[jimmontg]

The grit should be a bit on the rough side to get them flat quicker. Like Ray said don't go finer than 220 grit as they will be blue to black depending on the metal and the practice of the heat treater. My HT guys cover the blades with foil or some type of compound to keep the surface from too much decarburizing. It is up to me what they do. What kind of material are you using for the blades? If it's stainless then the HT will cover with foil for about $4 a blade. That stuff is expensive, but it is worth it if you don't want to sand a bunch of crap off the blade and stainless pretty much demands some kind of an air block barrier because of the high temperature soak time.

Now a high carbon steel like 1084 doesn't need it and just a final hand sand is all that is necessary. Make your tang flat as possible, the HT guy will straighten it to a certain degree and then you finish it. If you hand sanded it then warping shouldn't be much of an issue because you will not have made the blade hot in the grinding process. Uneven and hot grinding is the main cause of warpage.

I never buy precision ground raw material because first and foremost it's too expensive and second, it can hide a possible future warp. I buy hot roll bar or sheared sheet. I check and straighten before I grind it or profile it even. By doing this I almost never have a serious warping problem unless I just get impatient while grinding and don't keep it even and cool.