Support Gear

Gear

What is a Gear?

A gear is a component of a mechanical power transmission device that allows rotary motion to be transferred from one shaft to another or converted into linear motion. It is a circular object with evenly spaced, transverse or angled ridges called teeth. When two gears are connected through their teeth, they mesh and transmit power and motion from one mechanical element to another.

Gear Applications and Classification

Gears are widely used in various applications, such as vehicle transmissions, industrial machinery, and precision measuring instruments. They enable changes in rotational speed and torque, making them essential components in many power transmission systems.

Gears can be classified by type and tooth profile:

  • Gear Types: Spur gears, bevel gears, helical gears, sprockets, and timing pulleys
  • Toothing: Straight toothing, helical toothing, herringbone toothing, and arc toothing.
  • External and Internal Gearing: Gears are also categorized as externally or internally toothed based on the location of their teeth.

Bevel Gears and Pinion Gears

  • Bevel Gears: These have teeth cut on a conical surface and are used to change the direction of rotary motion. Bevel gears are often used in applications where the axes are neither parallel nor intersecting.
  • Pinion Gears: The pinion is usually the smaller gear in a pair. It meshes with a larger gear and is more exposed to wear and load, so material selection and heat treatment are particularly important in its manufacture.

Involute Toothing

Involute toothing is the most common gear tooth profile because it is easy to manufacture and inspect. The involute shape allows for smooth motion transfer even with slight changes in shaft center distance. Involute gearing is preferred as small manufacturing errors do not affect the gear ratio.

Gear Terminology

The manufacture and design of gears involve several key terms:

  • Normal module (mn): Basic parameter influencing tooth size and power transmission capability.
  • Number of teeth (z): The total number of teeth on a gear.
  • Pitch diameter (d): The theoretical diameter at which the gear teeth mesh.
  • Pitch (p): The arc length between two successive teeth on the pitch diameter.
  • Addendum circle diameter (da): The diameter at the top of the gear teeth.
  • Dedendum circle diameter (df): The diameter at the bottom (root) of the gear teeth.
  • Pressure angle (α): The angle at which the teeth transmit force; typically 20°.
  • Helix angle (β): The angle of helical teeth, usually between 8°–15°.
  • Handedness: Defined by standard SFS-EN ISO 2203, indicating whether the helix angle is right- or left-handed.
  • Profile shift coefficient (x): The ratio of profile shift to normal module.
  • Number of involute pairs in mesh: The number of teeth in contact at a given moment.

Materials Used in Gear Manufacturing

Gears are made from a variety of materials chosen for their application and wear resistance. The following material groups and their ISO markings are most commonly used in gear manufacturing in the machining industry:

Steels - ISO P

  • 42CrMo4: Used for gears subjected to high loads and torques due to its high strength and hardness. Especially suitable for power transmission gears.

Cast Irons - ISO K

  • EN-GJS-400-15 (Spheroidal graphite cast iron): Used in applications requiring excellent wear and impact resistance. Well-suited for large gears that operate at low speeds and with high loads.

Light Metal Alloys - ISO N

  • EN AW-7075 (aluminum alloy): Used in lightweight applications requiring high corrosion resistance.

Polymer Materials - ISO H

  • PA6 (Nylon): Used in light-duty and noise-sensitive applications. Its good wear resistance and low friction make it suitable for small gears in electronic and consumer devices.

Machining Methods for Gears

In gear manufacturing, machinists and machine shops use various methods depending on the required accuracy, volume, and material:

  • Gear hobbing: A common method where a rotating blank is cut using a hob tool. This is suitable for high-volume production.
  • Power skiving: A fast method that combines rotation of both blank and tool for cutting. Ideal when flexibility and speed are needed.
  • Shaping: The cutting tool, resembling a gear, moves linearly against the blank to form the teeth.
  • Broaching: A rapid method that uses special tools to cut gear teeth in one pass. Suitable for mass production.
  • Milling with a gear cutter: The teeth are shaped with a module-matched gear cutter and an indexing device.
  • 5-axis machining and segmental radius milling: Modern advanced 5-axis machines, such as multi-tasking lathes with a B-axis, can also machine bevel gears and more complex profiles, where traditional methods are not suitable. Multi-axis tool paths are programmed using advanced CAM software, and finishing of the tooth profile can be sped up with tools like segmental radius cutters.

Summary

Gears are key components in the manufacturing processes of machine shops and machining facilities, enabling efficient transfer of rotational motion and power. Different gear types and tooth geometries make a wide range of industrial and consumer product applications possible. Precise and skilled machining methods ensure gears are manufactured with high accuracy and durability. This ensures every gear meets the specific demands of its application and operates reliably, even under the most demanding conditions. Detailed terminology and precise sizing guidelines support gear design and manufacturing in machine shops to meet required standards and functional goals.