Turning produces rotationally symmetric surfaces by rotating a workpiece while a single-point tool moves relative to it. In straight turning the tool feeds parallel to the rotation axis and reduces diameter; in facing it moves radially and creates a flat end surface. Grooving and thread cutting use the same kinematic idea with different tool paths.

For diameter $D$ and spindle speed $N$, the surface speed is

$$V=\pi DN.$$

If a shaft is reduced from 50 mm to 46 mm diameter in one pass, the radial depth of cut is

$$d=\frac{50-46}{2}=2\ \mathrm{mm}.$$

The factor of two appears because a radial tool motion changes both sides of the diameter.

During facing, the local diameter decreases as the tool approaches the centre, so the local surface speed also decreases at constant spindle speed. Some machines vary spindle speed to keep surface speed closer to a chosen value.

Dimensional accuracy depends on commanded geometry, workholding, tool and workpiece deflection, thermal expansion and tool wear. Long slender workpieces are especially sensitive to lateral force because deflection can create taper or vibration.

Turning is therefore a specific geometric arrangement of the general metal-cutting process: workpiece rotation supplies the main cutting motion and tool feed generates the desired surface.