Buyer guide

CNC Machin Contact Service: 6 Proven Checks Before You Send an RFQ

A buyer guide for engineers and sourcing staff who are choosing a cnc machin contact service. It lists the checks that separate a supplier you can run production with from one that only answers the phone fast.

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±0.005 mm toleranceNo minimum order quantityQuote + DFM in 12 hoursISO 9001 / IATF 16949

cnc machin contact service team reviewing a machined part

On this page

1
Key takeaways
2
What to check before you commit to a cnc machin contact service
3
Tolerance talk that survives first contact
4
Quote content: what a real cnc machin contact service sends back
5
Lead time, order size and what they cost you in practice
6
Certifications, inspection and confidentiality
7
Step by step: from first email to a purchase order

Quick answer

Key takeaways

Ask for the machining route, not a price onlyA usable quote names the machine type, stock size and fixture plan. A number alone tells you nothing about risk.

Check tolerance against the feature, not the part±0.005 mm is realistic on a 50 mm bore and unrealistic across a 4,000 mm frame. Ask which features hold it.

MOQ decides whether you can iterateSuppliers with no minimum order quantity let you machine one prototype, inspect it, then correct the model.

Certificates matter by industryISO 9001 covers general work. IATF 16949, ISO 13485 and ISO 27001 are what automotive, medical and IP-sensitive buyers look for.

Slow answers before the order predict slow answers after itQuote speed is the cheapest test of how a supplier communicates once chips are flying.

Decision table

What to check before you commit to a cnc machin contact service

Match the check to your part and your program stage.

Check	What good looks like	Red flag
Tolerance	Feature-level callout with a stated limit	One blanket ±0.005 mm on the whole drawing
Quote content	Machine, stock, fixturing and finish listed	A single price with no process note
Lead time	Quote and DFM analysis in 12 hours	No date given, or a date with no basis
Minimum order	No minimum order quantity	Tooling charge before one prototype
Certifications	ISO 9001, IATF 16949, ISO 13485, ISO 27001	Certificates you cannot view
Inspection	100% inspection before shipment	Sample inspection only, no report
Finishing	In-house anodizing, plating, black oxide	Subcontractor with no schedule control
Confidentiality	NDA available on request	Drawings sent over personal email

Pick the supplier who answers the technical question

If two shops return the same price, choose the one that told you which features cannot hold ±0.005 mm. That answer is worth more than the discount you were offered.

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Check 1

Tolerance talk that survives first contact

Most first emails fail on tolerance. A drawing marked ±0.005 mm everywhere tells a machine shop nothing about intent. It also invites a quote that is either padded or quietly optimistic. Before you send the RFQ, mark the two or three features that actually control fit and function. Those are the ones worth the tight limit.

On a 50 mm bearing bore, ±0.005 mm is normal work for a 5-axis machining center with a probe. Across a 4,000 mm frame, the same number is a different problem: thermal drift, fixturing and machine geometry all enter the stack. A shop that answers this honestly will ask which features need the tight band instead of repeating your number back.

Surface finish follows the same logic. Ra 0.8–1.6 μm is a standard machined finish. Ra 0.2–0.8 μm needs a finishing pass, a sharper tool and often a different setup. If you need both a tight bore and a fine finish, say so early. It changes the tool list and the cycle time.

Ask one question in the first exchange: which features will you inspect, and with what? A supplier who names the inspection method, not just the tolerance, is telling you they have measured parts like yours before.

1
Mark critical featuresTwo or three dimensions that drive assembly, no more.
2
Give the material and temper6061-T6 machines differently from 7075 or 17-4PH.
3
State the finish per surfaceA cosmetic face and a sealing face rarely share a spec.

Check 2

Quote content: what a real cnc machin contact service sends back

A quote is a process plan with a price on it. If the reply is a number and a lead time, you cannot judge the risk. Ask for the machine class, the stock form and size, the fixture approach, and the finishing step. That is four lines of text and it tells you whether the supplier read the model.

Free DFM analysis is the other half. A useful DFM note flags a corner radius a 6 mm end mill cannot reach, a wall that will chatter at 0.8 mm, or a thread too close to a shoulder for the tap to seat. These are the notes that save a revision cycle. GreatLight returns quotation and free DFM analysis within 12 hours, and production can start within 24 hours once you approve.

Watch for quotes that hide finishing. Anodizing, electroless nickel and black oxide change dimensions slightly and add days. If they are not on the quote, they will appear later as a schedule problem.

Finally, compare like with like. Two quotes differ because one assumed bar stock and the other assumed a casting, or one included a fixture and the other did not. Read the assumptions before you read the price.

1
Machine class3-axis, 4-axis, 5-axis or mill-turn, named explicitly.
2
Stock formPlate, bar, forging or casting, with the size.
3
Finishing line itemAnodizing type, plating, black oxide, blasting.
4
AssumptionsWhat the price includes and what it does not.

Check 3

Lead time, order size and what they cost you in practice

Lead time is a schedule, not a slogan. Ask when the raw material arrives, when the first article comes off the machine, and when finishing and inspection finish. A shop running 127 high-precision CNC machines across three wholly-owned plants can absorb a rush job; a broker with one partner shop cannot.

