lathe
鏇 centers on a lathe: a machine for shaping wood or metal by rotating it against a cutting tool. The meaning is specific to that tool and its use.
鏇 combines 金 (metal) with 旋 (revolve, turn), suggesting a metal tool that revolves—a lathe. The phono-semantic structure is clear, with 旋 likely contributing both sound and meaning.
The metal radical 金 on the left and 旋 (revolve) on the right together picture a metal lathe spinning a workpiece.
For セン, imagine a lathe spinning a thousand (千, せん) times per minute: 千 -> セン, and the metal lathe revolves.