when I sharpen a 3 blade head I put one blade in a vice and the other 2 are sticking up and laying flat I take a good mil bastard file and stroke both of those blades at the same time, what you are doing is truing up the edge so it is smooth from rear to front, I rotate the head and do it again, do this until all 3 edges have been trued. then I use a diamond stone that is about 4x8, one side 300 grit the other side 600 grit, I lay the head down on the stone so 2 edges are laying flat on the stone stroke the head tip to rear, until you feel it running smooth, rotate the head and do 2 more edges, rotate until all 3 edges have been on the 300 grit do the same with the 600 grit, with each process lighten up the pressure, when you are finished with the 600 grit side do 5 strokes for each edge with just barley the weight of the head applying the pressure. to much pressure defeats your progress, its hard to believe how light of pressure you have to apply in order to get the edge you want.