CNC Machined Prototypes Services
This guide is for engineers and sourcing teams comparing CNC machined prototypes services before a build. It covers the checks that actually change the outcome: tolerance, lead time, minimum order, certification scope and how a shop quotes. Read it and you can tell a capable prototype supplier from a fast talker.
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What matters most when you pick a prototype shop
CNC machined prototypes services: what to compare
Use this table to score two or three suppliers side by side. Fill the right-hand column with what each shop actually tells you in writing.
| Check | What to ask for | Why it decides the job |
|---|---|---|
| Tolerance | The value held across the full batch | A single tight part proves nothing about repeatability |
| Machine fit | Axis count and maximum travel | Undercuts and deep pockets need 5-axis or mill-turn |
| Minimum order | Whether one unit is accepted | Locks your first-article cost before you commit |
| Lead time | Quote, first cut and ship dates | Prototype schedules slip when these are vague |
| Certification | Which standard, and its scope | Medical and automotive work needs the right one |
| Inspection | What is measured, and what report you get | Dimensional reports settle disputes later |
| NDA and file handling | Whether an NDA is signed before upload | Protects geometry you have not patented yet |
| Materials list | Grades the shop stocks or sources | 7075 and Ti-6Al-4V machine very differently |
The short version
Pick the shop that answers with numbers: a tolerance value, a machine list, three dates and an inspection scope. Everything else is a brochure.
Tolerance: read the number, not the claim
Every supplier page claims high precision. The useful question is what tolerance the shop holds across a batch of twenty parts, not what it achieved once on a lathe. Ask for a figure tied to a feature type: bores, flat faces and hole positions behave differently, and a single blanket number hides that.
At GreatLight we work to ±0.005 mm, or ±0.0002 in, on machined features. That value comes from 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. The machine set matters because a part with tight position tolerance on five faces is not a three-axis job.
Surface finish is a separate spec. As-machined surfaces land around Ra 1.6–3.2 μm, a good machined finish sits at Ra 0.8–1.6 μm, and fine finishing reaches Ra 0.2–0.8 μm. If your drawing calls for a seal face or a sliding fit, name the finish value. A shop that quotes without asking about it will quote the cheapest one.
- 1Name the featureTolerance on a bore is not tolerance on a pocket wall.
- 2Ask for batch dataFirst-article numbers alone do not show drift.
- 3Split finish from toleranceThey are quoted and inspected separately.
Machine fit and part size for CNC machined prototypes services
Send the shop a STEP file before you discuss price. Geometry decides the machine, and the machine decides the price. A housing with angled ports and a contoured internal channel needs 5-axis work or a mill-turn setup. The same part drawn as three flat plates can run on a 3-axis mill for a fraction of the cost.
Size sets the ceiling. GreatLight machines parts up to 4,000 mm, with travel of 4,000 × 400 × 150 mm on the large platform, 750 × 1,150 × 550 mm and 600 × 600 × 600 mm on medium platforms, and 500 × 500 × 450 mm or 500 × 310 × 200 mm on compact ones. A Ø400 mm rotary table covers round work that needs indexing.
Materials change the setup too. Aluminum 6061 and 7075 cut fast and hold tight tolerances well. Titanium TC4 (Ti-6Al-4V), Inconel and 17-4PH stainless move more under cutting heat, so they need lighter passes and more in-process checks. A prototype shop that treats all metals the same will miss your tolerance on the harder grades.
- 1Five-axis pays off whenThe part has undercuts, compound angles or five-sided features.
- 2Three-axis is enough whenFeatures are reachable from two or three orthogonal setups.
- 3Watch hard alloysTitanium and Inconel need slower feeds and extra inspection.
Lead time, minimum order and the quote you get back
Prototype schedules are short by nature. Ask three dates in writing: when the quote arrives, when the first cut starts, and when parts ship. 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%.
Minimum order is the quiet cost driver. Some shops price a single prototype at a production-slot rate, so the per-part number looks absurd. GreatLight runs no minimum order: one prototype or a 10,000+ part run, priced on the same basis. For first articles, that removes the argument about whether the build is worth a setup.
The quote itself should show material grade, finish, tolerance class and inspection scope. If it lists only a price and a date, you will discover the rest later. Read the DFM notes as carefully as the price. A shop that flags a thin wall or an unreachable corner before cutting is saving you a week.
- 1Get three datesQuote, first cut, ship. Vague timelines slip.
- 2Check what the price includesMaterial, finish and inspection should be line items.
- 3Read the DFM notesThey predict problems you have not hit yet.
Certification, inspection and confidentiality
Certificates only count inside their scope. ISO 9001:2015 covers general quality management. IATF 16949:2016 applies to automotive production, ISO 13485:2016 to medical devices, and ISO 27001:2022 to information security. If your prototype is a medical instrument housing, ask which standard governs the shop's process, not just which wall the plaque hangs on.
Inspection is where tolerance claims become evidence. GreatLight inspects 100% of parts before shipment, with a raw material check, in-process monitoring and a final inspection, and reports are available on request. For prototypes, request dimensional data on the critical features you named in the drawing. It costs nothing extra if the shop is already measuring them.
Confidentiality belongs in the first conversation. Uploads are handled as secure and confidential, and an NDA can be signed on request before you send files. For unpatented geometry, this is not paperwork; it is the only thing standing between your design and a competitor's catalog. Ask about it before the upload, not after.
