How to Get a CNC Machining Quote from China: What to Send and What to Check Before You Order
Send the same drawing to three CNC machining suppliers in China and you can get three prices that differ by a factor of three. That is rarely because one factory is three times more expensive than another. It is because each factory quoted a different interpretation of your request.
A CNC quote is not a price for a shape. It is a price for a complete manufacturing requirement: geometry, material, tolerance, finish, quantity, inspection and delivery. Leave any of those open and the supplier has two choices — stop and ask, which costs you days, or assume the worst case and add a risk premium, which costs you money. Peer guides on China sourcing consistently report that premium at 15–25% on incomplete requests for quotation (RFQs). The fix is not to negotiate harder. It is to send a complete RFQ the first time.
This guide explains exactly what to send, how a supplier should evaluate it, the mistakes that inflate price or cause rework, and how to compare quotes like for like. It is written for engineers and procurement managers ordering custom CNC machined parts — brackets, housings, shafts, fixtures and precision components — for medical, aerospace, semiconductor, industrial automation and automotive programmes.
What a CNC Machining Quote Actually Covers
Before you send anything, it helps to know what happens on the supplier's side. A competent supplier does not just read the price off a rate card. The engineering review should check:
- Can the part be made as drawn? Wall thickness, pocket depth, inside corner radii, thread depth, and features that need a second setup or a different process.
- What is the process route? CNC milling (3-axis and 4-axis), CNC turning, Swiss machining or wire EDM — and in what order, including any secondary finishing.
- What drives the cost? Material and stock size, machine time, setup and programming, tooling or fixtures, finishing, and inspection. Setup is a fixed cost. That is why one piece costs far more per unit than 50 pieces of the same part.
- What must be inspected? Which dimensions are critical to fit or function, and whether the part needs a dimensional report, first-article inspection, or a material certificate.
If a quote arrives with no questions, no DFM (design for manufacturability) comment, and no breakdown, treat that as a warning sign, not as speed. A good quote tells you what was assumed.
At Golden Rainbow, every RFQ goes through an engineering review before a price is issued. Drawings are checked for manufacturability, and open points are clarified with you before quoting — so the price you receive is for the part as drawn, not for a guess. Complete RFQs are answered within 24 hours on business days
The Complete RFQ Checklist: What to Send
Use this checklist for every part. If an item does not apply, say so explicitly — "no finish required, as-machined" is a specification; silence is not.
- 3D CAD model — STEP (.step /.stp), single watertight solid, correct units — Defines geometry for programming and cycle-time estimation.
- 2D drawing — PDF or DWG, dimensioned, with GD&T, threads and notes — Carries tolerances, finish and intent the model cannot carry.
- Part number and revision — Same number and revision letter on model and drawing, e.g. BRACKET_PIVOT_REV_C — Prevents the wrong version being machined.
- Material — Grade and temper, e.g. aluminium 6061-T6, stainless steel 304 or 316 — Alloy and temper change machinability, strength and price.
- Quantity — Exact quantity, plus quantity breaks if useful (1, 10, 50) — Setup is amortised over quantity; unit price falls with volume.
- General tolerance — Standard in the title block, e.g. ISO 2768-m — Applies to every dimension without its own callout.
- Critical tolerances — Only the 3–5 features where function demands it — Tight tolerances are expensive; mark only what matters.
- Surface finish — Ra value by feature, or finish name (anodised, bead-blasted, passivated) — Finish changes routing, cycle time and lead time.
- Threads and holes — Thread form, class and pitch, e.g. M6×1.0-6H; hole diameters — STEP files do not communicate thread callouts.
- Inspection required — Dimensional report, first-article inspection, or material certificate — and how many parts to inspect — "Inspect every part" and "first article only" are different cost lines.
- Delivery — Need-by date, ship-to country and address — Determines production scheduling and freight.
- Part function (one line) — What the part does and what it mates with — Lets the supplier offer DFM feedback that saves cost.
