“Turning” defines the work that is traditionally done on a lathe. As lathes have grown in sophistication, some of these machines have been given different names. “Turning centers” is a term sometimes applied to machines with particularly sophisticated capabilities related to secondary spindles and/or rotating tools for milling and drilling. Another term, “turn/mill machines,” describes machines that can be thought of as being just as capable at milling and drilling parts as they are at turning.
In turning, unlike in milling or drilling, the workpiece spins while the cutting tool does not. The cutting tool feeds along the length or diameter of the rotating part. The workpiece in turning can be held in a chuck or collet, to name two of the more common workholding methods. The turning machine may also include spindles for the cutting tools to accomplish non-turning operations such as milling and drilling. If this is the case, the machine stops the workpiece from spinning in order to perform these operations within the same machining cycle as the turning work. In fact, for some parts, the milling and drilling capabilities may be used so extensively that a non-turned, non-round part might also be produced on this type of machine.
Lathes, turning centers and turn-mill machines can have horizontal or vertical spindles. Horizontal spindles are more common. If the machine has a vertical spindle, then the spindle may locate below or above the machine. If the workpiece rests on a table driven by the spindle, then this machine is generally called a vertical turret lathe, or VTL. If the workpiece is held from above by the vertical spindle, then this type of turning machine is generally called an inverted vertical lathe.