Soft metals — aluminum and brass especially — pack into the teeth. Those pins then drag across the work and score it, which people usually blame on the file being worn out.
A file card is a short wire brush made for the job, drawn along the teeth in the direction of their cut. A brass pick lifts the stubborn pins.
The questions welders ask
Can I stop it clogging?
Rubbing chalk into the teeth before filing soft metal fills the gullets and stops metal keying into them, and it is the traditional answer. Using a coarser, single-cut file on soft metal helps too, because there is more room between teeth for the chip to escape.
Last reviewed 2026-08-14