Home Page   
EDinformatics Home
Home Page
Today is
Great Inventions --Great Inventors

Lawn mower

Gasoline-powered push rotary mower.
Gasoline-powered push rotary mower.

A lawn mower (or lawnmower) is a type of mower, used to cut grass to an even length. Two cutting mechanisms are in common use:

  • reel mowers, those with a set of spiral-cylindrical blades spinning on a horizontal axis. Cutting is by a scissor-like action between the moving spiral blades and a single stationary horizontal blade. The axle is attached to a gear that is then mounted on one of the wheels in order to spin the blades rapidly for good grass cutting action even when the mower is moving slowly.
  • rotary mowers, those whose blades spin horizontally on a vertical driveshaft. Cutting is due to a horizontal blade striking the grass at a high speed.

The two cutting mechanisms can lead to different results. On rotary mowers, the blade is usually not sharp enough to cut the grass cleanly. The speed of the blade simply tears the grass resulting in ragged tips. By contrast, the cylinder-type lawn mowers and manual lawn mowers usually work by scissor action on the blades and a cleaner cut is achieved.

Lawn mowers often allow the height of the lawn mower to be adjusted to control the height of the cut grass. On older or less expensive lawn mowers, this is accomplished by manually moving each wheel to a different slot on the chassis. A more recent innovation in rotary mowers is a "one-touch" height-adjust mechanism where the wheels are mounted on a frame separate from the rest of the lawn mower and the frame can be raised and lowered.

Lawn mowers need power for two purposes: to cut and to move. The act of pushing or pulling a reel mower provides power for cutting and moving at the same time. For rotary mowers, the power sources may vary: grass-cutting may be powered by either an internal combustion engine or an electric motor, while propulsion may share that power soure or be supplied by the user or another external source such as a tractor. Wheel-driven gear systems allow for cutting to be powered by the same external source as that used to propel the mower.

A late 19th century reel mower.
A late 19th century reel mower.

 

Rotary mowers

A rotary mower is often powered by internal combustion engines. Such engines can be either two-stroke or four-stroke cycle engines, running on gasoline or other liquid fuels. Internal combustion engines used with lawn mowers normally have only one cylinder. Power ranges from two to six horsepower (1.5 to 4.5 kW). The engines are usually carbureted and require a manual pull to start them, although an electric start may also be applied.

Electric rotary lawn mower with rear grass catcher.
Electric rotary lawn mower with rear grass catcher.

Rotary mowers powered by electric motors are increasingly popular. Usually, these mowers are moved by manual motive power— the on-board engine or motor only spins the blades. These have the disadvantage of requiring a trailing power cord that limits its range and so these are only useful for relatively small lawns, close to a power socket. There is the obvious hazard with these machines of mowing over the power cable resulting in the rapid cessation of cutting activity, and risk of electrocution. Installing a residual-current device (GFCI) on the outlet can reduce the risk of electrocution. Cordless (battery powered) electric lawn mowers are also available for small lawns.

Rotary mowers typically have an opening in the side of the housing where the cut grass is expelled. Some have a grass catcher attachment at that point to bag the grass clippings. Rear-catchers are another common design for the same purpose.

A mulching blade.
A mulching blade.

Special mulching blades are available for rotary mowers. The blade is designed to keep the clippings circulating underneath the mower until the clippings are chopped quite small. Other designs have twin blades to mulch the clippings to small pieces. This avoids the need for bagging the clippings or raking the clippings. Not only does this save labor, as no organics are removed from the lawn, less fertilizer is needed.

A deadman's switch is required in some places so that the operator can hold a switch to keep the engine running. Typically, this is an extra bar that is held against the handle. Should the operator drop "dead" or otherwise lose control of the lawn mower and release the bar, either the engine is turned off or the blade is disconnected by disengaging a clutch.

Riding mowers

A popular alternative for larger lawns is the riding (or ride-on) mower. These often resemble small tractors, with the cutting deck mounted amidships between the front and rear axles. An alternative layout for a ride-on is a rear-mounted engine with rear-wheel steering, and a front-mounted deck. These mowers are generally more maneuverable around tight corners than the tractor type, but are generally more expensive. Most of these machines cut using the horizontal rotating blade system, though usually with multiple blades.

Hover mowers

Hover mowers are powered rotary push mowers that use a turbine above the spinning blades to drive air downwards, thereby creating an air cushion that lifts the mower off the ground like a hovercraft. The operator can then easily move the mower as it floats over the grass. Hover mowers are necessarily light in order to achieve the air cushion and typically have plastic bodies with an electric motor, although small petrol engines have been used. A different style of movement is often employed with hover mowers whereby operators swing the mower in an arc around themselves because there are no wheels touching the ground to impede movement in sideway directions.

Hover mowers can also be applied to very long grass and even light scrub, since their lightness permits most operators to lift the mower up and then let it sink slowly down while the blades progressively chop up the vegetation. The lifting action is made even easier when the mower is swung around with the handle held against the operator's mid-body to provide leverage.

