It may be that you haven't the slightest need in your life for a chain saw or anything remotely resembling it. If so, you can skip reading this post; I will not be in the least offended. If, on the other hand, you have an interest in the subject, read on.
Last year sometime I promised the Bodger's forum that I would post something on chain saw sharpening. I never did, because, as Robin Wood says, life got in the way. So I propose to remedy that omission now.
A chainsaw is a very dangerous tool. It is said that it is not, and in fact only its users are dangerous. I disagree. It is a very dangerous tool, and a dull chainsaw is most dangerous of all, because you try to force it and it will then jam, kick back on you , and generally ruin your day, and send you to the emergency room of the hospital to boot. So if you own a chainsaw, and your chain gets dull (which it will in half an hour of cutting) you must learn how to sharpen it. If not, then you will spend more money buying new chains than you will spend having someone else cut wood for you.
All that out of the way, how do you go about sharpening a chainsaw? There are basically two approaches, (1) on-the-saw and (2) off-the saw. For both of these situations there are tools.
This is my complete armamentarium of chain saw sharpeners. Left to right, a gadget for Dremel moto-tool type sharpening jig. Next is a cheap but adequate filing jig. The thing with a red base is a really good filing jig, more coming up. At right, the orange machine -- the easiest way to do it, but the chain has to come off the saw. Behind it, the chainsaw toolbox, made entirely out of the log, which holds essential chainsaw supplies. Sticking out of this are various sizes of chainsaw files.
They look like ordinary round files. They aren't. Buy only labeled "chain saw" files. The chain you buy will have instructions on the size of file required. Follow these instructions religiously. In this country, benighted in the matter of units, they will be absurd fractional inch sizes; more enlightened places will give you millimeters.
I do not recommend the Dremel sharpening kit. Maybe OK for occasional users. Not for anything serious. Too easy to blow the angles involved. I do not recomment the cheap-but adequate jig either. It jumps out of the set angle at the slightest provocation.
OK, on to the red-based jig. This jewel is available on the 'net from Cutter's Choice (ex-Penn-Zip).
Now we have to point out that a chain saw tooth is an extremely sophisticated 3-D animal. The angles of the cut have to be just so. With an axe, you can eyeball the angles. With a chainsaw, you can of course try, but you will get poor results unless you have protractor eye/hand coordination. Much better to use the jig. So you look at the instructions that came with the chain, and set the correct angles into the jig. There are two of them, horizontal (most important) and vertical. Usually the vertical angle is zero and the horizontal 30 deg. Read the directions on the chain sheet! So now you clamp your jig on to the chain saw.
With the proper size file in the jig, pull the chain up to the file and you file away. You will note that every other tooth on the chain points in a different direction. So you file all the starboard teeth in one go. Then reverse the angle on the jig and do all the port teeth. You don't have to file very much if you keep up with it.
I usually keep at least two chains per saw on hand. After two-three sharpenings on-saw, I go to the machine, and put a machine-sharpened chain on the saw. Machine sharpening is a dream (but you have to get the chain off the saw and put it back on again, whereas the jig above will work in the deep woods, where there are no plugs for the machine).
This is a closeup of the orange machine at work. The chain sits in a guideway and is held steady by a pawl. The vertical angle is, unfortunately, not controllable on the orange machine, but the horizontal is. The grinding wheel is in the act of descending upon the tooth (you move it with your hand) and, assuming you adjusted it properly, will do a chain in about 5 minutes. Again, you do port and starboard teeth in one go.
The orange machine I bought from HarborFreight. It's quite cheap, around $40 these days. There are much better machines at Cutter's Choice, like the Jolly; but they cost four times as much. Orange Machine will do all my regular chains; good enough.