Bevel Gear

A bevel gear is a toothed rotating machine element used to transfer mechanical energy or shaft power between shafts that are intersecting, either perpendicular or at an angle. This results in a change in the axis of rotation of the shaft power. Aside from this function, bevel gears can also increase or decrease torque while producing the opposite effect on the angular speed.

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What is Bevel Gear?

Bevel gears are rotating mechanical components with teeth used to transmit mechanical energy or shaft power between perpendicular or angular intersecting shafts. This causes a change in the rotational axis of shaft power. In addition to this function, bevel gears can also increase or decrease torque, while having the opposite effect on diagonal speed.

Please note that bevel gears are usually paired and should not be used interchangeably. Bevel gears are assembled in a specific way because they inherently transmit thrust and radial loads, while spur gears mostly only transmit radial loads. All bevel gears are assembled in the best position for optimal performance.

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How to Define a Bevel Gear?

  • Pinion: The smaller bevel gear in the bevel gear set.
  • Gear: The larger bevel gear in the bevel gear set.
  • Pitch: Also known as circular pitch, pitch is the distance from a point on a tooth to the corresponding point of adjacent teeth on the same gear.
  • Pitch diameter: The diameter of the pitch circle. This is a predefined design dimension that identifies other gear characteristics such as tooth thickness, pressure angle, and helix angle.
  • Diametral pitch: The ratio of the number of teeth to the pitch diameter.
  • Pitch angle: The angle between the pitch surface and the axis of the shaft.
  • Pitch surface: A hypothetical truncated cone with a base diameter of a pitch circle.
  • Pressure angle: A predefined value described by the angle between the force line of the meshing teeth and the tangent line of the pitch circle at the contact point. Gears must have the same pressure angle to engage. The recommended pressure angle for straight bevel gears is 20 °.
  • Shaft angle: A predetermined value used to define the angle between the driven shaft and the drive shaft.
  • Addendum: The upper contour of the gear teeth.
  • Dedendum: The bottom profile of the gear teeth.
  • Total depth: The radial distance between the tooth tip circle and the tooth root circle of a gear. Please note that the teeth of the bevel gear are slightly tapered, therefore the total depth along the teeth is not constant. Therefore, the tooth tip angle and tooth root angle are used to describe teeth, rather than the tooth tip circle and tooth root circle.
  • Addendum angle: The angle between the upper surface of the tooth or the top surface of the tooth and the pitch surface.
  • Dedendum angle: The angle between the bottom surface or pitch surface of a tooth.
  • Depth of taper: The change in tooth depth on the tooth surface is measured perpendicular to the tooth surface.
  • Space width taper: The variation in spatial width measured along the surface of the court.
  • Thickness taper: The change of tooth thickness measured on the pitch surface.
  • Working depth: The change in tooth thickness measured on the tooth surface.
  • Clearance: The difference between the addendum of a gear to the dedendum of the mating gear.
  • Backlash: The amount of space that exceeds the thickness of a mating gear tooth. For bevel gears, there are different types of backlash depending on the orientation of the movement. Circular/Normal/Angular/Radial/Axial


Types of Bevel Gears

Straight Bevel Gears

Straight Bevel Gears

Straight bevel gears are the simplest form of bevel gears. When extended, the teeth are in a straight line intersecting the gear axis. The thickness of teeth is conical, making the outer or heel of the teeth larger than the inner or toe. Straight bevel gears have instantaneous contact lines, allowing for greater tolerance during installation.

Spiral Bevel Gears

Spiral Bevel Gears

A spiral bevel gear is the most complex form of bevel gear. The teeth of spiral gears are curved and oblique, in contrast to the teeth orientation of straight bevel gears. This results in more overlap between teeth, which promotes gradual engagement and disengagement upon tooth contact.

Zerol Bevel Gear

Zerol Bevel Gears

The teeth of the zero bevel gear bend along the length direction. These gears are also somewhat similar in appearance to spiral bevel gears. Their difference lies in the helix angle; The Zerol type has a 0 ° helix angle, while the helix type has a 35 ° helix angle.

Hypoid Bevel Gears

Hypoid Bevel Gears

A hypoid bevel gear is a special type of bevel gear where the axes of the shafts do not intersect or parallel. The distance between two gear shafts is called offset. The teeth of a hypoid bevel gear are helical, similar to helical bevel gears. A hypoid bevel gear without offset in design is a simple spiral bevel gear.

Miter Bevel Gear

Miter Bevel Gears

This is a bevel gear with a gear ratio of 1:1, which means that the number of teeth of the driving and driven gears is the same. Due to the fact that helical gears do not generate any mechanical advantages, this type of function is limited to changing the shaft or rotation.

Differences in Gear Tooth

Bevel Gear
  • Straight Teeth: The tooth surface of a straight bevel gear is a straight shape that intersects at right angles to the gear axis. Straight bevel gears are easy to manufacture and have low costs, but they produce significant noise and vibration during operation. Straight bevel gears are commonly used in applications with low speed and low precision requirements, such as manual tools and certain transmission systems.
  • Spiral Teeth: The tooth surface of a spiral bevel gear is helical and intersects with the gear axis at a certain helix angle. The tooth surface of spiral bevel gears gradually contacts and disengages, reducing noise and vibration, and providing smoother operation. Spiral bevel gears can withstand higher loads and speeds, making them widely used in applications such as automotive differentials, machine tools, and industrial machinery.
  • Zero Teeth: A zero tooth bevel gear is a combination of straight and helical teeth. It has a straight tooth surface of a straight bevel gear, but the helix angle is zero, that is, the tooth surface is parallel to the gear axis. Zero tooth bevel gears eliminate axial thrust in straight bevel gears and provide relatively smooth and quiet operation. Zero tooth bevel gears are typically used in applications that require lower noise and vibration, such as printers, machine tools, and differential transmission systems.

Helical Gear

Manufacturing Process


The precision required in gear production makes the manufacturing process rather difficult. Gear manufacturing is a separate business today that depends on several historical and contemporary procedures to maintain the ideal balance between cost, quality, and operations. There are different ways in which gears can be manufactured.

Post-Manufacturing Processes

After manufacturing, the designers can apply the following surface finishing methods.

  • Grinding – Grinding is a typical surface finishing technique that produces a surface with a smooth finish. It doesn’t matter if grinding is done continually or sporadically; the outcome remains the same.
  • Lapping – This procedure is used for delicate gears requiring high precision. Lapping is a low- to medium-speed process that uses tiny abrasive particles to smooth a surface.
  • Honing – This is another typical technique that polishes and smooths the surface. Additionally, tiny corrections can be made to the shape of the teeth.
  • Shaving – This technique involves removing incredibly thin layers from the surface to create a smooth profile. Since shaving is typically expensive, it is rarely used to manufacture gears.
  • Burnishing – In its simplest form, burnishing uses compression to smear a surface smoothly.
Gear manufacturing casting


The liquid material is poured into the hollow mold in the desired shape and then hardened.

Gear manufacturing forging


Forging is the process of heating and forming hot metal, using a press, mold, or hammer to hammer, press, or roll it into a design or shape suitable for a specific purpose.

Gear manufacturing Extrusion


Extrusion is a process in which a material undergoes plastic deformation by applying a force that causes the material to flow through a hole or mold.

Gear manufacturing Powder metallurgy

Powder metallurgy

When compacted metal powders are heated to just below their melting temperatures, this process, called powder metallurgy, is used to create metal.

Gear manufacturing Gear Machining

Gear Machining

Common cutting methods for helical gears include hobbing, shaping, broaching, and milling