3 Axis CNC Machining Factories Global: How to Vet Them

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  What matters before you send an RFQ
• 2
  Four supplier types you will meet
• 3
  Shop floor numbers to quote against
• 4
  What a full-process 3 axis shop actually controls
• 5
  How to test a ±0.005 mm claim
• 6
  Read the certificate, not the logo wall
• 7
  Quote line items that make suppliers comparable
• 8
  When 3-axis is the wrong choice
• 9
  Seven checks before you place the order

A 3-axis mill cuts on three linear axes. The work stays in one orientation, so every feature that faces another direction needs a second setup or a fixture that rotates the part. That single fact drives everything about supplier quality. A shop that owns its fixtures and its secondary operations can hold a datum from setup one to setup three. A shop that subcontracts the EDM or the turning loses that chain.

GreatLight runs 27 three-axis machines inside a cluster of 127 high-precision CNC machines, alongside 12 four-axis mills, 16 simultaneous 5-axis centers and 16 mill-turn centers. That mix matters for 3-axis work because parts rarely stay purely 3-axis. A housing may need a milled face, a wire-cut slot and a turned boss. Keeping those operations under one roof removes the re-datum risk that shows up when three vendors each hold a different reference.

Travel limits decide whether a job is even quotable. The largest 3-axis envelope here is 4,000 × 400 × 150 mm for long extrusions and rails. Medium work sits at 750 × 1,150 × 550 mm or 600 × 600 × 600 mm. Compact parts run on 500 × 500 × 450 mm and 500 × 310 × 200 mm machines with a Ø400 mm rotary table when a fourth index is needed. Send the bounding box with the RFQ, not just the drawing.

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  One datum chainMilling, EDM and turning quoted from the same reference.
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  Travel check firstConfirm the part fits before discussing tolerance.
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  Fixture ownershipAsk whether soft jaws are made in-house or bought.

±0.005 mm is ±0.0002 in. On aluminium at 20 °C, thermal expansion alone moves a 300 mm part by roughly 0.07 mm over a 10 °C shop swing. So a tolerance claim is really a claim about environment and measurement. Ask what the shop holds the room at, how long the part rests before final inspection, and which instrument produces the number.

The second question is where the tolerance applies. A drawing with a general note of ±0.1 mm and three critical dimensions at ±0.005 mm is a different job from a fully toleranced print. Send the critical list. It changes fixture design, cycle time and the inspection plan.

Third, ask about capability over volume. A shop can hit ±0.005 mm on one prototype and drift on part 400 when a fixture wears or chips load up. Repeatability comes from hard stops, torque-checked clamps and a first-article plus in-process check routine. Request the inspection method for the specific feature, not a generic quality certificate.

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  TemperatureA 10 °C swing moves 300 mm of aluminium by about 0.07 mm.
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  Critical dimension listSeparate general tolerance from the features that matter.
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  Drift checkAsk how the 400th part is verified against the first.

Certificates have a scope line and a site address. A group may hold ISO 9001:2015 at one plant and not at another, and the auditor's scope may exclude a process you need. Before you place a purchase order, request the current certificate and match the site address to the plant that will run your parts.

For automotive work, IATF 16949:2016 brings requirements that reach into your project: PPAP-style documentation, traceability, change control. For medical device sub-assemblies, ISO 13485:2016 adds design and process validation expectations. Neither is a marketing badge. Both add paperwork, and a supplier that cannot produce the records is a supplier that cannot support the audit you will face.

Data handling is the fourth layer. ISO 27001:2022 covers information security, which matters when you upload CAD, tolerance stacks and test data. GreatLight works under NDA on request, and uploads are treated as confidential. If your IP is the product, ask about file retention and who inside the shop can open the model.

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  Site addressThe scope must name the plant doing the work.
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  Process scopeCheck that your process is not excluded.
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  IP handlingNDA and file retention policy before upload.

Two quotes for the same part are rarely comparable. One hides setup in the piece price; the other lists it. To compare, force the same structure: material grade and cert, setup and fixture cost, machine rate, finishing, inspection and packaging. Without that, the cheaper number is often the one that assumed a looser tolerance or a simpler fixture.

Ask for the assumption list. Cycle time per part, number of setups, fixture amortization and whether the quote assumes a soft jaw or a dedicated plate. If the shop quotes 10,000 pieces on a fixture that only works for 500, the price is fiction.

Lead time needs the same treatment. A quotation and DFM analysis within 12 hours is a response metric, not a delivery metric. Production can start within 24 hours, and parts ship in 3–5 days on standard work, but the clock only starts once the drawing, material and finish are frozen. Historical late-delivery probability below 2% is a track record, not a guarantee for your specific part.

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  Same structureMaterial, setup, rate, finish, inspection, packing.
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  Assumption listCycle time, setups and fixture life in writing.
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  Clock startLead time begins when the drawing is frozen.

3-axis wins on flat plates, housings with features on one or two faces, heat sinks, manifolds with accessible ports, fixture plates and long rails. It is also the cheapest way to hold tight tolerance on a single face because the setup is rigid and the tool access is simple.

It loses when the part has compound angles, deep contoured pockets on five sides, or features that need continuous tool orientation. Those jobs either need many setups, which multiplies datum error, or a 5-axis center. A supplier that quotes a complex impeller as 3-axis work at a low price is either planning to use a 5-axis machine anyway or planning to miss the tolerance.

Undercuts, deep ribs with small radius corners, and holes that intersect on an angle also push you away from pure 3-axis. If the wall is thin, the clamping force of a 3-axis vise can distort it before the cutter touches metal. That is a fixture problem, and it is worth asking how the shop plans to hold the part before you compare prices.

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  Good fitPlates, housings, rails, fixture plates, single-face tolerance.
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  Poor fitCompound angles, five-side contours, deep undercuts.
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  Thin wallsClamping distortion is a fixture question, not a price question.