfaces, general tolerances are usually enough.
Tell the supplier which holes, shafts, slots, flat faces or threaded features are function-critical. This helps the process engineer choose inspection points and avoid unnecessary cost.
5. Specify Surface Finish and Post-Processing
Finishing can change dimensions, appearance and lead time. Common finishes include anodizing, passivation, polishing, brushing, plating, powder coating and bead blasting. If the part has a cosmetic side, note it on the drawing. If masking, color matching or edge protection matters, include that information before quoting.
6. Explain the Application Without Revealing Sensitive Data
A short application note can improve manufacturability review. For example, a part may be a fixture, housing, shaft, medical device component, semiconductor equipment part, robotics bracket or aerospace prototype. The supplier does not need confidential product details, but understanding function helps review material, tolerances and finish requirements.
RFQ Checklist
- 3D CAD file, preferably STEP or IGES.
- 2D drawing with critical dimensions, threads, fits and datum references.
- Material grade and acceptable alternatives if allowed.
- Quantity range for prototype and production stages.
- Surface finish, color, coating, passivation or polishing requirements.
- Inspection requirements, cosmetic surfaces and packaging notes.
- Target delivery schedule and any assembly constraints.
Related Reading
For RFQ preparation, start with the CNC machining quote page. For process selection, compare CNC milling services, CNC turning services and 5-axis CNC machining.
