well if you do use an old file you need to start by annealing it (red hot then let it cool as slow as you can) after that take a good file and lightly drag it across, if it catches and grabs at the metal it should be soft enough to use (you can also take a piece of a file that is the same and also check to see if you can harden it- red hot, quench in oil make sure to pre heat the oil with a piece of scrap when you harden your real blade) same file test but opposite results means it is hardened (to hard but thats not very important at this point since you havent even started to make the knife)
ya grinder, bench sander, etc etc. i use a 36x4 in bench sander with a 6 or 7 inch disk on the side. decent piece of equipment, for the initial shaping you can use a saw (some use a drill press to put an out line of holes then cut between them, thats more for those that really like exact patterns), some use an angle grinder to get a very rough shape (like me) then sand/grind it to shape.
form a lot of people they start at a rough rough grit (i start at 36 some go lower but at that point is mostly what ever your sander can get for it) then move to 80 -120-240ish-400ish, you dont want to go much past 400 before ht because you will have to redo work. get it shaped all the way, finnished to 400 grit and make sure to leave the blade off (size varies but some like .04 in left on the edge some like .02 etc etc, its harder to remove metal after the HT but its impossible to put it back and if it is to thin your blade will get messed up)
a lot of this is going to be trial and error once you understand the very very basics which it seems like you do for the most part or if not are very close, once you get some tips of how people do it them selves the new game starts.
good luck
-matt
