Sharpen paper shredder blades by feeding two to three lengths of aluminum foil, the size of a sheet of paper, through the machine. Some shredders have automatic blade sharpening and do not require the foil. Keep the machine operating correctly by oiling the blades, per the manufacturer's instructions.
Use the aluminum foil sharpening method at the first sign of dulling, and repeat it every two to three weeks. It cannot restore the blades if you wait until they are too dull already. If the foil or the unit's self-sharpening mode does not restore the blades, have a professional sharpen them.
Keeping the unit oiled according to the manufacturer's directions helps to maintain sharp cutting edges on the blades. Oil the machine by applying a thin coat of oil to a sheet of paper and running it through the paper cutter or by applying a thin stream of oil directly to the cutting blades and operating the device in the reverse mode. Oiling helps eliminate paper dust and lubricate the blades. Reoil the machine after every 30 minutes of cutting time.
Sharpening the blades removes a thin layer of metal from the blades to restore the edge. Eventually, even the professional is no longer able to restore their edge. Most manufacturers offer replacement sets of blades for their machines.