Out of curiosity, why do you want a concave grind?
Nothing special
Just fooling around with some cheap knives.
Just to be clear, I am not going to make a concave grind that is half way along the knife. It is the edge only (1-2 mm) that I wanted to sharpen in a concave shape.
Anyway, I found a knockoff copy of this sharpener, and it did the trick . Thanks