I asked this very question once...what I got from the responses was, "Do what you have to do to get the edge straight."
Sometimes I use the flats, sometimes the "edges," sometimes the corners. It seems somewhat intuitive to me - do what feels right at the time. The corners seem more aggressive than the edges; the edges seem more aggressive than the flats.
One time I dinged the old Kobra good - the edge had deflected enough to really scare me. I wound up using the chakma as a hammer flatten it enough to where "wiping" would work again. (I'm not going to recommend this at this point.) Like they say - if it's stupid and it works, it isn't stupid.
I agree with Yvsa. It seems sometimes that the khuk winds up sharper after a workout and a good steeling than it did before. I've been told that steeling can work-harden the edge and that the new edge can be decarburized through the forging and quenching process, but regardless of the physics at work, the edges seem to get better with use and regular steeling.
From what I understand of steeling, it's the localized forces that're doing the work. When I'm trying to move a lot of metal I rest the chakma on my leg and run the edge over it, letting the weight of the blade do the work; this is more effective than common sense would dictate. If I've given the khuk a good workout I may bear down on the blade while I'm doing this. When less work needs to be done, I just swipe the chakma along the edge in the same manner that I'd steel a kitchen knife.
Well IMO anyway.
