The flat file is for rakers, not cutters

Use a flat file on a chainsaw chain when you’re lowering the depth gauges — sharpening the cutters is a round-file job.

Round files are sized to the chain’s pitch and match the curve of the cutting tooth. A flat file can’t follow that arc, so you’d just grind a flat spot into the cutter and make the saw dull, grabby, and harder to control.

The depth gauges (the little ramps in front of each cutter) are a different story. They have flat tops and need to stay level with each other at a specific height. That’s a flat-file job, ideally with a depth gauge guide so you don’t take off too much.

So: round file for the teeth, flat file for the rakers. Wrong file, wrong job.