The development of the lawn trimmer was not attributed to any specific person or company. However, the original lawn trimmers were created sometime between 1968 and 1970. Prior to 1970, the line trimmers we know today did not exist.
It’s difficult to imagine manually edging sidewalks, driveways, parking lots, and shrub beds with hand-held trimmers. The physical strain on our back, arms, and legs would be overwhelming after a full day of pushing a manual edger along seemingly never-ending sidewalks and driveways. Moreover, it’s hard to envision maintaining any turf without the assistance of a powered trimmer. Consequently, many of us fail to appreciate the benefits that line trimmers offer.
Line trimmers, also known as weed eaters or grass trimmers, are essential tools in the vast range of landscaping equipment. They are used to create clean edges along sidewalks, shrubbery, flowerbeds, and parking lots. The convenience and efficiency provided by these tools are often overlooked in contemporary society. The evolution of line trimmers since their inception in the early 1970s includes advancements such as more durable line, expanded attachment options, and improved engines. These enhancements aim to provide users with additional time and faster results amidst the ever-increasing busyness of modern lifestyles.
The fundamental function of a trimmer involves the engine propelling a hardened steel shaft, supported by multiple bearings, within an aluminum tube through a centrifugal clutch. The shaft is connected to a “head” that contains a nylon line, which spins at a rapid rate of revolutions per minute (RPM). As a result, the nylon line swiftly strikes the blades of grass causing them to be severed precisely at the point of impact. Consequently, the grass is effectively trimmed.
Originally, lawn mowers were run on petrol to avoid the risk of electrocution caused by cutting the power cord. These early models used two-stroke engines with a capacity of about 28 to 32 cubic centimeters, powered by a mixture of “super” petrol and oil. Nowadays, they are still powered by a combination of unleaded petrol and oil, but electric trimmers are gaining popularity.
A leader in engine technology, Honda has achieved a significant milestone with Mini 4-Stroke engines. These engines are powered by the only 360′ inclinable 4-stroke engine currently available, making them capable of running properly at any angle. The new Honda trimmers, equipped with these engines, provide reliable power, exceptional fuel efficiency, and do not require special gas/oil mixtures, eliminating the risk of using improperly mixed fuels. Additionally, they operate quietly, produce minimal smoke, and are environmentally friendly.
The New 4-Stroke Honda engine is designed to produce less smoke and noise compared to the two-stroke engine cycle. In the two-stroke cycle, the fuel/oil mixture is unable to combust completely due to less time available for combustion and higher engine RPM of about 7000. In contrast, four-stroke cycles operate at around 4000 RPM, resulting in reduced vibration of the engines cooling fins and subsequently lower noise levels.
Increased RPM results in an amplified intake noise due to more air and fuel being drawn through the engine’s carburetor and inlet port. Despite the use of silencers, the noise levels remain high. Moreover, the increased intake leads to the generation of additional exhaust gases, resulting in louder exhaust noise. While mufflers provide some relief, the decibel reading remains high.
A typical 2-stroke trimmer has a carburetor that mixes fuel and air for burning in the engine. The carburetor atomizes liquid petrol, and the airflow transports the atomized gasoline to the engine’s cylinder, where it is ignited.
Powered by Super petrol and oil mixtures, these trimmers emit lead through their exhaust unit during fuel combustion. This lead is then deposited within a 12-foot radius on the ground. While there is no solid evidence connecting engine emissions to lead poisoning, this expelled lead is believed to pose risks to both humans and the environment. As a response to public concerns, a campaign was initiated with the aim of eliminating lead from fuel. Consequently, unleaded petrol was developed as an alternative to its leaded counterpart. However, unlike leaded petrol, unleaded petrol lacks lubricating properties which necessitates increased usage of oil. Consequently, more smoke is released during the combustion of this less efficient oil.
Unleaded petrol contains a significant amount of carcinogens such as Benzene, Xylene, heptane, and others that are known to cause cancer. Medical research has confirmed the carcinogenic properties of these chemicals, and there is growing support for the idea that the rise in cancer cases is directly linked to the increased use of unleaded petrol.
