Helical gears are circular gears with angled rather than straight teeth. The angled design of the teeth causes them to engage other gears differently than spur gears, which have straight teeth. As properly matched helical gears come in contact with one another, their level of contact increases gradually, rather than engaging the entire tooth at once. In mechanical systems, this contact causes less impact loading and provides smoother, quieter operation. Helical gears are also stronger and longer lasting than spur gears.
There are a number of important measurements that should be considered when selecting helical gears. Like other gears, a helical gear’s number of teeth, pitch diameter, outside diameter and center distance are all factors in its performance and effectiveness. Helical gears also have center angle and tooth angle measurements, which help define the nature of the gear. Interestingly, if aligned correctly, properly matched helical gears can be used to drive perpendicular shafts, although they are typically used to transmit power between parallel shafts.
There are both single and double helical gears. Single helical gears are the most familiar type, and consist of a single line of angled teeth around the perimeter of the gear. Double helical gears use two tracks of mirrored, angled teeth. These tracks are often separated by a gap for different machining purposes, but can be in direct contact with one another (continuous double helical gears). Double helical gears are stronger than single helical gears and have zero sideways force.
Helical gears can be produced by numerous manufacturing methods in a variety of materials. The methods used include shaping, milling, hobbing and casting. Typically, a number of finishing methods are also employed. Materials used range from steel and cast iron to aluminum bronze and different hard synthetics. The materials used in gear design also play a large role in its performance and should be evaluated based on the application (where temperature, speed and load all help determine requirements).
