Weed eaters have become a common tool for lawn care and weed control alongside the lawn mower. Most weed eater users understand the basic function of a trimmer but do not fully grasp the way a weed eater works. There are various parts within the trimmer that interact to allow the user to cut the weeds. Care should be used when operating a weed trimmer because the line cutting the weeds moves at speeds up to 4,000 revolutions per minute.
Weed eaters use a monofilament line to cut grass and light brush depending on the model. When the head holding the line is rotating at a fast enough speed the line stiffens because of centrifugal force. The stiffer the line becomes, the harder it is. This hardness acts similar to a knife when struck against grass or soft wood. As the line strikes the grass it wears down because of the force between the two objects. In time the trimmer line needs replacement because it has worn itself down in length to where it cannot maintain the stiffness.
Weed eaters use one of two types of engine: gas and electric. Gas-powered trimmers use mainly a two-cycle engine although various manufacturers are building more efficient four-stroke engines. Gas weed eaters use a gas/oil mix to lubricate the engine thereby allowing its parts to run properly. These engines use a simple combustion cycle using a simple starting system, carburetor and exhaust. The starting system is most often a pull cord that causes the spark at the spark plug; this spark fires the fuel mixture to ignite and start the engine.
Electric-powered engines use no fuel but are operated either by cord or battery. These trimmers operate similar to power tools in that a constant electric supply operates the motor. Corded trimmers are more capable of constant operation but are limited in the range they can be used because of being tethered to an electric outlet; battery operated motors have a farther range but are limited in the amount of time before recharging is required. Battery-run weed eaters usually have battery packs that can be interchanged to resupply power to the motor.
The Power Supply
The power supply is controlled by the trigger. The trigger allows the trimmer motor to run at various speeds depending on how tight the trigger is held; higher speeds are reached the more the trigger is depressed. The trigger is usually found near the top or middle of the shaft. An on/off switch is found at the motor. This switch allows the motor to stop without needing to disconnect anything. On gas-powered units, the choke or throttle is used to regulate the air and fuel flow through the carburetor and motor. On electric trimmers the cord or battery pack is usually attached at the top where the handle grip is located.
All weed eaters use gears. The motor converts power to work via the gear system. A clutch connects to the drum; the drum connects to the shaft that spins the trimmer head. The shaft is found in the pole of the trimmer and is the main moving part.
The Trimmer Head
The trimmer head is the part of the weed eater that holds the monofilament line that cuts the grass. When the shaft is moving it turns the trimmer head at a high rate of speed. This is what allows the centrifugal force that holds the line straight. Some trimmer heads come equipped with line feeders that automatically advance the line once the button is pushed; this button is found either on the handle or at the tip of the trimmer head.