What is a Rotary Lawn Mower?

Keith Koons

A rotary lawn mower is a conventional cutting device that has horizontal blades mounted beneath the unit in order to trim grass. The unit operates by a gasoline or electrically-powered engine, which propels the sharpened blades in a circular motion around a centralized pivot shaft. As long as the cutting unit remains within perfect balance, a rotary lawn mower can trim large amounts of grass faster than many other comparably-designed mowers, and the result is often a much more uniform pattern as well. An overwhelming majority of the world’s current lawnmowers implement the rotary design due to its simplicity, performance, and relatively low maintenance costs.

A rotary lawn mower has blades mounted beneath the unit.
A rotary lawn mower has blades mounted beneath the unit.

The key to making a rotary lawn mower operable is the actual cutting blade itself, which is normally made from a solid cast of steel. Different manufacturers will implement various lengths and features of the rotary blade to increase the cutting and mulching capacity of the lawnmower while it is in use. Since the heavy deck forces grass to lean forward as the rotary lawn mower passes over it, the blades are designed with an angular pattern across the sharpened side to generate a lifting air pattern. This forces the grass to stand back upright so a smooth, uniform cut will be made across the entire cutting surface.

Conventional push mowers are considered rotary lawn mowers.
Conventional push mowers are considered rotary lawn mowers.

The technology behind the rotary lawn mower is thought to be an improvement on reel designs due to several factors. Since reel lawnmowers rely on a vertically-powered circular motion where several inline blades strike the grass in tandem, there is a large amount of upkeep to ensure that the device cuts properly. Damage to even a single blade could lead to sporadic patches of uncut grass, but in a rotary-style lawnmower, this is far less of an issue since the blade is propelled at high revolutions by an engine.

There are also several variations of a rotary lawn mower available to the general public. Self-propelled rotary lawn mowers add a drive belt to the wheels in order to eliminate the need for the device to be manually pushed, and riding lawnmowers also implement this technology by utilizing a larger, more powerful motor to carry the operator while the device is in motion. Some rotary lawn mowers also utilize two separate blades that are mounted side by side to grant a larger cutting radius, and industrial mowers may have up to eight vertically-aligned blades to mow large fields or crops. A mulching rotary lawn mower creates a more powerful updraft so that the individual blades of grass will remain within the cutting chamber longer, allowing for finer cuts that will be more easily absorbed by the soil.

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