Tooth contact pattern plays an important role in gear manufacturing in general and in spiral bevel gear manufacturing in particular. Contact pattern is the area on the active tooth surface where the pinion rolls/slides around the gear during the action. There are two types of the tooth contact pattern: immediate contact pattern and combined contact pattern. The immediate tooth contact pattern is the area where pinion contacts to the gear in each particular moment of time.
The immediate spiral bevel gear tooth contact is not commonly measured because of technical difficulties. In order to practically measure the immediate contact one would need to hold the pinion from rotation and apply torque to the gear. The print on the tooth will be the immediate tooth contact. During rotation, the immediate tooth contact will move over the tooth and it will generate the combined tooth contact (contact pattern), that we often see at the traditional gear production factory. The contact pattern is commonly measured for validation of the tooth geometry and sensitivity of the gears to misalignment. The position, location, form, and direction of movement of the immediate tooth contact may significantly change the life of the gear.

Our spiral bevel gear tooth contact simulation software calculates the immediate tooth contact and the combined tooth contact as well. The calculation results show how the immediate contact moves along the working tooth and produces the combine tooth contact pattern. The same contact can bee seen on a rolling tester. We calculate the tooth contact based on the original design or based on the inspection result from a real gear. The older inspection procedures direct installing the gear and the pinion on a rolling tester in order to generate the contact pattern. More advanced and more accurate method is based on scanning the active tooth surfaces of the gear and the pinion on a CMM machine. The CMM would measure co-ordinates of many points on the tooth surfaces. Then, software builds a 3-dimensional CAD model and calculates the immediate and combined contact patterns.

Before introduction of DDS Tooth Contact Analyzes (TCA) software in 2002, it was impossible to inspect the immediate tooth contact on spiral bevel gears.

Images below show an example of tooth contact simulation on one of our gear set.

Click on image for higher resolution: 

1. Nominal shaft position. No shaft misalignment.

2. Horizontal misalignment. Mounting distance error.

3. Vertical misalignment. Hypoid offset.

4. Angular misalignment. Error in angle between shafts.

Thanks to introduction of Direct Digital Simulation method in 1986 in Russia and later in Sweden, Japan, USA and in China, accurate spiral bevel gear tooth contact pattern calculation has become available. Today, we can examine, with high accuracy, the results of the tooth contact calculations.