Locally CNC Machining Service: 5 Essential Checks Before You Send a PO
This guide is for engineers and buyers comparing shops for a locally cnc machining service. It lists the checks that decide whether parts arrive on tolerance and on schedule: process capability, lead time, MOQ, certificates and inspection paper. Read it before you release a drawing.
In this article
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Key takeaways
What a locally cnc machining service should be able to show
Numbers below come from our own shop floor in Dongguan. Use the same columns when you audit any supplier.
| Check | Weak answer | Strong answer |
|---|---|---|
| Tolerance claim | "We hold tight tolerances" | ±0.005 mm stated with the inspection method |
| Machine list | 3-axis only, no count | 127 machines, 16 simultaneous 5-axis |
| Max part size | Not stated | Up to 4,000 mm, travel 4,000 × 400 × 150 mm |
| Quote turnaround | "We will get back to you" | Quote plus free DFM within 12 hours |
| Production start | Same as quote time | Can start within 24 hours of PO |
| Minimum order | "Depends on the part" | No MOQ, from 1 prototype to 10,000+ |
| Certificates | ISO 9001 only, no scope | ISO 9001, IATF 16949, ISO 13485, ISO 27001 |
| Surface finish | "Smooth finish" | Ra 0.2–0.8 μm fine, Ra 0.8–1.6 μm standard |
Pick the shop that answers with numbers
A locally cnc machining service earns the order when it can state its tolerance, its machine list, its lead time and its certificates without hedging. Everything else is a brochure.
Process capability: which machine actually cuts your part
A locally cnc machining service is only as good as the spindle that touches your geometry. Ask which machine class will run the job, not which class the shop owns. A part with undercuts, angled holes or a contoured face needs simultaneous 5-axis work; a prismatic bracket with three orthogonal faces is fine on a 3-axis mill and will cost less.
For our shop, the split is 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. That mix matters because quoting a 5-axis part on a 3-axis machine means multiple fixtures and a tolerance stack you cannot hold. Conversely, quoting a simple plate on a 5-axis center wastes money.
Part envelope decides the rest. Our maximum processing size is 4,000 mm, with large travel at 4,000 × 400 × 150 mm and medium travel at 750 × 1,150 × 550 mm or 600 × 600 × 600 mm. Compact work runs on 500 × 500 × 450 mm and 500 × 310 × 200 mm machines. If your part is 900 mm long and needs a rotary table, confirm the Ø400 mm table is available before you plan the setup.
Tolerance follows from that setup. We hold ±0.005 mm (±0.0002 in) on machined features, with a 99.99% qualification rate. Those numbers only hold when the drawing datums match the fixturing, so send the model and the 2D drawing together.
- 1Send STEP plus PDF drawingThe 3D model shows geometry; the 2D drawing carries datums, tolerances and finish callouts.
- 2Name the critical featuresMark the 3–5 dimensions that decide fit. The rest can run at general tolerance.
- 3Ask about workholdingThin walls and tall bosses need soft jaws or vacuum plates. That is a cost line, not a footnote.
Lead time: quote speed, production start and shipping
Lead time is three numbers, not one. The first is how fast you get a price and a manufacturability review. The second is how fast chips start flying after the PO. The third is how fast parts leave the dock. A shop that is quick on the first and slow on the second is not fast.
We quote and return a free DFM analysis within 12 hours. Production can start within 24 hours of a confirmed order. Parts ship in 3–5 days. Our historical late-delivery probability is below 2%. Those figures describe our standard flow; a part needing a custom fixture or an outside finish will take longer, and we will say so in the quote.
The trap is a shop that treats the quote as the promise. Ask what happens if a first article fails. Ask who pays for the rework. Ask whether the finish is done in-house or sent out, because an outside anodizer adds days that never appear on the original quote.
For scheduling, work backwards from your assembly date. Add buffer for incoming inspection on your side. A three-day shipping window sounds generous until your QC finds a burr on one cavity.
- 1Quote and DFM in 12 hoursYou get a price and a list of features that will be hard to machine.
- 2Start within 24 hoursAfter PO and material confirmation, not after the drawing is re-read.
- 3Ship in 3–5 daysStandard flow. Custom fixtures and outside finishing extend it.
MOQ, materials and finishing under one roof
Minimum order quantity is where prototype work dies. A shop that wants 500 pieces to start a setup is not set up for engineering iterations. We have no minimum order quantity, from one prototype to 10,000+ part runs. That covers the awkward middle: five units for a bench test, then fifty for a pilot, then a production release.
Material coverage should be broad enough that you do not source yourself. We machine aluminium 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12; stainless 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH; steel 1018, 1045, 4130, 4140, 4340, A36 and tool steel; copper and brass C101, C103, C110, beryllium copper, C27400, C28000 and C36000; titanium TA1, TA2, TC4, plus Inconel and magnesium AZ31B / AZ91D; and plastics ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre.
Finishing is the hidden lead-time risk. If the shop machines in-house but sends every part out for anodizing, your schedule depends on a third party you cannot audit. We run anodizing (clear, colour, hardcoat, conductive), electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing, plus laser marking with a minimum character height of 1.5 mm.
One warning on laser marking: if your part number string is small, 1.5 mm is the floor. Scale the text or move the mark to a flat face.
- 1Prototype to productionOne piece or 10,000+, same shop, same inspection standard.
- 2Titanium and InconelTC4 (Ti-6Al-4V) and Inconel need slower feeds and better coolant. Not every shop runs them.
- 3Finishing in-houseKeeps the schedule inside one building and one quality system.
Certificates and inspection: what the paper actually covers
A certificate is not a score. It is a scope document. ISO 9001:2015 tells you the shop runs a documented quality system. IATF 16949:2016 adds the automotive-specific controls, including traceability and change management. ISO 13485:2016 is the medical device standard. ISO 27001:2022 covers information security, which matters when you send proprietary CAD files.
