file, rasp
鑢 centers on a metal tool used for smoothing or shaping by abrasion: a file or rasp. The meanings are tightly linked to this single concrete object.
鑢 combines 金 (metal) with 慮, which likely contributes the sound and may relate to the idea of careful, repeated action, fitting a metal file used for smoothing.
Metal 金 on the left, and the right side 慮 suggests careful thought. Imagine a metal file that requires careful, repeated strokes to smooth a surface.
For ロ, picture a row of metal files lined up on a workbench: row -> ロ, and each file is ready for smoothing.