Andrew, this really doesn't answer your question, but it's what I believe. Others might dissagree addamently, but here goes, (this is based on 35 years in the industry and being 4th generation in the bus). The best angle is 30, but as the teeth start to get cut way back I start to cut them straighter across to save the chain. They will still cut to where you don't have to lean on them. Sometimes I put those almost used up chains on an old saw just for flushing stumps. If you follow the mark on the top of the chisel with straight even file strokes the saw will cut well. Don't vary your stroke upwards and downwards as you file. If you look at the sharp edge of a sharp chain it will look shiny. Look at a new chain and you'll see what I mean. If it looks dull it still has pits and chips in it and needs more filing. Every couple strokes tap your file across the bar to knock filings out of it. The cleaner the file is the better it will cut.
The most important thing is to keep it sharp in the first place. If your cutting close to the ground don't rock your saw back and forth, if you do, you'll stick the tip in the ground. If it's sharp you don't need to rock on it, if you need to rock on it, it's not sharp. If you're on your knees and can't see the tip on the other side, only cut 3/4 of the way through. Get a pevy or kant hook and roll it over. If I can't roll it and don't have help, I'll cut 3/4 of the way through for 3 or 4 blocks with my good saw and then grab one of the old stump saws and let it be the one to cut through and hit the dirt. Good luck, Joe.
I have seen some hand filed chains that bad though. I got one on a saw I traded for that I swear had 70 degrees on some, and 0 on others. Worst looking chain I have ever seen.
