1 China 4 Axis CNC Machining Factory Guide

A 4-axis mill adds one rotary axis to the usual X, Y and Z travels. In most shops that rotary sits on the table as an A-axis, turning about X. The part is clamped to a chuck, a faceplate or a tombstone, and the cutter reaches features that would need a second or third setup on a 3-axis machine.

That single rotary move is the whole point. Holes on a bolt circle, flats at 90° to each other, slots running around a shaft, cross-drilled ports: all of these can be cut in one program with one datum. Fewer setups means fewer re-clamping errors and a tighter stack-up between features.

Typical capacity in a Dongguan plant runs from a Ø400 mm rotary table up to 4,000 mm of processing length. Small medical and electronics parts sit on the compact end of that range. Long shafts, extrusions and frame rails need the larger travels, and the rotary table has to be sized to the part and fixture together, not just the part.

Indexing is not the same as simultaneous motion. Many 4-axis jobs index to an angle, lock, then cut. The rotary axis is a positioner, not a contouring axis. If your drawing needs a continuous helical path or a blended surface wrapped around a complex form, that is 5-axis territory.

The clearest fit is a part that is roughly cylindrical or prismatic with features distributed around a common axis. Think a manifold block with ports on four faces, a drive shaft with keyways and cross-holes, a valve body with radial bores, or a sensor housing with connectors pointing in different directions.

Second good fit: parts where feature-to-feature position matters more than the finish on any one face. Because everything is cut from one datum, the angular spacing between holes stays consistent. That is hard to hold when you flip a part three times on a 3-axis machine.

Parts with a deep cavity on one face and nothing on the other faces usually do not need the fourth axis. A 3-axis machine with a good vise and the right tooling will run them faster and cheaper. Adding a rotary table adds setup time, fixture cost and a compliance check that a flat part never needs.

Very small parts can be awkward too. Below roughly 20 mm, the rotary chuck and fixture often swallow the part. A 3-axis machine with a multi-part fixture usually wins on cost per piece at that size.

A capable 4-axis shop holds ±0.005 mm on milled features when the material, tooling and fixture allow it. That is the floor, not the everyday number. On a long part on a rotary table, thermal growth and chuck runout matter more than the machine's positioning spec.

Ask where the tolerance applies. A ±0.005 mm callout on a bore in an aluminum block is routine. The same callout on an angular position two hundred millimeters from the rotary center is a different problem, because any runout at the chuck is multiplied by the radius.

Surface finish follows the same logic. Ra 0.8–1.6 μm is a normal machined finish on aluminum and mild steel. Ra 0.2–0.8 μm needs a finish pass with a sharp tool and a stable setup. Ra 1.6–3.2 μm is the as-machined range and is often all a functional part needs.

We inspect 100% of parts before shipment, with raw material checks, in-process monitoring and a final inspection. Reports are available on request. If your drawing carries a true position callout, say so up front so the inspection plan is built around it.

Aluminum is the easy case. 6061 and 6061-T6 cut clean and hold tight tolerances on a 4-axis setup. 7075 gives higher strength but is more prone to chatter on long reaches. 2024, 5052, 5083, 6063, 6082 and ADC12 are all stocked and machined here.

Stainless is where the setup starts to matter. 303 and 304 are common; 316 and 316L are used for medical and marine work. 17-4PH (SUS630) can be machined in the solution-treated condition and aged afterward, which avoids distortion on a thin-walled rotary part. 420, 430, 431 and 440C cover the harder wear parts.

Steel grades 1018, 1045, 4130, 4140, 4340, A36 and tool steel are all standard. Titanium TA1, TA2, TC4 (Ti-6Al-4V), Inconel and magnesium AZ31B / AZ91D are available but need slower feeds and more rigid fixturing. On long titanium shafts, we often reduce the unsupported length rather than push the speed.

Plastics are cut here too: ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre. PEEK and carbon fibre are abrasive and need carbide or diamond tooling. On a rotary table, plastic parts clamp lightly because they deform. Tell us the material grade on the drawing and we will set the clamping pressure accordingly.

Machine count is a weak signal on its own. A shop with twelve 4-axis mills is useful only if those mills are free when your job lands. Ask what the rotary tables are rated for and whether the shop has a fixture already close to your part family.

Certifications matter when your industry requires them. ISO 9001:2015 is the baseline. IATF 16949:2016 covers automotive and EV work. ISO 13485:2016 covers medical devices. ISO 27001:2022 covers information security, which matters if your drawings are sensitive.

Communication is a real selection criterion. You want a named engineer who answers in your time zone, reports a slipping schedule early, and can read a GD&T frame without a phone call. Ask for the DFM analysis before you commit. We return a quotation and free DFM analysis within 12 hours, and production can start within 24 hours after that.

Confidentiality should be settled early. Uploads are secure and confidential, and an NDA is available on request. There is no minimum order quantity, so a single prototype and a 10,000-part run go through the same first-article process.