Worm Gear

Information about Worm Gear

“Worm gear” redirects here. For the computing term "WORM drive", see Write Once Read Many.

Worm and worm gear

A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm gear (which is similar in appearance to a spur gear, and is also called a worm wheel). The terminology is often confused by imprecise use of the term worm gear to refer to the worm, the worm gear, or the worm drive as a unit.

Like other gear arrangements, a worm drive can reduce rotational speed or allow higher torque to be transmitted. The image shows a section of a gear box with a bronze worm gear being driven by a worm. A worm is an example of a screw, one of the six simple machines.

Explanation

A gearbox designed using a worm and worm-wheel will be considerably smaller than one made from plain spur gears and has its drive axes at 90Â° to each other. With a single start worm, for each 360Â° turn of the worm, the worm-gear advances only one tooth of the gear. Therefore, regardless of the worm's size (sensible engineering limits notwithstanding), the gear ratio is the "size of the worm gear - to - 1". Given a single start worm, a 20 tooth worm gear will reduce the speed by the ratio of 20:1. With spur gears, a gear of 12 teeth (the smallest size permissible, if designed to good engineering practices) would have to be matched with a 240 tooth gear to achieve the same ratio of 20:1. Therefore, if the diametrical pitch (DP) of each gear was the same, then, in terms of the physical size of the 240 tooth gear to that of the 20 tooth gear, the worm arrangement is considerably smaller in volume.

A double bass features worm gears as tuning mechanisms

Direction of transmission

Unlike ordinary gear trains, the direction of transmission (input shaft vs output shaft) is not reversible, due to the greater friction involved between the worm and worm-wheel, when a single start (one spiral) worm is used. This can be an advantage when it is desired to eliminate any possibility of the output driving the input. If a multistart worm (multiple spirals) then the ratio reduces accordingly and the braking effect of a worm and worm-gear may need to be discounted as the gear may be able to drive the worm.

Worm gear configurations in which the gear can not drive the worm are said to be self-locking. Whether a worm and gear will be self-locking depends on the lead angle, the pressure angle, and the coefficient of friction; however, it is approximately correct to say that a worm and gear will be self-locking if the tangent of the lead angle is less than the coefficient of friction.

An enveloping (hourglass) worm has one or more teeth and increases in diameter from its middle portion toward both ends. ¹

Double-enveloping wormgearing comprises enveloping worms mated with fully enveloping wormgears. It is also known as globoidal wormgearing. ²

Applications

Worm drives are a compact, efficient [efficient only in terms of volume; heat friction issues cause vast inefficiencies ranging up to 50%] means of substantially decreasing speed and increasing torque. Small electric motors are generally high-speed and low-torque; the addition of a worm drive increases the range of applications that it may be suitable for, especially when the worm drive's compactness is considered.

Worm drives are used in presses, in rolling mills, in conveying engineering, in mining industry machines, and on rudders. In addition, milling heads and rotary tables are positioned using high-precision duplex worm drives with adjustable backlash.

In the era of sailing ships, the introduction of a worm drive to control the rudder was a significant advance. Prior to its introduction, a rope drum drive was used to control the rudder, and rough seas could cause substantial force to be applied to the rudder, often requiring several men to steer the vessel, with some drives having two large-diameter wheels to allow up to four crewmen to operate the rudder.

A worm drive controlling a gate. The position of the gate will not change after being set

Worm drives have been used in a few automotive differentials. The worm gear carries the differential gearing. This protects the vehicle against rollback. This has largely fallen from favour due to the higher-than-necessary reduction ratios. The exception to this is the Torsen differential, which uses worms and planetary worm gears in place of the bevel gearing of conventional open differentials. Torsen differentials are most prominently featured in the HMMWV and some commercial Hummer vehicles, and as a center differential in some all wheel drive systems, such as the Audi Quattro. Very heavy trucks, such as those used to carry aggregates, often use a worm gear differential for strength. The worm drive is not as efficient as a hypoid gear, and such trucks invariably have a very large differential housing, with a correspondingly large volume of gear oil, to absorb and dissipate the heat created.

Worm drives are used as the tuning mechanism for many musical instruments, including guitars, double-basses, mandolins and bouzoukis, although not banjos, which use planetary gears or friction pegs. A worm drive tuning device is called a machine head.

Plastic worm drives are often used on small battery-operated electric motors, to provide an output with a lower angular velocity (fewer revolutions per minute) than that of the motor, which operates best at a fairly high speed. This motor-worm-gear drive system is often used in toys and other small electrical devices.

A worm drive is used on jubilee-type hose clamps or jubilee clamps; the tightening screw has a worm thread which engages with the slots on the clamp band.

• • [ e] Gears
Gear systems	Spur gear systems • Worm gear • Rack and pinion • Epicyclic (planetary) gearing • Harmonic drive • Cycloidal drive • Non-circular gear
Gear shapes	Straight cut gear • Bevel gear • Helical gear • Hypoid gear
Geartooth profiles	Involute • Cycloid
Gear mechanics	Transmission • Differential • Gear coupling • Gear train • Bicycle gearing • Continuously variable transmission
See also	Ball screw • Leadscrew • Jackscrew • Belt drive • Chain drive • Gear manufacturing

Notes

1. AGMA Standards, "Gear Nomenclature, Definition of Terms with Symbols", p. 3.
2. AGMA Standards, "Gear Nomenclature, Definition of Terms with Symbols", p. 4.