In terms of spin-trimmer heads, there are four types available based on their line-dispensing method. Fixed-line heads cannot hold extra line and need pre-cut lengths for replacement. This is how the original trimmer head mechanism works.
Manual heads involve stopping the machine and manually unwinding the line inside the head to complete the task. This method was later improved to increase efficiency. Semi-automatic heads require tapping the spindle head on the ground while the throttle is engaged. This tapping, combined with an open throttle, causes the line to advance and feed out through the guide holes in the spindle head. This advancement is made possible by the development of advanced components that can withstand the high rotational forces.
The line on automatic heads is fed automatically when the throttle reaches a specific speed during operation. This is the latest innovation, although it is not widely adopted yet. In terms of popularity, tap-and-go (Semi Automatic) heads are the most common type. Many users find them more convenient as they allow for controlling the line length without having to stop the machine. Nevertheless, manual heads are still widely favored.
String typesString diameter varies greatly and comes in round-cut and edged varieties. There is much debate over which type and diameter trims grass the best, but there is no definitive answer to this debate. Diameter plays a crucial role in determining the lifespan of most string. Generally, thicker diameters tend to last longer. The range of diameters available is from 0.066 mm to 2.60 mm. To determine the appropriate size of string for your trimmer’s head, consult the owner’s manual.
Manufacturers offer a variety of string options with different characteristics. Some claim their string has increased durability through the use of stronger and higher quality nylon material. Others suggest that the shape of the string, whether it is smooth or edged, allows for more efficient trimming of turf. However, it is important to note that certain edged strings may not feed properly in automatic-feed heads. Additionally, certain types of string may spin unevenly, causing an erratic cutting pattern. While some string may provide excellent cutting performance, it may also wear out more quickly.
The string used in the unit should be of high-quality and designed specifically to prevent welding or fusing. When the string comes into contact with vegetation, it exerts a pulling force which generates heat inside the head. Cheaper string options may fuse together and block the unit. If a softer string must be used, it is recommended to spray it with silicone spray after reloading the spool. While this may not completely resolve the fusing issue, it does help in reducing string fusion.
Wearing appropriate safety gear is highly advised to prevent eye injuries caused by popular nylon line lawn trimmers. These trimmers can operate at speeds of up to 7000 revolutions per minute, expelling small fragments of nylon line that pose a risk of penetrating the eye and causing corneal lacerations. Additionally, dirt and grass debris can also contribute to these injuries. If left untreated, these injuries can lead to severe fungal infections and potential vision loss.
Shafts are an essential component of trimmers and their durability is extremely important. While most shafts are made of hardened steel, flex shafts have not been given much attention due to their widespread use. However, as long as a strong and reinforced unit is labeled as the shaft, it should be resistant to breaking easily. The use of flex shafts offers advantages such as reduced vibrations and shock absorption, providing comfort and preventing damage to gear and clutch. Moreover, even if the drive housing of a flex shaft becomes bent, it can still be operated. In contrast, if the drive housing of a solid-shaft unit gets bent, immediate replacement is necessary.
When it comes to fuel mix for 2-cycle machines like trimmers, it is advised by most manufacturers to use the best quality gasoline and oil in the correct ratio. However, it is crucial to only utilize products that are specified for trimmers and 2-cycle engines. For instance, even though there are excellent oils available for outboard engines, they should not be used for 2-cycle engines. Additionally, it is worth noting that certain manufacturers offer extended warranty periods if their own oil is used.
One advantage of higher-quality oil is its ability to reduce emissions. This will become a significant issue for all of us in the next decade due to upcoming emission regulations. In terms of fuel, some manufacturers advise against using alcohol-based gasoline. They claim it can cause damage to fuel systems, fuel lines, and petrol cap lids. It also leads to vapor locking. When oil is mixed with this type of fuel in 2-cycle engines, they tend to separate over time instead of remaining mixed. The latest trimmers, like those made by Stihl, have similar designs but can be either petrol-powered or electric depending on consumer preferences.
