CNC Machining Service Free Sample: What to Check Before You Commit

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  Key takeaways
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  What to Judge From a Free Sample Part
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  A Free Sample Tests Capability, Not Kindness
• 4
  Which Tolerances and Finishes a Sample Should Prove
• 5
  Match the Part Geometry to the Right Machine
• 6
  Lead Time, MOQ and What the Free Sample Covers
• 7
  What Certifications Tell You About a Shop
• 8
  How to Run a Free Sample Trial in 6 Steps

A cnc machining service free sample exists to remove doubt before money moves. You send a real part file, the shop programs it, cuts metal, inspects it and ships it. What you get back is a physical answer to questions a website cannot answer: can they hold your tolerance, can they hit your finish callout, and do they read drawings the way your team does.

The sample is also a test of communication. Every question you asked during quoting should show up in the part. If you flagged a thin wall, a deep pocket or a tight bore, check how those features came out. That tells you whether your notes travel from the sales desk to the machine.

Keep the scope honest. One sample part cannot prove a 10,000-piece run, and it cannot prove a process the shop does not have. It can prove that the shop's quoting, programming, machining and inspection steps line up on your part. That is enough to justify a first production order, not a blanket commitment.

Treat it as a paid trial with a zero price tag on the machining. The value is not the saved cost of one part. The value is avoiding a scrapped batch, a late program launch or a supplier you have to replace in month three.

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  Send a real production fileNot a simplified test block. Use the geometry that worries you.
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  State the critical dimensionMark one or two features as the ones that decide pass or fail.
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  Ask for the inspection reportDimension values, not a pass stamp.
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  Keep the sample partCompare it to later production parts as a baseline.

Start with the tightest callout on your print. At GreatLight the working tolerance is ±0.005 mm (±0.0002 in), but that number only matters where your drawing demands it. A 200 mm aluminum bracket with one ±0.02 mm bore and a general ±0.1 mm profile is a normal job. The sample should show the bore measured, not just the outside length.

Surface finish is the second filter. As-machined faces land around Ra 1.6–3.2 μm. A high-quality finish callout of Ra 0.8–1.6 μm is normal for sealing faces, bearing seats and sliding surfaces. Fine finishing down to Ra 0.2–0.8 μm is achievable but it costs time, so a shop that promises it everywhere is either slow or guessing.

Material choice affects what is realistic. Aluminum 6061-T6 and 7075 cut clean and hold tight tolerance well. Stainless 316L and 17-4PH move more under cutting heat, so a thin-wall stainless part at ±0.005 mm needs a different strategy than the same shape in aluminum. Say which material you will use in production, and send the sample in that material.

Check how the shop reports finish. A visual comparison to a roughness gauge is weak. A reading from a profilometer or a stated Ra band tied to specific faces is usable. If the report is a single line that says fine finish, ask for face-by-face values.

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  Tight feature firstMeasure the ±0.005 mm callout, not the general profile.
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  Finish by faceSealing and sliding faces need their own Ra value.
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  Match the production materialA sample in a different alloy proves less.
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  Watch thin wallsBelow 1 mm in stainless, expect to talk about fixturing.

The machine type behind your sample decides what geometry is practical. A three-axis mill cuts prismatic parts with features reachable from one direction: plates, housings, brackets, manifolds with simple pockets. A four-axis mill adds a rotary table, so you can machine around a cylindrical part and hit features on several sides in one setup.

Five-axis machining is what makes undercuts, compound angles, deep cavities and contoured surfaces practical. GreatLight runs 16 simultaneous 5-axis machining centers, plus 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. If your part has an angled port, a twisted blade or a face that cannot be reached from three directions, ask which machine will cut it.

Size matters as much as axis count. The largest travel here is 4,000 × 400 × 150 mm, with 750 × 1,150 × 550 mm and 600 × 600 × 600 mm cells for mid-size work, and compact 500 × 500 × 450 mm cells for small parts. A long shaft or a large frame may not fit every machine, so confirm the work envelope before you assume the price.

Turned parts follow a different rule. A mill-turn center handles a shaft with cross holes, flats and slots without a second setup, which protects concentricity. If your part is mostly round with a few milled features, say so at quoting time. It changes both the process plan and the price.

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  Prismatic partThree-axis or four-axis work, one or two setups.
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  Undercuts and compound anglesFive-axis, or extra setups and cost.
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  Round with cross featuresMill-turn keeps concentricity in one setup.
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  Long or large partsCheck the 4,000 mm envelope first.

Ask what the free part includes before you celebrate. Machining and programming are commonly covered on a first sample. Material, surface finishing, laser marking and freight may not be, and heavy parts or exotic alloys usually fall outside the free scope. Get this in writing in the quote so there is no surprise invoice.

Lead time is the second commercial filter. 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. A sample slot usually fits inside that flow. If a shop quotes four weeks for a single sample, production will not be faster.

Minimum order quantity tells you how the shop is set up. No minimum order quantity is normal here, from one prototype to 10,000+ part runs. Some suppliers wave the MOQ to win the sample and then impose one at production. Confirm the MOQ in the same document as the price.

Confidentiality belongs in the same conversation. Uploads are secure and confidential, and an NDA is available on request. If your drawing is under a customer NDA already, send it through a channel that matches your obligations and ask the shop to sign before files move.

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  Free scopeMachining and programming, or everything? Get it written.
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  Quoted lead timeCompare the sample's actual arrival to the quote.
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  MOQ at productionNot only at the sample stage.
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  NDA timingSign before files are transferred, not after.

Certificates are a filter, not a finish line. ISO 9001:2015 covers a working quality management system. IATF 16949:2016 is the automotive standard and matters if your part goes into a vehicle program. ISO 13485:2016 applies to medical devices and their components. ISO 27001:2022 covers information security, which is the one most buyers forget to check.

Read the certificate scope, not just the logo. A certificate with a narrow scope may not cover the process your part needs, such as die casting or surface finishing. Ask for the certificate number and the issuing body, and check the validity date. A shop that sends a clear PDF without being pushed twice is easier to work with.

Inspection records are the practical side of quality. Here every part is inspected before shipment: raw material check, in-process monitoring and final inspection, with reports on request through a reported 99.99% qualification rate. For a sample, ask for the final inspection data on your critical features and keep the file.

If your industry needs traceability, ask how material lots are recorded and whether the sample part carries a heat or lot number. That is the difference between a part you can use and a part you have to re-qualify from scratch.

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  Scope over logoCheck which processes and sites the certificate covers.
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  Information securityISO 27001:2022 matters if drawings are sensitive.
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  Inspection dataRequest values for the critical features only.
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  TraceabilityAsk for lot or heat numbers when the industry requires them.