Rotary Blades

• If you cut the grass with a modern push lawn mower that is equipped with an engine, running off of either gas or electricity, it likely uses a rotary blade. This blade is installed horizontally on the mower and spins around at a high speed. Though the blade is sharp, it isn't actually sharp enough to slice through the thin grass blades as it passes over them, so it shortens the grass height more by ripping, or tearing, off the top portions of the grass. You cannot actually see a rotary blade while mowing. The blade is located underneath the mower.
  
  

Cylindrical Blades

• The second type of lawn mower blades are called cylindrical blades. If you own a manual predecessor to the engine-equipped mowers, it uses this type of blade. These mowers are also called reel mowers. When you push it, the mower uses rapidly spinning spiral blades that twirl forward and trap the grass against a single stationary horizontal blade. Caught between these two sets of blades, the grass is sheared shorter. This type of blade mimics the cutting action that a scissor uses. A basic push mower's cylindrical blades are easily visible while you mow.
  
  

Mulching Blades

• In addition to its regular rotary blade, a mower can also have a mulching blade. Unlike the straighter rotary blade, a mulching blade is usually curvy or wavy. The blade may have teeth that direct the grass clippings back over the mower's blade where they are repeatedly cut again, or it may have teeth that chop the clippings down further. The even-smaller shreds of grass are then spread back onto the lawn to feed the soil by feeding moisture and nutrients back into it.
  
  

Blade Concerns

• Cylindrical blades can often last for years without the need for replacement or sharpening. Rotary blades should be checked, possibly once a month during the mowing season, to make certain they are not damaged or dull. A dull or damaged blade will give your lawn very ragged, uneven edges. To sharpen the blade, you have to first turn the mower over and remove the blade. Sharpen the blade with either a metal file or a mower blade grinder. Sharpen dull mulching blades with the same tools.