China Wholesale CNC Prototype Processing Service

A prototype has one job: tell you whether the design works. If the part will be injection molded, die cast or forged in production, a machined prototype gives you the same material behavior and the same wall stiffness as the final part. Printed resin does not. That difference matters when you are testing a snap fit, a thread, or a bearing bore.

CNC subtractive work holds dimensional accuracy that additive processes usually cannot match on tight features. At GreatLight we machine to ±0.005 mm (±0.0002 in) on critical dimensions, with surface finish from Ra 0.2–0.8 μm on sealing faces up to Ra 1.6–3.2 μm as-machined on general surfaces. If your drawing calls out a press-fit pin hole or a mating spigot, that is the reason to choose milling over printing.

The trade-off is geometry. Deep internal channels, hollow lattice structures and undercuts that cannot be reached from any tool direction are still cheaper to print. A good rule: if the production part will be machined, prototype it on a CNC. If it will be molded, a machined prototype still validates fit and function, but check that draft angles and wall thickness match the molding intent.

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  Choose CNC whenTight bores, threads, sealing faces, functional snap fits, metal parts.
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  Choose printing whenDeep internal channels, lattice or organic geometry, non-load-bearing form checks.
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  Choose both whenYou need a machined functional core and a printed housing for a fit check.

Three-axis milling handles the majority of prototype work: plates, brackets, housings with features on one or two faces. Setup is simple and the per-part cost stays low. GreatLight runs 27 three-axis machines, with travels of 500 × 500 × 450 mm and 500 × 310 × 200 mm for compact parts.

Four-axis work adds a rotary table (Ø400 mm at our shop), so features on four sides of a part can be cut in one setup. That removes the repositioning error you get from flipping a part by hand. If your prototype has a pattern of holes around a cylindrical body, or a shaft with milled flats and cross-drilled ports, four-axis is usually the right call.

Five-axis simultaneous machining lets the tool approach from five directions at once. For prototypes this matters in two ways. First, complex contoured surfaces can be cut without a custom fixture. Second, the tool stays at an efficient angle to the surface, which improves finish on curved faces and reduces hand polishing later. GreatLight operates 16 simultaneous 5-axis centers, and 16 mill-turn centers for parts that need turning and milling in one cycle.

Part size sets the upper limit. Our largest travel is 4,000 × 400 × 150 mm, so long extrusion-like profiles are possible. Medium frames cover 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. If a prototype exceeds those envelopes, we will tell you at the quotation stage rather than after the material is cut.

The most common mistake in prototyping is picking a material because it machines easily, then discovering the production part behaves differently. Match the alloy family to the production intent wherever the budget allows. For aluminum housings and brackets, 6061-T6 is the default; 7075 gives higher strength where weight matters; 2024 and 6082 are common alternatives. ADC12 appears when the production route is die casting.

Stainless prototypes span 303 and 304 for general work, 316 and 316L where corrosion resistance is the driver, and 17-4PH (SUS630) when you need precipitation-hardened strength. 440C and 420 come up on wear surfaces such as cams and valve components. Carbon and alloy steels including 1018, 1045, 4130, 4140 and 4340 are stocked for structural prototypes, and tool steel is available for mold inserts and forming dies.

Titanium and high-temperature alloys are machined on request: TA1, TA2, TC4 (Ti-6Al-4V), Inconel, and magnesium AZ31B or AZ91D. These cut slower and cost more per hour, so reserve them for parts where the material property is the thing under test. On the polymer side, POM and ABS cover most functional checks, PC and PMMA where you need clarity or impact resistance, and PEEK or carbon fibre when temperature or stiffness is the constraint.

A practical note on parity: ask for the production alloy and temper, not just the alloy family. 6061 and 6061-T6 machine similarly but do not test the same. If the prototype is for a stress calculation, the heat treat condition is part of the test, not a detail.

A prototype that measures wrong is worse than no prototype, because you build decisions on it. Every order at GreatLight passes three checkpoints: incoming raw material verification, in-process monitoring during cutting, and final inspection before shipment. That is 100% inspection, not sampling. Inspection reports are available on request, and for medical or automotive programs we align the report format with what your quality team already uses.

The shop holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. The first two cover general and automotive quality systems, the third covers medical device work, and the fourth covers information security. If your program requires traceability from material certificate to finished part, say so at the quote stage so the paperwork is built into the routing rather than added afterward.

Confidentiality is usually the first question from a design team. Uploads are handled as confidential, and a non-disclosure agreement is available on request before you share files. For pre-launch products, we can restrict the part to a named engineer on our side. Ask for the NDA early; it costs a day and removes a month of internal debate.

Timing works like this. Quotation and a free DFM review come back within 12 hours. Production can start within 24 hours of drawing release. Standard prototype parts ship in 3–5 days. Historical late-delivery probability at our plants is below 2%. Those numbers describe our standard flow, not a guarantee for every geometry; a part that needs custom workholding will take longer, and we will say so up front.

Most prototype delays come from the drawing, not the machine. A few items are worth checking first. Specify tolerances only where they matter. A drawing with ±0.01 mm on every dimension forces extra setups and slower cutting for no functional gain. Mark the three or four dimensions that actually control fit and let the rest run to general tolerance.

Add a datum scheme. Prototype parts are often measured on a CMM, and without defined datums the inspection report will not match your assembly stack-up. If a face or bore is the functional reference, call it out. Also state the material temper, the finish on each surface, and whether edges should be broken or left sharp. Deburring a 0.2 mm edge costs seconds; discovering a sharp edge on an assembled unit costs a teardown.

Threads deserve a specific mention. State the thread standard explicitly, and check that the thread depth in the model is reachable by a standard tap or thread mill. Blind holes modeled deeper than the tool can reach are a common cause of a second operation. If the prototype will be anodized, remember that hardcoat adds thickness and can change a thread fit; mask or specify accordingly.

Finally, tell us what the part is for. A cosmetic cover and a load-bearing bracket with the same drawing get different machining strategies, different fixturing and different inspection focus. One sentence of context at the quote stage is worth more than a page of notes after the first article.