When my rotary razor gets dull as long as there is no holes in the screen I take the rotors out and place them blade down on a flat semi-fine Arkansas stone. And with my finger pressing on the back make small counter clock wise circles about the size of a Quarter making 10 or 12 circles. Take off and do the next two rotors the same way clean off with water and put back in your face razor and your good to go. I just got tired of spending $25.00 for new blades and tried this about 30 years ago, been doing it ever since. Hey saving a few bucks for important stuff like bullets or gas money....