How-to Sharpen Mower Blades
Rotary blade type of mowers cut grass by slicing it off at a high speed. Some rotary blades revolve at 2,500 per minute. But if those blades become dull or nicked the RPM (revolutions per minute) speed becomes ineffective at cutting the grass. To keep the blades sharp you can sharpen them and it doesn't take much time if you know how to do it and have the correct tools to do so.
To perform this task you will need to turn over the mower and remove the cutting blade. You might have to remove the gas in the mower, it just depends on your mower. Some can be tipped over and not leak out any gas, while others this causes a problem. Next, disconnect the spark plug temporarily, this is also for safety reasons, you wouldn't want the mower to start while going through this process.
When you turn the mower deck over, take a block of wood and wedge it between the under-deck and blade. Take an adjustable wrench and put on a pair of work or leather gloves.
Remove the blades and clean off the blades and dirt. You should also use a scrapper to remove any built of grass residue from the underside of the deck. Clamp the blade into a bench vice to prepare it for manual sharpening. Carefully examine the blade for nicks, the size of the nicks can effect the files you pick to sharpen the blade. The bigger the nick the coarser the file, at first. Most of the time if the nicks are minimal and the blades just need to be sharpened, a medium to fine metal file is usually what you will end up needing.
The next step is to oil the blade with a fine machine oil. Then grip the file with both of your hands and move it across the bevel edge of the blade in a sweeping, smooth motion from the center to the blade. Be sure that you are sharpening the blade away from your body. Remember to stay with the same angle as the bevel of the blade, if you are inept at this you could use angled clamps to help you with this.
Only file the beveled edge of the blade, you should avoid the flat side unless you want to smooth out any nicks in the blade.
Try to stroke the blade the same number of strokes using about the same pressure. You want to try and keep the blade balanced so that they don't vibrate when attached back to the undercarriage of the housing. Unbalanced blades also don't cut as well.
For a quicker way to sharpen the blade, you could use a bench grinder, but use caution with this tool. If you take off too much you can destroy the blade. You still have to clamp the blade at the correct angle and follow the bevel.
If you have to use the grinder free-hand be sure you have a steady hand and use even pressure. Too much pressure or uneven pressure will destroy the blade or at least cause it to be unbalanced. It is best to use some type of clamps, also be sure to wear safety goggles, a tiny stray bit of metal could end up destroying your eyesight, it is very important that you protect your eyes during this process.
With just a little bit of effort and a few minutes of your time you can re-sharpen your lawnmower blades. You'll be able to save money and the inconvenience of having to take it to the hardware or shop to be sharpen and then having to haul it back again. Keep in mind however, that eventually you may have to replace the blade entirely.
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