I tried one of the inexpensive Harbor Freight sharpeners and ended up with the same result. The plastic in that machine left a lot to be desired accuracy wise, but it did demonstrate the potential of the machine it was copied from. That is the
Oregon 542654. It does a very nice job without a lot of fuss. Use it as shown in the video and take very light cuts, just enough to get back to a sharp edge, and avoid heating up the tooth enough to burn the temper out of it, and the chain will last a long time. And if you've got several chains, you can wait until you have them all to sharpen and do them all at once, saving a bit of setup. I bolted the sharpener to a piece of wood, then use a pair of clamps to hold that to the bench. Not cheap, but a lot cheaper than paying someone else to sharpen the chains, and a whole lot cheaper than buying a new chain every time!