cold chisel
鏨 centers on a metal tool used for cutting or carving: a cold chisel. The meaning is specific to this tool and does not extend to abstract ideas.
鏨 combines 金 (metal) with 斬 (cut), suggesting a metal tool for cutting. The exact historical development is uncertain, but the component relationship is clear.
The top 斬 means cut, and the bottom 金 means metal. Picture a metal cutting tool: a cold chisel.
For サン, imagine the sun glinting off a cold chisel as you work: sun -> サン, and the metal tool catches the light.