CNC turning and milling – what's the difference?

Turning and milling, at first glance, appear to be very similar processes and achieve similar results. So, what is the difference – and why do we offer both processes? While many of our customers will already know the answer, others may find this a useful insight into what goes on behind the scenes in the world of metal fabrication!

CNC machining

Often turning and milling are generically referred to as “CNC machining” – our customers often ask for CNC machining rather than for turning or milling by name. Of course, it's our job to make sure that the most appropriate process is used each time.

Put simply, the difference between the two processes comes down to which part moves – in general terms, the metal or the machine.

Turning

Items processed by a lathe will be cylindrical and must be on-centre. Turned parts can range from simple rings to complex curved components. CNC turning is the most efficient way to mass-produce these kinds of parts.

Various cutting tools can be installed within the lathe tooling head (pictured below) to perform different cutting operations sequentially, to produce parts in a one-pass process. Straight cuts, tapers and contours can all be created by varying the angle and depth of the cut.

Milling

Milled parts are not necessarily cylindrical. Milling machines use multi-point cutting tools; and there can be more than one tool working on the piece at a time. Milling may be the preferred choice if the part needs anything which is off-centre or angled (such as holes or cuts), or for secondary features such as indentations or grooves.

Milling can be used to shave material from the surface of the workpiece using a tooling head with multiple cutters (plain milling or face milling); or to shape its edges using a cutting tool with a thread (profile milling or side milling).