We hold all four. If your program is automotive, ask for IATF 16949 and for the PPAP level you need. If it is a surgical instrument or a diagnostic housing, ask for ISO 13485 and for material traceability back to the heat lot. Sending a medical part to a shop with only ISO 9001 is a compliance problem before it is a quality problem.
Inspection is the other half. We inspect 100% of parts before shipment, with raw material check, in-process monitoring and final inspection. Reports are available on request. Decide before the order which report you want: a dimensional layout on the critical features, a material certificate, a finish thickness reading, or all three.
Confidentiality belongs in this section too. Uploads are secure and confidential, and an NDA is available on request. If your drawing cannot leave the building without a signed agreement, ask for it on day one, not after the quote.
- 1Match the certificate to the industryIATF 16949 for automotive, ISO 13485 for medical, ISO 9001 as the floor.
- 2Specify the reportSay which dimensions get measured and at what frequency.
- 3NDA before filesSign first, then upload. That order protects both sides.
Red flags when you audit a locally cnc machining service
Most bad outcomes are visible before the PO. The clearest red flag is a quote with no questions. Any shop that prices a part without asking about datum strategy, wall thickness or finish has either seen it a hundred times or has not looked at it. Ask for the DFM notes. If there are none, you are buying a promise.
The second flag is a missing machine list. If a supplier cannot name the spindle count, the axis configuration and the travel envelope, it is brokering the work. Brokering is not automatically wrong, but you should know, because it changes who owns the tolerance and who handles rework.
The third flag is vague quality language. "High precision" and "strict QC" mean nothing. ±0.005 mm, Ra 0.8–1.6 μm, 100% inspection before shipment: those are auditable. Ask for the inspection report format before you order, and check that it lists the features you care about.
The fourth flag is a schedule that has no slack. If quote, production and shipping are all described as "fast" with no numbers, you have no way to plan your own line. Get the three numbers in writing.
- 1No DFM feedbackA serious shop returns notes even when the design is easy.
- 2No machine listYou cannot judge capability without the axis count and travel.
- 3No inspection formatIf you cannot see the report structure, you cannot rely on it.
Step by step: how to qualify a shop in one week
Run these in order. Each step produces a document you can compare across suppliers.
- 1Send the model and the drawingSTEP or IGES for geometry, PDF for datums and tolerances. Note the critical dimensions, usually 3–5 of them.
- 2Ask for the DFM notes with the priceExpect a list of thin walls under 0.8 mm, pockets deeper than 4× the tool diameter, and any feature needing a special cutter.
- 3Get the three lead-time numbersQuote turnaround, production start after PO, and ship date. Ours are 12 hours, 24 hours and 3–5 days.
- 4Confirm the machine class and travelMatch your part envelope to the machine. Large travel is 4,000 × 400 × 150 mm; compact is 500 × 310 × 200 mm.
- 5Check certificates against your industryISO 9001:2015, IATF 16949:2016, ISO 13485:2016, ISO 27001:2022. Ask which scope applies to your part.
- 6Agree the inspection reportPick the dimensions, the sampling, and the format before the first chip. 100% inspection before shipment is our default.
- 7Sign the NDA, then release filesUploads are secure and confidential. If you need an NDA, request it before sending CAD.
- 8Run a first article before the full runNo MOQ means you can order one piece, measure it, then release the batch. Use that.
Questions buyers ask before the first order
How do I compare quotes from different local shops fairly?
Normalize the scope first. Ask each shop to quote the same revision, the same material condition, the same finish and the same inspection report. A low price that excludes anodizing or a first article is not comparable.
Then compare the DFM notes. Two shops at the same price are not equal if one flagged a thin wall that will deflect and the other stayed silent.
What tolerance can a locally cnc machining service actually hold?
We hold ±0.005 mm (±0.0002 in) on machined features with a 99.99% qualification rate. That figure assumes a rigid setup, a stable material and a drawing whose datums match the fixturing.
Very thin walls, long unsupported bores and soft plastics will not reach that. Tell us the function of the feature and we will say what is realistic.
Is there a minimum order quantity for prototypes?
No. We run from one prototype to 10,000+ part runs. A single piece gets the same process planning as a batch, though the per-piece cost is naturally higher.
Many customers order one or two units for fit checks, then release the production quantity once the first article measures out.
Which certifications should I ask for?
ISO 9001:2015 is the baseline for any supplier. Add IATF 16949:2016 for automotive and EV programs, ISO 13485:2016 for medical devices, and ISO 27001:2022 when information security is part of your audit.
How is surface finish specified?
Use Ra values. We work to Ra 0.2–0.8 μm for fine finishes, Ra 0.8–1.6 μm for standard machined surfaces, and Ra 1.6–3.2 μm as-machined. Call out the finish on the specific faces that need it.
A blanket Ra 0.4 μm on every face raises cost with no functional gain. Put the callout where it matters.
Can you handle large parts as well as small ones?
Yes. Maximum processing size is 4,000 mm, with large travel at 4,000 × 400 × 150 mm. Medium work runs on 750 × 1,150 × 550 mm and 600 × 600 × 600 mm machines, and compact parts on 500 × 500 × 450 mm and 500 × 310 × 200 mm centers.
A Ø400 mm rotary table covers 4-axis work on cylindrical and indexed features.
Send a drawing, get a price and DFM notes in 12 hours
Upload your STEP and PDF. We return a quotation, a manufacturability review and the three lead-time numbers. No MOQ, 100% inspection before shipment, NDA on request.
12-hour quoteNo MOQ±0.005 mm100% inspection
More from the shop floor
We publish setup notes, tooling trials and inspection data from the factory floor.
