CNC Machined Service Customized: What to Check Before You Order

• 1
  Seven things that decide whether a custom quote is usable
• 2
  Matching part and order profile to the right custom setup
• 3
  Tolerance: decide it feature by feature, not on the title block
• 4
  Surface finish: the line item that quietly doubles cycle time
• 5
  Material and quantity: how order size changes the process
• 6
  Certification and paperwork: read the scope, not the logo
• 7
  Quoting and lead time: what a complete quote contains
• 8
  How to qualify a custom machining supplier in six steps

Most custom quotes go wrong at the tolerance callout. A drawing that says ±0.005 mm on every dimension forces the shop to hold the same accuracy on a clearance hole and on a bearing bore. That is money spent on features that will never be measured after assembly.

A better approach is to tolerance only what mates. Bearing seats, dowel holes, sealing faces and press fits earn tight limits. Bolt clearance, outside profiles and non-critical step heights usually run fine at ±0.1 mm. Mark the rest as general tolerance and reference the drawing standard.

The shop then plans its setups around the tight features and relaxes the rest. On a 5-axis center, one setup can reach several angled faces, which removes the stack-up that comes from flipping the part three times. That is where ±0.005 mm becomes repeatable rather than lucky.

Ask one question before you commit: which dimensions will be inspected on the report? If the answer is vague, the tolerance callout is decoration. We inspect 100% of parts before shipment and can issue reports on request, so the answer is always traceable to a number.

Finish is where a custom quote can look cheap on paper and expensive in practice. As-machined surfaces at Ra 1.6–3.2 μm come straight off the cutter with normal feeds. Moving to Ra 0.8–1.6 μm needs a finer step-over and a sharp tool. Fine finishing at Ra 0.2–0.8 μm adds a separate light pass and often a second setup.

So the useful question is what the surface actually does. A sealing face, a sliding bore or an optical mount may need the fine band. A bracket that bolts to a frame does not. Specify the band per surface group, not for the whole part.

Some finishes are applied after machining and change the dimension. Anodizing builds a layer on aluminium. Hardcoat builds more than clear anodize. Electroless nickel and hard chrome change size too. If a bore must stay at a press-fit diameter after coating, say so and give the final target.

Bead blasting, tumbling, brushing and polishing all hide tool marks rather than remove material, so they are safe for cosmetic parts. Laser marking is a separate step: keep character height at 1.5 mm or more so the mark stays readable on a curved or textured surface.

The material list a supplier shows you matters less than what they know about machining it. Aluminium 6061 and 7075 cut cleanly and hold tight limits. 304 stainless work-hardens, so light cuts and sharp tools matter. Titanium TC4 and Inconel move under heat and need different feeds and coolant strategy.

Ask how the shop handles stress. A part cut from a plate can bend after the fixture is released, especially with thin walls or long slots. The fix is usually a roughing pass, a stress-relief step, then finishing. That adds time, so it should appear in the quote, not in a phone call after the parts are scrapped.

Quantity is the other lever. A cnc machined service customized to your print should not force you into a large first order. We hold no minimum order quantity, so a single prototype and a 10,000+ part run both fit. Fixing the process at the prototype stage is what keeps the later runs consistent.

If you plan to scale, ask at the start whether the prototype setup can become a production fixture. Changing the fixture later resets the first-article approval. Keeping the datum scheme identical across both stages saves a full qualification loop.

A certificate on a web page tells you the system exists. It does not tell you whether your part falls inside the audited scope. Before you order, check that the certificate number is current and that the standard matches your industry.

For general industrial parts, ISO 9001:2015 covers the quality system. Automotive work usually needs IATF 16949:2016, which brings traceability and process controls with it. Medical device components are typically ordered under ISO 13485:2016. If your drawings and files are sensitive, ISO 27001:2022 covers information security.

Paperwork is part of the deliverable. Ask what arrives with the box: material certificate, inspection report, first-article report, coating thickness record. We keep raw material checks, in-process monitoring and final inspection in the flow, and we release reports on request.

Confidentiality belongs in the same conversation. Uploads are kept secure and confidential, and an NDA is available on request. If your part is a pre-launch design, settle that before sending the STEP file, not after.

A quote that lists only a price per piece is incomplete. You cannot compare two suppliers without knowing what is inside the number. The useful quote breaks out material, machining time, finishing, inspection and any fixture or programming charge.

Then check the timing claims. We return a quotation and a free DFM analysis within 12 hours. Production can start within 24 hours of approval, and parts ship in 3–5 days. Historical late-delivery probability is below 2%. Those are the numbers to hold us to, and they should be written into the order.

DFM feedback is the part buyers skip and later regret. A machinist who reviews the model can flag a corner radius smaller than the cutter can reach, a pocket deeper than four times its width, or a thread that has no run-out room. Fixing those in the model costs minutes. Fixing them after machining costs a new order.

Watch for quotes that are silent on finishing and inspection. They are usually not cheaper; they are just unfinished. Add the missing operations and compare again.