Up until last week I would have argued tooth and nail about the 2&1 hand file sharpeners being the best, and yes they have a spot with me in my chainsaw bucket when out in the woods for touch ups.
I just recently purchased and have been using a power care hand grinder with round stones for sharpening (dremal), boy oh boy, game changer, I can sharpen a 20" chain in under 2min better then factory sharp, only worry about lowering the rakers after 5 sharpens. Bought at homedepot for $35, and extra grinding stones 3 pack for $5 each.
To put things into perspective I literally just cut about 10 or 11 cords of log rounds ranging from 8" to 32" thick on the same chain and can probabaly do another 10 cords before the chain is worn out (more likely the actual drives vs the cutting tooth) The grinder comes with an adjustable guard for degree pitch, I thought it was cheesy and took it off, I just follow the existing line on the tooth for the 30deg angle you need.
The best part is if you hit metal or the ground and you mis shape the cutter, you can reshape it in no time, the only con I see and with experience, it will come naturally is to sharpen each tooth evenly, if you dont, you will get a curve cut when you want to go straight.
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