A rotary-blade lawn mower is designed to cut grass by slicing it off at great speeds. The blades will rotate on many mowers at approximately 3,000 revolutions per minute. But at this great speed the blades become ineffective if chipped or dented. However, keeping the lawn mower blade sharp is often a straightforward task that only takes a few minutes with the appropriate tools and techniques.

As the job will require the mower to be turned over to remove the blade, for safety reasons it would be worthwhile to drain the gas depending on the model. It is possible to tilt some models without leakage, although others can't. In any case, at least remove the spark plug for the duration of the task. This is predominantly necessary for those models that have an auto-starter attached. There is a very small chance that the mower could start accidentally, but make that zero chance anyway.

Turn the mower deck over and lodge a piece of wood between the under-deck and the blade to prevent the blade from twisting. Wear suitable protection on your hands, such as leather gloves, and use the right sized or an adjustable wrench for your lawn mower.

Take out the blade and wipe off any dirt residue and grass. At the same time, use a scraper or putty knife to remove any built up grass from the under-deck section as well. Now clamp the mowers blade into a vice bench for manual sharpening. Inspect the blade for cracks. The size of any chips present, will determine if you need to use a medium to fine metal file or in some cases a larger course file.

Lightly oil the lawn mower blade with fine machine oil. Now take metal file in both hands and shove it across the bevelled edge from the centre to the edge in a smooth motion. Aim to keep the file at an identical angle as the bevel as much as possible.

Be cautious not to file the flat edge, unless it's essential to level off a chip that has pushed metal out, making it uneven at that location.

With equal pressure make the same amount of strokes on both sides of the blade. The intention here is to maintain the blades balance, having an identical amount of metal on either side of the nut hole. If the blades are out of balance, this will cause extreme vibration to the mower.

The ultimate device to sharpen a lawn mowers blade is an electric bench grinder, but if used inappropriately they have the potential to wipe out the blade very quickly. It's vital to clamp the blades at precisely the right angle. Most grinders will make this easy, by using attached clamps.

If you are carrying out this task free hand, be certain that you have an extremely steady hand. Or else, you may end up grinding too much off the blade in a single stroke. That could either wreck the blade, or at the very least make if off balance. By understanding the proper technique and using the appropriate clamps you can have this job completed in minutes. Always wear eye protection, of course. Flying fragments of metal can devastate eyesight for life.

As it can take only a few moments to re-sharpen, the effort is worthwhile, as you'll save a visit to the store. On occasions, though, it can be simpler to replace the lawn mower blade if the damage is too significant.