boring tool
鏜 centers on a metal tool used for boring or enlarging holes. The meaning is specific to a boring tool.
鏜 combines the metal radical 金 with the phonetic component 堂, suggesting a metal tool whose name is related to the sound トウ. The exact historical development is uncertain.
The left side 金 means metal, and the right side 堂 looks like a hall or workshop. Imagine a metal boring tool used in a workshop to drill precise holes.
For トウ, picture a toe being bored by the tool: toe -> トウ, and the metal tool makes a hole.