Send the same controlled file set to every supplier you approach. If each supplier quotes a different revision, a different material or a different quantity, the prices cannot be compared — and the cheapest quote may simply be the one that assumed the least.
File Formats: STEP and PDF First, STL Never
Send a STEP file and a 2D PDF. That pair is the minimum correct package.
The STEP file (.step /.stp) is the geometry. It stores solid geometry that any mainstream CAM system can import as a watertight solid, without vendor lock-in. Before sending it, check three things: it opens as a closed solid in a free viewer, it is exported from the same revision as your 2D drawing, and the filename carries the part number and revision.
The 2D PDF drawing is the intent. It carries everything the model cannot: tolerance callouts, GD&T symbols, surface finish, thread specifications, the material callout to grade and temper, and the notes block. Without it, a supplier can see the shape but cannot know how tightly it must be controlled.
Other formats, in brief:
- IGES (.igs) — an acceptable fallback if STEP is unavailable. It carries surface data rather than solid geometry and can produce small gaps on import. Note it in your RFQ and ask the supplier to confirm the import is clean before quoting.
- DWG / DXF — useful for the 2D drawing. DXF alone is not enough for a 3D machined part; it carries no depth data.
- STL — do not send STL for a CNC quote. It is a triangle-mesh approximation made for 3D printing. The facets are not true geometry and cannot represent curved surfaces accurately enough for tight machined tolerances.
- Photographs and screenshots — useful for a first conversation about a replacement part. A part cannot be cut from a picture.
If the STEP model and the 2D drawing disagree, resolve the conflict before you send the RFQ. State on the drawing which document controls. Do not leave the supplier to choose.
Material, Tolerance and Surface Finish: Be Specific Where It Counts
Specify material to grade and temper — 6061-T6, not just 'aluminium' — or the quote cannot be accurate.
Material: name the grade and temper, not the family. "Aluminium" is not a specification. Aluminium 6061-T6, 7075-T651, stainless steel 304 and stainless steel 316 differ in strength, corrosion resistance, machinability and price. A documented failure in peer sourcing guides is an engineer who specified "7075" without the "-T6" temper: the parts were dimensionally correct and failed strength testing, and the whole run was scrapped. One word on the drawing would have prevented it. Golden Rainbow machines aluminium, stainless steel, brass, copper, tool steel and other engineering metals to customer drawings — but the grade and temper must be on the drawing for the quote to be accurate.
Tolerance: use a general standard, then tighten only the critical features. Put ISO 2768-m (medium class) or your equivalent general tolerance in the title block. That covers every unspecified dimension automatically. Then call out the three to five features that are critical to function — bearing bores, sealing surfaces, locating datums, mating fits. The cost of tighter tolerance is not linear: in peer cost tables, ±0.05 mm is a normal mating-tolerance band, while ±0.01 mm on a feature can cost three to five times as much as ±0.10 mm, because it needs slower cutting and more inspection.
Golden Rainbow's published capability, subject to drawing review, is a standard tolerance of ±0.05 mm, with tight tolerances down to ±0.01 mm achievable on selected features. That "subject to drawing review" matters: whether ±0.01 mm is achievable depends on the feature, the material and the size. A supplier who promises ±0.01 mm on every dimension of every part, without seeing the drawing, has not done the engineering.
The most expensive mistake here is the blanket tight tolerance: putting ±0.01 mm on every dimension, including clearance holes, chamfers and non-critical lengths. The shop must then treat every feature as high-precision. Use the general standard for the rest, and tighten only where failure to hold the tolerance would cause a functional problem. If you are unsure which features are critical, say so in the RFQ and ask for DFM feedback — that is part of the engineering review.
