I use the Stihl sharpening tool. I was skeptical at first but after I bought one, and watched a video on YT, I love it!!!! It's fast, easy and gets the chain very sharp. It also maintains the height relationship between the cutting teeth and the raker teeth (aka heigth gage). Watch a video on it and you'll understand better. It's about $30 and you should get some spare round files but they are only about $3 each. Highly recommend this tool. I have the electric chain sharpener you get from Northern Tool but this far easier.