Buyer's guide

CNC processing in more than 100 industries

This page is for engineers and buyers comparing suppliers for CNC processing 100 industries work. It lists the checks that actually change a quote: part size against machine travel, tolerance stack, certification scope, order quantity, and what a supplier asks you before cutting metal. Read it and you can shortlist three shops instead of thirty.

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±0.005 mm tolerance1 pc to 10,000+ partsISO 9001 / IATF 16949Quote in 12 hours

CNC processing 100 industries parts machined on 5-axis centers

On this page

1
Key takeaways
2
What to compare before you commit
3
Why machine travel decides your supplier shortlist
4
Reading tolerance and surface finish as cost signals
5
Which certification your part actually needs
6
Order quantity, lead time and what the quote covers
7
How to prepare an RFQ that gets a usable quote

Quick read

Key takeaways

Match the part to machine travel, not to a brochureA 4,000 mm frame and a Ø30 mm bushing rarely come off the same machine. Ask which spindle holds your part.

Tolerance is a cost switch±0.005 mm is achievable, but only where the drawing calls for it. Blanket tight tolerances raise price on every feature.

Certification has a scopeISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022 cover different things. Ask which one applies to your part.

No MOQ changes prototyping mathOne prototype and a 10,000-part run are both normal. Setup cost, not quantity, drives the unit price curve.

Ask what the quote includesMaterial certificate, inspection report and finish are separate line items at some shops. Get it in writing.

Selection criteria

What to compare before you commit

Same part, three types of supplier

Criterion	Job shop (general)	GreatLight (Dongguan)
Machine count and type	Often 5–20 mixed machines	127 CNC machines, 16 five-axis
Largest part envelope	Rarely beyond 1,500 mm	4,000 mm maximum processing size
Tolerance on request	±0.05 mm typical	±0.005 mm where called out
Surface finish range	As machined only	Ra 0.2–0.8 μm to Ra 1.6–3.2 μm
Order quantity	Batch work, high MOQ	No MOQ, 1 pc to 10,000+
Certifications	ISO 9001 at best	ISO 9001, IATF 16949, ISO 13485, ISO 27001
Quote turnaround	3–7 days common	12 hours with free DFM analysis
Confidentiality	NDA sometimes refused	NDA on request, secure uploads

Pick the supplier who asks the hard questions

If a shop quotes without asking about datums, material grade or finish function, the price is a guess. Send your drawing to a team that will push back on tolerance and setup before cutting metal.

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Envelope and setup

Why machine travel decides your supplier shortlist

Most sourcing problems start before the quote. A drawing with a 2,800 mm rail and a 0.02 mm flatness callout cannot be made on a 600 mm mill, no matter how good the shop is. The first filter is the work envelope. GreatLight runs 4,000 × 400 × 150 mm travel on the large machines, 750 × 1,150 × 550 mm and 600 × 600 × 600 mm on the mid-size mills, and 500 × 500 × 450 mm or 500 × 310 × 200 mm on the compact ones. A Ø400 mm rotary table covers round parts that need milling on the face and the OD in one setup.

Ask which spindle will hold your part, not how many spindles the shop owns. A shop with 127 machines still sends your 4,000 mm beam to one specific gantry. If that machine is booked, your lead time moves. Suppliers who answer this question clearly are usually the ones who also flag DFM issues early.

Setup count is the second filter. A part that fits in one 5-axis setup avoids the re-fixturing error that shows up as a 0.03 mm step between faces. A part that needs four operations on three machines will cost more and drift more. When a shop proposes fewer setups than you expected, ask how they hold the part. The answer tells you whether they have actually thought about your geometry.

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Large parts4,000 mm travel, 5-axis gantry work for frames, rails and housings.
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Round partsØ400 mm rotary table for milling flats and drilling on a turned blank.
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Small precise partsCompact mills with ±0.005 mm capability on critical features.
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One-setup work16 simultaneous 5-axis centers reduce re-fixturing error.

Tolerance and finish

Reading tolerance and surface finish as cost signals

Tolerance is not a single number for a whole part. It is a stack: datum position, feature size, flatness, concentricity. A drawing that says ±0.005 mm on everything forces the shop to slow down every cut. A drawing that reserves ±0.005 mm for the bearing bore and leaves ±0.1 mm on clearance holes is cheaper, faster, and just as functional. When you review a quote, check whether the shop questioned your tolerances. Silence usually means they priced the tightest reading.

Surface finish works the same way. As-machined surfaces land around Ra 1.6–3.2 μm. A good milled finish reaches Ra 0.8–1.6 μm. Fine finishes at Ra 0.2–0.8 μm need slower feeds, sharper tooling, or a secondary operation. If your part is an internal bracket, as-machined is fine. If it is a sealing face or a sliding bore, specify the finish and expect the price to follow.

Materials set the floor. Aluminium 6061-T6 cuts fast and holds ±0.005 mm on moderate features. 17-4PH stainless and Inconel move more after machining, so the shop has to plan the sequence. Titanium TC4 (Ti-6Al-4V) needs lower cutting speeds and more coolant. PEEK and carbon fibre behave differently again, and carbon dust needs extraction. Tell the supplier the material grade, not just the family. "Stainless" covers 303 and 316L, and they machine nothing alike.

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Tight on features onlyReserve ±0.005 mm for fits and bores, open up the rest.
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Name the finishRa 0.8–1.6 μm is a normal milled finish; Ra 0.2–0.8 μm costs more.
3
Give the grade6061-T6, 316L, 17-4PH, TC4, PEEK — grade changes the cutting data.

