BASIC OF HELICAL GEAR

Before understanding the concept of helical gear, we must understand the each term used in gear drive mechanism and we have already discussed it i.e. various terminology used in gear in our previous post i.e. gear terminology. So before going ahead, i will request to my readers to find out the gear terminology in our previous post as well as the concept of spur gear, advantage, disadvantage and applications of spur gears in our last post i.e. Basics of spur gear, advantage, disadvantage and applications.

We will discuss here the basics of helical gears and finally we will see the various advantages, disadvantages and applications of helical gears.

So let us start our discussion about basics of helical gears

Helical gears are used to transmit the power and motion between two non- intersecting shafts. Helical gears are similar with spur gears but teeth will be cut over the surface of helical gear at an angle with the axis of gear, while in case of spur gears teeth were made straight and parallel with the axis of gear.

Helical gears will be prepared with teeth of both type of hand i.e. Right hand teeth and left hand teeth. Following figure shows the spur gear, helical gear of left hand teeth and right hand teeth.

Image courtesy: Google

If the thumb of our left hand is following the inclination of tooth of gear, that helical will be termed as left hand helical gear.

If the thumb of our right hand is following the inclination of tooth of gear, that helical will be termed as right hand helical gear.

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Helical gears could be used for connecting parallel shafts and non parallel shafts also. When we consider connecting and transferring power and motion between two parallel shafts with the help of helical gears, in that case opposite hand teeth will mesh with each other i.e. right hand helical gear teeth will lean with left hand helical gear teeth.

While if we are considering for connecting and transferring power and motion between two non-parallel shafts, acting at right angle with each other, with the help of helical gears, in that case same hand teeth will mesh with each other i.e. right hand helical gear teeth will lean with right hand helical gear teeth and vice versa. Helical gears those are used for connecting two non-parallel shafts will be termed as crossed helical gears.

We have assumed above that both shafts are acting at right angle to each other and hence we have indicated that mating helical gear will have same hand teeth but suppose if both shafts are not acting at right angle then in that case both gears might have similar or opposite hand teeth according to the shaft angle.

Figure shows here, the helical gears connecting two parallel shafts and crossed helical gears connecting two non-parallels shafts.

Image courtesy: Google

Helical gears those are used for connecting and transferring motion and power between two parallel shafts will operate quite smoothly and silently as compared with spur gears. There will be gradual contact between helical gear teeth i.e. engagement will start at one end of a gear tooth with other mating gear tooth and will spread gradually and continuously as both mating gears rotate. Helical gears are preferred to use in automobile applications due to its characteristic of silent operation and capability to work smoothly under heavy load.

Pair of helical gears those are used for connecting and transferring motion and power between two parallel shafts must have similar helix angle, pitch and pressure angle but both helical gears must have opposite hand teeth i.e. if driving helical gear is of right hand teeth then driven helical gear must be of left hand teeth.

There are two important terms i.e. helix angle and shaft angle those are quite important to understand here, let us see first shaft angle, i will request to my readers to correct me if i am wrong anywhere by giving your feedback or comments in comment box below.

Shaft Angle

In case of crossed helical gears, shaft angle will be defined as the angle between the ends of shafts those are rotating in opposite directions.

Image courtesy: Google

Helix angle

Helix angle of a helical gear will be defined as the angle between axis of gear and an imaginary line, which will be tangent to the gear. Helix angle will be in a range of 0 to 90 degree for a helical gear.

When a pair of helical gear meshes with each other, there will be creation of axial thrust load on gear due to helix angle of gear teeth and therefore gearbox designer has to select such bearings those are able to absorb and support this axial thrust load.

We will discuss various advantages, disadvantages and applications of helical gears in our next post.

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