Need. The newly bought knife needs sharpening. When sharpening a knife, the knife should be wetted and ground at a 30-degree angle. Gently grind back and forth, cross back and forth, and apply force evenly. Add water to prevent the edge from being damaged by a grindstone that is too dry. Sharpening a knife means grinding these off at the edge of the knife, and exposing the steel will be sharper. The methods of grinding include manual grinding and machine grinding.