1. RFQ checklist — send this, get a usable quote
A quote is only as good as the brief behind it. Before you contact a shop, assemble:
- A CAD model in STEP or IGES (not a PDF or a screenshot — a model is the only thing a shop can program from).
- Material and grade — "6061-T6" or "304 stainless", not just "aluminum". Grade drives machinability, cost and finish.
- Quantities and annual volume — prototype, pilot, or production; the answer changes the process and the price.
- Tolerances only where functional — over-tolerancing every dimension is the fastest way to inflate a quote.
- Surface-finish needs — visible-face requirement, anodize, bead blast, passivation.
- Threads, bores, and any post-processing, and whether a treatment applies before or after coating.
2. DFM checklist — design so it machines cheaply
Design-for-manufacturing is where most cost is won or lost, long before the RFQ:
- Wall thickness at or above ~0.8 mm (more where structural); thin walls chatter and warp.
- Hole depth under ~4:1 depth-to-diameter; beyond that, special deep-drill tooling is slow and risky.
- Internal corners leave a radius (a rotating end mill always leaves one); never design a sharp corner.
- Thread engagement ~1.5–2× the diameter; more buys almost no strength.
- Reach — confirm every critical feature is reachable from one side, or with a simple flip, before adding a 4th or 5th axis.
3. Tolerance & surface-finish guide
| Callout | Typical value | When to specify |
|---|---|---|
| Milled / turned tolerance | ±0.003 mm (milling) / ±0.002 mm (turning) (±0.0002 in) | Critical, functional dimensions on capable equipment |
| Ground tolerance | ±0.002 mm | When fit or geometry demands it |
| As-machined finish | Ra 3.2 µm | Non-visible, functional surfaces |
| Smooth milled finish | Ra 1.6 µm | Visible or sealing surfaces |
| Ground / polished | Ra 0.8 / 0.4 µm | Sealing, sliding or cosmetic-critical |
Reference ISO 2768-m on a drawing to set a default band for un-dimensioned features, so you only pay tight tolerances where they matter.
4. Material quick-reference
| Material | Machinability | Typical use |
|---|---|---|
| Aluminum (6061, 7075) | Excellent | Frames, enclosures, prototypes |
| Stainless (303, 304, 316, 17-4PH) | 303 free-cutting; 304/316 slower | Medical, food, marine |
| Steel (1018, 4140) | Good | Shafts, jigs, wear parts |
| Brass / copper | Excellent | Electrical, thermal parts |
| Titanium (Ti-6Al-4V) | Difficult | Aerospace, implants |
| PEEK / Delrin (POM) | Easy but soft | Insulators, wear pads |
5. Glossary
- First article — a sample machined and measured before the run is released; it proves the program.
- Cpk / Ppk — process-capability indices; Cpk ≥ 1.33 in production, Ppk ≥ 1.67 at initial capability for key characteristics.
- Setup — one clamping of the part; each extra setup adds time and a datum error.
- DFM review — a shop's check of your drawing for manufacturability before quoting.
Frequently updated articles
Deep-dive buyer guides published for CNC Precision Machining:
- Aerospace CNC Precision Machining: Materials, Documentation, and the Tolerance Expectations That Matter
- Aluminum CNC Precision Machining: Alloys, Stability, and the Tolerance Decisions That Matter
- Aluminum vs Stainless for CNC Precision Machining: The Decision Table for Tolerance, Weight, and Corrosion
- China CNC Precision Machining Sourcing: What to Verify Before You Pay
- CNC Precision Machining Factory
- CNC Precision Machining for Medical: Tolerances, Materials, and the Documentation a Device Maker Needs
- CNC Precision Machining Lead Times: What Drives Them and How to Plan
- CNC Precision Machining Parts Manufacturer
- Quality Assurance at CNC Precision Machining
- CNC Precision Machining Services
- CNC Precision Machining vs Alternatives: Choosing the Material–Process Pair That Wins Your Part
Where to go next
For the service overview, see the services page; for quality evidence, the quality page; for direct questions, contact the team.
What tolerance should I specify on my parts?
±0.003 mm on milling, ±0.002 mm on turning, and ±0.002 mm on precision grinding and wire EDM — put the number on the feature, not in the drawing title block.
What should I send for a quote?
A 3D model plus a 2D drawing with GD&T, the material, prototype and production quantities, surface finish, and which features are critical. You get DFM notes and an itemised quote.
What is your minimum order?
One part. Prototypes run on the same machines as production, so MOQ 1 is real, not a loss-leader.
Where do you ship?
In short, We ship to Austria, Belgium, the Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, the Netherlands, Spain, Sweden and the United Kingdom in Europe; Brazil, Canada, Mexico and the United States in the Americas; China, Israel, Japan, Singapore and Sri Lanka in Asia; Australia and New Zealand in Oceania; and South Africa in Africa — plus other countries and regions worldwide, shipped from our base in Dongguan, China.
Ready to price your part? Send the drawing and ask for a quotation that names the setups, the machining and finishing windows, and the exchange dates. Contact the team to plan the job.
Standards referenced on this page
- ASTM A276/A276M-17 — Standard Specification for Stainless Steel Bars and Shapes
- ASTM B211/B211M-19 — Standard Specification for Aluminum-Alloy Rolled or Cold Finished Bar, Rod, and Wire
- ISO 9001 — Quality management systems — Requirements