CNC outsourcing services

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  Key takeaways
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  What to compare across CNC outsourcing services
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  The first check in CNC outsourcing services: machine fit
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  Tolerance and surface finish: what the number really buys
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  Inspection evidence before parts ship
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  MOQ, quote clarity and lead time milestones
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  Material and finish choices that affect the decision
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  How to vet a supplier in seven steps

Most sourcing problems start with a machine that cannot reach the feature. Before price, confirm the quoted machine can physically hold the part and reach every face. Our largest work envelope is 4,000 × 400 × 150 mm, which covers long rails, beams and extrusion profiles. Medium machines run 750 × 1,150 × 550 mm and 600 × 600 × 600 mm, and compact machines cover 500 × 500 × 450 mm and 500 × 310 × 200 mm.

Axis count matters as much as size. A part with angled ports, deep contoured pockets or undercut walls usually needs 5-axis work to avoid four or five separate setups. Every extra setup adds a datum shift and a chance for stack-up error. We run 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers.

Mill-turn is the option people forget. Shafts, bushings and connectors with a turned body and milled flats can be finished in one machine, which keeps concentricity between the bore and the milled features. Splitting that work across a lathe and a mill means two datums and a re-chuck.

Ask which machine will actually run your part, not what the shop owns. A supplier with 127 machines can still quote your job onto the wrong one if nobody checks the drawing first.

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  Long and thinUse a 4,000 mm travel machine with steady support to control deflection.
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  Complex geometryUse 5-axis to cut setups and hold position between features.
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  Round plus flatsUse mill-turn to keep bore-to-flat relationships in one setup.

A tolerance is only meaningful with a size, a feature and a datum. ±0.005 mm on a 20 mm bore in aluminium is normal work for a good machine. The same number across a 1,500 mm aluminium frame is a different problem, because thermal drift and fixture movement enter the picture. When a drawing shows one general tolerance block, ask which features are critical and which are loose.

Material drives the achievable result too. Aluminium 6061, 7075 and 6082 cut cleanly and hold tight limits with light finishing passes. Stainless 316 and 17-4PH work-harden, so heavy radial cuts and slow feed tend to burn the edge. Titanium TC4 and Inconel need lower cutting speeds, more coolant and patience. Ask the supplier how they plan to hold the limit on your specific alloy.

Surface finish is quoted as Ra. As-machined surfaces sit around Ra 1.6–3.2 μm, high-quality finishes land at Ra 0.8–1.6 μm, and fine finishing reaches Ra 0.2–0.8 μm. Finer finish costs cycle time, so specify it only where a seal, bearing or optical surface needs it. Cosmetic faces and sliding faces rarely need the same value.

One more point. If a callout says Ra 0.4 μm on a deep pocket wall, ask how they will measure it. A stylus may not reach the wall, and an optical method gives a different number.

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  State the datumTolerance without a datum scheme is not inspectable.
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  Match alloy to targetAluminium for tight limits, titanium and Inconel for heat and strength.
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  Specify finish where it mattersRa 1.6–3.2 μm for general faces, finer only for sealing or sliding.

Any shop can say it inspects. Ask what happens at each stage. We run a raw material check on incoming stock, in-process monitoring during the run, and a final inspection before shipment, with 100% inspection on the parts that ship. Reports are available on request. If your part is safety-related, ask for the dimensional report with the drawing balloon numbers attached.

Certifications set the floor for some industries. General industrial work is covered by ISO 9001:2015. Automotive and EV programs usually require IATF 16949:2016. Medical device parts fall under ISO 13485:2016, and data handling falls under ISO 27001:2022. Check that the certificate covers the plant that will run your parts, not just the group.

For regulated work, ask about traceability. Can they tie a finished part back to a heat number, a machine and an operator? That trail is what an auditor will ask for, and it is much easier to build during the run than to reconstruct afterwards.

Confidentiality belongs in this section too. Uploads should be stored securely and access limited to the people quoting and machining the job. A signed NDA is available on request if your drawings are sensitive.

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  Three-stage checkIncoming material, in-process, final before shipment.
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  Report on requestAsk for ballooned dimensions, not just a pass stamp.
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  Certificate scopeConfirm the certificate names the plant doing the work.

MOQ is where small programs get stuck. Tooling and setup costs push many suppliers to demand a minimum run, which makes a one-off prototype uneconomic. We work with no minimum order quantity, from a single prototype through to runs of 10,000+ parts, so the same process scales with your program.

A quote should be readable by an engineer. Look for separate lines for material, setup, cycle time, finishing, inspection and freight. A single lump-sum number hides where the cost sits and makes it hard to see what a design change would save. If a feature is expensive, you want to know that before you commit.

Lead time has three parts and they should be quoted separately. A quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours of release. Parts ship in 3–5 days for standard work. Historical late-delivery probability sits below 2%, but treat any single promised date with care until you see the milestones behind it.

A free DFM review is one of the most useful things a supplier can offer. It catches thin walls, deep pockets with no tool access, and tolerances that cost more than they are worth. Take the review seriously and revise the drawing before the first chip is cut.

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  No MOQOne piece or 10,000+, same process and supplier.
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  Itemized quoteMaterial, setup, cycle, finish, inspection, freight on separate lines.
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  Milestone datesQuote, start and ship dates quoted as three separate commitments.

The material list tells you how broad a supplier's experience really is. We machine aluminium 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12. Stainless grades include 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH. Steels cover 1018, 1045, 4130, 4140, 4340, A36 and tool steel.

For tougher jobs, titanium TA1, TA2 and TC4, plus Inconel and magnesium AZ31B or AZ91D, are available. Plastics include ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre. If your drawing calls for a material outside this set, ask early rather than after the quote.

Finishing often decides whether a part is usable. Anodizing comes in clear, colour, hardcoat and conductive versions. Plating options include electroless nickel, zinc, silver and gold. Powder coating and black oxide cover wear and appearance needs. Bead blasting, tumbling, brushing and polishing handle texture. Laser marking and engraving are available with a minimum character height of 1.5 mm.

Pick a finish based on function. Hardcoat anodizing for wear surfaces. Electroless nickel for uniform coverage on complex shapes. Black oxide for a low-cost, mildly corrosion-resistant finish on steel. Each one adds lead time, so include it in the schedule from day one.

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  Wide material rangeAluminium, stainless, steel, copper, titanium, magnesium, plastics.
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  Finish for functionHardcoat for wear, electroless nickel for uniform coverage.
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  Report on requestAsk for inspection records with the finished parts.