CNC Hardware Processing Factory: 7 Essential Checks

• 1
  What to settle before you request a quote
• 2
  How a cnc hardware processing factory compares to other sourcing routes
• 3
  What a cnc hardware processing factory actually controls
• 4
  Tolerance, finish and the numbers behind them
• 5
  Certifications and what each one covers
• 6
  Lead time, MOQ and how quotes are built
• 7
  Materials and finishes that fit your part
• 8
  7 steps to qualify a cnc hardware processing factory

A cnc hardware processing factory turns a drawing into a metal or plastic part by removing material under program control. The work is not limited to one machine type. Milling cuts pockets, faces and slots, turning produces shafts and threaded features, and mill-turn centers do both in one setup. That last point matters because every extra setup adds a datum shift.

At GreatLight the floor holds 127 high-precision CNC machines: 16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Maximum processing size reaches 4,000 mm, with a Ø400 mm rotary table for parts that need work on several faces. That spread is what lets one factory quote a 20 mm bracket and a 900 mm frame without subcontracting.

The practical question for a buyer is not how many machines a shop lists. It is whether the machine that will run your part can hold your tolerance across the whole batch. A three-axis mill can hit ±0.005 mm on a simple plate. Add a deep cavity with a 0.5 mm corner radius and the same job may need a five-axis setup or EDM.

So ask which machine is planned for your part and why. A factory that answers with a machine model, a fixture idea and a hold strategy is a factory that has already thought about your print.

Tolerance and surface finish drive the price more than material does. A general machined surface sits around Ra 1.6–3.2 μm. A fine finish of Ra 0.2–0.8 μm needs slower feeds, sharper tooling and more gauging, so it costs more per part. If your drawing says Ra 0.4 μm on a face that only touches a gasket, you are paying for nothing.

The same logic applies to ±0.005 mm. That is roughly ±0.0002 in and it is a real capability, not a marketing line. But it only holds when the feature is reachable, the material is stable and the setup is rigid. Thin walls, long unsupported bores and soft plastics all push the achievable number looser.

A useful habit is to mark which dimensions are functional and which are reference. A good factory will come back with a DFM note: this bore can be ±0.02 mm, this one needs ±0.005 mm, this wall is too thin to thread. That note is worth more than a lower unit price, because it prevents a scrapped batch later.

Inspection backs the claim. GreatLight inspects 100% of parts before shipment, with raw material checks, in-process monitoring and a final pass, and reports on request. Ask what is measured, on which features, and with what instrument. Vague answers about quality control usually mean the tolerance is hoped for, not verified.

Certificates are often listed in a row as if they were interchangeable. They are not. ISO 9001:2015 covers a general quality management system. IATF 16949:2016 adds the automotive-specific controls for traceability, change management and defect prevention. ISO 13485:2016 applies to medical devices and brings tighter process validation. ISO 27001:2022 covers information security, which is what protects your drawings and CAD files.

For an automotive bracket, IATF 16949 matters because your customer will ask for it. For a surgical instrument housing, ISO 13485 is the one that gets the part through your own quality gate. For a consumer electronics enclosure, ISO 9001 plus a signed NDA is usually enough.

GreatLight holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. All uploads are treated as secure and confidential, and an NDA is available on request. If a supplier cannot tell you which certificate applies to your project, the certificate is decoration.

One more check: ask for the scope statement on the certificate, not just the logo. A certificate that covers machining of aluminum parts says nothing about die casting or surface finishing done elsewhere.

Two factories can quote the same part with the same price and still be very different suppliers, because the quote hides the schedule. Ask what happens after you approve. At GreatLight, quotation and a free DFM analysis come back within 12 hours, production can start within 24 hours, and parts ship in 3–5 days. Historical late-delivery probability stays below 2%.

Minimum order quantity is the other divider. Some shops will not open a machine for fewer than 500 pieces, which kills prototyping. GreatLight runs no minimum order quantity, from one prototype to 10,000+ part runs, on the same floor and the same inspection process.

Ask how the quote is structured. Material, machining time, finishing, inspection and freight should be separate lines. A single lump sum makes it impossible to see which change will save money. If the engineer suggests switching 316L to 304 for a non-corrosive part, or dropping hardcoat anodizing where wear is not a factor, you want that visible.

Finally, ask what happens if a dimension is out. A factory with in-house finishing and inspection can rework and re-inspect without waiting on a third party. That is the difference between a two-day recovery and a two-week one.

Material choice is usually settled by function, then adjusted by machinability. Aluminum 6061-T6 and 7075 cover most brackets and housings. Stainless 303 machines easily, 316L resists corrosion, and 17-4PH (SUS630) gives high strength after heat treatment. Titanium TC4 (Ti-6Al-4V) and Inconel are used where weight or temperature demands it, but they cut slowly and cost more.

Plastics behave differently. POM and PA are stable and machinable, PEEK handles heat and chemicals, and carbon fibre reinforced stock wears tooling fast. A shop that treats plastic like aluminum will blow tolerances on thin walls.

Finishing is where drawings often go quiet. Anodizing in clear, colour, hardcoat or conductive form changes the surface, adds thickness and can affect a tight bore. Electroless nickel, zinc, silver and gold plating, powder coating and black oxide each suit different environments. Bead blasting, tumbling, brushing and polishing handle appearance and edge break.

Laser marking is worth planning early. Minimum character height is 1.5 mm, so a 0.8 mm serial number on a small boss will not read cleanly. Move the mark to a flat face, or accept a larger character.