Apr 072013

GearGears (or cogs) are toothed wheels used for the transmission of power in many mechanical systems.

When two gears are meshed with each other, a definite velocity ratio is obtained. Velocity ratio (or gear ratio) is the ratio between the angular velocity of driving gear and the angular velocity of driven gear.


Gears are typically used for short distance power transmission. They are compact and have high transmission efficiency when compared to other power transmission systems.

Classification of Gears:

Gears can be classified into many types based on several criteria. The classification of gears is listed below:

  1. Based on the peripheral velocity of gears
    1. Low velocity gears – Gears with peripheral velocity < 3 m/s
    2. Medium velocity gears – Gears with peripheral velocity = 3-15 m/s
    3. High velocity gears – Gears with peripheral velocity > 15 m/s
  2. Based on the position of axes of revolution
    1. Gears with parallel axes
      1. Spur gear
      2. Helical Gear
        1. Single Helical Gear
        2. Double Helical Gear (or) Herringbone Gear
    2. Gears with intersecting axes
      1. Bevel Gear
        1. Straight bevel gear
        2. Spiral bevel gear
        3. Zerol bevel gear
        4. Hypoid bevel gear
      2. Angular gear
      3. Miter gear
    3. Gears with non-parallel and non-intersecting axes
      1. Worm gear
        1. Non-throated worm gear
        2. Single-throated worm gear
        3. Double-throated worm gear
      2. Hypoid gear
      3. Screw gear (or crossed helical gear)
  3. Based on the type of gearing
    1. Internal gear
    2. External gear
    3. Rack and Pinion
  4. Based on the tooth profile on the gear surface
    1. Gears with straight teeth
    2. Gears with curved teeth
    3. Gears with inclined teeth

Advantages of Gear Drives:

  1. Transmission efficiency is high.
  2. Large power can be easily transmitted.
  3. Maintenance is easy.
  4. Gear drives are compact.
  5. They have zero slip.
  6. They have good durability and precision

Disadvantages of Gear Drives:

  1. Installation is difficult.
  2. Manufacturing of gears is complex and expensive.
  3. Tooth wear may occur during power transmission.
  4. Inaccuracies in gear tooth cause noise and vibrations.

 Applications of Gear Drives:

Gear drives are extensively used in several machines and mechanical systems. They have innumerable applications. Some typical applications of gear drives are:

  1. Watches
  2. Hoists
  3. Lathes
  4. Milling machines
  5. Drilling Machines
  6. Grinding Machines
  7. CNCs
  8. Automobile steering mechanisms and differentials
  9. Gear boxes
  10. Mechanical power transmission systems

If you have any other ideas about gear, you can share it by commenting on this article :)

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Written by

I am a mechanical engineer with a passion for technical stuff. I am the founder and former editor-in-chief of Mechteacher.com.

  • muhammad usman

    plz send the defination of safety gears