Significant CNC Machining Service: How to Judge One Before You Send a Drawing
A significant cnc machining service is not the one with the biggest machine list. It is the one that can hold your tolerance, quote in 12 hours, and document every inspection step. This guide gives engineers and buyers the checks that separate a capable shop from a risky one.
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What matters most in a significant cnc machining service
Judging criteria for a significant cnc machining service
Numbers come from GreatLight's own capability sheet, so you can compare a candidate shop against a known baseline.
| Criterion | What to ask | Baseline to compare against | Red flag |
|---|---|---|---|
| Tolerance | Achievable tolerance on my tightest feature? | ±0.005 mm (±0.0002 in) | Only quotes the tolerance of a simple test block |
| Axis capability | How many simultaneous 5-axis centers? | 16 five-axis, 12 four-axis, 27 three-axis | Counts total machines, not simultaneous axes |
| Part size | Maximum travel on the largest machine? | 4,000 × 400 × 150 mm | Cannot name the travel of any machine |
| Surface finish | Which finish range do you guarantee? | Ra 0.8–1.6 μm standard, Ra 0.2–0.8 μm fine | Promises Ra 0.2 μm on every material |
| Lead time | Quote turnaround and first-article ship date? | Quote in 12 h, parts ship in 3–5 days | Vague dates, no DFM feedback before cutting |
| Minimum order | Do you run one prototype? | No MOQ, one piece to 10,000+ | Minimum charge that makes prototypes uneconomic |
| Inspection | What is inspected, and what report do I get? | 100% inspection, reports on request | Sampling only, no dimensional record |
| Certification | Which certificates apply to my industry? | ISO 9001, IATF 16949, ISO 13485, ISO 27001 | Certificate expired or scope excludes machining |
The verdict: pick the shop that answers the process question
A significant cnc machining service is proven by the process plan it sends back with the quote. If the supplier names the machine, the setup count, the inspection method and the finish route, the price is worth comparing. If not, keep looking.
What a significant cnc machining service actually has to hold
Every shop advertises tight tolerance. The useful question is narrower: what tolerance can this shop hold on the feature that decides whether your assembly works? A flat plate with a few clearance holes is easy. A thin-wall housing with a 0.05 mm bore-to-bore position callout is not, and the two jobs should not be quoted the same way.
Our floor holds ±0.005 mm (±0.0002 in) across the qualified process range. That number only means something next to a finish spec and an inspection method. A bore measured with a micrometer on the bench and the same bore measured on a CMM in a temperature-controlled room can differ by more than the tolerance itself. Ask which method will be used, and ask for the report.
Finish and tolerance trade against each other. If you call out Ra 0.2–0.8 μm on a deep pocket, the shop has to slow the cutter and may need a second operation. If Ra 0.8–1.6 μm is acceptable, one pass often finishes the job. Decide which surfaces actually need the fine range before you release the drawing.
Geometry sets the floor, not the machine brand. A part with features on five faces will need either multiple fixtures or a five-axis setup. Each extra fixture adds a datum shift. On a 200 mm part, three setups can stack 0.03 mm of error before the cutter touches metal.
- 1Write the tolerance on the critical featureGeneral title-block tolerance hides where the risk sits and invites optimistic quoting.
- 2State the inspection methodCMM, gauge, or optical. The method has to be able to see the tolerance you asked for.
- 3Separate cosmetic from functional surfacesFine finish on a non-sealing face only adds cost and cycle time.
Axis count, part size and the setup decision
A significant cnc machining service should tell you which machine will run your part and why. GreatLight runs 16 simultaneous five-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. That mix exists because not every part earns a five-axis setup.
Five-axis pays off when the part has angled faces, deep pockets, or features that would otherwise need three or four fixtures. One setup means one datum, and the position error between features stays inside the machine's own accuracy. For a part with a Ø400 mm rotary table envelope, the table itself becomes the fourth and fifth axis, so you skip the re-clamp.
