Gears are indispensable mechanical devices, a crucial part of engines that convey speed, allow speed alteration, and change movement direction. There are different types of gears, each with distinct specifications and requirements ranging from complex to simple.

Most times, complex machines comprise different gears, even though this is not always the case. For instance, simple machines like clocks comprise gears that moderate the speed of the clock’s hand. This guide delves into the discussion on gears and their expected types, basic parameters for gear design, and applications of gears. Continue reading to the end to discover helpful tips on manufacturing quality gear. Let’s get to it! 

What Are Gears?

Gears used in machines
Gears used in machines

Gears are mechanical components of a machine comprising toothed wheels that mesh with each other for torque and speed transmission. These machine elements usually have a cylindrical or cone-shaped body with sets of teeth created all over the body. 

Transmission occurs when two or more gears work in sync. The power transmission causes a change in speed and torque. These toothed wheels are widely used in different industries, ranging from large gears used in marine systems to small clocks and precision measuring instruments.

Parameters of Gears

The parameters of a gear design are technical properties critical to the proper performance and longevity of a mechanical gear. Here are the basic parameters to consider for effective gear design:

Gear Shape

Mechanical gears are generally cylindrical, with teeth well-arranged around their body. Gears are available in elliptical, conical, triangular, and square forms. Non-circular gears are unlike circular gear systems because they lack a constant gear ratio for rotary speed and torque. Non-circular gear types can perform distinct irregular motion requirements, including reverse and changing speed.

Torsion Angle

The torsion angle is the gear’s tooth inclination angle in proportion to the cylinder’s axis. Increasing the gear’s torsion angle results in a more significant thrust direction. Torsion angles lower than 25 degrees are best suited to lessen the thrust for helical gears.

Number of Teeth

Teeth are the pointed or spiked faces outside the gear’s circumference. The number of teeth and other variables like pressure angle and value of modules are crucial to determining the dimensions of a gear. Besides, the number of teeth in a gear design is essential in calculating the gear speed (gear ratio) using the expression:

Input gear’s number of teeth / Number of teeth of the output gear.

Twist Direction

A gear is left-handed when it has teeth on the left side, while right-handed when its teeth are to the right. Before power transmission can occur in a pair of bevel or helical gears, both gears meshed together must have opposing twist directions. For instance, two helical gears with teeth moving in a direction will not mesh. However, screw and worm gears mesh despite being unidirectional.

Gear Axes Configuration

Gear axes configurations have three variations, including parallel, non-parallel (non-intersecting), and intersecting. Mechanical gears with parallel axes configuration maintain a parallel position with shafts rotating in the opposite direction. In contrast, gears with non-parallel axes cut across different planes, and intersecting gears intersect on the same plane. Moreover, parallel and intersecting gear configurations exhibit greater speed and efficiency than non-parallel gears.

Module

The module is a gear tooth’s size measured in millimeters. As a result, the module indicates the size of the gear teeth. It is crucial to consider this parameter when gearing. The module is the value derived through the division of the pitch diameter by the number of teeth in a gear. The expression is represented as:

Module = Pitch diameter / Number of teeth

How Does a Gear Work?

Operation of a gear
Operation of a gear

Mechanical gears follow a series of processes before transferring speed and torque. All you see when you use mechanical gear is two gears engaging their teeth to transfer motion. In this section, we will explore what happens behind the scenes.

To begin with, you should understand that these gears are often connected to components known as shafts. The gear’s rotation occurs along the shaft. Both gears involved in an intermeshing are usually called the driven and the driving gears. While the driving gear initiates the rotation, the driven gear provides the final rotation relative to the impact of the driving gear. The driven gear meets any rotation that the driving gear creates.  

Generally, motion transfer often occurs between the driving and the driven gears. This motion transfer can lead to movement in some gears while changing the direction of rotation in others. However, the gears paired can be engineered to have varying sizes in machines that require gear intermeshing to influence speed and torque.

