Our externally toothed gears
A fixed gear ratio can be achieved by adjusting the number of teeth on both gears. Depending on the design, the rotational speed is reduced or increased, and the transmitted torque is adjusted accordingly.
External-tooth spur gears are among the most widely used machine elements in gear manufacturing. They are used, among other things, in industrial gearboxes, machine tools, conveyor systems, packaging machines, vehicles, servo drives, as well as in agricultural and construction machinery.
We manufacture external-tooth gears according to drawings and technical specifications, either as single pieces or in small batches.
External-tooth gears for technical applications
Therefore, several technical issues must be clarified before manufacturing:
Concentricity, shaft alignment, and bearing arrangements also affect performance. Even a correctly manufactured external gear can wear out prematurely if the shafts are not properly aligned.
Have external-tooth gears manufactured according to drawings
The following information is particularly relevant for the manufacturing inspection:
Tooth Width
Head circle and foot circle diameters
Straight or helical teeth
Bevel Angle and Bevel Direction
For a replacement part project, an existing sample and information about the assembly can supplement the drawing data. The mating gear should also be taken into account whenever possible, as wear or older custom dimensions can affect interchangeability.
Advantages of External Gears
The teeth engage in a positive-lock manner. Unlike in a friction-wheel drive, the gear ratio cannot be altered by slippage.
High Efficiency
Properly designed and adequately lubricated spur gear stages can achieve an efficiency of more than 98 percent. The actual values that can be achieved depend on the type of gearing, bearings, lubrication, and operating conditions.
Fixed gear ratio
The number of teeth on the drive and driven gears determines the gear ratio. This keeps the ratio of rotational speeds constant during operation.
High load-carrying capacity
Material, tooth width, module, and heat treatment can be tailored to the loads encountered.
Long Service Life
With adequate lubrication, proper alignment, and appropriate loading, external gears can be used for extended periods of operation.
Established Manufacturing Processes
External gears can be manufactured using proven processes. This facilitates the production of individual parts, replacement parts, and recurring small production runs.
Different Designs
Depending on the requirements, straight-toothed or helical-toothed spur gears may be suitable. Both designs have different characteristics in terms of running behavior, load capacity, and bearing arrangements.
Wide Range of Applications
External gears can be used in applications ranging from small precision mechanical gearboxes to heavy-duty industrial drives.
External-tooth gears and how they work
In an externally toothed gear, the teeth are located on the outer circumference. Two externally toothed spur gears mesh at their tooth flanks and rotate in opposite directions.
The ratio of the number of teeth determines the gear ratio. For example, if the driving gear has fewer teeth than the driven gear, the rotational speed is reduced. At the same time, the torque available at the output increases, minus the losses within the gear stage.
Power is transmitted in several steps:
- The drive wheel is set in motion by a shaft or a motor
- Its tooth flanks press against the tooth flanks of the mating gear
- The counterwheel begins to rotate in the opposite direction
- The number of teeth determines the change in rotational speed
- The module and engagement angle ensure that the teeth fit together geometrically
For a stable meshing, both gears must have the same module and the same meshing angle. In the case of helical gears, the helix angle and helix direction must also be matched.
The tooth flanks roll and slide against each other during meshing. Proper lubrication reduces friction, heat generation, and wear.
External-tooth gears with straight or helical teeth
External-tooth spur gears can be designed with straight or helical teeth. Which design is more suitable depends on the rotational speed, load, noise requirements, and bearing configuration.
Straight-toothed spur gears have teeth that run parallel to the shaft axis.
Typical characteristics include:
For a simple, low-speed gear stage, straight-tooth gearing may be sufficient. At higher speeds and when there are stricter requirements for operating noise, helical gearing is often chosen.
External-tooth gears for industrial and automotive applications
External-tooth gears are used in virtually all areas of mechanical and plant engineering.
Typical applications include:
Industrial Gearboxes
Spur gear sets transmit torque between parallel shafts and provide fixed reduction or multiplication ratios.
Machine Tools
External-tooth gears are used in main drives, feed mechanisms, tool changers, and auxiliary units.
Conveyor Systems
Reduction gears drive conveyor belts, roller conveyors, hoists, and other transport systems.
Packaging Machines
Gears transmit motion to transport, positioning, and machining units.
Manual transmission
External-tooth spur gears create different gear ratios and transmit engine power to the drivetrain.
Transfer case
The drive power is distributed to various axles or auxiliary units.
Electric Motors with Reduction Gears
High engine speed is converted into lower output speed with higher torque.
Servo Drives and Robot Axes
Compact gear stages transmit motor motion to axles and joints.
Agricultural and Construction Equipment
External-tooth gears are used in mower drives, conveyor systems, metering systems, and hydraulic pump drives.
Pumps and Compressors
Gear stages transmit the drive power to pump or compressor units.
Printing Presses
Gears drive rollers, conveyor units, and processing stations.
Precision Engineering and Measuring Instruments
In small sizes, external gears are used to achieve specific gear ratios and create compact mechanisms.
