Xometry CNC Machining Services: How to Choose Before You Upload CAD
Xometry CNC machining services work like a marketplace: you upload a model, get an automated quote, and the platform routes the job to a partner shop. This guide is for engineers and buyers who need to judge whether that model fits their part, and what to check before releasing a drawing.
In this article
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Five things to settle first
What each sourcing model is actually good at
Match the model to the risk in your part, not to the logo on the quote.
| Criterion | Distributed platform | Single plant (GreatLight) |
|---|---|---|
| Quoting | Automated, minutes | Engineer-reviewed, within 12 hours |
| DFM feedback | Often automated flags | Direct engineer comments on the model |
| Tolerance proof | Per shop, varies | ±0.005 mm with inspection reports |
| Certificates | Shop-dependent | ISO 9001, IATF 16949, ISO 13485, ISO 27001 |
| MOQ | Varies by partner | None, one part to 10,000+ |
| Lead time | Capacity-driven | Ship in 3–5 days after start |
| Rework owner | Split across parties | One team, one accountable process |
| Best for | Simple geometry, loose tolerance | Tight features, regulated parts |
The verdict
Use a distributed marketplace when geometry is simple, tolerance is loose and the cheapest qualified path wins. Use a single plant when tolerance, certificates, traceability or IP make a defect expensive.
What Xometry CNC machining services change about your project
A marketplace model sells capacity. You upload a STEP file, an algorithm prices it against machine time and material, and the order is placed with a shop in the network. For a bracket with generous tolerances and a flat finish, that is a good deal. You get a number in minutes and someone else worries about scheduling.
The trade-off appears when the drawing carries real requirements. The platform does not machine your part. A partner shop does, and that shop may change between your prototype and your production run. Process knowledge built on run one does not automatically transfer to run two.
That matters most for features that depend on setup. A true position callout on a bolt circle, a thin wall that moves after clamping, a bore that must stay round after heat treat: these are won or lost in fixture design and in-process checks, not in a quoting engine.
None of this makes the marketplace model wrong. It makes it a specific tool. The rest of this page is about deciding when that tool fits and when a single plant with its own machines and metrology lab is the better buy.
Tolerance, surface finish and the gauges behind them
Every supplier can print ±0.005 mm on a website. The question is which feature, over what length, and measured with what. A tolerance is a contract about a specific dimension, not a property of the shop. Ask which dimensions the quote actually covers.
On a 4,000 mm part, thermal drift and machine geometry dominate. On a 20 mm part, tool runout and clamping dominate. The same ±0.005 mm figure needs completely different controls in those two cases, and a per-part quote cannot explain that to you.
Surface finish behaves the same way. Ra 0.8–1.6 μm is a normal as-machined band for aluminum and mild steel. Ra 0.2–0.8 μm needs a finishing pass, a sharper tool and often a different strategy, which shows up in price. If your finish callout is cosmetic, say so and save the money.
Before you approve a first article, ask for the inspection method by name: micrometer, bore gauge, CMM, optical comparator. A report that lists values without listing the instrument is not traceable. GreatLight inspects 100% of parts before shipment, with raw material check, in-process monitoring and a final report on request.
- 1Tight on a few featuresCall out critical dimensions only; blanket tolerances raise cost without adding function.
- 2Finish by functionSealing surfaces and bearing fits need Ra 0.2–0.8 μm; covers do not.
- 3Datum firstA drawing with no clear datum cannot be inspected the same way twice.
Certifications, material traceability and your audit trail
Certificates belong to a legal entity and a scope. ISO 9001:2015 covers general quality management. IATF 16949:2016 applies to automotive production parts, and ISO 13485:2016 to medical devices. If your part is regulated, the shop cutting it must hold the relevant certificate, not just the platform in the middle.
Traceability is the practical test. Can the supplier show the mill certificate for the heat of 17-4PH that went into your part? Can they show which machine ran which operation? A distributed network makes that chain longer and harder to reconstruct after the fact.
Material choice is where DFM pays for itself. 7075 aluminum machines cleanly but is not weldable. 316L resists corrosion but work-hardens and needs slower feeds. PEEK holds dimensions at temperature but costs many times more than POM. A short conversation beats a rejected first article.
GreatLight machines aluminum 6061, 7075 and ADC12; stainless 303, 304, 316L, 17-4PH and 440C; steels 1018 through 4340; copper and brass grades; titanium TA2 and TC4; Inconel; and engineering plastics from ABS to PEEK and carbon fiber.
