I think stihl sell a attachment for their grinder that is for hedge blades but it may not be feasible just to sharpen one hedge trimmer unless you have HAD as well as CAD. You can do it a number of ways....one is to do them while the blades are still attached to power head, the other (the way I do it) is to remove and separate top from bottom blades and sharpen them individually. A die grinder with a flat round scotch brite 3M style pad is one way but that's no the best if you need to remove a lot of metal and probably better as a maintenance sharpen. If you have cut some wire and really need to take them back a stone, grinder wheel or file is the way to go. You can use a raker file, its good for removing metal stock but leaves a streaky rough finish. I have tried most ways and use a die grinder and small round grinding stone wheel (same shape as a car tyre but way smaller) and disassemble blades first by removing them and unscrewing bolts. Get unit in sturdy position upside down on bench and remove base plate, gasket and go from their. Just take a good look at things so you can put it back together in correct order. When finished smother gears with lithium grease and be careful not to let any of the needles in the main bearing come out and get lost amongst the gears. Don't be scared the junkman would be more than qualified to do this easy peasy, just take ya time, if ya get stuck somewhere I can help from the bottom of the earth.
