What process can be performed using a lathe or a mill to ensure a concentric hole?

The process of boring is specifically designed to create a precise and concentric hole in a workpiece. Boring is often performed after the initial drilling operation, where a hole has been created but may not meet the required diameter or concentricity. A boring bar is used to enlarge the hole, and this tool is held in the machine in such a way that it can be adjusted to ensure that the hole is perfectly aligned with the workpiece's rotation, ensuring concentricity.

In contrast, while drilling creates the initial hole, it may not be as accurate in terms of diameter or alignment. The turning process focuses on shaping the exterior of a cylindrical workpiece and is generally not used for creating holes directly. Milling, while capable of producing holes as well, typically involves flat surfaces or features. Therefore, boring stands out as the correct answer for ensuring a concentric hole using either a lathe or a mill.