Various Types of Gears Used in Machines

Various types gears in machines
Various types gears in machines

Gears are of various kinds, each with unique properties. Gears are categorized in mechanics based on variables such as teeth configuration, function, and direction of motion. Here are commonly used types of gears and their uses:

Bevel Gear

A bevel gear has a conical shape with teeth surrounding its body. Bevel gears transfer force between shafts that intersect perpendicularly or at a particular angle at higher velocity ratios. This type of gear is not commonly used across industries because it is costly. However, bevel gears are widely used in mixers and crushers. Meanwhile, bevel gears often come in different types; here are some of them:

  • Straight Bevel Gears: These gears have a simple setup; the teeth are upright, while the pitch of the gear is conical. They operate at incredibly high speeds and can transfer power between perpendicular shafts.
  • Miter Gear: These are bevel gears with a speed ratio of 1. These gears can change the direction of power transmission without altering speed. There are spiral miter and straight miter gears. However, it is vital to employ thrust bearings when using spiral miter gears since they produce thrust force in the axial direction.
  • Spiral Bevel Gear: This subtype of bevel gear has a bend in its tooth line, which conforms to excellent contact points between the gear’s teeth. This results in stronger gear with a seamless transmission. However, spiral bevel gears are costly.

Helical Gear

Helical gears
Helical gears

As the name implies, helical gears have a helix shape like helical springs. These gears are often used in manufacturing industries and machines. The teeth on a helical gear are set at an angle or inclined to the shaft. Moreover, helical gears make less noise and operate smoothly due to their better teeth meshing. Helical gears can handle more load since they use more teeth to transfer motion and speed.

Besides, helical gears transfer load in the axial direction, creating a thrust force and requiring bearings to help handle the thrust load. Helical gears are a perfect fit for transmission operations that demand high speed. Moreover, helical gears have right-hand and left-hand twists that need opposite-hand gears to achieve a meshing pair. Helical gears come in different types, including:

  • Single or Double Helical Gear: Helical gears can be subcategorized into two, provided the gears have teeth on one or both helixes. The gears are single helical if it has teeth on only one helix. It doesn’t matter whether the teeth are on the left or right hand; so far, one side contains the teeth. Meanwhile, a gear is called double helical if its teeth are on both hands with a gap between both faces. Since the teeth overlap, the double helical gears transfer motion more efficiently and smoothly.
  • Screw Gear: Screw gears often come in pair of helical gears working at a twist angle of 45º. They have a design similar to most fasteners and usually operate on non-intersecting and non-parallel shafts. They have a low load carriage capacity due to the single tooth contact. Hence, these gears are not suitable for transferring immense power.

Spur Gear

Spur gears
Spur gears

Spur gears are machines’ most commonly used gear type due to their simple design. They transfer power in the same plane when both shafts (the driving and the driving) maintain a parallel position. The spur gears’ teeth are parallel to the shaft axis to attain larger gear reductions. Hence, it transmits the power between parallel shafts when it engages/connects with another spur gear. These gears efficiently transmit high power and motion due to their parallel design. The smaller meshing pair is called the pinion, while the larger meshing pair is called the gear.

Spur gears differ from other gear types because they do not transfer load in the axial direction. Spur gears are ideal for low-speed applications, gear pumps and motors, washing machines, speed reducers, windup alarm clocks, and conveyor systems. However, spur gears make a loud noise and cause vibration on each impact.

 Worm Gear

Worm gears
Worm gears

Worm gears comprise two primary components: the worm wheel and the worm (the shaft and the mating gear). Here, the shaft has a screw cut, similar to a drill, and does not intersect. Transmission often occurs quietly and smoothly since less friction occurs between the hard and soft worm wheels. However, worm gears are not ideal for high-speed or extreme operations since they are not the most efficient gear type. Worm gears are commonly used in agricultural machinery.

Rack and Pinion Gear

Rack and pinion gears
Rack and pinion gears

The rack and pinion gear come in pairs comprising two circular gears: the pinion engages a liner gear (a rack). These pairs convert rotary motion into linear. Rack and pinion gears are primarily used in automobile steering systems. These gear systems are available in either helical or straight gears.

Internal Gear

This gear type has teeth on the inside cones. The internal gear usually meshes with an external gear to transfer motion as both gears rotate in the same direction. However, various problems occur when using this gear type because of the variation of the external and internal gear’s number of teeth. Moreover, internal gear is primarily used in shaft couplings.

