we sharpen ours with a 6" grinder, i would be guessing somewhere around a 60* angle.
they are very crude so the angle isnt very important, however i noticed that with a sharper angle like 45* it will cut tall grass really well, but dulls much quicker after running through some branches or dirt. the higher angle will still cut great, and holds up to more abuse.
there is nothing too special to getting the blades out, i like to remove the pin from the hub and drop the hub/2 blades all together. i find that easier than unbolting each blade. either way works just fine though.
