Regarding putting a decent edge on a shovel blade -- I have a Gerber folding shovel. What do you use to put a good edge on it? A grinder? Dremel tool?
I used to be a purist and do all the work with an 8"+ file. But I have found that if I'm careful, I can do most of the grunt work with a cheap, 4-amp angle grinder. I use very light pressure and many fast passes to avoid ruining the temper of the shovel. When I have established a rough 45-degree bevel, a few last quick passes with essentially no pressure will take off the 1/2-mm of steel on the bevel that has been hardened. If I don't do this, the file will bounce right off in places. If the file bites into the metal, all along the bevel, I've got it right. I always finish with a file. I can easily put on an edge that will cut rope, roots, veggies, or leather work boots (!).