Applications of Gears

Gears used in automotive applications
Gears used in automotive applications

Gears are essential components of mechanical systems responsible for efficient power and torque transmission between two or more rotating shafts. Typical applications of gears include:

  • Automotive Industry: Gears like rack and pinion, helical, and spur gears are widely used in different parts of automobiles, such as differentials, transmission, and steering systems. These gears help to control speed, change direction, and transmit power between components.
  • Aerospace Industry: Various gears, such as spur and helical gears, are widely used in aircraft engine and landing gear systems. They are also used as control mechanisms for efficient power transmission and precise movement.
  • Industrial Machinery: Gears such as spur, worm, and bevel gears are vital elements that transfer motion and power between rotating shafts in various industrial machinery like conveyor systems, textile machines, packaging equipment, and printing presses. 
  • Marine Applications: Toothed wheels are vital components of marine propulsion systems such as outboard motors, ship propulsion systems, and outboard motors. They help convert engine power into thrust force.
  • Construction and Mining Equipment: Heavy machinery such as cranes, excavators, loaders, and bulldozers rely on mechanical gears to perform different functions, such as operating hydraulic systems, driving tracks, and lifting loads. 

Design Tips for Gears Manufacturing

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image

Since there are different types of gears for different applications, different factors contribute to effective gear manufacturing and choosing the one that best meets your intended application’s demands. We’ll discuss helpful design tips for successful gear manufacturing:

Design Standards

Gears often have varying specifications and no universal industry standard because there is no one-size-fits-all standard in gear manufacturing. Manufacturers fabricate gears according to different specifications, standards, and engineering tolerances. Besides, gear designs either match the design specification of the machine or system or the manufacturer’s standard.

However, various countries have established standards that work for their industries. For example, countries like Germany, Japan, and the United States have associations. The American Gear Manufacturers Association creates standards that serve the industries in the United States.

Budget/Costs

Manufacturing companies desire the most efficient and functional machines to handle their operations. In most cases, you may have to customize gears with engineering drawings or recommendations to meet their various needs. However, cost is one of the crucial factors to consider when designing custom gears. The materials, production, preferred surface finishes, precision, and lubrication requirements often influence price.

You must consider your budget even though using a gear that meets the necessary specifications is vital. However, in situations where regular gears meet the required standard, it would be best to choose them instead of going for customized gears that will incur additional costs.

Operational and Environmental Conditions

The service conditions of gears are factors crucial to their longevity and functionality. Operating conditions often include stress and friction, which the teeth are exposed to. Meanwhile, environmental conditions include temperature, humidity, and cleanliness. These service conditions influence gear type and design factors, including construction, lubricant, lubrication method, and surface treatment options.

Transmission Requirements

Generally, mechanical gears transfer motion and torque from one component to another in a machine. However, the direction of motion and increase in speed or torque output depends on the design and construction of the gear. Therefore, the specification and application requirements, including directional changes or increase in speed or torque, are essential considerations when designing gears. These factors may affect the choice of gear, design and configuration.

Dimensional/Space Restrictions

Dimensional restrictions are constraints to the space the gears occupy. For example, gears are usually positioned at the center between two shafts. However, they are sometimes positioned further away from the center to better fit within the gear system. Consequently, the teeth profile and thickness must be altered in such situations. Besides, using a particular gear and design that suits the space best is an ideal alternative to effectively managing dimensional limitations.

Conclusion

Gears are core components of different motors and machines. They are the building blocks of speed and torque because they increase the torque output and improve the direction of rotation between different machine components. Depending on the gear types, gears mesh together with carefully engineered teeth to produce varying motion and torque. This guide has extensively discussed various types of gear and their applications to make informed decisions about the kind of gear you need for your project.

Zintilon is the ideal expert to contact whenever you need to machine gears or choose the right ones for your machines. We offer extensive machining services for gear-cutting operations. Our experienced and highly skilled teams can work with different materials to ensure your custom-made gear meets the requirements of your intended applications. Upload your CAD files now; our online quotation platform delivers instant and reliable quotes.

FAQ

What Are the Common Materials Used for Gear Manufacturing?

Manufacturers use different metallic and non-metallic materials to machine gears for various applications. Cast iron, steel, fiber, plastic, nylon, etc., are typical materials used to produce mechanical gears. However, the needs of the gears often determine the ideal material choice.

Are Gears Different from Sprockets?

While gears intermesh perfectly to transfer motion and torque, sprockets don’t intermesh perfectly. Sprockets only transfer torque along the parallel axis and over longer distances. On the other hand, gears transfer short-term torque along any orientation.

What Are Some Common Maintenance Practices for Optimal Gear Performance?

Standard maintenance practices for optimal gear performance include routine inspection for wear, constant lubrication, replacing worn or damaged components, and ensuring alignment and meshing of gears.

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