Understanding the Role of Small Gears in Modern Machinery

As equipment becomes increasingly miniaturized, more and more industries are starting to use small gears. For example, they are used in products such as toys, household appliances, power tools, and servo drives. Generally, small gears have around 20 teeth and diameters as small as 1.27mm (0.05 inches). They are typically manufactured to standards such as MIL-I-45208A, MIL-STD-45662A, and ISO 9001:2000.
This article aims to provide an understanding of the types of small gears, how they are produced and processed, and the factors that should be considered when designing small gears.

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What are Small Gears?

Small gears are compact in size and can be installed in smaller equipment spaces for transmitting motion and power between different components. They can be made from various materials and are generally divided into two types: metal and plastic. Metal gears can be processed in several ways, including hobbing, milling, powder metallurgy, and metal injection. Plastic gears are typically produced through plastic injection molding.

Types of Small Gears

Spur Gears

Straight gears installed parallel to each other, with simple structures and high precision, but usually noisy during transmission.

Helical Gears

Gears with teeth at an angle, allowing for simultaneous contact with multiple gears, resulting in smooth operation and low noise.

Bevel Gears

Cone-shaped gears, usually at 90 degrees, with straight, spiral, or crown teeth, used to change the direction of power rotation.

Spiral Bevel Gears

Gears with a twisted angle of 45 degrees, generally used in light-load transmission systems.

Worm Gears

Composed of a spiral gear and a circular gear, worm and worm gear transmission is smooth and quiet, suitable for high-impact load applications.

Rack and Pinion Gears

Comprising cylindrical gears and gear racks, used in parallel shaft configurations. Rack and pinion gears convert rotational motion into linear motion but generate significant friction and stress.

Hypoid Gears

Similar to bevel gears but with a larger spiral angle, used in applications where the drive and driven shafts are offset, allowing for greater reduction in a smaller space.

Internal Gears

Gears with teeth cut on the inside of a cylinder, used in planetary gear transmissions and shaft connections.

Miter Gears

A type of bevel gear with a speed ratio of 1, used to change the direction of power transmission without changing speed.

Spiral Bevel Gears

Cone-shaped gears with curved teeth, offering higher efficiency and strength than straight bevel gears, and reducing vibration and noise.

Gear Racks

Gear racks have teeth of uniform size and spacing along a plane or straight rod, converting rotational motion into linear motion.

Double Helical Gears

Also known as herringbone gears, these gears have two parallel helical faces with opposite spiral angles, eliminating thrust loads and providing smoother operation.

Materials Used in Small Gears

Gears are generally made of metal, plastic, and composite materials. 


The most common material for gears, with a high strength-to-weight ratio, high wear resistance, and the ability to improve physical properties through heat treatment.


Offers good machinability and corrosion resistance, suitable for gears in corrosive environments.


Known for its strength and corrosion resistance. Varieties such as phosphor bronze are especially wear-resistant.

Cast Iron

Has good wear resistance and strength, commonly used for large gears but also applicable to small gears.

Ductile Iron

Combines the strength of steel with the machinability of cast iron, used for gears requiring toughness.


Lightweight and corrosion-resistant, suitable for applications where weight is a concern.

Powder Metallurgy

Used for sintered gears, offering good machinability and material properties, customizable through the sintering process.

Nickel Alloy Steel

Selected for its strength and hardness, suitable for high-strength applications.

Copper Alloys

Including brass, phosphor bronze, and aluminum bronze, each alloy has unique properties such as antimicrobial (brass) and wear resistance (phosphor bronze).


Polyoxymethylene (POM)

Known for its high strength, hardness, and good frictional properties, making it suitable for gears.


Similar to polyacetal, with strength and durability for gear applications.

Nylon (Polyamide Resin)

Has good wear resistance and strength, commonly used for plastic gears.

Non-Metal (Composite Materials):

Micarta, Textolite, Formica, Dilecto, Spauldite, Phenolite, Fibroc, Fabroil, Synthane, Celoron**: These materials consist of layers of canvas or other materials impregnated with plastic, forming a dense hard block, suitable for gears operating at high speeds and quietly.

