Turning Centre
Turning centre is the name for the CNC turning machine built for complete production work — the machine that starts as a CNC lathe and adds the tools, axes and automation to make a round part start-to-finish without leaving the machine. Where a basic CNC lathe turns, faces, bores and threads with a single-point tool moving on two axes, a turning centre carries a turret full of tools that index automatically, and often much more: driven tools that mill and drill, a spindle that can be locked or positioned as a C axis, a sub-spindle that takes the part to machine its other end, and the bar feeder and parts catcher that let it run on its own. The idea behind the turning centre is the same idea behind every machining centre — keep the part in one chucking, do everything the part needs, and let the machine make complete parts while the operator sets up the next job. This entry sets out what a turning centre is, what its extra capabilities do, and where it earns its keep.
From lathe to turning centre
The plain CNC lathe and the turning centre share their bones — the spindle that rotates the work, the turret that holds the tools, and the two axes, X and Z, that move the tool along and across the work — and for purely round work the two-axis lathe is already a complete machine: it turns diameters, faces ends, bores holes, cuts threads and parts the finished piece off the bar. The turning centre adds what round-only turning cannot do, and the additions all point one way: toward parts that need more than round features, made without a second machine. The first addition is the turret’s capacity and speed: a production turning centre carries a dozen or more tools, internal and external, in its turret, and indexes from one to the next automatically in the middle of a cycle, so a part can be drilled, bored, turned, threaded and grooved by successive tools with no hand between them. The second is the work that goes beyond turning, and it is what most separates the turning centre from the lathe.
Live tooling and the C axis
The defining capability of the turning centre is its ability to machine features that are not round, and it comes from two additions working together. The first is live (driven) tooling: the turret carries, alongside its static turning tools, holders whose own small spindles rotate cutting tools like a mill’s, powered from the machine rather than by the work’s rotation. The second is the C axis: the turning spindle can be told to stop rotating, or to rotate slowly and precisely to a commanded angle, instead of spinning freely for the cut. Put them together and the work held in the chuck becomes a rotary table: the spindle indexes the part to an angle, and a live end mill or drill in the turret mills a flat, drills a cross hole, cuts a keyway or makes a bolt circle on it. A shaft that needs flats milled on its side, a boss drilled across its axis, a coupling with a milled hex and a drilled pin hole — each can be finished while the part still sits in the chuck it was turned in, which is the whole point: the features that would otherwise send the part to a milling machine and a second setup are done in the one, with the concentricity of the round and the flat guaranteed by the single chucking.
The sub-spindle and done-in-one
The second great capability of the production turning centre is the sub-spindle — a second, opposed spindle that reaches in and takes the part from the main chuck, gripping the finished end so the machine can work on the end that was previously held. A part that must be machined on both ends — a fitting threaded one end and counterbored the other, a roller with centres in both faces — is, on a lathe without a sub-spindle, a two-operation job: cut the first end, remove the part, rechuck it by that end, and cut the second, with every risk that the rechucking shifts the part and loses the concentricity between its ends. With a sub-spindle, the first operation runs in the main chuck, the machine transfers the part to the sub-spindle automatically, the second operation runs on the far end, and the finished part drops into the catcher — both ends machined, and machined true to each other, in one uninterrupted cycle. Add the bar feeder that feeds a long bar through the spindle for the machine to cut part after part from, and the turning centre becomes the complete production cell this wiki treats under lights-out machining: bar in one end, finished parts out the other, running unattended through the night.
Where the turning centre earns its keep
The turning centre is not the cheapest way to make a simple round part — for that, a plain turning machine is enough — but it earns its cost where the part’s roundness is not the whole story. Its natural work is the production of rotational parts with secondary features: the fittings, couplings, pulleys, bosses and shafts that need a flat here, a cross hole there, a hex somewhere and a thread at each end. Against sending those parts to a lathe and then a mill, the turning centre wins on every axis that matters: one setup instead of two removes the rechucking error and the concentricity risk; one machine and one operator instead of two cut the handling and the labour; and the bar-fed, cycle-driven machine makes complete parts at a rhythm and a consistency no hand-fed pair of operations can match. For a run of such parts the turning centre is often the difference between a job that needs tending and a job that runs — and the machine that this wiki’s entries on proving out and the machining job cycle describe is, at its most productive, the turning centre finishing parts in one chucking while the shop’s attention goes to the next job.
The centre of the turning world
The turning centre is best understood as the mature form of the turning idea that the lathe began. The manual lathe turned round parts with a hand on the wheel; the CNC lathe automated the turning; and the turning centre completed the automation by bringing the milling and the drilling and the second-end working into the same machine, until the round part — turned, milled, drilled, threaded and finished on both ends — is made complete from bar stock by one program on one machine. Beyond it lie the specialised cousins this wiki will treat in their own entries — the Swiss-type lathe for long slender bar work and the mill-turn machine for parts that are as much milled as turned — but the turning centre is the workhorse of the family. For the shop making parts that are round and more than round, the turning centre is the machine that turns the drawing into the finished part, unchucked only when it is done.