External links

Write Once, Read Many (alternatively Write One, Read Multiple or Write Once, Read Mostly or WORM) refers to a kind of computer storage media that can be written to once, but read from multiple times.
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A gear is a component within a transmission device that transmits rotational force to another gear or device. A gear is different from a pulley in that a gear is a round wheel which has linkages ("teeth" or "cogs") that mesh with other gear teeth, allowing force to be fully
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screw thread is a helical or tapered structure used to convert between rotational and linear movement or force.

Screw threads have several applications:

Fasteners such as wood screws, machine screws, nuts and bolts.

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Revolutions per minute (abbreviated rpm, RPM, r/min, or rÂ·min⁻¹) is a unit of frequency: the number of full rotations completed in one minute around a fixed axis.
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torque (or often called a moment) can informally be thought of as "rotational force" or "angular force" which causes a change in rotational motion. This force is defined by linear force multiplied by a radius.

The SI unit for torque is the newton meter (N m). In U.S.
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A screw is one of the six simple machines. A simple screw is a helical inclined plane. A screw can convert a rotational force (torque) to a linear force and vice versa. The ratio of threading determines the mechanical advantage of the machine.
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simple machine is any device that only requires the application of a single force to work. Work is done when a force is applied and results in movement over a set distance. The work done is the product of the force and the distance.
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range of input/output ratios in addition to its infinite number of possible ratios; this qualification for the IVT implies that its range of ratios includes a zero output/input ratio that can be continuously approached from a defined 'higher' ratio.
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electric motor converts electrical energy into mechanical energy. The reverse process, that of converting mechanical energy into electrical energy, is accomplished by a generator or dynamo.
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Introduction

A press, or a machine press is a tool used to work metal (typically steel) by changing its shape and internal structure.

A forge press reforms the workpiece into a three dimensional object—not only changing its visible shape but also the
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A rolling mill is a machine or factory for shaping metal by passing it between a pair of rolls.

Rolling mills are often incorporated into integrated steelworks, but also exist as separate plants and can be used for other metals, and other materials.
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belt conveyor consists of two pulleys, with a continuous loop of material - the conveyor belt - that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward.
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rudder is a device used to steer ships, boats, submarines, aircraft, hovercraft or other conveyances that move through air or water. Rudders operate by re-directing the flow of air or water past the hull or fuselage, thus imparting a turning or yawing motion to the craft.
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A milling machine is a machine tool used for the complex shaping of metal and other solid materials. Its basic form is that of a rotating cutter or endmill which rotates about the spindle axis (similar to a drill), and a movable table to which the workpiece is affixed.
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A rotary table is a precision work positioning device used in metalworking. It enables the operator to drill or cut work at exact intervals around a fixed (usually horizontal or vertical) axis.
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duplex worms and wheels are manufactured with slightly different modules and/or diameter quotients. As a result of this, different lead angles on both tooth profiles are obtained.
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backlash is a popular extreme negative reaction against something that has gained popularity, prominence, or influence. While sometimes a backlash represents a categorical rejection of the idea, aesthetic, product, or fad in question, it often is more reflective of a collective
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differential is a device, usually consisting of gears, that allows each of the driving wheels to rotate at different speeds, while supplying equal torque to each of them.

Purpose

A vehicle's wheels rotate at different speeds, especially when turning corners.
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Torsen traction, an automotive part adding differential, was invented by American Vernon Gleasman and manufactured by the Gleason Corporation. Torsen is a contraction of TORque SENsing.

There are currently three types of Torsen differentials.
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Hummer

Division of GM
Founded 1995
Headquarters Detroit, Michigan, United States

Industry Automobile
Products (H1) Sport utility vehicles (H2, H3, H4), Large pickup truck (H1)
Parent General Motors
Slogan Like nothing else.
Website www.hummer.
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Four-wheel drive, 4WD, or 4x4 ("four by four") is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive power from the engine simultaneously.
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Audi AG

Public (Xetra: NSU )
Founded 1910
Founder August Horch
Headquarters Ingolstadt, Germany

Key people Rupert Stadler, chairman
Industry Automotive
Products Luxury Automobiles, Engines
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quattro (four in Italian) is a registered trademark of Audi AG for all wheel drive (AWD) systems used on Audi brand automobiles. quattro was first introduced in 1980 on the permanent-AWD Audi Quattro and has since been applied to all AWD models that Audi sells.
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Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, and recycled concrete.
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hypoid is the name given to a type of helical (spiral) gear. The main application of this is in a motor vehicle differential, where the direction of the drive carried by the propeller shaft (drive shaft) has to be turned through 90 degrees in order to power the driven wheels.
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Gear oil is a motor oil made specifically for transmissions, transfer cases, and differentials in automobiles, trucks, and other machinery. It is of a higher viscosity to better protect the gears and usually is associated with a strong sulfur smell.
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The guitar is a musical instrument with ancient roots that is used in a wide variety of musical styles. It typically has six strings, but four, seven, eight, ten, and twelve string guitars also exist.
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double bass (also known as the contrabass, string bass, upright bass, bull fiddle, or simply bass) is the largest and lowest pitched bowed string instrument used in the modern symphony orchestra.
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mandolin is a musical instrument which is plucked, strummed or a combination of both. It is descended from the mandora. The most common design as originated in Naples, Italy has eight metal strings in four pairs (courses) that are plucked with a plectrum.
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baglama (Greek μπαγλαμάς) is very different from the Turkish baglama.

It is a half-sized version of the bouzouki. The Greek baglama has a small body, with a bowl, that is either made from staves or carved from solid wood.
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