Three-axis still wins on flat plates, brackets, and simple pockets. Fixturing is cheap, cycle time is short, and the tolerance is easy to hold. Pushing that job onto a five-axis center adds hourly rate without adding accuracy.
Size decides the machine before anything else. Maximum processing size is 4,000 mm, and the large travel is 4,000 × 400 × 150 mm. Medium machines cover 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Compact machines handle 500 × 500 × 450 mm and 500 × 310 × 200 mm. If your part falls between two classes, the larger machine usually costs more per hour but needs fewer setups.
- 1Five-axisAngled features, contoured surfaces, deep pockets, or any part needing four or more setups.
- 2Four-axisCylindrical parts with cross-holes or slots that must stay in one angular relationship.
- 3Three-axisPrismatic parts where all features are reachable from one or two directions.
Materials and finishes that change the quote
Material choice moves the quote more than most buyers expect. Aluminum 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12 cut fast and hold tolerance well. Stainless 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH (SUS630) machine slower, work-harden if the feed is wrong, and wear tooling faster.
Titanium TA1, TA2, TC4 (Ti-6Al-4V), Inconel and magnesium AZ31B / AZ91D sit at the hard end. They need lower cutting speeds, more coolant, and a shop that has run them before. If a supplier quotes titanium at the same price as 6061, they have either misread the drawing or plan to learn on your part.
Steel grades 1018, 1045, 4130, 4140, 4340, A36 and tool steel cover most structural and mold work. Copper and brass C101, C103, C110, beryllium copper, C27400, C28000 and C36000 machine cleanly but move with temperature, so thin walls need light passes. Plastics such as ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre behave differently again: PEEK and carbon fibre are abrasive, while POM and PA can deflect under clamp pressure.
Finishing is a separate line item. Anodizing (clear, colour, hardcoat, conductive), electroless nickel, zinc, silver and gold plating, powder coating and black oxide, bead blasting, tumbling, brushing and polishing all add days. Laser marking and engraving need a minimum character height of 1.5 mm, so plan your part numbers accordingly.
- 1Anodizing before or after machiningHardcoat builds 25–50 μm per surface. Mask threads and bores that must stay in tolerance.
- 2Plating and blind holesElectroless nickel reaches into blind holes; zinc and powder coating do not.
Certification, inspection and what the paperwork covers
Certificates answer a specific question: can this shop be audited against the standard my customer requires? ISO 9001:2015 covers general quality management. IATF 16949:2016 applies to automotive production. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters when you send CAD files and drawings across borders.
A certificate is not a substitute for an inspection plan. GreatLight inspects 100% of parts before shipment, with raw material checks, in-process monitoring, and final inspection, and reports on request. The qualification rate is 99.99%. Ask what happens to the parts that fail that check, and whether you get the data or just a pass stamp.
Confidentiality is part of the selection, not an afterthought. Uploads are kept secure and confidential, and an NDA is available on request. If your drawing carries export-controlled geometry or a customer's unreleased product, settle the NDA before the RFQ, not after the PO.
Certification scope matters. A certificate that covers assembly but not machining does not help you. Ask for the scope statement and check that CNC turning, milling and the finishing processes you need are inside it.
- 1AutomotiveIATF 16949:2016 plus PPAP-style dimensional reports.
- 2MedicalISO 13485:2016 plus traceable material certificates.
- 3ITAR-adjacent or IP-sensitive workISO 27001:2022 plus a signed NDA before file transfer.
Lead time, MOQ and the real cost of a slow supplier
Quotation and free DFM analysis come back within 12 hours, and production can start within 24 hours. Parts ship in 3–5 days for the standard range. Those numbers matter because they compress your own schedule risk. The historical late-delivery probability is below 2%, which is a useful figure to compare against a shop that quotes 4–6 weeks with no data behind it.
No minimum order quantity runs from one prototype to 10,000+ part runs. That range tells you the shop can switch between a single setup for a prototype and a pallet of fixtures for a production run without sending you elsewhere. A shop that only takes 500-piece orders will not give a prototype the same engineering attention.
