All push mowers use a single blade that spins rapidly to cut the grass. The blade is connected to the engine shaft with a single bolt that passes through the center of the blade. After dutifully cutting your lawn for a season, your blade will begin to dull. Dull blades leave telltale signs in your lawn like shredded ends and uncut areas. If the blade isn't taken off of the mower and sharpened, your lawn may suffer from fungus and disease infiltration through the shredded grass ends. Sharpening a blade is a relatively simple process and you need just a feel tools to complete the task.
Grasp the wire on the back of the mower's sparkplug and pull it off.
Lay the push mower on its side. Look for the bolt in the center of the blade and slide your adjustable wrench onto it. Grasp the blade with one gloved hand and turn the bolt counterclockwise with the other hand to loosen it. Remove the bolt and blade from the mower.
Clamp the blade down in the center of the table vise so you can access each end where the actual cutting edge is. Look over the blade carefully and you'll see each end has an edge that slowly bevels to a sharp cutting edge.
Plug in your angle grinder and turn it on. Grind the push mower blade along the cutting edge. Follow the existing bevel and slowly slide the grinder along the edge in a slow, back-and-forth fashion. Keep grinding until the edge is smooth and free from nicks. Repeat the process on the other edge.
Remove the blade from the vise and balance it in the middle with your index finger. A balanced blade will sit level on your finger when balanced in the middle. If it tips toward a certain direction, it means that side of the blade is heavier than the other. Grind more material off the side it tips toward and recheck until the blade maintains a perfect balance.
Install the blade back on the push mower the same way it came off. Screw the bolt back into place and turn your adjustable wrench counterclockwise to tighten it.
Stand the mower back up on all four wheels and reconnect the sparkplug wire.