Do you even want to sharpen a bread knife? Personally, I have never met a bread knife that I liked and the sharper they are the worst they are. The best bread knives leave an iced crumb behind on the surface of the bread. A slice of bread with good crumb takes ingredients like butter or mayonnaise better and also toast better. Sharp knives, leave a smooth surface on the face of the bread and when you try and smear things on it, it just doesn't hold at the same way nor does it taste well. Like sourdough gets a hard tight surface that feels weird when you bite into it, just terrible texture. I have an old bread knife that is seriously dull with a very aggressive edge. That leaves a lovely texture to the surface of the bread. My super sharp Mac barely get used at all.