Gear Teeth

A gear tooth is the curving that are seen in the gears. Gear teeth can come in the shape of square curved or even triangular. It is essential that, for gears to run without noise and smoothly, the gear teeth should be able to transmit a constant angular velocity. Constant angular velocity roughly means there is exact following of the speed of the Driver gear by the Gear that is driven. The different shapes of a Gear Teeth is best illustrated by the following diagrams:


So the next question that comes to everybody's mind is what is the type of gear teeth that is the best. Ideally a gear teeth should show the following attributes.

• Gears need to be have teeth that should mesh properly.
• Involute curves to be modeled on the teeth.
• A curve that provides for a constant velocity as the gear is turning.

Elements of Gear Teeth
Elements of Gear Teeth that form part of the Gear Teeth are described here.

• Tooth surface - This forms the side portion of a gear tooth.
  
  
• Tooth profile - This is one side of a tooth that happens to be in the cross section between the root circle and the outside circle.
  
  
• Flank - Flanks are the contracting or working side of the gear tooth.
  
  
• Top land - This a gear tooth's top surface.
  
  
• Bottom land - The surface found at the bottom of the space between the adjacent teeth.
  
  
• Crown - Crown is a modification made in the flanks that makes the gear tooth to have a little outward bulge in its center area. The purpose behind crowning is for ensuring the flank's center carries the full share of the load. This is in spite if the gears are bit misaligned or get deflected under load.
  
  
• Root circle - Root circle is the tangent that is formed at the bottom of the tooth spaces in a typical cross section.
  
  
• Pitch circle - Pitch circles are the tangents that is formed in mating gears.
  
  
• Gear center - Gear center is the center of the pitch circle. Line of centers In two engaging gears, this joins the centers of the pitch circles.
  
  
• Pressure angle - Pressure Angle is defined as the slant that is formed at the particular point of the gear tooth flank.
  
  
• Line of action - Line of action is the line where the Gear teeth comes in contact with each other as it goes constantly in and out of mesh.
  
  
• Pitch point - Pitch Point is the intersection formed between the axes of the line of action and the line of centers.
  
  
• Addendum - Addendum is defined as the perpendicular or radial distance between the tip of a teeth and pitch circle.
  
  

Involute Gear Profile: Adding new Dimension to the Gear technology It has been seen that there are Gear Tooth, which do not transmit constant angular velocity. This happens as the center distance between the gears is not correctly held to the already calculated design dimension. The result is pulsations and vibrations. Now to rectify this problem a Technology called Involute Gear profile has been successfully adopted. This has evolved as the most popular Gearing technology today. In this technology the tooth shape is made in such a way that it will transmit a constant angular velocity. This velocity would not be affected even when there is variation in the center distance. This shape is referred to as an involute. An involute can be defined as a curve. It can be traced by a point on taut cord that unwinds from a circle. This circle is referred to as a base circle. The involute can also be referred to as a kind of spiral. The curvature when it is drawn from a base circle goes on to become straighter. At infinity this invariably becomes a straight line. The working of an Involute Gear profile is described here. In this process, it is the pitch diameter that forms the effective contact diameter. Here the contact diameter does not remain constant, that is why it is the pitch diameter which can be really said to be the average contact distance. As shown in the illustration. The teeth starts engaging with the top gear tooth coming in touch with the bottom gear tooth. This happens inside the pitch diameter. Eventually what happens is that even though there is continuous change in the contact point diameter. But there is no alteration in the speed. Thus a Gear tooth of involute profile is able to produce a rotational speed ratio that is constant.