Basic Of Gears – Terminologia / Nomenclatura de engrenagens

Basic Of Gears – Terminology / Gear nomenclature

Basic Of Gears – Terminology / Gear nomenclature

Gears:

Introduction:

Slippage and creep in belt or cable drives is a common phenomenon when transmitting motion or power between two shafts. The effect of slip is to reduce the speed ratio of the drive. In precision machines where a defined speed ratio is important (as in clockwork mechanisms, special purpose machines, etc.), the only positive drive is by means of gears or sprockets.

Gear nomenclature Gear nomenclature

Gear Terminology:

  • Additive term: The radial distance between the pitch circle and the top of the teeth.
  • Action Arc: It is the arc of the Partial Circle between the beginning and the end of the
    engagement of a given pair of teeth.
  • Approach Arc: It is the arc of the partial circle between the first gear contact point
    teeth and Pitch Point.
  • Arc of Recession: That arc of the Partial Circle between the Partial Point and the last point of the
    gear tooth contact.
  • Retaliation: Play between the corresponding teeth.
  • Base Circle: The circle from which the involute curve on which the tooth profile is based is generated.
  • Center Distance: The distance between the centers of two gears.
  • Chord Addendum: The distance between a string, passing through the points where the pitch circle intersects the tine profile, and the top of the tine.
  • Chord Thickness: The tooth thickness measured along a chord passing through the points where the pitch circle intersects the tooth profile.
  • Circular Pitch: Millimeter of circumference of the partial circle per tooth.
  • Circular Thickness: The thickness of the tooth measured along an arc following the pitch circle.
  • Clearance: The distance between the top of a tooth and the bottom of the space in which it fits into the meshing gear.
  • Contact Ratio: The ratio of the length of the Action Arc to the Circular Pitch.
  • Dedendum: The radial distance between the bottom of the tooth and the pitch circle.
  • Diametric pitch: Teeth per mm of diameter.
  • Face: The working surface of a gear tooth, located between the pitch diameter and the top of the tooth.
  • Face Width: The tooth width measured parallel to the gear axis.
  • Flank: The working surface of a gear tooth, located between the pitch diameter and the bottom of the teeth
  • Wheel: The larger of the two meshing gears is called the wheel.
  • Pinion: The smaller of the two meshing gears is called the pinion.
  • Earth: The upper surface of the tooth.
  • Line of action: That line along which the point of contact passes between the teeth of the gear, between the first and the last point of contact.
  • Module: Relationship between pitch diameter and number of teeth.
  • Pitch Circle: The circle whose radius is equal to the distance from the center of the gear to the starting point.
  • Diametric pitch: Ratio between the number of teeth and the diameter of the pitch circle.
  • Throw Point: The point of tangency of the pitch circles of two meshed gears, where the Line of Centers intersects the pitch circles.
  • Pressure Angle: Angle between the Line of Action and a line perpendicular to the Line of Centers.
  • Profile change: An increase in the outer diameter and root diameter of a gear, introduced to decrease the practical number of teeth or obtain a non-standard center distance.
  • Ratio: Proportion of the number of teeth in the corresponding gears.
  • Root Circle: The circle that passes through the bottom of the tooth spaces.
  • Root Diameter: The diameter of the Root Circle.
  • Working Depth: The depth to which a tooth extends into the space between the corresponding gear teeth.

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