Factors Influencing Material Choice

When choosing materials for gears, considerations typically include the operating environment, strength requirements, wear resistance, and cost. Key factors are strength and wear resistance.

Strength Selection

Strength is the primary factor in material selection. Gears must withstand forces without failure, so materials should have high tensile strength, yield strength, and fatigue resistance. High-strength materials are generally used in environments with high torque and heavy loads.

Wear Resistance

Since gear operation involves contact, materials should have high wear resistance to maintain efficiency. Hard and wear-resistant materials are usually chosen.

Small Gear Manufacturing Processes

Gear manufacturing techniques are varied, each suitable for different types of gears, materials, and precision requirements. The choice of gear manufacturing technology depends on specific requirements such as material, size, precision, and quantity.


Generally used for small modulus gears, typically for helical and spur gears, sprockets, and splines.

CNC Machining

Can be used to machine gears with high precision, including spur gears, turbines, helical gears, and sprockets. The process is complex, involving blank preparation, precision machining, and final gear grinding.


Generally used for internal gear machining.

Powder Metallurgy

Involves injecting metal powder into a mold and then sintering it to complete the process. This method is commonly used for producing small modulus gears.

Metal Injection

Metal is injected into a mold, followed by debinding and sintering to produce gears. This process can be used to produce small modulus gears in batches at a lower cost.

Heat Treatment of Small Gears

Heat treatment processes significantly impact the performance, durability, and application range of small gears. Based on the provided information, the main heat treatment methods for small gears include:

Carburizing and Quenching

Suitable for low-carbon steel or low-carbon alloy steel, such as 20, 20Cr, 20CrMnTi. After carburizing and quenching, the tooth surface hardness can reach 56~62HRC, while the tooth core remains highly tough. This treatment gives gears high bending strength and contact strength, as well as good wear resistance, commonly used for important gear transmissions under impact loads.


After nitriding, no further heat treatment is required, and the tooth surface hardness can reach 700~900HV. Gears treated with nitriding have high hardness, low process temperature, and minimal deformation, making them suitable for internal gears and gears that are difficult to grind.


Generally used for medium carbon steel and medium carbon alloy steel, such as 45, 40Cr, 35SiMn. After tempering, the tooth surface hardness is usually 220~280HBS. Due to the lower hardness, gear forgings can be precision machined after heat treatment.


Normalizing can eliminate internal stress, refine grains, and improve mechanical properties and machinability. Gear forgings that do not require high mechanical strength can be normalized, and large-diameter gear forgings can be treated with cast steel normalizing.


The carbonitriding process is shorter in time and has the advantages of nitriding. It can replace carburizing and quenching, and the materials used are the same as those for carburizing and quenching.

Surface Hardening

Commonly used for medium carbon steel and medium carbon alloy steel, such as 45, 40Cr steel. After surface hardening, the tooth surface hardness is generally 40~55HRC. The characteristics include high resistance to fatigue pitting, high anti-adhesion ability, and good wear resistance.

Isothermal Quenching

Isothermal quenching involves fully heating the blank to an appropriate temperature above the Ac3 line to obtain uniform austenite, then rapidly cooling the blank to the “nose” temperature of the austenite isothermal transformation diagram in a low-temperature furnace for isothermal transformation, and finally air cooling to room temperature.

These heat treatment methods each have their characteristics and applicable ranges. Choosing the appropriate heat treatment process is crucial for improving the performance of small gears and extending their service life.

Challenges in Producing High-Precision Small Gears

Producing high-precision small gears faces various challenges, including the demand for precise geometric properties, tight tolerances, material selection, cost constraints, and more.

Complex Geometries

The shapes of small gears are becoming increasingly complex, with the addition of applications such as internal and external meshing gears.

Tighter Tolerances

Increasing demands for strict dimensions require higher precision in production.

Material Selection and Post-processing

Material selection must consider both the difficulty of machining and the precision achievable, as well as durability and cost constraints.

Manufacturing Technologies

Traditional methods are often insufficient for high-precision small gears. Powder metallurgy is increasingly used for small gears with high strength, while metal injection molding is used for batch production to meet customer requirements.

