Try the edge of the fine stones of a Spyderco sharpmaker.
you can also use a lansky with the fine grits
starting with the 30 degree angle, then 20, then finishing with the 17-doing it that way maintains the rounded edge.
(That takes forever)
Or try "reverse sharpening" instead of cutting into the large bench stone, try "stropping" away from the stone. Sounds strange, it works, takes practice.
I find most factory applied convex edges are too thin (Blackjack) and a slight flattening
thickens them a bit and doesnt reduce the cutting ability at all because the blade right past the edge bevel is still convex, and offers little resisitance when slicing or chopping.
IMO, the Spyderco edge isnt really a true convex, its more of a flat convex. I actually prefer it, seems easier to maintain.
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Anthony P. Lombardo
-will destroy knives for
food-