Lacking proper skills and tools and equipment, one can bend the blade while sharpening a serrated knife. The best way to sharpen a serrated knife without bending the blade is using a whetstone or a sharpening rod. Take precautions and make the slow-motion stroke in order to make the blade sharpen without bending it. Some people suggest sandpaper but in reality, it doesn’t work as perfectly as a whetstone or a sharpening rod. You can try it.