Kinematics - Spur Gears

 Spur gears or straight-cut gears are the simplest type of gear. Sometimes, many spur gears are used at once to create very large gear reductions.They consist of a cylinder or disk, and with the teeth projecting radially, and although they are not straight-sided in form, the edge of each tooth thus is straight and aligned parallel to the axis of rotation. These gears can be meshed together correctly only if they are fitted to parallel axles. 

Retrieved from Wikipedia.org

Two meshing gears transmitting rotational motion. Note that the smaller gear is rotating faster. Although the larger gear is rotating less quickly, its torque is proportionally greater.

Parts of a Spur Gear

• Diametral Pitch - The number of teeth per one inch of pitch circle diameter.
• Module - The length of the pitch circle diameter per tooth.
• Circular Pitch - The distance between adjacent teeth measured along the pitch circle diameter.
• Addendum - The height of the tooth above the pitch circle diameter.
• Center Distance - The distance between the axes of two gears in mesh.
• Circular Tooth Thickness - The width of a tooth measured along the pitch circle diameter.
• Dedendum - The depth of the tooth below the pitch circle diameter.
• Outside Diameter - The outside diameter of the gear.
• Base Circle Diameter - The diameter on which the involute teeth profile is based.
• Pitch Circle Diameter - The diameter of the pitch circle
• Pitch Point - The point at which the pitch circle diameter line and the rear face of the rack.
• Pressure Angle - The angle between the tooth profile at the pitch circle diameter and a radial line passing through the same point.
• Whole Depth - The total depth of the space between adjacent teeth.

A close up of two spur gears in mesh