CNC processing services in Belgium: how to pick a supplier

• 1
  What matters most when you compare suppliers
• 2
  Which process fits which part
• 3
  How to judge tolerance on CNC processing services in Belgium
• 4
  Lead time, order size, and what a quote should include
• 5
  Certifications and materials that decide the shortlist
• 6
  Surface finish and secondary operations
• 7
  Step by step: from drawing to delivered parts

Tolerance is the first number engineers look at, and the first one suppliers misuse. A shop that claims ±0.005 mm on every part is either not reading the drawing or not being honest. That number is a capability limit, not a default. It applies to specific features, on specific machines, with the right fixturing. On a 4,000 mm long part, thermal growth alone can eat the whole band.

The practical question is which features need tight tolerance and which do not. A bearing bore at Ø40 H7 needs the tight band. The clearance hole next to it does not. Marking that difference on the drawing lets the shop spend time where it matters and keeps the price down. If every dimension carries the same tight tolerance, expect either a high quote or a quiet refusal.

Datum choice decides whether the number is real. A part measured from three different datums will show three different results. Pick datums that match how the part sits in the machine and how it functions in the assembly. For round parts, hold roundness and concentricity, not just diameter. For flat parts, hold flatness and parallelism. Diameter alone tells you very little.

Ask what the shop measures with. A CMM report on a first article is normal. A hand caliper on a ±0.005 mm bore is not. Request raw material certificates, in-process checks, and a final inspection report. If a supplier cannot name the instruments used on your part, the tolerance claim is a marketing line.

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  Apply tight tolerance only where it functionsBearing seats, sealing faces, and mating bores.
• 2
  State datums on the drawingOne primary datum, then secondary and tertiary.
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  Match the instrument to the toleranceCMM for ±0.005 mm, calipers for ±0.1 mm.
• 4
  Request a first article reportBefore the full run starts, not after.

Lead time gets confused with shipping time. Machining days and transport days are separate. A shop with free capacity can start production within 24 hours of a confirmed order and ship parts in 3–5 days. Add transport to Belgium, plus customs clearance, and the door-to-door window grows. A local Belgian shop saves the transport leg but may have a longer queue.

Order size changes the process, not just the price. One prototype to a few hundred parts suits 3-axis or 5-axis milling and turning. Above roughly 10,000 parts, die casting plus finish machining usually wins on unit cost, but adds tooling cost and tooling lead time. Vacuum casting sits between the two for low-volume cosmetic or functional shells. The right answer depends on annual volume, not on the first order alone.

No minimum order quantity matters more than people expect. A supplier who will run one part lets you test the design before committing. A supplier with a 500-piece minimum forces you to guess. Ask directly whether a single prototype is possible, and whether the setup cost is charged once or per batch.

A complete quote lists material grade, stock size, machining operations, finishing steps, inspection, packaging, and freight terms. A quote that says only a unit price hides the parts that will appear on the invoice later. Ask for the finishing specification in writing: anodizing type and thickness, plating, or powder coat color code. Vague finishing is the most common source of rejected deliveries.

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  Separate machining days from transport daysAsk for both numbers.
• 2
  Match process to annual volumePrototype, low volume, or 10,000+ run.
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  Confirm the minimum order quantityOne piece should be an option.
• 4
  Get finishing written into the quoteType, thickness, color code.

Certifications narrow the list fast. ISO 9001:2015 covers general quality management and is the baseline. Medical device work needs ISO 13485:2016, which adds traceability and process validation requirements. Automotive and EV parts need IATF 16949:2016, which brings PPAP-style documentation. If your data is sensitive, ISO 27001:2022 covers information security, which matters when drawings leave your network.

Check that the certificate covers the site doing the work. A group certificate for one plant does not automatically cover a second plant. Ask for the certificate scope and the address on it. Then ask who signs the inspection report and whether that person is at the same site.

Material availability drives both price and schedule. Aluminum 6061-T6, 7075, and 6082 are common and easy to source. Stainless 303, 304, 316L, and 17-4PH cover most corrosion and strength needs. Titanium Ti-6Al-4V and Inconel cut slowly and wear tools, so expect longer machining time and a higher price. Plastics like POM, PEEK, and PC machine cleanly but move with temperature.

Some materials need heat treatment between operations. Annealing, normalizing, quenching, and tempering change hardness and stress state, and they change dimensions. If your part has a heat treatment step, the shop must leave grinding allowance. Skipping that step produces a part that is straight on the bench and bent after treatment. Ask where heat treatment happens and who measures the result.

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  Match certificate to industryISO 9001, IATF 16949, ISO 13485, ISO 27001.
• 2
  Confirm the site on the certificateScope and address, not just the logo.
• 3
  Plan for heat treatment distortionLeave grinding allowance.
• 4
  Check material grade, not just family6061-T6 differs from 6061.

Surface finish is specified as Ra, and the number should match the function. Ra 1.6–3.2 μm is standard as-machined finish and suits most brackets and housings. Ra 0.8–1.6 μm is a finer machined finish for mating faces and sliding surfaces. Ra 0.2–0.8 μm needs slower passes, sharper tools, or a grinding step, and it adds cost quickly.

Cosmetic parts follow different rules. Bead blasting, brushing, and polishing change how light reflects, and they can hide or reveal tool marks. Anodizing comes in clear, color, hardcoat, and conductive types, and each one behaves differently on the same alloy. Hardcoat anodizing adds a thick oxide layer that grows the part by a few micrometers per surface, which matters on a tight bore.

Laser marking and engraving need room. A minimum character height of 1.5 mm keeps the mark readable after finishing. Smaller text fills in or fades. Put the mark on a flat or gently curved face, away from sealing surfaces and high-stress fillets.

Electroless nickel, zinc, silver, and gold plating each have a purpose. Nickel gives uniform coverage on complex shapes. Zinc protects steel at low cost. Silver and gold serve conductivity and contact resistance in electronics. Say which one you need and why, because the wrong plating can change fit or electrical behavior.

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  Ra 1.6–3.2 μm for general partsAs-machined default.
• 2
  Ra 0.8–1.6 μm for mating facesSliding and sealing surfaces.
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  Hardcoat anodizing grows the partAllow for oxide thickness on bores.
• 4
  Laser marks need 1.5 mm minimum heightSmaller text fades after finishing.