A shiny, rounded cutter means your file is done.

If the cutter you just filed looks shiny and rounded instead of having a sharp, matte edge, the problem is your file, not your technique.

A sharp chainsaw file bites into the steel. It throws off little curled shavings and leaves a clean, crisp edge with a faint burr on the opposite side. That’s what you want to see.

A worn file just skates over the surface. Instead of cutting, it polishes the metal. So when you look at the cutter after a pass, the cutting edge will look smooth, glazed, almost burnished—like somebody rubbed it with a fine stone. The filings turn into fine gray dust instead of curls, and you’ll feel like you have to lean on the file to make anything happen. That’s the sign.

You can also check the file itself. The tiny cutting rows on a fresh round file look rough and grippy. Once they’re worn, the file’s surface looks flattened and shiny, and it won’t “grab” your fingernail the way it did when it was new. If it slides over the chain like a butter knife, it’s toast.

Don’t try to squeeze another sharpening out of a dead file. It’ll take you twice as long, overheat the chain, and leave you with a cutter that looks bad and cuts worse. A replacement file is a few bucks—a new chain is not.

Throw it out the moment the shine shows up.