Standard CNC Machining Services: What to Check Before You Order

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  Key takeaways
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  Standard CNC Machining Services Compared by Part Type
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  What Standard CNC Machining Services Actually Cover
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  Tolerance and Surface Finish: Pick the Line You Can Measure
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  Lead Time, MOQ and What the Quote Should Contain
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  Certifications, Inspection and Material Traceability
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  Materials and Finishes That Suit Standard Machining
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  7 Steps to Qualify a Standard Machining Supplier

Standard covers milling, turning and drilling on 3-axis mills and 2-axis lathes. The tool approaches from one direction per setup, the part is refixtured for the next face, and the operator or probe re-datum each time. That is the whole model. It is fast to program, fast to quote and easy to inspect.

Where it breaks down is reach. A cross hole on a shaft, a pocket with an undercut, a contoured face that leans away from the spindle. Standard machining can still make these parts, but you pay in setups, fixtures and rework risk. Three setups instead of one means three chances to lose your datum.

At GreatLight we run 127 high-precision CNC machines, of which 27 are three-axis and 16 are mill-turn centers. Those two groups carry most standard work. The 12 four-axis mills and 16 simultaneous 5-axis centers pick up the jobs where reach or setup count decides the price.

So the first question is not which shop, it is which machine group. Send a part print with the critical faces marked and a shop can tell you in one line whether standard work fits or whether you are buying a five-axis job at standard prices.

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  Fits standardPrismatic bodies, brackets, plates, bushings, simple housings.
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  Fits mill-turnShafts, fittings, parts with turned and milled features on one axis.
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  Needs 4 or 5 axisUndercuts, compound angles, contoured surfaces, one-setup datums.

Tolerance is the single largest cost lever on a quote. A ±0.005 mm callout on a bore means a specific machine, a warm-up cycle, a temperature-stable room and a CMM report. On a mounting hole that only locates a cover, ±0.1 mm does the same job for a fraction of the effort.

General machining holds roughly ±0.05 mm on milled features and ±0.025 mm on turned diameters without special measures. Tighten to ±0.005 mm and you are buying inspection as much as cutting. That is fine when the function needs it. It is waste when it does not.

Finish follows the same logic. As-machined surfaces sit around Ra 1.6–3.2 μm. A high-quality finish lands at Ra 0.8–1.6 μm. Fine finishing reaches Ra 0.2–0.8 μm and usually adds a separate operation, sometimes hand work on contoured faces.

A practical habit: dimension only the faces that mate, seal or slide. Leave everything else to the shop's default. Drawings with a tight blanket tolerance across every dimension slow the quote and raise the price for no gain.

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  Functional facesCall out flatness, concentricity or a bore diameter. Those drive assembly.
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  Cosmetic facesSpecify finish and texture direction, not a tolerance.
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  Free surfacesLet the shop use its default. You will not measure them anyway.

A usable quote comes back with four things: price per quantity break, the machine group, the lead time from PO, and the inspection plan. If any of those is missing, you will be chasing it later. Ask for DFM notes too. Feedback on wall thickness or tool reach often saves a revision.

GreatLight returns a quotation and a free DFM analysis within 12 hours. Production can start within 24 hours, and parts ship in 3–5 days for standard work. Historical late-delivery probability is below 2%. Treat those as typical numbers for quoted standard jobs, not a promise on every part.

MOQ is a common trap. Standard job shops should quote one prototype and a 10,000-part run on the same line. GreatLight has no minimum order quantity. If a supplier quotes a 500-piece floor, you are paying for their setup, not for your part.

Watch for quotes that hide the inspection cost, exclude material certification or list a lead time that starts at quote rather than at PO. Those three items cause most of the schedule slip we see when a buyer transfers a job.

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  Quantity breaksAsk for 1, 10, 100 and 1,000 piece pricing. The curve tells you a lot.
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  Lead time basisConfirm whether the clock starts at PO, at material arrival, or at drawing approval.
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  Inspection planAsk which dimensions get measured and whether a report ships with the parts.

Certificates are scoped. ISO 9001:2015 covers general quality management. IATF 16949:2016 applies to automotive production. ISO 13485:2016 covers medical devices. ISO 27001:2022 covers information security, which matters when your drawings and CAD data are the asset.

A supplier holding all four is not automatically better for a bracket. What matters is that the certificate covers the process and site that will run your part. Ask for the certificate scope, not just the logo.

Inspection is where claims become evidence. GreatLight inspects 100% of parts before shipment, with raw material check, in-process monitoring and final inspection. Reports are available on request. Typical qualification rate is 99.99% across shipped work.

For anything regulated, decide up front what you need in writing: material certificates, first article inspection, CMM reports, or a certificate of conformity. Adding that after the parts are made costs more than asking before the PO.

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  ISO 9001:2015Baseline quality system for general industrial parts.
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  IATF 16949:2016Required for most automotive production programs.
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  ISO 13485:2016Needed for medical device components and their records.
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  ISO 27001:2022Covers how your design files and data are protected.

Standard machining works across a wide material range, but the choice changes feeds, speeds and sometimes the machine. Aluminum grades like 6061, 7075 and 6082 cut fast and hold tight tolerances well. Stainless 303 and 304 machine cleanly; 316L and 17-4PH are tougher on tool life.

Steels such as 1018, 1045 and 4140 are routine. Titanium TC4 (Ti-6Al-4V) and Inconel are machinable but slow, and they punish light fixturing. Copper alloys like C36000 cut freely; beryllium copper needs tighter process control. Plastics from POM and ABS to PEEK each behave differently.

Finishes are usually a separate step. Anodizing, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing and polishing are all available. Laser marking needs a minimum character height of 1.5 mm to stay legible.

Two practical notes. Hardcoat anodizing adds thickness and can close a tight bore, so mask or ream after coating. Polished cosmetic surfaces on complex geometry often need hand work, which is the one place where standard machining still competes with manual bench time.

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  Easy group6061, 6082, 303, 304, 1018, C36000, POM, ABS.
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  Moderate group7075, 17-4PH, 4140, 316L, PEEK, magnesium AZ31B.
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  Hard groupTC4, Inconel, 440C, beryllium copper. Expect longer cycle times.