Lawn mower

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A lawn mower (often spelled as one word—lawnmower) is a type of mower, used to cut grass to an even length on a smaller scale. Mowers were invented in Britain in 1830 by Edwin Beard Budding, primarily to cut the lawn on sports grounds and expansive gardens. Since many sports had just been invented in Britain that required a flat soft ground (such as croquet, cricket, soccer and rugby), a more efficient way of making uniform length grass was needed, and so the mower was born.

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Electric_mower-250px.jpg
Electric rotary lawn mower with rear catcher, side view
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A old petrol-powered lawn mower

The design from 1830 is of a reel mower, and it was manually powered. Nowadays most are engine powered.

Contents

Cutting mechanism (rotary and reel)

There are two main types of cutting mechanisms in common use:&mdash

  • those where a set of spiral-cylindrical blades spin on a horizontal axis (reel mower). Cutting is by 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.
  • those whose blades spin horizontally on a vertical drive-shaft (rotary mower).

Cutting is due to a horizontal blade striking the grass at speed.

Propulsion system

Mowers may be pushed or pulled by:

  • a person
  • a tractor
  • a horse
  • a bullock

(Horse or bullock power is a thing of the past but was definitely employed in the past on larger areas of grass).

Alternatively, the mower may be self-propelled using its own engine.

Power mechanism

A mower needs a power source to action the grass cutting mechanism and also for propulsion.

Whether rotary or reel blade systems are utilised, one of the following power sources will be used:&mdash

  • wheel driven gear system where the wheels are driven by a person, a tractor, a horse or any other unit that pushes or pulls the mower.
  • internal combustion engine
  • electrical motor
  • n.b.steam engines have not yet been known to enter commercial production, as at 2005. Nuclear, solar, fuel-cell powered and even compressed air engines are also "off-market" but conservationists are expected to make the case for these in due course.

Wheel driven gear systems allow for cutting to be powered by the same external source as that used to propel the mower. Powered mowers use a either the combination of an engine to rotate the cutters and an external source for propulsion or in the case of self-propelled mowers the engine both propels the mower and rotates the cutters.

Push mowers

Manually pushed mowers

The simplest kind of mower is the manual reel mower which is pushed, invariably by a person.

Powered mowers

Powered mowers utilise some kind of engine to rotate the cutting blades . Engines may be of the electrical or internal combustion type. A powered push mower is the simplest type of powered mower: the engine rotates the cutters while a person pushes the mower forward. Refer also to self-propelled mowers below.

Internal combustion powered mowers

Internal combustion engines applied to lawn mowing are invariably of the four stroke or two stroke variety using gasoline (sic. petrol) as a fuel (diesel fuel has not yet been applied to lawn mower engines although the high torque characteristics of diesel engines would suit lawn mowing especially in situations of extensive vegetation, albeit at the cost of heaviness and starting complexities).

Internal combustion engines used with lawn mowers normally have only one cylinder. Power ranges from 2 to 6 horsepower (1.5 to 4.5 kW). The engines are usually carburetted and require a manual pull to start them, although an electric start may also be applied.

Electrically powered mowers

In the last fifty or so years it is common to find power mowers with an electric motor as the power source although this has 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 followed by much anguish on the part of the mower operator.

Underneath electric mower, showing mulching blade
Enlarge
Underneath electric mower, showing mulching blade

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.

Self-propelled mowers

All mowers which require a human to push or maneuver them become quite tiring once the area of grass to be cut becomes more than a few tens of square meters. There are self-propelled mowers in which the wheels are powered but the operator is still required to walk behind the mower to steer it. These are only slightly more expensive than regular push mowers. A popular alternative for larger domestic properties is the ride-on mower. These often resemble small tractors, with the cutting deck mounted amidships between the front and rear axles. Such machines are convenient for large lawns. 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.

Rotary mowers

An alternative mechanism for cutting grass is a horizontally spinning blade held close above the grass surface. This type is usually referred to as a rotary mower. One of the first companies to exploit this principle commercially was the Australian Victa company, in 1947.

The rotary mower is powered by two-stroke or four-stroke internal combustion engines running on petrol or other liquid fuels, although versions with electric motors been available for many years and are cbecooming more popular. Cordless (battery powered) electric lawnmowers are also available for small lawns.

Rotary mowers are always powered, using either internal combustion engine or an electric motor. Usually, these mowers are moved by manual motive power— the onboard engine or motor only spins the blades. The most common type is fitted with wheels, but an alternative is the hover mower, in which the spinning blade also acts as a fan providing a lift force, lifting the mower bodily clear of the ground on the same principle as a hovercraft. Such mowers are very light and easy to maneuver, provided the grass surface is fairly even. 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.

Special "mulching" blades are now also 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.

On rotary mowers, the blade is seldom sharp enough to cut the grass blades. The speed of the blade simply tears the grass resulting in brown tips. By contrast, the cylinder-type lawnmowers and manual lawnmowers usually work by scissor action on the blades and a cleaner cut is achieved.

Different grass lengths may be desirable at different times of the year or in different parts of the lawn. The height of the lawnmower can usually be adjusted to control the height of the cut grass. On older or less expensive lawnmowers, this is accomplished by manually moving each wheel to a different slot on the chassis. A more recent innovation is a "one-touch" height-adjust mechanism where the wheels are mounted on a frame separate from the rest of the lawnmower and the frame can be raised and lowered. In general, vertical mowers can cut closer to the ground than horizontal mowers.

A "deadman's switch" is required in some countries 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 lawnmower and release the bar, either the engine is turned off or the blade is disconnected by disengaging a clutch. The switch may be mandated by local legislation.

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. 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 are 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 with their lightness, most operators are able to lift the mower up and then let it sink slowly down while the blades progressively chop up the vegetation (when lifted, of course the air cushion disappears). 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.

Professional mowers

Professional grass-cutting equipment (used by large establishments such as universities 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. Either type may use rotating blades or the cylindrical blade type cutters.

Other mowing aids

Edge trimmer

Edge trimmers (also called line trimmers or whippersnappers in Australia) are specialized, electric or petrol-engine powered, hand-held mowers for cutting grass near fences, trees and other areas too small or rough for a mechanized lawnmower. 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).

Petrol-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 petrol-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.

Robotic mowers

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

See also

External links

de:Rasenmäher fr:Tondeuse à gazon nl:Grasmaaier sv:Gräsklippare

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