When blades are new, the sharp tips are as wide as the rest of the blade. As they get used and resharpened, the sharps tips become more narrow than the rest of the blade, and narrower each time you sharpen them. To refine my question: How narrow can they get before they are no longer safe to use? It seems to me that as long as they are balanced you should be able to use them completely up, but is this true?? Is there a point at which they become unsafe? When do you retire the blade? Thanks.