Properly Sizing and Using External Gears
In external-tooth spur gears, the shafts must be arranged parallel to each other. Deviations in the center distance or alignment alter the tooth engagement and can cause uneven loading on the tooth flanks.
The key requirements include:
Lubrication is also a critical factor. Without an adequate lubricating film, friction and temperature increase. The tooth flanks can wear out prematurely or become damaged.
External-tooth gears from Dittler GmbH
By combining multiple machining processes, we can produce not only external gear teeth but also bores, hubs, flat surfaces, keyways, and other functional features, depending on the component. Our quality management system is certified according to DIN EN ISO 9001.
To inspect components, we use standardized testing procedures as well as a physically separate measuring room equipped with 3-coordinate measuring technology. Many of our customers do not require standardized catalog gears. Instead, they are looking for a single part for an existing machine, a replacement for a component that is no longer available, or a small production run based on their own drawings. We tailor our processes to meet these manufacturing needs.
External-tooth gears for fixed gear ratios
Straight-toothed spur gears feature a simple design and do not generate axial forces. Helical spur gears typically run more smoothly at higher speeds and can withstand higher loads thanks to multiple teeth bearing the load simultaneously.
To ensure a long service life, the gearing, center distance, shaft bearings, and lubrication must be properly matched. Especially for replacement parts, compatibility with the existing mating gear is crucial.
We manufacture externally toothed gears according to drawings and technical specifications, either as single pieces or in small batches. Depending on the component, additional turning, milling, and grinding operations can also be incorporated into the process.
Request Information on External Gears Now
Please send us your drawing and the available technical specifications via the contact form. Information regarding the module, number of teeth, tooth width, material, heat treatment, bore, quantity, and mating gear is particularly helpful.
For replacement parts, please also provide information about the existing gear stage, if possible. This allows us to verify whether the new gear is compatible with the existing gear pair and determine which manufacturing method is suitable for the component.
Frequently Asked Questions About External Gears
What is an external gear?
An external gear has teeth on its outer circumference. It meshes with a mating gear and transmits rotational motion and torque. Two external spur gears rotate in opposite directions.
What are external-tooth gears used for?
External-tooth gears are used in industrial gearboxes, machine tools, conveyor systems, packaging machines, vehicle transmissions, pump drives, and numerous other types of machinery. They are particularly well-suited for power transmission between parallel shafts.
How is the gear ratio calculated?
The gear ratio is determined by the ratio of the number of teeth on the driving gear to the number of teeth on the driven gear. If the driven gear has twice as many teeth as the driving gear, the driven gear's rotational speed is approximately halved. At the same time, the available torque increases, taking into account the resulting losses.
What data is required to manufacture an external gear?
Key specifications include module, number of teeth, mesh angle, profile offset, tooth width, and type of gearing. Additional specifications include material, heat treatment, bore, hub, tolerances, and quantity. For helical gears, the helix angle and helix direction are also required.
What is the difference between external and internal gear teeth?
In an external gear, the teeth are located on the outer circumference of the gear. In an internal gear, the teeth are located on the inside of a hollow gear. Two external gears rotate in opposite directions, while an external gear and a directly meshing hollow gear rotate in the same direction.
When is a straight-toothed external gear used?
Straight-toothed spur gears are often used at low to medium speeds. They have a simpler design and do not generate axial forces from tooth engagement. At high speeds, however, they can produce more noise than helical gears.
When is an external helical gear design appropriate?
Helical gearing is preferred when smooth operation, higher speeds, and uniform power transmission are important. Multiple sets of teeth can carry the load simultaneously. However, this generates axial forces that must be absorbed by suitable bearings.
Why do the shafts have to be precisely aligned?
An incorrect center distance or a non-parallel shaft alignment alters the load distribution across the tooth flanks. As a result, the gearing can only bear the load in certain areas. This increases noise, friction, and wear and can shorten the service life of the entire gear stage.
What role does lubrication play in external gears?
Lubrication separates the tooth flanks as they slide past each other, reduces friction, and dissipates heat. It also protects against wear and corrosion. The appropriate type of lubricant depends on the rotational speed, load, operating temperature, and design of the gearbox.
Can external-tooth gears be manufactured as single pieces?
Yes. External-tooth gears are often needed as replacement parts, for special-purpose machines, or as one-off components for test setups. This requires clear gear tooth data and a component geometry that can be manufactured using available tools.
Can an externally toothed gear be reproduced based on a sample?
An existing sample can provide important dimensions and gear tooth characteristics. However, for reproduction, the module, number of teeth, angle of engagement, material, and other specifications must be accurately determined. The existing counter gear should also be taken into account to ensure that the new gear teeth fit the gear stage.
What materials are used for externally toothed gears?
The choice of material depends on torque, speed, wear requirements, and size. Heat-treated steels or case-hardened steels are frequently used. For lower loads or special environments, stainless steel, non-ferrous metals, or engineering plastics may also be suitable.