INVOLUTES and their CONSTRUCTION

INVOLUTE

• An involute is a curve that is traced by a point on a taut cord unwinding from a circle or regular polygon, which is called a base or (plane figures for part of this unit which includes a line, triangle, square, hexagon) The involute is a form of spiral, the curvature of which becomes straighter as it is drawn from a base circle and becomes a straight line at infinity.
• An involute drawn from a small base circle is more curved than one drawn from a larger base circle
• The involute of a circle has a property that makes it important to the gear industry: if the teeth of two mating gears have the shape of an involute, their relative rates of rotation are constant while the teeth are engaged. 
• With teeth of other shapes, the relative speeds rise and fall as successive teeth engage, resulting in vibration, noise, and excessive wear
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