I also touch up my chains every couple tankfuls.
Whenever a kerf wanders to one side while cutting...usually means that the teeth on one side are cutting more wood, (teeth are longer on one side than the other side causing the saw to cut at an angle). That means you need to take your file to the teeth on the side the kerf, (saw bar), is turning towards and file only the teeth on that side. In other words...the teeth on both sides of the bar need to be equal in length when you are done filing.
An electric grinder is hard on chainsaw teeth. You will heat the teeth up and discolor them, changing the hardness or temper. A grinder also tends to take off too much metal and reduces the life of a chain. Just my observations.