Surface finish: give a Ra value, not an adjective. "Nice surface" is not a specification. Ra 3.2 µm is a common as-machined finish. Ra 1.6 µm typically needs a dedicated finishing pass. Ra 0.8 µm, needed for bearing journals and sealing surfaces, can double machining time relative to Ra 1.6 µm and may need grinding as a secondary operation. Default to the coarser finish everywhere, and tighten only the surfaces where you can explain why that surface needs it. Golden Rainbow's typical finish is Ra 1.6 µm, with Ra 0.8–3.2 µm achievable depending on material and process — confirm the finish per feature on the drawing, and note which faces are cosmetic.
Quantity and Lead Time: Ask for Breaks, State Your Intent
Quantity changes the quote logic, not just the total. Setup, programming and fixture work are fixed costs. Spread over one part they dominate the price; spread over 50 they shrink. Ask for prices at two or three quantities — for example 1, 10 and 50 — so you can see where the unit price levels out. A supplier that quotes 1 piece and 50 pieces at the same unit price has not separated setup from material.
State your intent as well as your quantity. Is this a prototype to validate fit, a low-volume test run, or the first production batch? What is the expected annual volume if the part goes to production? A supplier that knows you will order 2,000 parts a year can invest in dedicated fixtures; a supplier quoting a one-off order of 20 parts will not.
Golden Rainbow's standard terms, for planning purposes, are: MOQ 1 piece — prototype and low-volume orders are welcome. Prototype lead time is typically 3–7 business days after the order and drawing are confirmed. Low-volume and production lead time is typically 10–15 business days, depending on quantity, complexity, finishing and inspection scope. Confirm the exact lead time on your quote: complex geometry, tight tolerances, anodising or plating, and 100% inspection all add time, and finishing is often the longest step in the schedule.
How to Compare Quotes Like for Like
Once the quotes come back, do not compare the bottom-line numbers first. Compare whether every supplier quoted the same thing.
- Technical basis: Same STEP file, same drawing revision, same material grade, same finish, same quantities
- Price breakdown: Unit price separated from setup, tooling, inspection, packaging and freight
- Lead time: Production time plus shipping time, and whether finishing is included
- Inspection: What is inspected, how many parts, and what report you receive
- DFM feedback: Did the supplier flag a cost or risk issue, or just price the drawing as-is?
- Communication: How fast and how specifically did they respond to clarification questions?
Red flags: a quote that is far below the others with no explanation; a quote with no DFM comment at all on a complex part; a supplier who cannot say which process — milling, turning, Swiss machining or wire EDM — they would use for your tightest feature; and a quote that does not state the drawing revision it is based on. The cheapest quote is only useful if it reflects the same part, the same quality requirement and the same delivery expectation.
Ask for the quote in writing, with the part number, revision, material, quantity, finish, lead time and inspection scope stated on it. That document becomes the reference for the order, the first-article approval and any repeat batch.
7 Common Mistakes That Inflate Cost or Cause Rework
- Sending only a 3D model, or only a drawing. The model gives geometry; the drawing gives intent. One without the other forces the supplier to guess.
- Over-specifying tolerances. Every dimension at ±0.01 mm can raise the quote by 30–60% with no functional benefit. Use ISO 2768-m as the default.
- Naming material by family only. "Aluminium" or "steel" leaves the alloy and temper open. Specify the grade, for example 6061-T6.
- Vague finish requirements. "Nice surface" or "smooth" cannot be quoted or inspected. Give a Ra value or a named finish per feature.
- Missing revision control. If the model is Rev C and the drawing is Rev B, the supplier cannot know which version to cut. Match them, and put the revision in the filename.
- No inspection requirement stated. If you do not say what to inspect, the supplier must either quote 100% inspection (expensive) or skip it (risky). State first-article, in-process and final inspection, and whether you need a material certificate.
- Skipping the prototype. Ordering 1,000 pieces from a new supplier with no prior sample is the most expensive way to discover a fit problem. Start with a small prototype run, approve the first article, then commit to volume.
DFM Tips: Small Design Changes That Cut Cost
You can cut more cost with a design change than with any negotiation. These are general rules — confirm limits for your material and size with engineering before you release the drawing:
- Inside corners: End mills leave a radius in every inside corner. Draw inside radii slightly larger than the cutter, and keep the same radius where possible so one tool can cut them all.
