China Wholesale 4 Axis CNC Machining Service

A 3-axis mill moves the tool in X, Y and Z while the part stays clamped. A 4-axis mill adds a rotary axis, almost always A, that turns the workpiece while the cutter is engaged. That single motion changes the setup plan: the operator can present a second, third or fourth face to the tool without unclamping the part.

The practical gain is not only fewer setups. Every re-clamp introduces a new datum, and each datum adds stack-up error. On a bracket with bores on two perpendicular faces, holding true position on a 3-axis machine may need two fixtures and two tolerance stacks. Turn the part 90° on a rotary table and the bores come off the same datum.

There is a second, quieter benefit. A part that spins on the A axis can be cut around its circumference with a single continuous path, so slots, flats and hole patterns stay evenly spaced. That is why 4-axis work shows up on shafts, couplings, valve bodies and long extrusions rather than on flat plates.

The trade-off is setup thinking, not just setup count. Once the part rotates, the programmer has to model the rotary centerline, the fixture and the stock position accurately. A 4-axis program built on a sloppy centerline will cut tapered features and scrap the run.

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  Fewer datumsFaces cut in one setup share one reference, so stack-up shrinks.
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  Continuous wrapSlots and hole patterns stay indexed around a diameter.
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  Long partsIndexing suits shafts and extrusions that will not sit on a trunnion.

Four-axis work sits between two extremes. It costs less per hour than simultaneous 5-axis and it removes setups that a 3-axis machine cannot remove. The parts that benefit most share one trait: the features to be machined lie on more than one face, but the tool can still reach them along a straight approach from the side.

Typical candidates are cylindrical or prismatic parts with cross holes, milled flats, keyways and slots around a diameter. Manifolds, motor housings, flanges, drive shafts, sensor bodies and long structural extrusions all fall in this group. If the drawing shows a hole pattern on a cylinder, 4-axis is usually the cheaper way to hit it.

Four-axis is the wrong answer in three cases. If the part needs undercut geometry or a tool that must tilt to clear a wall, you need the two rotary axes of a 5-axis center. If every feature is reachable from one direction, a 3-axis machine with a simple fixture will be faster and cheaper. And if the part is a thin, floppy plate, rotating it on a table can induce chatter that no axis count will fix.

A useful rule before you quote: count the number of distinct tool approaches. One approach means 3-axis. Two to four approaches around a common centerline means 4-axis. Any approach that needs the tool to lean means 5-axis.

Rotary capacity sets the ceiling on 4-axis work. GreatLight runs 12 four-axis mills with a Ø400 mm rotary table, alongside 27 three-axis machines, 16 mill-turn centers and 16 simultaneous 5-axis machining centers. For long parts the envelope reaches 4,000 × 400 × 150 mm, and the smaller travels cover 750 × 1,150 × 550 mm, 600 × 600 × 600 mm, 500 × 500 × 450 mm and 500 × 310 × 200 mm.

The Ø400 mm table is the number to check first. A part that swings past the table diameter either needs a larger machine or a redesign. Weight matters too: a heavy billet on a rotary table limits how fast the axis can index, so cycle time grows even when the geometry is simple.

Tolerance is the second gate. We hold ±0.005 mm (±0.0002 in) on 4-axis work, with surface finish from Ra 0.2–0.8 μm for fine requirements, Ra 0.8–1.6 μm for typical mating faces, and Ra 1.6–3.2 μm as-machined. Reaching the fine end usually means a finishing pass with a small stepover, which adds time.

Materials behave differently once the part rotates. Aluminium 6061, 7075 and 6082 cut fast and hold a good finish. Stainless 303, 304, 316L and 17-4PH work-harden, so the programmer keeps the cutter engaged. Titanium TC4 (Ti-6Al-4V), Inconel and magnesium AZ31B need lower cutting speeds and more attention to heat. Brass C36000 and copper C110 are straightforward but gummy.

Wholesale pricing comes from volume and routing, not from a single discount code. The quote should show the machine, the number of setups and the inspection step. If a supplier cannot say which machine will run your part, the price is a guess and the delivery date is a guess.

Ask for the certificates that match your industry: ISO 9001:2015 for general quality, IATF 16949:2016 for automotive, ISO 13485:2016 for medical devices and ISO 27001:2022 for information security. All four are held here. Certificates prove a system exists; they do not prove your part was measured, so also ask what is inspected and when.

Inspection practice is the real differentiator. We inspect 100% of parts before shipment, with a raw material check, in-process monitoring and a final inspection, and we supply reports on request. For a first article, that paperwork tells you more than a sample photo.

Confidentiality is part of the sourcing decision. Uploads are secure and confidential, and an NDA is available on request. If your drawings carry export-controlled geometry or an unreleased product, settle that before the RFQ, not after the first chips are cut.

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  Routing detailWhich machine, how many setups, what fixture.
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  Inspection planWhat is measured, at which stage, and reported how.
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  CertificatesMatch the standard to your industry, not to a logo wall.
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  NDA firstSign before drawings move, especially for unreleased products.

The quote stage is where 4-axis work is won or lost. Within 12 hours we return a quotation with a free DFM analysis. That analysis flags features that need a different approach: a hole that cannot be reached at the programmed angle, a wall too thin to clamp, a tolerance that calls for a grinding step instead of milling.

Production can start within 24 hours of approval, and parts ship in 3–5 days. There is no minimum order quantity, so the same process runs one prototype or a 10,000+ part run. Keeping the prototype and the production run on the same machine type removes a whole class of surprises at ramp-up.

Finishing is scheduled with the machining, not after it. Anodizing in clear, color, hardcoat and conductive versions, 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.

For parts that rotate on the A axis, masking and fixturing for finishing deserve a note on the drawing. A hardcoat anodize on a bearing bore changes the fit, and a bead blast on a sealing face can ruin the surface finish you paid for on the mill.