Helical Gear and Spur Gear Characteristics.

  Helical or "dry fixed" gears provide improved functionality over spur gears. The front edge of the tooth is not parallel to the axis of rotation, but is positioned at an angle. Because the gear is bent, this angle makes the splines part of the propeller. Helical gears can mesh in parallel or cross directions. The first refers to the case in which the axes are parallel to each other. This is the most common address. In the latter case, the axes are not parallel and the gears in this configuration are also called "oblique gears". Angled teeth engage more gradually than spur gear teeth, making them smoother and quieter. With parallel helical gears, each pair of teeth first contacts at a single point on one side of the sprocket. Then a moving contact curve gradually grows to a maximum across the tooth's surface and then retracts until the tooth breaks contact at a single point on the opposite side. In spur gears, the teeth are suddenly in line contact across ...