Hybrid Helical Gears

Thrust can be eliminated by using double helical or herringbone gears, but this significantly increases gear manufacturing and mounting cost. (Figure 11)

Figure 11 Double helical gear. (Marshek)

The opposing alignment of the helix angels cancels out the thrust force produced. These gears are seldom used by Hansen due to the advance in variable helix design in single helical gears and the cost of manufacturing double-helical gears.

Although helical gears usually operate on parallel shafts, they can be made to operate on nonparallel, nonintersecting shafts (Figure 12). They are then called crossed helical gears (previously called "spiral", or "skew", gears). Crossed helical gears theoretically have point contact, and can therefore carry only light loads. A common application is driving the distributor and oil pump from the camshaft in automotive engines.

Figure 12 Non parallel helical application. (Marshek)