For 35 years or so, I've found Granberg's file guide to be the simplest way to keep precise razor edges on LP-3/8" and std 38" chain. Minimal metal removal. Very simple to set and hold angles, and set depth-gauges. Clamps on bar and separately clamps chain to avoid wobbling while filing. Never had a chain that wouldn't cut straight, with nice BIG chips. I've tried the electrically-powered grinders with the ~3/16" diam stones. No thanks.