# Important Informations About Helical Gears And Design Calculations

The main difference between the spur gear and helical gear is the orientation angle of gear teeth according to the axis of the gear. If this angle is 0, this type of gear is called spur gear. But if there is an angle between the teeth orientation and axis of the gear, these types of gears are called helical gears. The angle between the orientation of teeth and the axis of gear is called as helix angle.

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This angle can be leaned to both the left side and right side in helical gears. According to this orientation, helical gears are called left-hand helical gears and right-hand helical gears.

In helical gear pairs, one of the used gear must be left hand and another one must be the right hand to obtain flat and even construction. With this type of assembly, the shafts attached to these helical gear pairs will be parallel, which is the desired construction.

The most important advantage of helical gears is the smooth operation compared with spur gears. This is because of the different engagement of helical gear teeth compared with spur gears. In spur gears, the engagement of teeth of driving and driving gear is sudden, when it is working. All the teeth pairs on spur gear pair come into contact, carry and transmit the load and, suddenly give this load to the next teeth pair.

But in the helical gear pair’s engagement, there is no sudden transmittance of load between adjacent teeth on driving and driven gears. Because of the angled design of helical gear teeth, when a tooth leaves contact with the opposite tooth, the next tooth comes in contact before it left. This leads to a much more smooth operation because of the smooth teeth change.

Another advantage of this angled tooth design is the capability of carrying more loads than spur gear counterparts. Because more than one teeth are in contact to carry the load. In spur gears, only one opposite tooth pair carry the load.

But there is a disadvantage of this angled design of teeth in helical gears. There is an axial force on shafts because of the angled transmittance of the load. Bearings that are assembled to the shaft must be selected properly if helical gears are used.

## What Are The Typical Helix Angles Used On Helical Gears?

As you understand from the previous section, helix angles affect the working conditions of gear pairs and shafts. So, it must be designed and optimized very well.

The typical helix angles that are used on helical gears range from 15 degrees to 45 degrees.

## Calculator For All Types Of Pitches Of Helical Gears

### Gear Velocity Ratio Calculator

The use of the calculator above is very simple. You just need to enter;

• The pitch diameter of your helical gear.
• Number of teeth in your helical gear.
• Degree of helix angle.

Normal diametral pitch is unitless. Another pitch value is calculated as a unit that you entered in the pitch diameter section above.

If you want to convert your units into other sets of units, you can use the MB-Unit Converter tool for it.

After you enter the required value, just click on the ‘Calculate!’ button to calculate all pitch values related to helical gears. If you want to do another calculation, click on the ‘Reset’ button then enter new values.

If we need to describe these pitch values special to helical gears;

• The description of circular pitch is the same with spur gears. Distance between same points on adjacent gear teeth.
• The normal circular pitch is the distance between the same points of adjacent teeth in the pitch diameter surface in the normal direction.
• The diametral pitch of a helical gear is the same as spur gears. It’s the ratio of the number of teeth to diameter.
• Normal diametral pitch is the diametral pitch in the normal surface on helical gear teeth.
• Axial pitch is also the distance between the same points on adjacent teeth which are measured on the axial direction of the pitch surface.

## Forces On Helical Gear Teeth During Working The diagram shows planes and forces with angles on a helical gear(G. M. Maitra, Handbook of Gear Design).

In helical gear strength analysis, there three types of forces appear on helical teeth. To examine the strength of a helical gear, we need to examine these three forces. These forces are; radial force, tangential force, and axial force.

• Radial force on helical gear teeth is the force that tries to disassemble gear mesh. This radial force acts towards to center of the helical gear.
• Tangential force is the main force that drives the gears. This force is perpendicular to the axis of the shaft that helical gear is assembled and tangential to the pitch surface.
• An axial force is a force that pushes the gear along the shaft. This force is also called thrust force. The bearings must withstand this force.

The plane that hosts the radial force and normal force is called the normal plane.

The plane that hosts the radial and tangential forces is called the transverse plane.

The plane that hosts axial and tangential forces is called the tangential plane.

## Three Types Of Angles Used In Helical Gear Design

Unlike spur gear design, in helical gears, there are three types of angles of interest. First of all, is the helix angle which is stated above. The second and third angles are the normal pressure angle and transverse pressure angle. The helix angle must be defined every time because it is the most important angle. And one of the pressure angles of a helical gear must be defined along with the helix angle.

The other can be found by using this calculator;

Select the known pressure angle value then enter the pressure angle value with helical angle value to find out other pressure angles of your helical gear.

You can calculate all the required forces by using the pieces of information and diagram above.