Certification and traceability

Which certification your part actually needs

Certificates are issued to a scope, not to a company in general. ISO 9001:2015 covers a quality management system. IATF 16949:2016 adds automotive-specific requirements such as APQP, PPAP and traceability through the production line. ISO 13485:2016 is the medical device standard and brings its own documentation and process-validation expectations. ISO 27001:2022 covers information security, which matters when your drawings and CAD files sit on a supplier's server.

A supplier can hold all four and still not have your part in scope. If you build automotive parts, ask for the IATF certificate and check that the machining process is listed. If you build surgical instruments, ask how the supplier controls material traceability and cleaning. The certificate is the entry ticket; the process description is the substance.

Traceability is the practical part. A raw material certificate linked to a heat number, in-process records, and a final inspection report let you answer a customer complaint six months later. GreatLight inspects 100% of parts before shipment and runs raw material checks, in-process monitoring and final inspection. Reports are available on request. Ask for a sample report before you place the order, not after.

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ISO 9001:2015Baseline quality system for general industrial work.
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IATF 16949:2016Automotive programs, PPAP and line traceability.
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ISO 13485:2016Medical devices, validation and documentation control.
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ISO 27001:2022Protects your CAD files and drawings on the supplier side.

Quantity and quote

Order quantity, lead time and what the quote covers

There is no minimum order quantity here, so a single prototype and a 10,000+ part run both go through the same route. That does not mean they cost the same per part. The first part carries programming, fixturing and first-article inspection. By part 500, the fixture is amortized and the cycle time is stable. If you are planning a bridge build, ask for the price at three quantities and look at where the curve flattens. That point tells you when tooling becomes worth it.

Lead time splits into three parts. Quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours of approval. Parts ship in 3–5 days for typical work. The historical late-delivery probability is below 2%, which is a track record, not a promise. For a new part with an unusual feature, add time for the first-article review.

Read the quote as a scope document. Does it list material grade, finish, tolerance class and inspection? Does it include the material certificate? Is finishing a separate line? A quote that says "CNC machining, aluminium" is not comparable with one that says "6061-T6, clear anodize, Ra 1.6 μm, FAI report included." When two quotes differ by 40%, the difference is usually scope, not margin.

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Three-quantity pricingAsk for 1, 100 and 1,000 pieces to see the cost curve.
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12-hour quoteQuotation and free DFM analysis within 12 hours.
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3–5 day shippingTypical parts ship in 3–5 days after production starts.
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Scope, not priceCompare material, finish, tolerance and reports line by line.

RFQ preparation

How to prepare an RFQ that gets a usable quote

1
Send 3D and 2D togetherSTEP or IGES for geometry, PDF drawing for tolerance, datum and finish callouts. A 3D file alone hides your GD&T intent.
2
Mark critical featuresNote which dimensions carry ±0.005 mm and which are free. This single step often cuts quote price by 10–20%.
3
State the material gradeWrite 6061-T6, 316L, 17-4PH or TC4. Avoid "aluminium" or "stainless" — cutting data and price depend on the grade.
4
List finish and functionSay whether the surface is cosmetic, sealing or sliding. Anodize, bead blast and polish are not interchangeable.
5
Give quantity and target dateInclude prototype, bridge and production volumes. Mention if the part goes into an automotive or medical program.
6
Ask for DFM feedbackRequest the free DFM analysis with the quote. Thin walls, deep pockets and sharp internal corners are where cost hides.
7
Confirm inspection and NDAState whether you need a first-article report, material certificate, or an NDA before files move. Secure uploads are standard here.

FAQs

Questions buyers ask before ordering

How do I know if my part needs 5-axis machining?

If the part has features on multiple faces that must stay in one datum relationship, 5-axis saves setups and protects position tolerance. If it is a flat plate with holes on one face, 3-axis is faster and cheaper.

A practical test: count the setups the 3-axis route needs. Two or three setups with a 0.02 mm position callout across faces is a strong signal to move to 5-axis.

What is the largest part you can machine?

The large machines cover 4,000 × 400 × 150 mm travel, which handles long frames, rails and structural housings. Mid-size mills cover 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Compact machines cover 500 × 500 × 450 mm and 500 × 310 × 200 mm.

Send the bounding box of the finished part plus stock allowance. A part that fits the envelope on paper can still fail if the fixture pushes it outside the travel.

Can you hold ±0.005 mm on every dimension?

The machines can reach ±0.005 mm, but applying it to every dimension raises cost without adding function. We recommend reserving tight tolerance for fits, bores and mating surfaces, and opening up clearance features.

Temperature, material stress and fixture rigidity all affect the result. On 17-4PH or Inconel, we usually discuss which features truly need the tight band before quoting.

Do you work with one-off prototypes?

Yes. There is no minimum order quantity, so one prototype and a 10,000+ part run both fit. Prototypes go through the same inspection route as production parts.

For a first article, expect a DFM note if a feature is hard to machine as drawn. Fixing it at the prototype stage is cheaper than at part 5,000.

How is my design kept confidential?

Uploads are secure and confidential, and an NDA is available on request. Information security is covered by ISO 27001:2022.

If your program requires restricted file access or a named engineering contact, say so in the RFQ and it gets set up before files move.

What finishes can be applied after machining?

Anodizing (clear, colour, hardcoat, conductive), electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing. Laser marking and engraving are available down to 1.5 mm character height.

Finish choice affects dimensions. Hardcoat anodize builds on the surface, so specify whether the coating is included in the final tolerance.