Lead time, minimum order quantity and what the number hides
A short quote turnaround is not a short lead time. On a platform, the clock starts when a partner shop accepts the job, and that can take a day or more for less common processes. Ask for days-to-ship, not days-to-quote.
GreatLight returns a quotation and a free DFM analysis within 12 hours, can start production within 24 hours, and ships parts in 3–5 days. Historical late-delivery probability sits below 2%. Those are process figures for our own floor, not a promise about anyone else's.
MOQ is the other hidden cost. A platform may quote one piece, but the partner shop may not want it, so the price carries a setup penalty. We run no minimum order quantity, from one prototype to 10,000+ part runs, so a design change between piece one and piece fifty does not reset your commercial terms.
Volume changes the manufacturing method, not just the price. Prototypes usually run on 3-axis or 5-axis mills. At a few thousand parts, die casting or vacuum casting may beat machining on unit cost. If nobody raises that question, you may pay machining rates for a part that should be cast.
IP, NDAs and who can see your CAD file
Uploading a model to a platform means the file is stored, parsed and shown to shops you have not met. For consumer brackets, that is fine. For an unreleased drivetrain or a surgical instrument, it is a legal exposure, not a technical one.
Ask three questions. Where are the files stored, who can open them, and what happens when the project ends? A supplier holding ISO 27001:2022 has a documented answer for information security management, which is what an auditor will ask about.
GreatLight keeps uploads secure and confidential, and signs an NDA on request. Files stay with the engineering team that quotes and programs the part; they are not broadcast to a bidding network.
One more practical point. The engineer who reviews your DFM should be the engineer who programs the job. When those are different people, comments get lost between the quote and the machine.
Six steps before you release a purchase order
Run these in order. Each one can stop the purchase.
- 1Classify the partMark critical features with their tolerance and finish. If nothing is tighter than ±0.05 mm and Ra 3.2 μm, a marketplace quote is usually fine.
- 2Check the certificate scopeMatch the certificate to the industry: IATF 16949:2016 for automotive, ISO 13485:2016 for medical. Verify the legal entity name on it.
- 3Ask for the inspection planRequest the instrument and the sampling for each critical dimension. 100% inspection with a report is the baseline for regulated work.
- 4Test the DFM responseSend one model and read the feedback. Specific comments on tool access, wall thickness or datums are a good sign. Generic flags are not.
- 5Confirm MOQ and setupAsk what a quantity of one costs and what changes at 100, 1,000 and 10,000 pieces. Setup should amortize, not repeat.
- 6Lock the confidentiality termsSign the NDA before upload, and confirm who inside the supplier can open the file.
Questions buyers ask next
Is an instant quote accurate enough to budget with?
For simple geometry, an automated quote is usually within a reasonable band and good for early budgeting. It is priced from the model and a material assumption, so it cannot see your datums, your fixture or your inspection requirement.
Treat it as a starting number. Ask for a firm quote once the drawing is frozen and the finish callout is final.
Can a distributed network hold ±0.005 mm?
Yes, if the individual shop has the machines, the fixturing and the metrology to prove it. The tolerance is a property of the shop that cuts the part, not of the platform that quotes it.
Ask for the inspection report from the first article and check which instrument measured each critical dimension.
What MOQ should I expect for prototypes?
Marketplaces often quote one piece, but the partner shop may add a setup charge that makes it uneconomic. GreatLight runs no minimum order quantity, from one prototype to 10,000+ part runs.
That matters when you expect design changes between the first piece and the first small batch.
How do I keep my CAD files confidential?
Sign an NDA before uploading, and ask where files are stored and who can open them. ISO 27001:2022 is the certificate that covers information security management.
A supplier that cannot answer those questions in writing should not receive an unreleased design.
When is a single plant cheaper than a network?
When the part needs multiple operations under one setup chain: machining, deburr, anodize, laser marking, final inspection. Each handoff adds freight, queue time and a chance of damage.
One plant with in-house finishing removes those handoffs, which usually shows up as fewer surprises rather than a lower line-item price.
What lead time is realistic for machined parts?
GreatLight returns a quote and DFM analysis within 12 hours, starts production within 24 hours, and ships parts in 3–5 days. Historical late-delivery probability is below 2%.
Add time for finishing and for first-article approval if the part is regulated. Those steps do not compress by asking nicely.
Send one part and compare the answers
Upload a model and we return a quotation plus a free DFM analysis within 12 hours, with no minimum order quantity.
12-hour quote100% inspectionNo MOQNDA on request
More from the shop floor
We publish setup notes, tooling trials and inspection data from the factory floor.
