What is mill-turn machining?

Mill-turn is machining a part complete on a mill-turn machine: a machine that turns and also mills and drills with driven tools. The main spindle works as a C-axis, so the workpiece can be held at a fixed angle or rotated under control. A Y-axis reaches features off the centre line, and a sub-spindle takes the part over for the back end. A flange with a turned outside, a hole pattern on a pitch circle and a spanner flat can then come off the machine without a manual reclamp.

How is a mill-turn machine built?

Designs vary: a lathe with live tooling in the turret and a C-axis, a machine with Y-axis and sub-spindle, or a multitasking machine with a tilting milling spindle beside a turret. What can be done in one pass depends on the axes, the reach, power and stiffness of the live tooling, and the clamping length in main and sub-spindle. A transfer to the sub-spindle is a second setup, only automated: the coaxiality between front and back features then depends on the alignment of both spindles and the clamping in the sub-spindle.

How does mill-turn work in practice?

Mill-turn saves manual setups, waiting time between machines and the position error a reclamp can introduce between turned and milled features. The price is a higher hourly rate and more programming time, because turning and milling have to fit together in one program. In machine minutes it is not necessarily quicker; heavy milling can go faster on a machining centre. In lead time it often wins. Whether it comes out cheaper than turning plus milling on two machines is decided by quantity, hourly rates, programming time and how much milling the part carries.

What is mill-turn often confused with?

Mill-turn is not plain turning: a lathe without driven tools only does round work. Where a lathe with live tooling ends and a mill-turn machine begins is not a fixed line; a Y-axis, a sub-spindle and a milling spindle are the usual distinguishing features. Mind the related term turn-milling as well: it names a method in which a milling cutter machines a rotating workpiece, a process rather than a machine type.

How do you see mill-turn in Blake?

In Blake mill-turn is estimated as a process of its own, with separate lines for material, machining, setup and programming, at the hourly rate you set for the mill-turn machine. The result, quantity breaks included, is labelled as an estimate. More on mill-turn.