Clamping your chainsaw bar in a vice allows all of your personal
energy to be focused on getting the proper angle and depth. Level your file. And then as you file, be sure to equally level your chain filing zone to the last one. By making everything equal, you remove the strain/friction on any given link, which causes it to quickly dull again.
Always be sure your bar oil is topped up when fueling, to reduce chain friction. A person can hit a rock or a nail and refile the chain to serviceable levels. You should get a lot more life out of the chain. I hope you haven't been tossing out all those chains. You can probably rehab them.
When doing crappy chainsaw jobs that require ground level cutting (near stones), or places where metal might be (nails, wires on
fence posts, or in demo jobs), put an old rehabbed chain on your saw, so that you don't mess up a newer chain for more delicate work like rough carpentry.
"Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it's the only thing that ever has."-Margaret Mead "The only thing worse than being blind, is having sight but no vision."-Helen Keller