Full Service CNC Machining: How to Choose a Supplier

• 1
  Key takeaways
• 2
  Full service cnc machining: what to compare between suppliers
• 3
  What full service cnc machining includes
• 4
  Matching tolerance and geometry to the machine
• 5
  Material and finish choices that change the quote
• 6
  MOQ, lead time and the paperwork you should expect
• 7
  Mistakes that make a supplier look better than it is
• 8
  Step by step: qualifying a full service cnc machining supplier

Full service cnc machining means one supplier handles the whole chain: reviewing your CAD, choosing the material, machining, finishing, inspecting and shipping. You are not the project manager between a machine shop, a heat treater and an anodizer. That matters most when a part touches four or five processes and every handoff adds a week.

The chain usually runs like this. DFM review of your STEP file, material selection from stocked grades, roughing and finishing on 3-axis, 4-axis or 5-axis centers, turning or mill-turn work for round features, then surface finishing, then inspection and packing. GreatLight runs these steps under one roof across 127 high-precision CNC machines in a 7,600 m² plant.

The benefit is not only time. When one team owns the tolerance stack from blank to finished part, they can hold ±0.005 mm on critical features instead of blaming the previous vendor. If a finishing operation moves a bore by 0.01 mm, the same shop sees it and fixes the process.

It also simplifies accountability. One purchase order, one inspection report, one shipping document. For small engineering teams, that is often worth more than a lower unit price.

• 1
  One PO, one reportMachining, finishing, inspection and shipping under one quality system.
• 2
  Fewer handoffsEach outsourced step adds transit time and its own tolerance drift.
• 3
  Design feedback earlyDFM comments arrive with the quote, before you commit to tooling.

Tolerance and geometry are two separate questions, and suppliers blur them. Tight tolerance on a simple turned pin is routine. Tight tolerance on a deep pocket with a 3° draft wall and an intersecting cross-hole is a different job. Ask which machine will run your part, then ask what it holds on that feature.

For most metal parts, ±0.005 mm is reachable on critical features with the right setup and temperature control. Surface finish is the same story: Ra 0.8–1.6 μm is a normal machined finish, Ra 0.2–0.8 μm needs a deliberate finishing pass, and Ra 1.6–3.2 μm as-machined is fine for brackets and covers. Do not specify Ra 0.4 μm everywhere. It adds cost and cycle time where nothing touches the surface.

Geometry decides the machine. Angled holes, contoured faces and undercuts belong on a simultaneous 5-axis center, where the tool follows the surface in one setup. Slots on a shaft, cross-drilled holes and parts that are mostly cylindrical belong on a mill-turn center, which avoids re-chucking and the position error that comes with it. A 3-axis machine still wins on flat plates with holes on one face.

Part size is the other limit. GreatLight machines up to 4,000 mm, with travels of 4,000 × 400 × 150 mm on the large frame, 750 × 1,150 × 550 mm and 600 × 600 × 600 mm mid-size, and 500 × 500 × 450 mm compact. If your part sits near an envelope edge, say so in the RFQ. A 5 mm overhang can change the setup and the price.

• 1
  5-axisAngled holes, contoured surfaces, undercuts. 16 simultaneous centers.
• 2
  Mill-turnShafts and cross-drilled round parts without re-chucking. Ø400 mm rotary table.
• 3
  3-axisFlat plates, one-face hole patterns, simple pockets. 27 machines.
• 4
  4-axisIndexed work on multiple faces of a prismatic part. 12 mills.

Material availability drives lead time more often than machining does. Aluminum 6061 and 6061-T6, 7075, 6082 and 2024 are stocked in most shops. Stainless 303, 304, 316L, 17-4PH and 440C are common. Titanium TC4 (Ti-6Al-4V) and Inconel cut slowly and wear tools, so expect a different price curve even though the geometry is identical.

Some materials bring process rules. Magnesium AZ31B and AZ91D need chip control and dedicated handling. Beryllium copper machines well but needs coolant discipline. Plastics like PEEK and POM move with temperature, so hold your tight tolerance callouts for after the part stabilizes, or accept a wider band on as-machined plastic.

Finishing is where turnkey service earns its place. Anodizing in clear, color, hardcoat or conductive form, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing all run as part of the same order. Laser marking is available down to 1.5 mm character height. Below that, plan a different marking method.

One practical note. Hardcoat anodizing builds thickness and can close a tight bore. Tell the shop which features must stay to size before finishing, and they will mask or compensate. Discovering this after plating is expensive.

• 1
  Stocked and fast6061-T6, 304/316L, 1018, C36000 brass, ABS, POM.
• 2
  Slower, tighter processInconel, TC4 titanium, 17-4PH, PEEK, magnesium.
• 3
  Finish before toleranceHardcoat and plating change dimensions. Flag critical features first.

A supplier that only wants production volume will price your prototype high on purpose. Ask directly: what is the minimum order quantity? GreatLight runs no minimum order quantity, from one prototype to 10,000+ part runs, on the same machines. That matters when you need a fit-check part this week and a pilot run next month.

Lead time has three separate clocks: quoting, production start, and shipping. A realistic turnkey shop quotes with free DFM analysis within 12 hours, starts production within 24 hours of approval, and ships parts in 3–5 days for typical work. Complex 5-axis parts or outside finishing will take longer. Any shop that quotes one number for every part is guessing.

Inspection is the part buyers forget to specify. Ask for 100% inspection before shipment, with raw material check, in-process monitoring and final inspection, plus dimensional reports on request. If your industry needs material certificates or first article inspection, say so in the RFQ. It changes the labor, not the machine.

Confidentiality is a real requirement for many programs. Uploads are handled as secure and confidential, and an NDA is available on request. If your drawings are under an NDA already, mention it before you send files so the right agreement is in place.

• 1
  No MOQOne prototype or 10,000+ parts, same process and inspection.
• 2
  Three clocksQuote 12 h, production start 24 h, ship 3–5 days.
• 3
  Inspection scope100% before shipment; reports on request.
• 4
  NDA on requestSecure uploads; agreement can be signed before files move.

The most common mistake is comparing unit prices across quotes with different assumptions. One quote includes material certification, another does not. One includes deburring, another charges it separately. Normalize the scope before you compare numbers, or you will pick the lowest quote and pay for it in rework.

The second is accepting a tolerance claim without a measurement plan. Ask how the shop will verify the feature: which instrument, what temperature, what sampling. A CMM report on first article plus 100% inspection before shipment is a reasonable baseline for production parts.

The third is ignoring capacity. A shop with 127 machines and three plants absorbs a spike. A shop with two machines cannot, and your schedule becomes their problem. If your program has a ramp, ask about capacity now, not at the ramp.

Finally, do not treat certifications as decoration. ISO 9001:2015 covers general quality systems. IATF 16949:2016 applies to automotive work. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security. A supplier serving all four has built the documentation habits that keep your program out of trouble.

• 1
  Normalize scopeSame material, finish, inspection and packaging before comparing price.
• 2
  Ask for the measurement planInstrument, sampling and report type. A claim without a method is a guess.
• 3
  Check capacity headroomMachine count and plant count tell you who can absorb a volume ramp.