Order size matters more than most buyers expect. If the supplier has a minimum order quantity, you cannot machine one prototype, inspect it, fix the model and machine again. That loop is how tolerance problems get solved before tooling is cut. No minimum order quantity means you can run one part, then a 10,000+ part run on the same process.

Material availability is the hidden variable. Aluminum 6061 and 304 stainless are usually on the floor. Inconel, Ti-6Al-4V and beryllium copper often are not, and that gap is measured in weeks, not days. Put the material grade in the first email so the answer reflects it.

If a date sounds too good, ask what it is based on. A date tied to a specific machine and a specific stock size is a plan. A date with no basis is a wish.

1
Ask for three datesMaterial in, first article, ship.
2
Prototype firstOne part before a run proves the process.
3
Name exotic grades earlyInconel and titanium change the schedule.

Check 4

Certifications, inspection and confidentiality

Certification requirements follow the industry, not the part. General industrial work usually needs ISO 9001:2015. Automotive and EV programs look for IATF 16949:2016. Medical device work looks for ISO 13485:2016. If your drawings and models are sensitive, ISO 27001:2022 covers information security, which is separate from part quality.

Inspection is where a supplier proves the tolerance claim. Ask what is checked, on what equipment, and whether a report comes with the shipment. GreatLight runs raw material check, in-process monitoring and final inspection, with 100% inspection before shipment and reports on request. That sequence catches a drifting dimension before the last operation, which is cheaper than catching it at goods-in.

Confidentiality is a process, not a promise. Uploads should be secure and confidential, and a mutual NDA should be available on request before you send production drawings. If a supplier hesitates on an NDA, treat that as the answer.

For regulated programs, ask who signs the inspection report and how long records are kept. Traceability is what an auditor asks for first.

1
Match cert to industryISO 9001, IATF 16949, ISO 13485, ISO 27001.
2
Ask for the inspection planWhich features, which equipment, which stage.
3
NDA before drawingsSign first, then upload production files.

How to run the first contact

Step by step: from first email to a purchase order

Six steps that keep the RFQ clean and the schedule predictable.

1
Send the model, drawing and material in one messageAttach STEP plus a 2D drawing marked with critical features. Name the grade and temper, for example 6061-T6 or 17-4PH. Missing material data is the most common cause of a slow quote.
2
State quantity in two numbersGive the prototype quantity and the expected annual volume. One part and 10,000 parts are different processes, and the answer changes with both numbers on the table.
3
Ask for the DFM note with the priceRequest a short note on thin walls, deep pockets, small radii and thread callouts. A supplier who returns notes has read the geometry.
4
Confirm the tolerance band per featureReply with the two or three features that need ±0.005 mm and let the rest sit at general tolerance. This is where cost is won or lost.
5
Review the quote assumptionsCheck the machine class, stock form, finishing line items and inspection scope. Ask about anything that is not written down.
6
Approve one prototype, measure it, then release the runInspect the first article against the drawing, correct the model if needed, and only then commit to volume. Keep the inspection report with the part.

FAQs

Questions buyers ask before the first order

How fast should a cnc machin contact service reply?

For a complete RFQ with a 3D model, drawing and material grade, quotation and free DFM analysis within 12 hours is a reasonable benchmark. If the file set is incomplete, expect a question back rather than a price.

Speed matters because it predicts the rest of the project. A supplier who answers slowly at the quoting stage usually answers slowly when a dimension is out of spec.

Can I order a single prototype?

Yes, when the supplier has no minimum order quantity. That lets you machine one part, inspect it, adjust the CAD model and machine a second version without paying for tooling you may throw away.

The same process then scales to 10,000+ part runs. Ask whether the prototype process matches the production process, because they should not be different unless there is a reason.

What tolerance can be held on a large part?

GreatLight works to ±0.005 mm on suitable features, with a maximum processing size of 4,000 mm. The tight band applies to specific features that are machined in one setup with probing, not to every dimension on a large frame.

Send the drawing and we will tell you which features can hold the tight band and which need a looser callout. That answer belongs in the quote, not in a dispute later.

Do I need an NDA to send production files?

If the parts are proprietary, yes. Uploads are handled as secure and confidential, and an NDA is available on request. Sign it before you send production drawings, not after.

For programs that carry customer IP, ISO 27001:2022 gives you a documented information security framework on top of the NDA.

Which certifications should I ask to see?

Ask for the certificate that matches your industry: ISO 9001:2015 for general work, IATF 16949:2016 for automotive, ISO 13485:2016 for medical, and ISO 27001:2022 when information security is in scope.

Check the certificate scope and expiry date rather than the logo. A certificate that does not cover the process you are buying is not worth much.

How do I compare two quotes that differ by a lot?

Read the assumptions before the price. One quote may assume bar stock while the other assumes a casting, or one may exclude finishing and inspection. Put both onto the same scope and the gap usually shrinks.

If the gap survives, ask what is different in the process. A cheaper quote with no inspection plan is not cheaper, it is unpriced risk.