Place the grinder on top of a sturdy work bench and plug it into an electrical outlet. Make sure the grinder has plenty of clearance on both sides so you can work the blade freely.
Adjust the metal blade guard to the right of the grinding wheel so the lawn mower blade's cutting surface touches the grinding wheel when you slide the blade against the guard.
Put on your eye protection.
Switch on the power to the grinder.
Slide the lawn mower blade against the metal guard until the blade makes contact with the grinding wheel. Run the entire cutting surface against the grinding wheel. Repeat on the other side of the blade.
Place the lawn mower blade on the balancing spindle. If the blade tilts to one side, grind a little more off the heavy end of the blade and then place it on the balancing spindle again. Repeat until the blade stays level on the balancing spindle.