CNC Service for Sale: How to Pick a Supplier You Can Trust
Anyone can quote a price per part. What matters is whether the shop can hold the tolerance on your drawing, inspect it, and ship on schedule. This guide is for engineers and buyers comparing a CNC service for sale, and it lists the checks that separate a real manufacturing partner from a broker.
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Key takeaways
What to compare before you buy
Use this as a checklist when you request quotes from two or three suppliers.
| Criterion | What to ask | Why it decides the order |
|---|---|---|
| Tolerance | Can you hold ±0.005 mm on this feature? | Tells you if the machine and process fit the drawing |
| Machine mix | How many 5-axis and mill-turn centers? | Fewer setups, tighter position control on complex parts |
| Certifications | Which QMS covers my industry? | IATF 16949, ISO 13485 and ISO 27001 map to different risks |
| MOQ | Can you run one piece, then 10,000? | Prototype and production can stay on one process |
| Lead time | Quote time, first-article time, ship time? | Vague answers usually mean the shop is a broker |
| Inspection | Do you send dimensional reports? | You need data for incoming inspection and traceability |
| Finishing | Is anodizing or plating done in-house? | External finishing adds days and hides tolerance drift |
| Confidentiality | Will you sign an NDA? | Protects drawings and tooling on new products |
Which process fits which part
Rough guidance for early sourcing decisions.
| Part situation | Process to ask about | Reason |
|---|---|---|
| Single prototype, tight geometry | 5-axis CNC | Complex faces in one or two setups |
| Shaft with milled flats | Mill-turn | Turning and milling share one datum |
| Thin-walled housing | 3-axis or 4-axis | Simple access, lower cost per part |
| Metal internal channels | 3D printing (SLM) | Machining cannot reach the cavity |
| Low-volume sheet parts | Sheet metal fabrication | Faster and cheaper than solid machining |
| Large frame over 1,000 mm | Large-travel CNC | Fits the 4,000 mm envelope |
Buy capability, not a price
If the shop can name the machine, the tolerance and the inspection method for your part, order a sample. If it can only give a number, keep looking.
Match the tolerance to the machine, not the price
The first question on any CNC service for sale is simple: can this shop hold the tolerance your drawing calls for? A general machine shop can hit ±0.05 mm all day. Once you ask for ±0.005 mm, the answer depends on the machine, the fixturing, the thermal state of the shop, and the skill of the operator. Those four things are not visible on a price sheet, so ask directly.
Look at the machine list. GreatLight runs 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers and 16 mill-turn centers. Five-axis work matters when a part has features on several faces at once: fewer setups means less accumulated position error. Mill-turn matters for shafts and housings where turning and milling features share a datum.
Size is the other half of capability. Maximum processing size is 4,000 mm, with travels such as 4,000 × 400 × 150 mm for long parts and 750 × 1,150 × 550 mm for medium frames. Compact travels of 500 × 500 × 450 mm cover small, dense parts. If your part sits outside a shop's travel, no amount of skill will fix it.
Finishing is where tolerance quietly drifts. Anodizing adds a few micrometres; hardcoat adds more. If the shop finishes parts in-house, they can compensate before coating and check after. If finishing is subcontracted, ask who measures the part when it comes back.
- 1Tight featuresPut the ±0.005 mm callouts on the drawing and ask for a capability comment.
- 2Complex geometry5-axis and mill-turn reduce setups and protect datums.
- 3Surface finishRa 0.8–1.6 μm is a normal machined finish; Ra 0.2–0.8 μm needs specific tooling.
Certifications tell you which risks the shop manages
A certificate is not a badge for the wall. It tells you which failure modes the shop has a system for. ISO 9001:2015 covers general quality management. IATF 16949:2016 adds automotive requirements such as traceability, change control and PPAP-style documentation. ISO 13485:2016 is the medical device standard, focused on process validation and record keeping.
ISO 27001:2022 is different from the other three. It covers information security, which matters when you send CAD files, drawings and bills of materials to an overseas supplier. If your product is unannounced, this is the certificate that protects the design, not the part.
Certification also tells you how the shop handles a nonconformance. Ask what happens when a dimension is out. A documented shop quarantines the parts, tells you, and proposes a disposition. An undocumented shop ships it and hopes you do not measure. The difference shows up on your incoming inspection bench.
None of this replaces your own checks. For a first order, request material certificates and a first article inspection report. For later orders, ask for in-process monitoring records. GreatLight inspects 100% of parts before shipment and can supply reports on request.
Read the lead time as a process, not a promise
Lead time is easier to check once you split it into stages. Quotation and DFM analysis are one stage. Material purchase is another. Machining is the third, and inspection and packing is the fourth. If a supplier gives one number with no breakdown, they may be quoting a target rather than a schedule.
GreatLight returns a quotation and free DFM analysis within 12 hours, and production can start within 24 hours of approval. Parts ship in 3–5 days for typical jobs. Historical late-delivery probability is below 2%. Those numbers describe normal jobs; a part with a difficult geometry or a rare alloy will take longer, and a good supplier will say so up front.
