Buy SS CNC Machining Parts: What to Specify

Stainless is not one material. A quote for 304 is not a quote for 316L, and neither one predicts what 17-4PH will cost. When you buy SS CNC machining parts, the alloy drives cutting speed, tool wear, and how much stock you can take in one pass. 303 machines fastest because of its sulfur content, so it suits bushings, fittings, and high-volume turned parts where corrosion resistance is moderate. 304 gives better corrosion resistance and weldability but tends to gum up on finishing passes.

316 and 316L add molybdenum for chloride resistance. They belong in marine hardware, food equipment, and medical fixtures. 17-4PH is a precipitation-hardening grade. It machines in the annealed state and then reaches high strength after heat treatment, which makes it common for shafts, valves, and aerospace brackets. 420, 430, 431, and 440C cover the harder wear applications such as knife components and pump parts.

One rule of thumb from the shop floor: if a part needs deep pockets or thin walls, 303 and 304 behave very differently. 303 chips break cleanly. 304 work-hardens at the cut, so a light finishing pass on a thin rib can push the material past the point where the tool cuts it cleanly. Tell us the wall thickness at the quoting stage and we will pick the grade or the strategy that holds the feature.

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  303Best machinability, moderate corrosion resistance, turned parts
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  304 / 316LBetter corrosion resistance, watch work hardening on thin walls
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  17-4PHAnnealed machining, then heat treat for high strength
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  440C / 420Hardened wear parts, slower cutting, more tool wear

Our general machining tolerance is ±0.005 mm. That figure applies to specific dimensions you call out, not to every feature on the drawing. A 300 mm long stainless shaft cannot hold ±0.005 mm over its full length without a second operation or a temperature-controlled setup, so we flag those features before quoting rather than after.

Geometry matters as much as the number. A stainless part with a 6:1 depth-to-diameter ratio in a bore is a different job than an open pocket. Deep holes need peck drilling and sometimes a gun drill, and the tool can wander. Thin floors deflect under cutting force. Sharp internal corners in a milled pocket require a small cutter, which means slower feed rates and more passes. If you can add a corner radius, the part gets cheaper without losing function.

We run 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. Maximum processing size is 4,000 mm, with travels of 4,000 × 400 × 150 mm on the large frames and 750 × 1,150 × 550 mm on the medium ones. A Ø400 mm rotary table handles parts that need access from several faces in one setup. Fewer setups usually means tighter true position between features.

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  Call out critical dims±0.005 mm applies to the features you mark, not the whole drawing
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  Deep boresAbove 6:1 depth-to-diameter, expect peck drilling and longer cycle time
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  Corner radiiA radius instead of a sharp corner removes a small-cutter operation

Stainless parts often look finished when they leave the machine, which hides the fact that surface finish is a separate decision. As-machined surfaces sit around Ra 1.6–3.2 μm. A high-quality finish is Ra 0.8–1.6 μm, and fine finishing reaches Ra 0.2–0.8 μm. Each step up adds passes and inspection time.

For stainless, bead blasting is the usual way to even out tool marks and give a uniform matte look. Tumbling and brushing work for small parts in bulk. Polishing goes further for sanitary or appearance-critical faces. Laser marking is available for part numbers and traceability codes, with a minimum character height of 1.5 mm so the mark stays legible after finishing. We also run electroless nickel, zinc, silver, and gold plating, powder coating, black oxide, and anodizing on the aluminum side of the shop.

Passivation deserves its own line on the purchase order. Machining leaves free iron on the surface, and that iron is where corrosion starts. A nitric or citric passivation step after machining removes it. If your part goes into a washdown environment or a medical device, specify passivation and ask for the report.

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  Bead blastingEvens out tool marks, uniform matte finish
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  PassivationRemoves free iron after machining; specify it for wet environments
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  Laser markingMinimum character height 1.5 mm, survives finishing

Every order gets 100% inspection before shipment. That covers a raw material check, in-process monitoring, and a final inspection, with reports available on request. For stainless parts that will be welded or heat treated, we can supply mill certificates so you know what went into the part.

Our plants hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. The last one matters more than it sounds. It covers information security, so your drawings and models stay controlled. Uploads are secure and confidential, and an NDA is available on request if your program needs one.

On timing: quotation and free DFM analysis come back 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%. There is no minimum order quantity, so a single prototype and a 10,000+ part run go through the same process. If your project has a hard date, say so early and we will tell you whether the schedule is realistic.

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  12 hoursQuotation and free DFM analysis turnaround
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  3–5 daysTypical shipping window after production start
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  No MOQFrom one prototype to 10,000+ parts