The were on primary land is seen often. And sharpening the primary land make the end mill perform almost the same as new one. The width of the wear land develops very fast after a time period of use , resulting in rough surface finish and chipping. Sharpening must be done before it occurs. In general, when the width of were land become 0.2 - 0.4 mm ( in case of roughing end mill : 0.5 mm ) resharpening is required.