MOQ is the other number buyers worry about. There is no minimum order quantity here: the same process runs from one prototype to 10,000+ part runs. That matters because switching shops between prototype and production forces a new first article, a new fixture and a new set of process risks.
Ask about material availability before you commit to a date. Aluminum grades such as 6061, 7075 and 6082 are usually in stock. Titanium and Inconel take longer. If your schedule is tight, let the shop choose the grade within the specification rather than naming a rare alloy.
A quote is a document, not a number
When you compare a CNC service for sale, compare the quote line by line. A price that excludes material, finishing, inspection reports or freight is not cheaper; it is incomplete. Ask for the quote to list material grade, tolerance assumption, surface finish, inspection level, packing and shipping terms.
Send a complete data package: 3D model, 2D drawing with GD&T, material, finish, quantity and any critical dimensions. Missing GD&T is the most common reason a quote comes back wrong. The shop will assume general tolerances and the part will meet the drawing on paper but not in your assembly.
Ask one technical question before you buy. For example: how will you hold the bore position on this part? The answer tells you whether an engineer read the drawing or a salesperson ran a price calculator. Shops that answer with a process, a fixture idea and a measurement method are the ones worth a first order.
Keep the communication channel stable. One contact person who knows your project prevents the drawing revision from being machined against an old file. If the shop offers an NDA, sign it before you upload production files. GreatLight signs NDAs on request and treats uploads as confidential.
Five traps that cost time and money
The first trap is the lowest price. A quote that is 30% below the others usually leaves something out: inspection, finishing, or the material grade. Compare scope, not just the number. Ask what is excluded.
The second trap is an unstated tolerance. If the drawing says general tolerance and the shop quotes to it, the part may not fit a mating component. Call out the critical dimensions explicitly. General tolerances are for non-functional features.
The third trap is finishing after measurement. Anodizing and plating change the dimension. If the part is measured before coating only, the final part may be out of tolerance. Ask when the final measurement happens.
The fourth trap is a broker in the middle. If the shop cannot say how many machines it runs or how it inspects, it may be passing your job to another factory. You lose control of the schedule and the quality data.
The fifth trap is a silent revision. If you update the drawing and the shop does not acknowledge it, the next batch may follow the old file. Use one contact and confirm revisions in writing, with the revision number quoted back to you.
Step by step: how to place a first order
A short sequence that avoids most first-order problems.
- 1Prepare the data packageSend STEP model, 2D drawing with GD&T, material, finish, quantity and critical dimensions. Missing GD&T forces the shop to guess.
- 2Request the quote and DFM notesAsk for both at once. A DFM comment on a thin wall or an unreachable feature is worth more than a lower price.
- 3Check the tolerance assumptionConfirm the shop is quoting ±0.005 mm where the drawing needs it, and general tolerance elsewhere. Mixed quoting is normal.
- 4Confirm material and finishName the alloy and the finish. If the finish is anodizing, ask whether the tolerance is measured before or after coating.
- 5Approve the first articleAsk for a first article inspection report with the actual measured values, not just a pass stamp.
- 6Set the shipping and inspection termsState the receiving requirements, packing method and any labeling needed for your incoming inspection.
- 7Review the first run before scalingRun one part or a small lot, check it in your assembly, then release the 10,000-part order.
Questions buyers ask before ordering
What tolerances can a CNC service for sale realistically hold?
On a well-maintained machine with proper fixturing, ±0.005 mm is achievable on critical features. General features usually run at ±0.05 mm or looser.
Tighter than ±0.005 mm is possible on small parts, but it needs grinding or lapping, a temperature-controlled environment and a longer schedule. Discuss it before the quote.
Do I need a minimum order quantity?
No. GreatLight runs from one prototype to 10,000+ part runs with no minimum order quantity.
For one-off parts, expect to pay setup and programming time. That cost is spread across the batch once quantity goes up.
How fast can parts ship?
Quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours of approval, and typical parts ship in 3–5 days.
Rare alloys, heavy finishing or very large parts extend the schedule. The shop should tell you which stage is the constraint.
Which certifications should I check?
Match the certificate to your industry. ISO 9001:2015 is the baseline. IATF 16949:2016 covers automotive. ISO 13485:2016 covers medical devices. ISO 27001:2022 covers information security.
For new product development, ISO 27001 matters because it governs how your CAD files and drawings are handled.
Will you sign an NDA before I send drawings?
Yes. An NDA is available on request, and uploads are treated as secure and confidential.
Sign the NDA before uploading production files. For early RFQ work, a simplified model without internal features is usually enough.
What should be in the inspection report?
A useful report lists the measured value for each critical dimension, the nominal and tolerance, the instrument used, and the date. A pass or fail stamp alone is not enough.
Ask for material certificates on the first order, and in-process records when the part has tight or difficult features.
Send your drawings and get an engineer's review
Upload your files and get a quotation with free DFM analysis within 12 hours. No minimum order quantity, NDA on request, 100% inspection before shipment.
12-hour quoteNo MOQ100% inspectionNDA on request
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