SA CNC Processing Services: How to Pick the Right Supplier

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  Key takeaways
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  What to Check in SA CNC Processing Services
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  Tolerance and Finish: What SA CNC Processing Services Can Hold
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  Machine Mix and Part Size in SA CNC Processing Services
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  Materials, Certifications and Inspection Records
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  Lead Time, MOQ and Quote Clarity
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  Common Mistakes When Buying SA CNC Processing Services
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  Step by Step: Qualifying an SA CNC Processing Services Supplier

Tolerance is the number that decides whether a supplier can make your part at all. GreatLight quotes ±0.005 mm (±0.0002 in) on turned and milled features, but that figure only applies when the setup supports it. A 20 mm aluminium bracket and a 400 mm steel housing do not behave the same way in the same machine.

Heat is the usual reason a tight tolerance drifts. On a 300 mm 4140 steel shaft, roughing generates enough heat that the part grows, gets measured oversize, then shrinks after cooling. Good shops rough, wait, then finish. Ask how they handle that sequence.

Surface finish follows the same logic. As-machined surfaces sit at Ra 1.6–3.2 μm. A high-quality finish needs Ra 0.8–1.6 μm, and fine work reaches Ra 0.2–0.8 μm. That last range usually needs a smaller stepover, a sharper insert and more time, so it costs more.

If your print mixes a tight bore with a loose cosmetic face, say so. Suppliers price to the tightest feature on the drawing unless you tell them which dimensions are functional.

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  Fine finishRa 0.2–0.8 μm for sealing faces and sliding surfaces.
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  High finishRa 0.8–1.6 μm for most mating interfaces.
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  As machinedRa 1.6–3.2 μm for non-critical cosmetic surfaces.

A supplier can list 127 machines and still not have the right one for your part. What matters is whether the geometry needs simultaneous 5-axis motion, a mill-turn cycle, or just a clean 3-axis setup. Each choice changes both price and risk.

Five-axis work pays off when you have angled holes, undercuts or contoured pockets that would need three or four separate fixtures on a 3-axis machine. Every extra setup adds a datum shift, and datum shifts are where tolerance stacks fail.

Mill-turn centers handle parts that are mostly round but carry milled flats, slots or cross-holes. Doing that in one cycle removes the concentricity error you get when a part moves from a lathe to a mill.

Size caps the conversation. A 4,000 mm maximum processing size with 4,000 × 400 × 150 mm travel covers long rails and frames. Compact work down to 500 × 310 × 200 mm runs on smaller, faster machines, which usually means a lower hourly rate.

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  5-axis16 simultaneous 5-axis machining centers for complex geometry.
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  Mill-turn16 mill-turn centers for round parts with milled features.
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  Large travelUp to 4,000 × 400 × 150 mm on long parts.
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  Rotary tableØ400 mm for 4-axis positioning work.

Material range tells you how wide a supplier's process window really is. Aluminium 6061 and 7075 machine easily. 17-4PH stainless, Ti-6Al-4V and Inconel do not. They work-harden, wear tools fast and move when you cut them. A shop that lists them usually has the tooling and coolant strategy to match.

Plastics deserve the same scrutiny. POM and PEEK hold tight tolerances well. ABS and PP flex under clamping pressure, so the fixture design matters more than the cutter. Ask how they hold a thin-walled PEEK part without crushing it.

Certifications are a filter, not a badge. For automotive and EV work, look for IATF 16949:2016 alongside ISO 9001:2015. For medical devices, ISO 13485:2016 is the one that matters. ISO 27001:2022 covers how your CAD files and drawings are stored, which matters if you send proprietary geometry.

Inspection is the last line of defense. GreatLight checks raw material on arrival, monitors in process and inspects 100% before shipment, with reports on request. That is a stronger commitment than sampling a batch and hoping.

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  Aluminium6061-T6, 7075, 2024, 6082, ADC12.
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  Stainless303, 304, 316L, 17-4PH, 440C.
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  TitaniumTA1, TA2, TC4 (Ti-6Al-4V), Inconel.
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  PlasticsPEEK, POM, PC, PA, carbon fibre.

Lead time is where most sourcing plans break. A supplier that quotes and returns free DFM analysis within 12 hours has already reviewed your model. One that takes three days to answer usually has a queue you cannot see.

GreatLight can start production within 24 hours of a released order and ships parts in 3–5 days. The historical late-delivery probability sits below 2%. Those numbers assume the print is final and the material is in stock or on a short lead.

MOQ is the other common blocker. There is no minimum order quantity here, so a single prototype and a 10,000+ part run go through the same process controls. That matters when you need to validate a design before committing tooling.

Quote clarity is easy to test. Send a STEP file plus a 2D print with GD&T and see whether the reply separates material, machining, finishing and inspection. A single lump-sum number hides where the cost really sits.

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  QuoteFree DFM analysis within 12 hours.
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  StartProduction can start within 24 hours.
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  ShipParts ship in 3–5 days.
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  RunsOne prototype to 10,000+ parts, no MOQ.

The most expensive mistake is quoting to the wrong tolerance. If a drawing shows ±0.005 mm on every dimension, the supplier prices every feature as critical. Mark functional dimensions and let the rest run at a looser band.

The second mistake is ignoring finishing until after the parts arrive. Anodizing removes a thin layer of material and can change a press-fit bore. Plating adds material. Both need to be in the tolerance plan from the start.

The third is treating certifications as paperwork. If your customer audits the supply chain, the certificate has to match the plant, the process and the date. An expired ISO 13485:2016 certificate is worse than none, because it looks like a gap you missed.

Finally, do not assume a low unit price survives the full order. Tooling, setup, finishing and inspection are where quotes diverge. Compare total landed cost across the whole batch, not the per-piece number on page one.

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  Over-tolerancingTightening every dimension raises cost with no functional gain.
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  Finishing afterthoughtAnodizing and plating shift dimensions after machining.
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  Stale certificatesCheck the plant name and expiry date, not just the logo.