Abstract: This invention is a tool designed to sharpen rotary cutter blades. In a first embodiment, an inside-threaded clamp is screwed down upon the blade, pressing it tightly against a platform from which a threaded shank rises, and holding the blade from turning. When an upper casing containing an inside angled abrasive strip is lowered over the clamp until contact is made against the blade surface, the abrasive strip is brought into contact with the blade edge. When the upper casing is rotated around the tightened clamp, the abrasive acts upon the blade edge and thereby sharpens the edge. A second embodiment is comprised of a blade holder for holding the cutting blade stationary and a ring member with an abrasive strip which fits around the blade holder such that the abrasive strip contacts the edge of the cutting blade.