Malcolm,
Sounds like you've got the long and short of it all right. If the file's going to be a chakma, it'll work fine left at full hardness. Set a big coffee can, etc., full of water close to your grinder, and dip the blade in often as you go along. If the blade hisses at all when dunked in the water, that's not good, don't wait so long next time, and if anywhere along the blade you get a color change (indicating burnt temper) that's really not good.
Work slowly until you get the proper hang of it, best to make many light passes on the grinding wheel to keep things straight and even. Bearing down to make things go faster will just make the blade heat up quickly, and removing too much metal at a time will wind you up with a "wobbly grind".
A 120 grit belt on a belt sander will smooth things up nicely, and I generally hand sand for final finish (got lots of time on my hands). Get your chakma smooth as you can, deep nicks and scratches on the surface will act as tiny teeth, boogering up the edge you are trying to burnish with it.
One last note. I'm assuming you are going to mount a handle when you are done. If so, do not leave your tang full hard, it'll snap like dry spaghetti if you put any kind of pressure on it. Wrap your chakma blade with a wet rag, leaving the tang exposed. Carefully heat the tang with a torch (don't have a torch? a burner on your stove, gas or electric, will suffice to heat the tang) until it turns a nice blue color, then you can go ahead and dunk it in some water. No more worries about it snapping, so go ahead and mount a nice handle.
Good luck and have fun
Sarge