Open CNC Machining Factory: 7 Proven Checks Before You Send an RFQ

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  Key takeaways
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  What to compare across open CNC machining factory quotes
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  Tolerance and machine fit at an open CNC machining factory
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  Lead time: separate the three clocks
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  Axis count and part geometry
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  MOQ, prototypes, and the cost of a single part
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  Certifications, material, and finishing scope
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  Inspection reports and what ships with the parts
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  Confidentiality and file handling
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  Step by step: from drawing to purchase order

Tolerance is where most RFQs go wrong. A drawing that says ±0.005 mm on a 300 mm aluminium bracket is not the same job as ±0.005 mm on a 40 mm stainless connector. The first needs thermal stability across the whole travel. The second needs a rigid setup and a probe to verify the datum before cutting.

Ask which machine will run the part, not which machines the shop owns. A 16-machine 5-axis fleet does not help if your job is scheduled on a worn 3-axis mill. At GreatLight, the 4,000 × 400 × 150 mm travel machines cover long parts, while the 500 × 500 × 450 mm and 600 × 600 × 600 mm cells handle tighter work with less thermal drift.

For features that must hold ±0.005 mm, expect in-process probing and a controlled temperature room. If a supplier quotes the tolerance but cannot describe how they verify it, the price is a guess. You will find out at first article.

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  State tolerance per featureBlanket tolerances hide the hard features and invite disputes.
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  Ask for the machine listMatch travel and spindle to your part envelope.
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  Confirm the datum strategyA probe check before cutting saves a rework cycle.

Quotes often blur three different times: how long to quote, how long to first cut, and how long to ship. A shop that quotes in 12 hours with a DFM note is useful. A shop that quotes in 2 hours with no comments on your drawing is not, because you will spend the next week resolving questions that should have been caught on day one.

Ask when the first chips fly. Production can start within 24 hours at GreatLight once the drawing and material are confirmed, and parts ship in 3–5 days for standard jobs. That is a scheduling claim, not a delivery guarantee. Treat any guaranteed date as a red flag unless the shop controls its own material stock.

Historical late-delivery probability is a better number than a promise. At GreatLight it sits below 2%. Ask your supplier for the same figure and how they measure it. If they track on-time shipment by order line, not by customer, the number means something.

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  Quote clock12 hours with DFM feedback is a working benchmark.
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  First-cut clock24 hours after drawing and material release.
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  Ship clock3–5 days for standard jobs, longer for exotic material.

Five-axis simultaneous machining removes setups on parts with undercuts, angled holes, or contoured surfaces. A turbine blade profile or a medical implant with internal channels is a five-axis job. A flat plate with four holes is not. Paying five-axis rates for a three-axis part is the most common overspend in low-volume buying.

The alternative is 3+2, where the table indexes and then the cut happens in three axes. It is cheaper and often accurate enough. Ask the shop to state which one they plan to use and why. If the answer is "five-axis" without a geometry reason, push back.

For mill-turn parts, one machine completes the OD and the face features without re-chucking. That matters when concentricity between a turned bore and a milled slot drives function. GreatLight runs 16 mill-turn centers alongside 16 simultaneous 5-axis machining centers and 27 three-axis machines, so the routing can match the geometry instead of the other way around.

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  Five-axis simultaneousUndercuts, contoured surfaces, angled features in one setup.
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  3+2 indexingCheaper, accurate on prismatic parts with angled faces.
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  Mill-turnConcentricity between turned and milled features.

A no-minimum-order shop is telling you something about how it is set up. If they can quote one piece and 10,000 pieces on the same process, they have the tooling flexibility and the inspection bandwidth to treat a prototype as a real job. That is not universal. Many shops hide setup cost in a minimum order quantity of 100 or more.

For prototypes, ask what changes between the one-off and the production run. If the answer is "nothing, we just run more," be careful. Prototype routing often uses soft jaws and manual checks. Production routing uses fixtures, in-process gauges, and a documented control plan. The tolerance should not change, but the method will.

Cost per part falls fast in the first 50 pieces and slowly after that. If a quote shows a flat per-unit price from 1 to 10,000, the supplier either did not model setup properly or is padding the small quantities. Ask for the setup fee as a separate line.

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  One piece to 10,000+A shop that quotes both ends is usually set up for both.
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  Separate setup from unit costYou can see where the money goes and negotiate from facts.
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  Prototype vs production routingSame tolerance, different fixtures and inspection.

Certificates matter only when they cover the process you are buying. ISO 9001:2015 is a baseline quality system. IATF 16949:2016 matters for automotive and EV programs, ISO 13485:2016 for medical devices, and ISO 27001:2022 when your drawings and CAD files must stay controlled. Ask for the certificate scope, not just the logo.

Material selection drives both price and lead time. Aluminium 6061, 7075, and 6082 are stocked and fast. Titanium TC4 (Ti-6Al-4V), Inconel, and magnesium AZ31B or AZ91D are machinable but need slower feeds and more tool changes. Stainless 17-4PH (SUS630) sits in the middle. If a supplier quotes titanium at aluminium speed, the quote is wrong.

Finishing is a separate scope with its own lead time. Anodizing, electroless nickel, zinc and black oxide, bead blasting, and laser marking all add days. Laser marking needs a minimum character height of 1.5 mm to stay legible. Put finishing on the RFQ line items so the quote cannot hide it.

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  Ask for certificate scopeISO 9001 alone does not cover medical or automotive controls.
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  Flag exotic materialsTitanium, Inconel, and magnesium change feeds and cost.
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  Quote finishing separatelyAnodize, plating, and marking add lead time.

100% inspection before shipment sounds like a strong claim until you ask what is measured. A shop can inspect every part with calipers on two dimensions and still miss the feature that matters. Ask which dimensions get measured, with what instrument, and against which datum. The answer should reference the drawing, not a general procedure.

Raw material check, in-process monitoring, and final inspection are three different gates. Ask which one produces a record you receive. First-article inspection and CMM reports are common requests. Some shops include them, some bill them. Get it in the quote so there is no argument after delivery.

If your part is functional, ask for the qualification rate on comparable work. At GreatLight it is 99.99%. That number is only meaningful when paired with the inspection method. A high rate with a weak method is a marketing figure.

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  Name the dimensionsInspection is only as good as the feature list.
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  Ask what ships freeMaterial certs, FAI, and CMM reports are separate items.
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  Match report to functionA functional part needs functional dimensions checked.

Your CAD files carry your design intent. An open CNC machining factory should tell you how uploads are stored, who can open them, and how long they stay on the server. "Secure and confidential" is a phrase, not a control. Ask whether access is role-limited and whether files are deleted after the run.

An NDA is a normal request, not an accusation. If a supplier hesitates, that is a data point. A written NDA plus ISO 27001:2022 scope gives you something to point at if a design leaks. For medical and aerospace work, this is usually a customer requirement before any file moves.

Keep the practical side in view. A shop that cannot receive a STEP file and a PDF drawing without email ping-pong will slow your program down. Test the upload path on the first RFQ. If it is clumsy, it will stay clumsy at volume.

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  Ask how files are storedRole-limited access and deletion after the run.
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  NDA on requestStandard practice for new designs and medical work.
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  Test the upload pathClumsy file handling slows every future order.