taper , rack , gear , gear , spur gear , v- gear , helical , gear parts , planetary , worm gear

What is a gear?
A gear is practically a toothed wheel that is used for the transmission of mechanical movements, usually they are used to transmit the circular movement from one axis to another, whether they are in a different place or position. We must bear in mind that a gear transmits the movement in the opposite direction.


Parts and characteristics of a gear
Being a fairly simple element in terms of its construction, we can find some main parts.

Septum or Arms
They are the elements that are in charge of uniting the cube with the crown, in some occasions we can find gears with the complete body and in other occasions some grooves in the body.

Gear partition

It is the circumference where the teeth meet.

Gear crown

This part is the central hole where an axis is placed to transmit movement.

Gear hub

It is the part that comes out of the gears and the number, shape and size can vary depending on each gear.

We can also find some important parts in the teeth such as:

Crest: Outer part of the tooth
Face: Upper lateral part of the tooth
Flank: Bottom of the tooth
Fund or valley: It is where the tooth begins
Gear tooth parts

As for the characteristics of a gear we can find a great variety, since these date important aspects for the operation of these devices.

Number of teeth: Total number of teeth that a gear has.
Tooth Height : Measurement that goes from the bottom to the crest.
Tooth foot: It is also known as dedendum and is the part that is between the primitive circumference and the interior.
Tooth head: It is also known as adendum and it goes from the diameter of the outer circumference and the primitive.
Tooth length : Total length of the tooth.
Outside diameter: Total circumference that goes from the ridges of the teeth.
Primitive circumference: Circumference in which the teeth make contact with each other.
Inner diameter: Circumference between the bottom of the teeth.
Pressure angle
Circular step : Distance that exists from one part of the tooth to the same part of another, to take this measurement, the original circumference is taken into account.
Thickness: Thick having a gear.
Gear characteristics

Izantux [Public domain], via Wikimedia Commons

Gear types
Although it is a very essential component within all machinery, we can find only a few types. These can be classified mainly into cylindrical and conical, although each one has its different types.

Straight Cylindrical
They are the most common, they are used when the axles are parallel and when large reductions, medium and / or small speeds are required.

Gear straight

Helical Cylindrical
This type of gear is characterized by having its teeth inclined and they are mainly used when high speeds and high power are required. One of its main characteristics is that its running is smoother and quieter compared to spur gears.

helical gear

Cylindrical in V
They are also known as fishtail or double helical since they incorporate two opposite placed helical gears, some may have a small slot between the two propellers. These are practically used for the same as the simple helical ones with the only difference that this type of gear eliminates the axial thrust that is generated in the simple ones.Gear in v

Straight taper
This type of gears allow to transmit the movement between axes placed at angles mainly at 90 degrees and they are so called due to the cone-shaped construction of one of the gears.

Bevel gear

Helical conicals
These types have different construction with respect to the straight ones, since their teeth are made inclined. These gears are used in the same way as the cylindrical helical gears, for high speeds and greater power and also their running is quieter and smoother.

Helical bevel gear

This type is characterized by working with a worm screw and a crown together. They are mainly used because they work without vibrations and have a constant speed at their output. One of the curious facts about this gear is that for each turn the screw makes, only one tooth advances at a time.

Endless gear

Arthur Clarke at English Wikipedia [Public domain], via Wikimedia Commons

It is also known as an epicyclic gear and is characterized by having a system of gears that rotate around a central one, hence it is called planetary since the central gear is known as the sun and those that rotate around it as planets. It is primarily used to make gear changes in systems that need it, such as in automotive automatic transmissions.

To make the speed changes there are three different functions.

Fixed outer ring: When configured in this way the output speed is lower
Fixed planetary gear: In this case the output speed is higher
Moving Ring and Gear: When both components are moving it is used to reverse the output turn (reverse of an automatic car)
Planetary gear

The operation of this type of gear is quite easy to understand since it is responsible for transforming from an angular movement to one in a straight line (rectilinear) or vice versa.

Gear rack