- 1Match the standard to the sectorAutomotive and medical work each need their own scope.
- 2Request reports up frontCritical-feature data is cheapest to ask for at quote time.
- 3Sign the NDA firstBefore the first STEP file leaves your network.
Finishing and secondary operations you will need
A prototype that fits but looks wrong can still fail a design review. Finishing is often what makes a part presentable to a customer or a test rig. Anodizing comes in clear, color, hardcoat and conductive versions. Electroless nickel, zinc, silver and gold plating cover conductivity and corrosion needs. Powder coating and black oxide handle larger frames.
Mechanical finishes matter for fit and feel. Bead blasting, tumbling, brushing and polishing change both surface texture and edge condition. If your prototype will be handled in a demo, say so. A brushed or bead-blasted face reads as a finished product, while a raw machined face reads as a test piece.
Laser marking and engraving puts part numbers, logos or orientation marks on the part. The minimum character height is 1.5 mm, so plan the marking size at the drawing stage. Below that, characters blur and the marking becomes unreadable after coating. It is a small detail that turns a pile of prototypes into a tracked set.
- 1Finish follows functionHardcoat for wear, plating for conductivity, bead blast for appearance.
- 2Plan marking early1.5 mm minimum character height before coating.
- 3Match the demoA finished surface changes how reviewers judge the part.
Where supplier selection usually goes wrong
The first trap is buying on price per part alone. A low quote that excludes finishing, inspection reports or a second setup is not a lower price; it is an incomplete one. Add the missing line items before you compare. The second trap is sending a drawing instead of a model. A 2D drawing leaves feature interpretation open, and interpretation is where prototypes come back wrong.
The third trap is skipping the material conversation. Aluminum 6061-T6 and 7075 look similar on a quote and behave differently on a load test. Stainless 303 machines freely; 316L galls and needs different feeds. If the shop does not ask which grade you need, ask them which grades they keep in stock.
The fourth trap is assuming the prototype shop can scale. A workshop that hand-fits one part may not hold the same tolerance across 10,000. GreatLight runs the same process from single prototypes to production runs, with 3 wholly-owned plants and 150 technicians. Ask directly: who makes the parts when the order grows.
- 1Compare complete quotesAdd finishing, inspection and setups before comparing.
- 2Send 3D modelsSTEP files remove feature ambiguity.
- 3Ask about scale-upThe prototype team may not be the production team.
Step by step: picking a CNC prototype supplier
- 1Prepare a model and a feature listSend a STEP file plus a short list of critical features with their tolerances and finishes. This is the document every quote should answer.
- 2Ask for a quote and DFM notes togetherSet a 12-hour expectation. A returned DFM note tells you an engineer read the file, not a sales script.
- 3Confirm the machine and setup planAsk which machine runs the part and how many setups it needs. Fewer setups means less accumulated error.
- 4Fix the tolerance and finish valuesWrite ±0.005 mm and Ra 0.8–1.6 μm into the purchase order if those match your function.
- 5Agree on inspection and reportsName the features to be measured and ask for dimensional data with shipment.
- 6Settle confidentiality before uploadSign an NDA if the geometry is unpatented. Do this before the first file transfer.
- 7Run the first article, then compareMeasure the delivered part against your feature list. Judge the shop on that data, not on the sample photos.
Questions buyers ask before ordering
How tight a tolerance should I specify for a prototype?
Specify only what the function needs. A non-critical bracket at ±0.1 mm machines faster and costs less than one held at ±0.005 mm. Reserve the tight value for fits, bores and datum features.
If you are unsure, send the drawing and ask which features drive the cost. A good shop will tell you which tolerances it can relax without affecting the assembly.
Can I order a single prototype with no minimum order?
Yes. GreatLight runs no minimum order quantity, from one prototype to 10,000+ part runs. The setup cost is absorbed into the per-part price rather than charged as a separate minimum.
For a single unit, expect the quote to reflect one-off setup time. That is normal and still cheaper than committing to a batch before the design is proven.
What file format should I send?
A STEP file is the standard for CNC prototypes because it carries solid geometry without version ambiguity. Send a PDF drawing alongside it for tolerances, finishes and marking notes.
Native CAD files are not required. If a feature is defined only in the drawing, say so, because the machinist programs from the model.
How do I know the shop can hold tolerance in a larger run?
Ask what changes between the prototype and the production run. If the answer is nothing except quantity, the process is stable. If the shop switches machines or moves the part to a different plant, ask for a new first article.
Batch inspection data from the prototype run is the best predictor. A shop that measures 100% of parts before shipment can show you the spread.
Which certifications matter for my industry?
ISO 9001:2015 covers general quality management and applies to most industrial work. IATF 16949:2016 applies to automotive production. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security.
Tell the shop your end market at the quote stage. It changes the documentation you receive with the parts.
What surface finish will I get if I do not specify one?
You will get an as-machined surface, roughly Ra 1.6–3.2 μm, with visible tool marks. It is fine for fit checks and internal parts.
For a demo unit or a customer-facing prototype, specify bead blasting, brushing or anodizing. Those operations add a step but change how the part is received.
Send a model, get a quote and DFM notes in 12 hours
Upload a STEP file and a feature list. An engineer reviews the geometry and returns pricing, DFM feedback and a lead time you can plan around.
12-hour quote100% inspectionNo minimum orderNDA on request
More from the shop floor
We publish setup notes, tooling trials and inspection data from the factory floor.