Specifically, there are also electric trimmers available that have the motor positioned very low to the base, eliminating the need for a long drive shaft. Instead, the head is directly connected to the engine’s spindle. The engine is composed of various materials. For instance, aluminium is utilized in the piston due to its lightweight nature and efficient heat conduction properties. Cast iron is employed for the cylinder face as it is highly durable. This cast iron is inserted and pressed into the aluminium barrel. The spark plug electrode incorporates platinum, which is chemically inert, durable, and capable of withstanding high temperatures. However, it should be noted that platinum holds more value than gold.
- Copper: is used in the electric motor as a coil to generate an electric field and rotate between two magnets so that rotation occurs.
- Iron: magnets for use in the electric motor.
- Ceramics: have been used in the spark plug as an insulator to keep the spark were it is wanted and to prevent heat damage to the electrode.
- Plastics: such as in the engine cover; is made of a thermosetting plastic since it must withstand the high temperatures generated by the motor or by sitting in the sun for long periods. Rubber: is a hydrocarbon and is used as an insulator in the sparkplug lead as it is flexible and can withstand vibration. Throttle: is made of steel or of a hard plastic depending on the model and manufacturer it really make no difference except that steel with last longer and plastic may be more comfortable to hold.
- Handle: Is usually made out of bent aluminium tubing covered in a coating of foam with a vinyl layer on top for good grip and comfort. Foam is basically latex that has been aerated with millions of air bubbles when being set. Polymerising vinyl chloride gas makes vinyl.
- Drive Shaft: Is made of hardened steel. So that it will withstand the twisting forces of the engine trying to rotate it. The basic process of hardening steel by heat treatment consists of heating the metal to a temperature at which austenite is formed, usually about 760 to 870 C (about 1400 to 1600 F) and then cooling, or quenching, it rapidly in water or oil. Such hardening treatments, which form martensite, set up large internal strains in the metal, and these are relieved by tempering, or annealing, which consists of reheating the steel to a lower temperature. Tempering results in a decrease in hardness and strength and an increase in ductility and toughness, this is done to prevent factures.
- Shaft housing: Is made of rolled Aluminium as this is very light and thus has an excellent strength to weight ratio. This is important as users do not want to have to carry around a very heavy piece of equipment nor do they want a material that will fail easily. Hans Christian Oersted, a Danish chemist, first isolated aluminum in 1825. Aluminium is refined from bauxite. Head: The head of the trimmer is used to hold the nylon line. The head consist of several different components depending on the type of head.
- Plastics: a thermo setting plastic that is very resistant to abrasion and is not brittle so that fractures and wear is minimal. Sometimes melamine formaldehyde is used but wide ranges of plastics are used because of the diversity of manufacturers.
- Metals: Springs are used in semi automatic heads to return the bump button’ back to its original position. A steel bolt is also used to attach the head to the drive shaft.
- Line: The cutting line is made of nylon. Nylon is a polyamide, they consist of highly ordered molecules, which give high tensile strength. Polyamides are made by reacting dicarboxylic acid with diamines (carbon molecules with the ion -NH2 on each end). Other types of nylon are synthesized by the condensation of amino acids. Polyamides have mechanical properties such as high abrasion resistance, low coefficients of friction (meaning they are slippery), and tensile strengths comparable to the softer of the aluminum alloys. Therefore, nylons are commonly used for mechanical applications, such as in lawn trimming. All these materials have improved over time due to advancements in manufacturing and design techniques such as CAD and CAM (Computer aided Design/Manufacturing)With the complexities of the internal combustion and electric engine the presence of simple machines can also be found.
- Lever: the way in which the trimmer is held gives the action of a third order lever when holding the trimmer stationary to keep it upright. The action of a third order lever is repeated when moving the head of the trimmer from side to side to cut the grass.
The wheel action powers the rotational motion, created by the engine and transferred through the drive shaft. This motion rotates the nylon line at a high velocity, making it capable of cutting grass. It can be seen as a straightforward process.
Bibliography
- http://www.lsu-eye.lsumc.edu/lawntrimmers.html”;http://www.lsu-eye.lsumc.edu/lawntrimmers.html
- http://www.tanakapowerequipment.com/loadit.html”;http://www.tanakapowerequipment.com/loadit.html
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