China CNC Precise Processing: What Decides Accuracy

Precise CNC processing covers a wide range, and most parts do not need the most expensive route. A bracket with holes on two faces can run on a 3-axis mill with two setups and stay inside ±0.05 mm all day. That is cheaper, faster and easier to inspect.

Five-axis becomes the cheaper option when setups start to stack. A hydraulic manifold with ports on five faces, or a housing with a deep cavity and an undercut, would need four or five fixtures on a 3-axis machine. Every re-clamp adds stack-up error and adds labor. One 5-axis setup removes most of that.

Geometry is not the only trigger. Thin-wall parts, long slender shafts and features that must stay concentric to a datum are often better off on a mill-turn center, where turning and milling happen without releasing the part. If your drawing has a true position callout of 0.01 mm across three faces, plan the process around that callout first.

What does not need it: flat plates, simple bushings, drilled flanges, parts held to ±0.1 mm. Sending those to a 5-axis center wastes machine time and money. We route them to the 27 three-axis machines or the 12 four-axis mills instead.

Our working tolerance is ±0.005 mm on critical features, which is ±0.0002 in. That number is not a blanket promise for every dimension on every drawing. It applies where the feature can be reached, measured and held stable through finishing. A 300 mm long aluminum beam and a 20 mm stainless pin do not behave the same way.

Maximum part size reaches 4,000 mm on the large travel machines, with a 4,000 × 400 × 150 mm envelope. Medium work runs on 750 × 1,150 × 550 mm and 600 × 600 × 600 mm machines. Compact parts go to 500 × 500 × 450 mm or 500 × 310 × 200 mm centers. Rotary work up to Ø400 mm sits on the 5-axis tables.

Surface finish depends on the cutter path and the final operation. As-machined surfaces land at Ra 1.6–3.2 μm. A finishing pass with the right insert and step-over brings that to Ra 0.8–1.6 μm. Where a sealing face or a bearing bore needs it, we can reach Ra 0.2–0.8 μm.

Thermal drift is the quiet problem. Aluminum grows about 23 μm per meter per degree Celsius. A shop that is not temperature-aware will chase a dimension all afternoon. We keep the spindles and fixtures stable, and we measure at the same temperature the part will be inspected at.

Aluminum is the easy case. Grades 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082 and 7075 all cut cleanly at high spindle speeds. 7075 holds a better finish on thin walls, but it stress-relieves less predictably after heavy stock removal, so we rough, let it rest, then finish. ADC12 covers die-cast blanks that need secondary machining.

Stainless is where feeds and speeds matter. Grades 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH (SUS630) all work-hard if the cutter rubs instead of cuts. 316L and 17-4PH in particular need a rigid setup and a constant feed. 17-4PH in the H900 condition will hold ±0.005 mm, but only with sharp tooling and coolant directed at the cut.

Steel grades 1018, 1045, 4130, 4140, 4340, A36 and tool steel are routine. Copper and brass, including C101, C103, C110, beryllium copper, C27400, C28000 and C36000, machine fast but move with heat, so we take light finishing passes.

Titanium and exotics need the most care. TA1, TA2 and TC4 (Ti-6Al-4V) cut at low surface speed with high coolant pressure. Inconel and magnesium AZ31B / AZ91D are handled on dedicated setups. Magnesium chips are a fire risk, so chip control is part of the plan, not an afterthought.

Plastics cover ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre. PEEK and carbon fibre are abrasive and wear tooling quickly. PMMA chips and cracks if the feed is too light. Each has its own cutter and its own clamping pressure.

Inspection starts before the first cut. Incoming bar stock and plate get a material check against the cert. If the grade does not match the drawing, the job stops there. That single step catches more problems than any final measurement.

In-process monitoring runs through the cycle. Operators check critical dimensions at defined intervals, and the CMM confirms the first article against the drawing before the run continues. For a 10,000 part order, that first article decides whether the rest of the run is worth making.

Final inspection is 100% before shipment. We check dimensions, threads, surface finish and any cosmetic requirement, and we can issue reports on request. The qualification rate across shipped work is 99.99%. That figure comes from our own records, not from a marketing claim.

The four certifications behind this are ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. The last one matters to buyers who send sensitive CAD data. Uploads are treated as confidential, and we sign an NDA on request.

Send a STEP file and a 2D drawing with the tolerance block. Within 12 hours you get a quotation plus a free DFM analysis. That analysis usually flags thin walls, tool reach problems, and tolerances that are tighter than the function needs. Fixing those before the cut saves money on both sides.

Production can start within 24 hours of an approved order. Parts typically ship in 3–5 days for standard work. Our historical late-delivery probability is below 2%. For anything with a hard deadline, tell the engineer at the quote stage, not after the PO.

There is no minimum order quantity. One prototype and a 10,000+ part run go through the same quoting process. Prototypes usually run on the 5-axis centers because the first article teaches us where the process is weak.

We run three wholly-owned plants covering 7,600 m² in Dongguan, plus a factory in Singapore at No.3 Joo Koon Circle, Singapore 629032. About 150 technicians work across 127 high-precision CNC machines. That includes 16 simultaneous 5-axis machining centers, 16 mill-turn centers, 12 four-axis mills and 27 three-axis machines.