I came across a post where someone mentioned this:
"A very good friend,who's also the oldest man in the village now,at 96,makes about a hundred or so of these in a year(they sell like hot-cakes
).He files a groove with a needle file that follows the desired shape,then just breaks the waste off,working like one does with a glass cutter!He does that to retain the original HT(with it's usually excellent qualities).Then he grinds the edge keeping it all cool."
http://forums.dfoggknives.com/index.php?showtopic=20958
I wonder what kind of needle file can do that, I feel like the ones I have would barely scratch the steel, granted they are cheap files.