The way I was told on 3 blades and have done it on Woodsmans (not 2nds) is put it on an arrow shaft and black the edges with a sharpie . Fine wheel on a 6" grinder and do 2 blades at once. Just enough to remove the sharpie black. Then with a fine file do 3 strokes across 2 blades at a time, then 2 then 1.
Last few , go really light on the file, only its own weight. I can make them shave in about 2 minutes each.
If you go from back to front it is easier cause it's hard to line the point up if you start there....
BTW, what this does is put a hollow grind on them so you only sharpen the very edge with the file. Last doe I took last year, I cleaned the VPA 200 up and it would still shave!