Sample CNC Processing Services: What to Check Before You Order

• 1
  Key takeaways
• 2
  Five checks against three supplier types
• 3
  What sample CNC processing services actually deliver
• 4
  Tolerance and machine setup: the two checks that decide the rest
• 5
  Lead time and quote turnaround in sample CNC processing services
• 6
  Inspection, materials and confidentiality: the fine print
• 7
  When surface finish and material choice change the sample
• 8
  Step by step: from CAD to a measured sample

A sample run sits between a CAD file and a production order. The output is a real part cut from real stock, measured, and shipped back to you. Engineers use it for three jobs: proving a fit, testing a function, or showing a customer something they can hold.

Those three jobs have different requirements. A fit check on a bracket may pass at ±0.1 mm and nobody cares about the surface. A tolerance study on a bearing housing needs ±0.005 mm and a documented measurement of that bore. Buying both at the same spec wastes money; buying both at the loose spec wastes time.

Sample CNC processing services are also the cheapest place to find a design mistake. Moving a wall by 2 mm in a CAD model costs nothing. Finding out after the die is cut or the casting tool is made costs the whole tool.

The limit is volume. If you need 5,000 identical parts with a smooth cosmetic surface, a machined sample tells you the geometry works but says little about your production cost. Sampling validates design, not unit economics.

• 1
  Good fit for samplingNew geometry, tight tolerances, low volume, or a part that must be shown to a reviewer.
• 2
  Poor fit for samplingHigh-volume parts where tooling, not machining, drives cost.
• 3
  Also worth samplingRevisions to an existing part where only one feature changed, so the change can be isolated.

Tolerance is the first question, and the answer must come with a measurement method. A shop that says ±0.005 mm should also say how it verifies that number: which CMM, which fixture, at what temperature. Without that, the tolerance is a claim, not a capability.

Be specific about which features need the tight tolerance. A part rarely needs ±0.005 mm everywhere. Mark the two or three critical dimensions and let the rest run at ±0.1 mm. This drops cost and cuts the chance of a false rejection at inspection.

Machine setup is the second check, and it is the one buyers skip. A feature on four faces can be cut on a 3-axis machine in four setups, or on a 5-axis machine in one. Each extra setup adds a repositioning error that stacks onto the tolerance budget.

Ask directly: which machine will cut this sample? At GreatLight, 16 simultaneous 5-axis machining centers cover angled and contoured features; 27 three-axis machines handle flat plate work faster and cheaper. A shop that routes every sample through one machine type is not matching the process to the part.

• 1
  State the datumA tolerance without a datum reference cannot be inspected the same way twice.
• 2
  Count the setupsFour setups at ±0.01 mm each can consume a ±0.005 mm budget before the first cut.
• 3
  Check the envelopeGreatLight machines up to 4,000 mm; the largest travel is 4,000 × 400 × 150 mm.

For a sample, speed usually matters more than unit price. The part is often on the critical path of a design review or a trade show. Ask for two numbers, not one: how long to quote, and how long to cut and ship.

A useful benchmark is 12 hours for a quotation plus free DFM analysis, with production starting within 24 hours of approval. Parts then ship in 3-5 days. That timeline assumes the drawing is complete and the material is in stock.

Material is the common delay. Aluminum 6061 and 7075, stainless 303 and 316L, brass C36000, and titanium TC4 sit in normal stock. An unusual alloy or a large plate may add days. If your schedule is tight, confirm stock before you approve the order.

Be careful with quotes that promise same-day shipment on a complex 5-axis part. Either the geometry is simpler than you described, or the inspection step is being trimmed. Both are problems you discover at assembly.

• 1
  Quote in 12 hoursIncludes free DFM analysis so you can fix issues before cutting.
• 2
  Start within 24 hoursCounted from drawing and material approval, not from first contact.
• 3
  Ship in 3-5 daysFor standard materials and finishes, after inspection.
• 4
  Late-delivery recordHistorical late-delivery probability below 2% across production work.

Every sample should arrive with evidence. At minimum that means dimensional data for the critical features, a material certificate, and surface measurement results. GreatLight inspects 100% of parts before shipment and supplies reports on request, covering raw material check, in-process monitoring and final inspection.

Certification matters by industry. ISO 9001:2015 covers general machining. Medical device samples should come from a shop holding ISO 13485:2016. Automotive and EV work points to IATF 16949:2016. If your drawing is confidential, ISO 27001:2022 covers information security, and an NDA is available on request.

Materials are the other half of the fine print. A sample cut from a substitute alloy can pass a fit check and fail a heat test. Ask for the exact grade on the certificate: 6061-T6 is not the same as 6061, and 316L is not 304.

Finally, confirm how your files are handled. Uploads should be encrypted and access-limited, and the shop should be able to sign your NDA before receiving the CAD. This is standard practice, but only if you ask.

• 1
  Inspection100% before shipment; raw material, in-process and final checks.
• 2
  CertificationsISO 9001:2015, IATF 16949:2016, ISO 13485:2016, ISO 27001:2022.
• 3
  Quality rate99.99% qualification rate on inspected work.
• 4
  ConfidentialitySecure uploads; NDA available on request.

A sample that will be evaluated for appearance needs a finish, not just a cut. As-machined surfaces run Ra 1.6-3.2 μm and show visible tool marks. Functional surfaces at Ra 0.8-1.6 μm are typical for sealing faces. Optical and bearing surfaces may need Ra 0.2-0.8 μm.

Finish also changes dimensions. Anodizing builds a few micrometres per surface, and hardcoat builds more. If a tight bore is anodized after machining, the shop must cut the bore undersize to compensate. Tell the shop the final finish before cutting, not after.

Material choice follows the function. Aluminum 6061-T6 is the default for enclosures and brackets. 7075 suits high-stress airframe parts. Stainless 17-4PH holds strength after heat treatment. PEEK and ULTEM cover insulating and high-temperature parts where metal is not an option.

Cosmetic finishes are available too: bead blasting, brushing, polishing, powder coating, black oxide, laser marking. Laser marking has a minimum character height of 1.5 mm, so plan part numbers and logos accordingly.

• 1
  As machinedRa 1.6-3.2 μm. Fine for hidden brackets and fit checks.
• 2
  FunctionalRa 0.8-1.6 μm. Sealing faces, sliding contacts.
• 3
  FineRa 0.2-0.8 μm. Bearings, optical seats, precision bores.