- Deep, narrow pockets: Pocket depth beyond about four times the pocket's smallest width is slower and risks deflection and poor finish. Widen the pocket, reduce depth, or split the part.
- Thin walls: Very thin walls and unsupported ribs deflect under cutting forces. Add a rib, increase wall thickness, or accept a looser tolerance on that feature.
- Threads: Thread engagement beyond 1.5 times the nominal bolt diameter adds almost no holding strength. Keep usable thread depth to 1.0–1.5× diameter, and allow drill-point relief below a blind hole.
- Standard holes and radii: A Ø7.33 mm hole or an R2.17 mm inside radius forces non-standard tooling. Use standard drill sizes and common radii where function allows.
- Fewer setups: Features that need many re-fixturings cost more than features that can be cut in one or two setups. Ask the supplier during DFM review whether a datum or orientation change would reduce setups.
Send the drawing early, before it is frozen, if you want DFM feedback to be useful. A suggestion that saves 20% is worth little after tooling is made.
What Happens After You Send Your RFQ to Golden Rainbow
- Send your drawings. Upload STEP / STP, PDF or DWG files, with material, quantity, tolerance and finishing requirements, via the Request a Quote page. You can also email Stella at stellachen@goldenrainbow.com or message on WhatsApp at +86 135 9028 8306.
- Engineering review. Golden Rainbow reviews manufacturability, process route, material, tolerances and inspection expectations, and clarifies open points with you.
- Quote within 24 hours. For a complete RFQ, you receive a quoted price and lead time, with DFM notes, within 24 hours on business days.
- Prototype and first article. Prototype orders start at 1 piece, typically in 3–7 business days. Approve the first article before committing to volume.
- Production and inspection. Low-volume and repeat production typically runs in 10–15 business days, depending on quantity, complexity and finishing. Parts are inspected against your drawing before shipment, and material and inspection documentation is provided as agreed on the quote.
Golden Rainbow supports CNC milling (3-axis and 4-axis), CNC turning, Swiss machining and wire EDM for medical, aerospace, semiconductor, industrial automation and automotive OEM programmes. If you are unsure which process fits your part — for example, whether a small, slender, feature-dense part should be Swiss-machined or conventionally turned — include that question in your RFQ. The engineering review is the right place to answer it.
Frequently Asked Questions
Do I need both a STEP file and a PDF drawing?
Yes, when you have both. The STEP file defines the geometry; the PDF defines tolerances, finish and material. If you have only one, send the 3D model for a geometrically complex part, and the 2D drawing for a simple but tolerance-critical part — and state material and quantity in your message either way.
What is the minimum order quantity?
1 piece. Prototype and low-volume orders are welcome, and you can request prices at several quantities to see where the unit price levels out.
How fast will I get a quote?
For a complete RFQ — STEP file, dimensioned PDF, material, quantity, tolerance and finish — Golden Rainbow replies within 24 hours on business days, with DFM feedback where applicable.
What tolerance can you hold?
Standard tolerance is ±0.05 mm. Tight tolerances down to ±0.01 mm are achievable on selected features, subject to drawing review. Do not apply ±0.01 mm to every dimension; mark only the features where function demands it.
Can you sign an NDA before I send drawings?
Yes — mention it in your RFQ message and the team will arrange confidentiality before you upload controlled drawings.
Send Your RFQ
The fastest way to get an accurate price is to send a complete package, not to send a drawing and wait for questions. Upload your STEP file and dimensioned PDF, state the material grade, quantities, critical tolerances and finish, and tell us your need-by date and ship-to destination.
Request a quote from Golden Rainbow — upload your drawings and get an engineer-reviewed quote within 24 hours on business days.
Contact: Stella — stellachen@goldenrainbow.com · WhatsApp +86 135 9028 8306
More from Golden Rainbow. Related reading: Choosing a Surface Finish for CNC Parts.
