Components - Gears

Alec Stevens
Flashcards by Alec Stevens, updated more than 1 year ago
Alec Stevens
Created by Alec Stevens almost 8 years ago
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A-Levels Resistant Materials (Components) Flashcards on Components - Gears, created by Alec Stevens on 05/09/2013.

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Question Answer
Spur The simplest kind of gears - just like a basic depiction of a gear. Have teeth/cogs sticking out which can engage with other teeth on other gears. Speed can be increased or decreased, and the direction of motion can be changed. Often used in simple gearboxes.
Helical A refinement of basic spur gears, these have angled, spiral looking, teeth which cross the side of the gear at a diagonal. The same improvement comes with these as with hypoid gears - the angle means a gradual engagement between teeth which reduces noise and stress on individual teeth. Because of their design, they can be run at 90 degrees to one another (google to understand this). The drawback is that they produce thrust along the axis of the gear which needs to be dealt with. There are double helical gears which look like a 'v' or tyre tread. These do not have the thrust issue.
Idler Gears An idler gear, which can be of any size, is placed between the input and output gears in order to ensure that they have the same direction. The idler gear turns opposite to the input gear, and the output gear turns opposite to the idler gear - so the output gear turns the same way as the input gear.
Worm and Wheel These gears transfer force and motion through 90° Reduction in rotational speed is possible. These can be usefully designed so they 'lock' if used in the opposite direction - e.g. the output cannot turn and drive the input. Seen in food processors, tuning pegs on instruments.
Bevel and Mitre These can have shafts at 90°, like those seen on the hand drills in the tech block. Different gear sizes can change the input/output speed ratio. Sometimes called crown gears. Not used for high speed applications as the stress on the teeth would cause them to break. Often very noisy because of the abrupt engagement of teeth.
Spiral or Hypoid These are a type of bevel gears, but because of the teeth (which look spiral shaped) engage more gradually, they can be used at much higher speeds. The gradual engagement reduces the noise and high impact force associated with crown/bevel and mitre gears.
Compound Trains Compound gear trains involve separate gear trains which mesh together. This often involves more than one gear on the same shaft at least once. Compound gears can significantly increase or decrease the number of possible rotational speeds.
Rack and Pinion Gears can also be used to turn rotary motion into linear motion. Found in cars steering systems, these gears consist of a 'rack' (a long piece of steel onto which gear profile have been cut) and a 'pinion' a gear wheel designed to mesh with the rack and move it from side to side as it rotates.
Simple and Compound Trains Simple gear trains consist simply of two gears whose teeth mesh together. The output direction is opposite to the input direction. The ratio of rotational speed from one to another would depend on the respective gear sizes - e.g. a small input gear would make a larger output gear turn slowly and vice-versa.
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