The meaning of "worm gear" is somewhat imprecise, and may refer to the worm, the worm gear or the worm drive. In this case, the term "worm gear" refers to the gear unit, also called the worm drive, which is a type of industrial gear that cannot only transfer torque, but can also, unlike other industrial gears, transfer motion, under both unusual circumstances and odd angles. that is composed of a spur gear and a worm. Worm gears, or worm drives, are composed of a spur gear and a worm, which is a threaded metal rod that looks much like a screw. Worms are different from screws in that they are machined only in the middle of the rod; their threads appear neither at its beginning nor at its end. Screws, on the other hand, have threads that extend all the way to the bottom. To make a worm gear, the spur is placed in contact with the worm at its threaded middle section. So, as the spur turns, the worm rotates, and as the worm rotates, the spur turns.
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History of Worm Gears
When worm gears were first being made during the era of shipbuilding, they were made of wood and frequently connected to hand cranks. Today, however, worm gears are most commonly made of steel, iron or bronze, though other material options are available, such as, for less demanding applications, nylon, plastics and other synthetic materials.
Design of Worm Gears
In addition to their defining characteristic of transferring motion under multiple circumstances, worm gears are also known for their ability to transfer motion between axes. To understand how, one must first know that if the axis of a gear is circular when viewed at its face, it extends from the middle of the gear’s circle, out into the z axis. One must also note that, with a worm, the axis goes through each end. So, when these two are combined to make a worm gear, the axis of the circular gear and the axis of the worm intersect. When they intersect, the worm gear’s trademark transfer of torque between two axes occurs. On top of all this, worm gears stand out for the level of control they allow their users over torque transfers like these; operators can either slow down or speed up the transfer of torque, per their application needs. Worm drives also assist in the immediate resolution or multiplication of torque and the enhancement of the accuracy of positioning systems.
Worm gears are manufactured first through the gashing of rough teeth, then the more precise hobbing. During this time, worm and spur tooth quantities, face widths and lengths and pitch diameters are all established. These quantities, lengths and widths all contribute to a worm gear’s performance; they are generally designed in accordance with the power transmission and noise and heat requirements of the application they will serve.
Types of Worm Gears
Though worm gears are commonly described as using spur gears, there are actually three different general gear configurations that may be used together with a worm to create a worm gear. They are: non-throated, single-throated and double-throated gears. Non-throated worm gears are made with gears that do not have a "throat," or groove, machined around the circumference of the worm or spur gear. Single-throated worm gears are throated around the spur gear only. In the case of double-throated gears, both the spur gear and the worm drive are throated. Note that the greater the throating, the higher loading a gear can support. In addition, some worm gears are made with an enveloping, or hourglass, worm, which is a worm that has one or more teeth and grows in diameter as it moves from its middle portion toward its ends.
Applications of Worm Gears
Depending on the application that they serve, worm gears have different connections. For example, in the case of a string bass guitar, which uses multiple worm gears to tune it, gears are connected to both strong and rods. To tune, the guitar tuning pins are connected to worms, which are connected to gears. In turn, these gears are connected to rods, which are each connected to a string. The connection between the strings, the tuning pins and the worm gears in between them stops the string from becoming too tense, thereby providing the guitar with the mechanism it needs for it to stay in tune. Worm gears provide tuning similarly to other instruments, such as mandolins, banjos and bouzoukis. (As a tuning device, they are known as machine heads.) Worm gears can also connect with clamp bands, for applications with hose clamps or jubilee clamps, by engaging their threads with the clamp band slots. Additional connections with which they commonly engage include those related to the operation of: presses, battery-operated motors, toys, rolling mills, rudders, elevators and escalators, rotary lifts, very heavy trucks and mining industry machines.