- Rotary mowers have rapidly spinning horizontal blades and are powered by gas or electricity, unlike reel mowers, which have between three and seven vertically spinning blades. Usually, a rotary mower only has one blade, which shreds the grass, ripping the tips off and sucks the grass up into the body of the mower. The grass eventually either lands in a sack or is thrown back out onto the lawn. Rotary mowers can be small, human-propelled machines, large farming tractors or residential-sized riding lawn mowers.
- Rotary mowers rip at the grass, which can damage it, making it more susceptible to disease and water loss. This turns the tips of the grass blades brown. The blades on a rotary mower spin on average about 3,000 times per minute. These fast, powerful blades make short work of long grass, but also cause around 25,000 injuries to North Americans per year as estimated by the American College of Foot and Ankle Surgeons. Rotary mowers should be used with caution. Children should be kept away from the mowers, and all debris such as rocks, sticks and small toys should be removed from the area before mowing.
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The quality of a rotary mower depends heavily on the blade. The ideal blade is tempered steel. Blades that are not tempered in the center can "bounce" as they spin, which causes bending and sometimes twisting. The hardness of the blades should be around 45, according the the Range of Rockwell scale. The harder the blade, the less it will vibrate at high speeds.
The tip of the blade should ride about 1/8 of an inch above the bottom edge and sides of the deck, and a 1/4 of an inch below the top of the bar across the chute that carries the grass either to the bag or out again to the lawn. This is for safety reasons. If you can see the blade protruding from the edges, you need to have it adjusted. The cutting width of the blade usually varies depending on the size of the mower, but the average is around 18 to 20 inches. Smaller rotary mowers, with smaller blades, cost less, use less gas and handle easier. In fact, some manufacturers now make "mini-mowers," which feature a cutting width of only 16 inches. These rotary mowers are perfect for small, compact lawns.