Dimensional Inspection

Traditional inspection methods struggle to detect precision, with common tools now including gear measurement centers, coordinate measuring machines, optical projectors, and gear profile testers.


Producing high-precision gears is costly, so choosing suitable processes and equipment is essential for managing costs.

Wear and Durability

Small gears must undergo tests for service life and wear resistance, with material selection and appropriate post-processing tailored to different operating conditions.

Applications of Small Gears

  • Biomedical Industry: Used in medical devices such as transfer pumps and small cutting equipment.
  • Commercial Products: Found in household appliances, power tools, and small mechanical devices.
  • Automatic Control Systems and Servo Mechanisms: Extensively used in automatic controllers and servo mechanism motors.
  • Instrument Drives: Small gears play a crucial role in the precision and reliability of instrument drives.
  • Watch Applications: High-precision small gears are frequently used in watches.
  • Industrial Robots and Toys: Small gears are used in the mechanical devices of industrial robots and electric toys.
  • Automotive Gearboxes: Hypoid gears, a type of small gear, are used in automotive gearboxes due to their ability to transmit power between non-intersecting shafts.
  • Machine Tool Drives: Gears are used in the speed and feed gearboxes of machine tools and motion units.
  • Textile and Jute Machinery: Small gears are used in the speed transmission devices of textile and jute machinery.
  • Heavy Gearboxes: In industries such as cement and sugar, as well as in cranes and conveyors, small gears are widely used for their ability to withstand large and heavy loads.
  • Gear Rack Systems: In gear rack transmission systems, small gears are crucial for reducing the required starting torque and reduction ratio, as well as improving linear stiffness and resonance frequency.

Design Considerations

When designing small gears, several key factors must be considered to ensure successful production and optimal performance. These include pressure angle, modulus, material selection, manufacturing tolerances, operating conditions, wear distribution, environmental conditions, and specific application requirements. Effectively addressing these factors is key to achieving high-performance and reliable gear operation.

Pressure Angle and Modulus

Pressure angle and modulus are fundamental parameters in gear design, determining the shape and size of gear teeth. Especially for small gears, smaller moduli are typically used to fit compact applications.

Material Selection

The choice of material is crucial for gear performance and durability. Factors such as tensile strength, durability, friction, and manufacturability must be considered. The material should have sufficient strength to resist static and dynamic loads without failing and should be ductile enough to be manufactured into the desired gear shape with the required precision.

Manufacturing Tolerances and Operating Conditions

Small gears are more sensitive to manufacturing tolerances and operating conditions compared to larger gears. This sensitivity is due to their smaller tooth sizes, resulting in much larger relative tolerances. Operational conditions such as offset in gearboxes and shafts under load, temperature changes, and humidity can severely affect gear performance. Designers must consider these factors to ensure reliable gear operation under expected conditions.

Gear Tooth Count and Wear Distribution

To distribute wear, dirt, and oil evenly across all gear teeth and avoid uneven wear, gears generally have prime tooth counts or coprime tooth counts. This consideration is particularly important for small gears, as the same teeth squeezing each other can lead to accelerated wear.

Environmental Conditions

The operating environment of the gear, including factors such as impact, vibration, and contact with corrosive substances, must be considered. The material and design of the gear may need to be adjusted to withstand these conditions without degradation.

Custom Gears vs. Standard Gears

Deciding whether to use standard gears or design custom gears is another important consideration. Custom gears can be tailor-made to meet specific requirements, such as installation or volume requirements, but the development cost may be higher and take longer. This decision will depend on the unique needs of the application and whether suitable standard gears are available.

Size, Performance, and Installation Requirements

Correct sizing is key to avoiding underestimating or overestimating the required gear size, which can lead to performance issues. Understanding horsepower, input speed, target output speed or torque, and the way the gear will be mounted is crucial for selecting or designing the appropriate

Maintenance and Wear

Common wear situations for small gears include the following. Understanding and regularly inspecting and maintaining them, along with proper lubrication and calibration, can help mitigate these failure modes. We aim to extend the lifespan of small gears through better design and production.

