Either a rotory shaver as shown. or foil type, both carry out a scissor action, therefore both the rotating cutters and the underside edges of the holes or slots in the foil would need to be sharp. My shaver is a Broun of the oscillating cutter type. I apply very fine pollishing compound to the outside of the foil and rub it into the foil holes. I then run the shaver for about 40 seconds, and keep gently rubbing the compound back into the holes. Then I remove foil and cutter and carefully clean; hay presto it shaves like a new one: on that basis, cannot see why the same method and simplicity would not apply to a rotory type, though I have never owned or tried one. Would be pleased to see the experiences of others.