CNC Processing Services Sydney: A 7-Check Buyer Guide

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  Key takeaways
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  Which supplier profile fits your part
• 3
  Tolerance: what ±0.005 mm really buys you
• 4
  Lead time: separate quoting from machining
• 5
  MOQ, certifications, and IP protection
• 6
  Materials and finishes that change the quote
• 7
  Inspection and the paperwork trail
• 8
  How to vet a Sydney supplier in 7 steps

Tolerance drives cost more than material does. A part held to ±0.005 mm needs finer fixturing, slower feeds, and more inspection than the same geometry at ±0.05 mm. Before you send a drawing, mark which dimensions are functional and which are reference. Shops quote the tightest callout on the print, even if it sits on a non-critical edge.

For most aluminum and stainless parts, ±0.005 mm is the practical floor on critical features like bores, bearing seats, and mating faces. Overall length on a 300 mm part is usually held closer to ±0.05 mm because thermal drift moves the number. If a feature does not touch another part, loosen it.

Surface finish follows the same logic. Ra 0.2–0.8 μm needs a finishing pass and often hand work; Ra 1.6–3.2 μm comes off the machine. Specify Ra only where a seal, bearing, or optical surface needs it. Blanket Ra 0.4 μm callouts across a whole drawing add cost with no functional gain.

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  Mark functional dimensionsTag the features that mate, seal, or rotate.
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  Loosen non-critical edgesReference dimensions do not need tight bands.
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  Ask for the CMM reportTolerance claims mean nothing without measurement data.

Lead time gets quoted as one number, but it has three stages: quote and DFM, production start, and actual machining plus finishing. A shop can return a quotation and free DFM analysis within 12 hours and still take a week to ship if the finish queue is full. Ask for each stage separately.

Production start within 24 hours is realistic when the shop has setup capacity and the material is in stock. Aluminum 6061 and 304 stainless are usually on the floor. Titanium TC4, Inconel, and 17-4PH often need a material order, which adds days before the first chip is cut.

Parts ship in 3–5 days on standard work. That window assumes no outside finishing. Anodizing, electroless nickel, and powder coating go to a plating line, and that queue is the real variable. If your deadline is fixed, book the finish before the machining slot.

Ask what happens when a dimension fails final inspection. A shop that reworks in-house holds the schedule. A shop that sends parts back to a subcontractor loses days you cannot recover.

No minimum order quantity matters more than buyers expect. A prototype shop and a production shop are often different companies, and moving between them means a new DFM cycle, new fixtures, and a second first-article inspection. A supplier that runs one prototype and a 10,000-part order on the same floor removes that step.

Certifications are not interchangeable. ISO 9001:2015 covers general quality systems. IATF 16949:2016 is the automotive standard and comes with the documentation automotive customers expect. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters if your drawings carry IP you cannot expose.

Match the certificate to the industry, not to the size of the order. A 200-part automotive bracket still needs IATF paperwork if the part goes into a vehicle program. A medical housing needs ISO 13485 traceability even in low volume.

Uploads should be handled under NDA on request, with restricted access and no third-party sharing. If a supplier cannot describe how files are stored and who can open them, treat that as a gap.

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  One part or ten thousandNo MOQ keeps prototyping and production under one roof.
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  Certificate to industryIATF for auto, ISO 13485 for medical, ISO 27001 for IP.
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  NDA on requestAsk how CAD files are stored and accessed.

Material choice sets the baseline cost and the machining strategy. Aluminum 6061, 7075, and 6082 cut fast and hold tolerance well. Stainless 303 and 304 are common but work-harden, so feeds and speeds need care. Titanium TC4 and Inconel cut slowly and wear tooling, which shows up as a higher hourly rate.

Plastics behave differently again. POM and PEEK hold tight tolerances but move with temperature. ABS and PMMA are easy to cut but can chip on thin walls. Carbon fibre needs diamond tooling and dust control. Tell the shop the material grade, not just the family.

Finishing is where quotes diverge most. Anodizing in clear, color, hardcoat, or conductive types changes both appearance and dimension. Hardcoat adds 20–50 μm per surface, which matters on a ±0.005 mm bore. Electroless nickel, zinc, silver, and gold plating each have their own thickness tolerance.

Bead blasting, tumbling, brushing, and polishing are cosmetic and rarely affect fit. Laser marking needs a minimum character height of 1.5 mm to stay readable. Put the finish callout on the drawing with a thickness band, not just a name.

100% inspection before shipment sounds like a strong claim, but ask what is measured. Raw material check, in-process monitoring, and final inspection cover different risks. In-process checks catch a drifting tool before a batch is scrap. Final inspection catches what already happened.

A 99.99% qualification rate is a process figure, not a guarantee on your part. The useful question is what the shop does with the failures. Rework, scrap credit, and root-cause notes on the next run separate a real quality system from a sorted bin.

Inspection reports should be available on request and tied to the drawing revision. First-article reports, material certificates, and CMM data are standard for automotive and medical work. For general industrial parts, a dimensional report on critical features is usually enough.

Keep your own drawing revision under control. A supplier quoting rev C while you ship rev D is one of the most common causes of a failed first article.

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  Ask what is measuredIn-process checks catch drift; final checks catch history.
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  Reports on requestFAI, material certs, and CMM data for critical features.
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  Lock the revisionConfirm the drawing revision on the quote.