Abrasive Wear

Characterized by surface damage caused by abrasive particles carried in the lubricant or embedded in the tooth surface. It appears as scratches or grooves on the teeth.

Scuffing or Scratching

Manifests as large areas of grooves on the teeth, leading to adhesive wear where metal is torn from one surface and transferred to another.

Pitting or Spalling

Pits or holes formed on the gear tooth surface due to overload. Severe pitting is known as spalling.


Very mild wear can result in a polished appearance of the teeth, giving them a satin or matte finish.

Corrosive Wear

Degradation of the teeth due to chemical or electrochemical action, typically producing uniform, fine pitting.

Overload Wear

Caused by sliding pressure leading to metal flaking off, creating indentations along the tooth and resulting in excessive backlash.

Causes of Failure

Bending Fatigue

Slow, progressive failure caused by repeated loading, leading to the formation, expansion, and sudden breakage of cracks.

Contact Fatigue (Pitting or Spalling)

Surface cracks and metal fragments detaching from the tooth contact area due to repeated stress. Common types include macro-pitting and micro-pitting.

Tooth Bending Fatigue

Cracks formed under repeated stress below the material’s yield strength, typically occurring at the tooth root fillet.

Surface Contact Fatigue

Cracking or pitting on the gear surface due to repeated stress below the material’s fatigue limit.

Thermal Fatigue*

Caused by cyclic temperature changes, leading to cracking and eventual failure.


Sudden overload or impact loads can cause immediate tooth breakage or create conditions for fatigue failure.


General wear during operation, including abrasive, adhesive, and corrosive wear, leading to material and gear function loss.


Severe wear caused by metal-to-metal contact, usually due to poor lubrication or excessive load, leading to local welding and material transfer.

Future Trends and Innovations

Emerging technologies in the field of small gear manufacturing are greatly impacting the future of the industry, enhancing precision, efficiency, and the ability to produce complex designs. These technologies are driving significant changes in small gear manufacturing, providing opportunities for improved accuracy, efficiency, and innovation. As these technologies continue to evolve, they will further enhance the capabilities and applications of small gears across various sectors.

Rapid Prototyping

  • Additive manufacturing is revolutionizing the production of small gears, creating gears with complex geometries and opening new opportunities in gear manufacturing.

Industry 4.0

  • The integration of Industry 4.0 technologies is transforming gear manufacturing processes. This includes the use of smart sensors, IoT (Internet of Things), and AI (Artificial Intelligence) to optimize production, improve efficiency, and reduce downtime. Industry 4.0 enables better data collection and analysis for smarter decision-making and predictive maintenance.

Automation and Robotics

  • Automation, including the use of robots and collaborative robots (cobots), is becoming increasingly important in small gear manufacturing. These technologies can be used for tasks such as gear loading/unloading, assembly, and inspection. Automation helps increase production speed, improve accuracy, and reduce labor costs. It also addresses the shortage of skilled labor by performing repetitive tasks, allowing human workers to focus on more complex aspects of the manufacturing process.

Digital Manufacturing and Cloud Solutions

  • The adoption of digital manufacturing and cloud solutions is making gear production processes more efficient and flexible. These technologies facilitate seamless integration of design, manufacturing, and inspection processes. Cloud-based platforms enable easy sharing and analysis of data across different production stages, enhancing collaboration and accelerating development cycles.

Advanced Metrology and Inspection Technologies

  • Precision metrology and advanced inspection technologies are crucial for ensuring the quality of small gears. These technologies, including laser scanning and coordinate measuring machines (CMM), provide accurate and detailed measurements of gear geometry. This ensures that gears meet strict quality standards and perform reliably in applications.

Emerging Materials and Surface Treatments

  • The development of new materials and surface treatment methods, such as clean steel and vacuum carburizing, is enhancing the performance of small gears. These advancements make gears more robust, durable, and suitable for specific applications like electric vehicles and wind power generation.

Hybrid Manufacturing Processes

  • Combining traditional gear manufacturing processes with additive manufacturing and other advanced technologies has created hybrid manufacturing processes. This approach efficiently produces gears with enhanced characteristics and performance


We hope this guide has given you insight into the basic information about small gear.
For small gear from China, contact us now.

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