I recently bought a less expensive rotary blade sharpener. It has a circle band (open in the middle) with a light sanding surface on one side and a buffing-type surface on the other side. The blade is held securely with a screw between two knobs with small handles. You place one side of the blade on the sanding surface and manually turn a few times, buff it on the other side and repeat with the other side of the blade.
I tried to sharpen two blades a couple of days ago and both seem to be worse afterwards. I haven't had time to go back and work with them, but am hoping that I didn't get the blade assembled back in the rotary cutter correctly. The picture posted by Oldswimmer looks like a much better sharpener and would probably be worth the difference in price if it will work. Has anyone tried a knife sharpener to sharpen a rotary blade?