Price is the last variable, not the first. A supplier who quotes 20% less but needs two extra setups, a second finishing vendor, and a rework loop has not saved you money. Ask for the process plan: which machine, how many setups, which inspection step, which finish vendor. If the supplier cannot describe that, the quote is a guess.
Buyers often forget freight and duty. Parts crossing borders can sit in customs longer than they spent on the machine. If your schedule is tight, ask which plant will run the job. GreatLight operates three wholly-owned plants, with a Singapore factory at No.3 Joo Koon Circle, Singapore 629032, alongside the 7,600 m² Dongguan site.
- 1Ask for the process planMachine, setup count, inspection method, finish route.
- 2Confirm which plant shipsIt changes transit time and duty, not just the price.
Seven steps to vet a significant cnc machining service
Run these in order. Each step either passes or gives you a specific question to put back to the supplier.
- 1Send the drawing with the critical tolerance markedMark the feature that decides assembly fit. If the supplier only repeats your title-block tolerance, they have not read the drawing.
- 2Ask for the DFM feedback before the priceA real shop flags thin walls, deep pockets, unreamed holes and tight radii within 12 hours. A quote with no comments is a red flag.
- 3Request the machine and setup countExpect a named machine class and a setup number. Three-axis for prismatic parts, five-axis when features sit on four or more faces.
- 4Confirm the finish route and vendorAnodizing adds 2–4 days, plating adds 3–5. Ask whether finishing is in-house and whether masking is included.
- 5Check the certificate scopeISO 9001, IATF 16949, ISO 13485 and ISO 27001 cover different risks. Confirm the scope includes CNC machining and your finishing process.
- 6Order a first article, not a full runSince there is no minimum order quantity, buy one or two pieces first. Measure them yourself before releasing the 10,000-piece order.
- 7Agree on the inspection record before shippingDecide which dimensions appear on the report and who signs it. Do this while the parts are still on the machine.
Questions buyers ask before releasing a PO
What tolerance can a significant cnc machining service hold on a production run?
GreatLight holds ±0.005 mm (±0.0002 in) across the qualified process range. That figure assumes a stable drawing, one material batch, and an inspection method capable of resolving the tolerance.
On thin walls, long bores, or free-machining plastics, the achievable tolerance narrows. Send the specific feature and we will tell you what the process can hold before you commit.
Do I need five-axis machining for my part?
Only if your features sit on four or more faces, are angled, or follow a contour. If everything is reachable from one or two directions, three-axis is faster and cheaper.
Five-axis removes stacked fixture error. On a 200 mm part, three setups can add 0.03 mm of position error that a single five-axis setup avoids.
How fast can I get a quotation and a first article?
Quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours, and parts ship in 3–5 days for the standard range.
The historical late-delivery probability is below 2%. Exact dates depend on material availability and finishing, so confirm the schedule with the process plan, not the headline number.
What is the minimum order quantity?
There is no minimum order quantity. The floor runs from one prototype to 10,000+ part runs on the same equipment and inspection process.
That matters for engineers who need a single fit-check part before releasing tooling or a production PO.
Which certifications should I check for my industry?
Automotive work needs IATF 16949:2016. Medical devices need ISO 13485:2016. General industrial work is covered by ISO 9001:2015, and IP-sensitive programs benefit from ISO 27001:2022.
Always read the scope statement. A certificate that excludes machining does not cover the process you are buying.
How is my design kept confidential?
Uploads are secure and confidential, and a non-disclosure agreement is available on request. Sign it before you transfer CAD files, not after the purchase order.
If your program carries export-controlled geometry, tell us at the RFQ stage so the file handling and plant routing can be set up correctly.
Send the drawing and get a real process plan
Quotation and free DFM analysis within 12 hours. No minimum order quantity, 100% inspection before shipment, and an NDA on request.
12-hour quote100% inspectionNo MOQNDA available
More machining notes from the floor
We publish setup notes, tooling trials and inspection data from the factory floor.
