In 1975 I was a factory mechanic for Homelite, a popular chain saw manufacturer at the time. Depending on the type of chain used, a correct file size for the chain you are using AND a raker gauge tool. You also need to file them as the chain gets sharpened, since the rakers must be cut back as the chain cutters shrink in size. For some people, it would be better to have them professionally sharpened, if you don't know what you are doing, you can ruin a good chain. You should always have at least 2, and prefeably 3 so that in the event you have one in the shop being sharpened you can still use the saw. Here is a little trick that you can use to get the "pitch" off the chains; put some Tide or other laundry soap with very hot water in a coffee can and let the chains soak for several hours. We found nothing better at getting the pitch off, this advice from a Canadian, Master Mechanic Jerry Fredrick, god rest his soul. Ed