Robotic mowers

Robotic lawn mowers represented the second largest category of household autonomous robots used by the end of 2003. A typical robotic lawn mower requires the user to set-up a border wire around the lawn that defines the area to be mowed.

Pull mowers

A pull mower is essentially the same as a manually pushed mower but the propulsion unit pulls the mowing unit instead of pushing it. Thus is the normal system when a tractor or animal-drawn mower is used.

Professional mowers

Professional grass-cutting equipment (used by large establishments such as universities, sports stadiums or local authorities, etc), usually take the form of much larger dedicated ride-on platforms, or attachments that can be mounted on a standard tractor unit or behind ("gang-mower"). Either type may use rotating blades or the cylindrical blade type cutters.

Other mowing tools

Edge trimmer

Edge trimmers (also called strimmers in the UK, or line trimmers or whippersnippers in Australia) are specialized, electric or gasoline-engine powered, hand-held mowers for cutting grass near fences, trees and other areas too small or rough for a mechanized lawn mower. The cutting device is either a monofilament nylon 1.6 to 3 mm diameter line, or a nylon or steel three-lobe blade.

Electric whippersnappers have the advantage of being very light, easy to maneuver and easy to operate devices. However, the length of power cord that can be deployed across the ground limits them and they are usually less powerful and robust than the petrol-engine ones. Electric machines normally are limited to 2.5 mm (0.100 inch) maximum diameter nylon because of their lower power output (400 to about 1200 watts).

Gas-engine powered trimmers usually have a minimum of 25 cc motors. At this size they can easily turn 2 mm (0.080 inch) line and some have nylon blades as accessories to the line-reel. A 32 cc engine can swing a 2.75 mm (0.110) line and often have metal-blade accessories.

While this type of trimmer is heavier, uses a gas-oil mix and vibrates significantly they are much more mobile (not attached to a power outlet) and are not very limited in maximum power for commercial use. Large trimmers, used for cutting roadside grass in large areas, may be quite heavy— being suspended from the body by a harness— and be a two-hand-controlled device.

For trimming close to fences and other snagging features, petrol-trimmers can be throttled back to limit the chance of the line catching or breaking off, or both. Speed-control is not possible with electric trimmers— they are essentially single-speed machines.

A line-trimmer works on the principle that a line that is turned fast enough is held out from its housing (the rotating reel) very stiffly by centrifugal force. The faster it turns the stiffer the line. Even round-section nylon line is able to cut grass and slight, woody, plants quite well. Some monofilament, designed for more powerful cutters, has an extruded shape— like a star— that helps the line slash the material being cut and it is able to cut quite large woody plants (small shrubs) or, at least, ring-bark them very effectively. These lines make disks less necessary for tough jobs.

The line is hand-wound onto a reel before the job is started— leaving both ends extending from the reel housing. The motor turns the reel and the line extends horizontally while the operator swings the trimmer about where the plants are to be trimmed. The operator controls the height that cutting takes place and can trim down to ground level quite easily. As the line is worn, or breaks off, the operator knocks the reel on the ground so that a release mechanism allows some of the line in the reel to extend and replace the spent portion. A small cutter on the line-guard ensures that the line length exposed for cutting does no exceed the length that can be swung efficiently by the motor. Newly extended line operates more efficiently because of its heavier weight and surface effects (the star-shaped edges).

Trimmers that have nylon or metal blades usually have straight driveshaft because of the higher torque required to turn the disk and because of the shock loads that are passed back from the blade to the driveshaft and its gearbox(es). Smaller line trimmers have curved driveshaft to make holding the cutting-head at ground level much easier and less strain on the operator.

Safety precautions, often ignored, with whippersnappers are that the operator should wear robust boots and clothing (especially trousers), goggles, hearing protection and gloves. The power should be disconnected (or the engine stopped) before the line is replaced or before any significant work is done in the line-reel area (such as removing grass stalks that have wound onto the reel). The line guard should not be removed because it stops material being flung back at the operator's legs and because it carries the cutter ensuring that the line length is not too long for the trimmer. When using a disk the operator can easily overload the driveshaft and damage the machine or strip the gearbox gears.

Clippers

Hand-powered or battery-electric grass clippers can used for the tightest spots, for example around flowers, however one has to be on their knees a lot. The simplest form of these is shears, like scissors with long blades.

History

Mowers were invented in Britain in 1830 by Edwin Beard Budding, primarily to cut the lawn on sports grounds and expansive gardens. The rise in popularity of sports such as lawn tennis, croquet, cricket, football and rugby helped prompt the invention. Lawn mowers became a more efficient alternative to simply relying on domesticated grazing animals.

One of the first companies to produce rotary mowers commercially was the Australian Victa company, starting in 1947.

See also

External links


 

 

Who were the Greatest Thinkers?

 

See Edinformatics List of

Great Thinkers --Great Minds

 

 

 

 

 

 

 



 

 

 



Questions or Comments?
Copyright 1999 EdInformatics.com
All Rights Reserved.