The spindle is the central part of a lathe that grips the material (workpiece) and rotates it.
The spindle spins the material at high speed, a cutting tool is brought against it, and material is removed to create a round shape.
It is the heart of turning.
A Closer Look
The spindle's rotational accuracy (freedom from runout) and rigidity have a major effect on machining precision.
Even a slight wobble in the spindle affects the roundness and dimensions of the machined part, which is why machine tool manufacturers pay such close attention to spindle precision and rigidity.
On a CNC automatic lathe, in addition to the main spindle at the front, there is usually a back spindle positioned opposite it, so that the reverse side of a part machined on the main spindle can be machined in the same cycle to produce a finished part.