Helical Gears, or "Dry Fixed" Gears, have teeth that are oriented at an angle to the shaft, unlike Spur Gears which are parallel. This causes more than one tooth to be in contact during operation and helical gears can carry more load than spur gears. The angled teeth engage more gradually than do spur gear teeth, causing them to run more smoothly and quietly.

an external contact helical gear in action

Helical gears can be meshed in Parallel or Crossed orientations. The former refers to when the shafts are parallel to each other; this is the most common orientation. In the latter, the shafts are non-parallel, and in this configuration the gears are sometimes known as "skew gears".

A disadvantage of helical gears is a resultant thrust along the axis of the gear, which must be accommodated by appropriate thrust bearings. However, this issue can be circumvented by using a Herringbone Gear or Double Helical Gear, which has no axial thrust - and also provides self-aligning of the gears. This results in less axial thrust than a comparable spur gear.

Another disadvantage of helical gears is also a greater degree of sliding friction between the meshing teeth, often addressed with additives in the lubricant.

Double Helical Gears are a variation of helical gears in which two helical faces are placed next to each other with a gap separating them. Each face has identical, but opposite, helix angles. Employing a double helical set of gears eliminates thrust loads and offers the possibility of even greater tooth overlap and smoother operation. 

Double helical gears overcome the problem of axial thrust presented by single helical gears by using a double set of teeth, slanted in opposite directions. A double helical gear can be thought of as two mirrored helical gears mounted closely together on a common axle. This arrangement cancels out the net axial thrust, since each half of the gear thrusts in the opposite direction, resulting in a net axial force of zero. This arrangement can also remove the need for thrust bearings. However, double helical gears are more difficult to manufacture due to their more complicated shape.

Like the helical gear, double helical gears are commonly used in enclosed gear drives.

Double Helical Gears

HOLK Bearing is a leading manufacturer of a wide range of power transmission products such as Gears, Chain Sprockets, Bearing Housings, Adapter Sleeves, Withdrawal Sleeves, Precision Lock Nuts, and many other bearing accessories.

We can produce a wide range of standard and bespoke gears like Spur Gears, Helical Gears, Internal Gears, Miter Gears, Bevel Gears, Worm Gears, Rack and Pinions and so on.

All HOLK's gears are made from top-notch quality steels and can be further adapted for high performance with coatings such as black oxide or zinc plating. 

To enhance the hardness and wear resistance of the tooth surface, the tooth surface can be subjected to high frequency quenching and heat treatment, thereby increasing the life of the chain sprockets and gears.

HOLK's helical gears grant high performances on a wide array of industrial applications. Their resistance to wear and fatigue is way above the standard requirements according to relevant ISO regulation. Thanks to our top-notch production capacity, we can offer many different series and also customised power transmission products. 

Aside from standard products, we can also produce special customized Chain Sprockets, Gears, Gear Racks, and many other industrial products according to customers' drawings and samples.