China 4 Axis CNC Machining Service

A 4 axis CNC machine adds one rotary motion to the usual X, Y and Z travels. On most of our mills that rotation comes from a Ø400 mm rotary table mounted on the machine bed, turning the workpiece around an axis parallel to X. The cutter still approaches from one general direction, but the part can now be indexed to several faces without being unclamped and set up again.

That single change is what makes the process worth quoting. A bracket with bores on two perpendicular faces, a shaft with flats and cross holes, a housing with ports at 90° to each other: on a 3 axis mill these need two or three separate setups, each one a fresh chance to lose position. Turn the part on a rotary table instead, and the relationship between those features is set by the machine, not by how carefully someone tapped it against a stop.

The gain is not unlimited. A fourth axis rotates; it does not tilt. Undercuts, deep pockets behind a shoulder, and blended surfaces that wrap around three directions at once still need a 5 axis center or a different process. For a lot of parts that land in the middle, though, a 4 axis setup gives most of the accuracy benefit at a lower hourly rate than simultaneous 5 axis work.

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  Good fitFeatures on 3–4 faces of a prismatic part, or radial features around a shaft.
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  Good fitPositional work where each face is machined flat, then indexed.
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  Poor fitContinuous contoured surfaces that need the tool normal to the surface.
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  Poor fitParts small enough to reach everything in one 3 axis setup.

Most 4 axis work is positional. The table rotates to an angle, locks, the cutter machines that face, then the table indexes to the next angle. Accuracy depends on the rotary table's positioning repeatability and on how well the setup was dialed in, not on how fast the controller can interpolate. This is the cheap, reliable version of 4 axis machining, and it covers the majority of parts we quote.

Simultaneous 4 axis motion, where the rotary axis turns while the tool is cutting, is used for cams, worms, and helical features. It demands more of the CAM programmer and the machine, and it is slower per feature. If a drawing shows a constant-lead helix or a radial profile that must be tangent all the way around, that is simultaneous work. A flat on a shaft is not.

Ask which one your part needs before comparing prices. A shop that quotes simultaneous 4 axis rates for a job that only needs indexing is charging you for capability you will not use.

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  IndexedTable locks at each angle. Fastest cycle, simplest programming, tightest repeatability.
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  SimultaneousRotary axis moves during the cut. Needed for helices and true cams.

Every time a part comes off the table, the next setup starts from a datum that was established by hand. Even with good fixturing, each re-clamp adds stack-up: vise jaw deflection, chip between the part and the stop, a slight burr on the face you are now resting on. Four setups do not simply add four small errors; they can add in the same direction.

On a rotary table the datum is the table center and the face you first indicated. That reference stays live through every index. We typically hold ±0.005 mm on features that are machined in the same setup, and we tell customers when a tolerance has to survive a re-clamp, because that is where the risk sits.

Setup reduction also shows up in the schedule. A job that needs four fixtures and four touch-offs takes longer to prepare than to cut. Fewer setups means the first part comes off the machine sooner, and the tenth part matches the first one more closely.

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  DatumRotary table center plus one indicated face, held through every index.
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  WatchTolerances between features cut in different setups, not the same one.

A 4 axis mill is common equipment in Guangdong, which is why the process is priced closer to 3 axis work than to simultaneous 5 axis. Our shop runs 12 four-axis mills alongside 27 three-axis machines, 16 simultaneous 5-axis centers and 16 mill-turn centers, so a job that outgrows indexing can be moved to a five-axis machine without changing supplier. Maximum processing size reaches 4,000 mm, and the large travel is 4,000 × 400 × 150 mm, which covers long extrusions and frame rails.

The real question is not whether a shop owns a rotary table. It is whether the shop can tell you when not to use it. A supplier that quotes 4 axis for every RFQ is selling machine time, not a process. We would rather move a part to 3 axis and save you the setup, or flag that it needs 5 axis, and we do that in the DFM notes that come back with the quote.

Distance adds two practical concerns. First, drawing interpretation: send a 3D model and a 2D drawing with datums marked, and note which dimensions are critical. Second, traceability: ask for the inspection report with the shipment. We inspect 100% of parts before shipment and supply reports on request, covering incoming material, in-process checks and final inspection.

Prototype quantities are not a problem. There is no minimum order quantity, so a single piece and a 10,000-part run go through the same first-article process. Quotation and DFM analysis come back within 12 hours, and production can start within 24 hours of approval.

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  Send3D model, 2D drawing with datums, critical dimensions marked, material and finish.
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  Ask forInspection report, material cert, and the setup plan for features on multiple faces.

Our general machining tolerance is ±0.005 mm (±0.0002 in) on features we can measure reliably in the same setup. That number is not a blanket promise for every dimension on a drawing. A bore on the rotary axis and a hole drilled 300 mm away on a long part behave differently, and the DFM notes will say so.

Surface finish depends on the operation. Fine finishes land at Ra 0.2–0.8 μm, standard high-quality machined surfaces at Ra 0.8–1.6 μm, and as-machined surfaces at Ra 1.6–3.2 μm. If a drawing calls for a sealing face, say so: that face gets a different insert and a different feed than a clearance face.

For parts that need it, finishing is handled in-house or through qualified vendors: anodizing in clear, colour, hardcoat and conductive; electroless nickel, zinc, silver and gold plating; powder coating and black oxide; bead blasting, tumbling, brushing and polishing; laser marking and engraving down to a 1.5 mm minimum character height. Marking position and depth should be on the drawing, because engraving after anodizing breaks the coating.

We hold ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. The first two matter for automotive and general industrial work; the third for medical device components; the fourth for how we handle your files.

Work through the drawing feature by feature. If most features sit on one face, a 3 axis mill is cheaper and just as accurate. Once features spread to three or four faces, or radiate around an axis, the fourth axis starts paying for itself. The tipping point is usually the second or third setup, not the part's overall complexity.

Look out for the cases where a fourth axis looks tempting but is wrong. A part with a contoured pocket that wraps around a corner needs the tool to tilt, and no amount of indexing solves that. A part with a tolerance between two features on opposite faces may be better machined on a mill-turn center, where turning and milling happen in one clamping.

When the part does fit, a 4 axis job in China is a practical route: the machine class is widely available, the tolerance band is tight enough for most brackets, shafts and housings, and the setup count stays low. Send the model and we will tell you which machine we would put it on, and why.

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  Choose 4 axisThree or more faces, radial features, two or more setups avoided.
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  Stay with 3 axisOne face, simple prismatic geometry, short cycle.
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  Move to 5 axisContoured surfaces, undercuts, tool must tilt to reach.