Product Related CNC Machining Services: What to Check Before You Order

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  Key takeaways
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  Which machining route fits your product
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  How tight does product related cnc machining need to be
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  Part size, geometry and machine travel
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  Material choice and what it does to lead time
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  How to judge a supplier's quality system
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  Lead time, MOQ and how quotes are built
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  Step by step: from drawing to shipped parts

Every print has a few features that carry the function and a lot of features that just hold the part together. Suppliers who quote ±0.005 mm across the whole drawing are either very expensive or not reading it. The practical move is to mark the functional fits, the bearing bores, the mating faces, and leave the rest at general tolerance.

Our own floor holds ±0.005 mm (±0.0002 in) where it matters, on machines that can repeat it. That number comes from 16 simultaneous 5-axis centers, 12 four-axis mills and 16 mill-turn centers, all under one roof. A tolerance is only real if the machine, the fixture and the inspection method all agree.

Surface finish follows the same logic. Ra 1.6–3.2 μm is as-machined and costs nothing extra. Ra 0.8–1.6 μm needs a finishing pass and a sharper tool. Ra 0.2–0.8 μm usually means a separate operation, sometimes lapping or polishing, and it should be reserved for seal surfaces and sliding fits.

One habit worth building: ask what the datum is before you ask about tolerance. Two suppliers can both claim ±0.005 mm and deliver different parts if one measures from a cast surface and the other from a machined bore. Datum callouts on the drawing remove that argument.

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  Functional features firstTighten only the fits, bores and mating faces.
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  General tolerance elsewhereCuts cycle time and inspection cost.
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  Finish is a separate specRa 0.8 μm and below needs its own operation.

Travel limits decide more quotes than tolerance does. A part that fits in 500 × 500 × 450 mm runs on the compact cells. Anything past 750 × 1,150 × 550 mm moves to a larger frame, and the maximum we process is 4,000 mm with a 4,000 × 400 × 150 mm envelope on the long machines.

Long parts bring their own problem. A 4,000 mm extrusion will sag between supports and spring back after clamping. If your part is long and thin, expect the supplier to ask about support points and stress relief before quoting, not after the first article fails.

Rotary work needs a fourth axis or a mill-turn. We run a Ø400 mm rotary table, which sets the practical limit for parts that need indexing around a bore. Beyond that diameter, the part usually gets repositioned, and every reposition adds a datum error.

Geometry also decides setup count. A part with features on five sides needs either 5-axis simultaneous machining or four separate setups. Four setups mean four chances to lose position. That is the real reason 5-axis costs more per hour but often less per part.

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  Compact cellUp to 500 × 500 × 450 mm.
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  Medium frame750 × 1,150 × 550 mm and 600 × 600 × 600 mm.
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  Long parts4,000 mm max, watch sag and clamping spring.
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  Rotary limitØ400 mm table for indexed work.

Aluminium 6061-T6 is the default for housings, brackets and prototype frames. It machines fast, takes anodizing well and holds tolerance. Switch to 7075 only when you need strength, because it costs more and cuts slower. 2024 has better fatigue behavior but poor corrosion resistance without coating.

Stainless 303 is the free-machining grade and the right pick for shafts and fittings. 304 and 316L resist corrosion better but gum up tools, so cycle times rise. 17-4PH (SUS630) sits in between and heat treats to high strength, which suits valve bodies and pump parts.

Titanium TC4 (Ti-6Al-4V) and Inconel are a different category. Tool life drops, feeds drop, and the same part can take three times the cycle time of aluminium. If the design does not need the temperature or strength, do not spec it.

Finishing adds a second lead time that buyers often forget. Anodizing, electroless nickel, zinc and powder coating all go out to controlled processes. Laser marking is done in-house with a minimum character height of 1.5 mm. Below that, the mark fills in and becomes unreadable.

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  Default aluminium6061-T6 for most housings and brackets.
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  Free-machining stainless303 for shafts, 304/316L for corrosion.
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  Exotics cost cycle timeTC4 and Inconel can triple machining time.
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  Marking limit1.5 mm minimum character height.

Certificates tell you what a plant is allowed to make, not what it made last week. ISO 9001:2015 covers general quality management. IATF 16949:2016 is the automotive standard and comes with traceability expectations. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters if you are sending CAD files.

The useful question is which certificate covers the line your part will run on. A plant can hold four certificates and still run your job on a cell that only falls under the general system. Ask for the scope statement, not the certificate number.

Inspection is the other half. We inspect 100% of parts before shipment, with raw material check, in-process monitoring and final inspection. Reports come on request. If a supplier cannot describe their in-process check without being prompted, that is a signal.

Confidentiality belongs in the same conversation. Uploads are handled as secure and confidential, and an NDA is available on request. For product related cnc machining work, the drawing is often the most valuable file the buyer sends.

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  Match certificate to lineAsk which cell your job runs on.
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  100% inspectionRaw material, in-process, final.
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  Reports on requestGet the format agreed before the run.
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  NDA on requestStandard practice for new product files.

Quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours after that, and parts ship in 3–5 days. Those windows assume the drawing is released and the material is standard. A custom extrusion or a heat-treat step will push the schedule out.

There is no minimum order quantity. A single prototype and a 10,000+ part run both go through the same quoting process. The difference is setup cost spread. One prototype carries the full setup; ten thousand parts carry almost none. That is why the unit price curve falls fast and then flattens.

A quote should list material, machining, finishing, inspection and freight as separate lines. When a supplier gives one lump number, you cannot tell whether they priced the tolerance or ignored it. Split quotes also let you compare two suppliers honestly.

Be cautious with quotes that arrive in an hour with no questions. A real DFM review usually finds at least one issue: a wall too thin for the tool, a corner radius below the cutter, a thread that needs a relief. No feedback often means nobody looked.

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  12-hour quoteIncludes free DFM analysis.
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  3–5 day shippingAfter production starts.
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  No MOQOne part or 10,000+.
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  Split the quoteMaterial, machining, finish, inspection, freight.