page_title: String trimmer
section_title: Design
hierarchical_section_title: String trimmer / Design
caption_attribution_description: English: In a fixed line style string trimmer, one pre-cut line is fed directly in to the appropriate inserts in to the head. After the line is worn down, the user replaces it. There is no "bump feed" system to dispense more line.
context_page_description: A string trimmer, also called a "weed eater", "whipper-snipper", "weed-whacker", "weed-whip", "line trimmer", "brush cutter" or "strimmer", is a garden tool for cutting grass and groundcover which uses a flexible monofilament line instead of a blade. It consists of a rotating spindle from which the string protrudes, at the end of a long shaft with a handle. String trimmers are commonly used for cutting low foliage near obstacles or on steep or irregular terrain.
context_section_description: A bump feed string trimmer works on the principle that a line spun fast enough is held out from its center (the rotating reel) very stiffly by centrifugal force; the faster the hub turns, the stiffer the line. Even round-section nylon line is able to cut grass and slight, woody plants quite well. Some monofilament lines designed for more powerful cutters have an extruded shape, like a star, that helps the line slash the material being cut; the line is thus 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 at which 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 a release mechanism allows some of the line in the reel to replace the spent portion. Newer models "auto-feed", where a small cutter ensures the exposed length does not exceed what can be swung efficiently. Newly extended line operates more efficiently because of its heavier weight and surface effects. The speed of the spinning hub is controlled by a trigger or throttle on the handle.
  A fixed line string trimmer has a trimmer head that takes pre-cut line inserts.  There is no wound spool of line in the trimmer head, the user instead feeds the pre-cut line in to the appropriate slots.  The advantages are that they're easier to feed line in to and troubleshoot than a bump feed system.
  For vertical cutting the whole machine can be tilted or some trimmers allow the head to be adjusted at different angles. Vertical cutting is not recommended near sidewalks or other concrete and pavement edges, because it leaves open grooves that allow water to collect and cause damage.
  String trimmers powered by an internal combustion engine have the engine on the opposite end of the shaft from the cutting head, while electric string trimmers typically have an electric motor in the cutting head, but there are other arrangements such as where the trimmer is connected to heavy machinery and powered by a hydraulic motor.
  The head contains a safety shield on the user side and a rotating hub which may also be called a head or spool. Disadvantages of a gasoline-powered string trimmer include its greater weight and the significant vibration that carries throughout the device, both of which interfere with its maneuverability and contribute to muscle fatigue, as well as the requirement that motor oil be added to its fuel (if it is equipped with a two-stroke engine). Advantages of gasoline-powered trimmers include mobility (because they are not attached to a power outlet) and the higher maximum power.
  Large trimmers, used for cutting roadside grass in large areas, are often heavy enough to require two hands to operate, and some are even fitted with a harness enabling the user's torso to bear some of their weight. These very large trimmers are often referred to as brush cutters. Brush-cutter types are usually made so a metal blade can be attached instead of the "string" (or monofilament). A metal blade enables cutting heavier woody brush.
  Trimmers that have nylon or metal blades usually require straight driveshafts to handle the higher torque required to turn the heavier disk, and because of the shock loads that are passed back from the blade to the drive shaft and its gearbox(es). Smaller line trimmers have curved driveshafts to make holding the cutting-head at ground level much easier and with less strain on the operator.
caption: A fixed line style string trimmer head.
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