Gear Tooth Contact

Figure 8 shows a pair of gears in various stages of rotation and this diagram helps in the study of the cycle of contact of a pair of gears rotating in the direction of the arrow.

Figure 8 Progressive tooth contact.

In (A) the driving tooth below the center line is in contact with the tooth on the center line of the driven wheel and the teeth marked A and B are about to mesh. This engagement has just taken place in view (B), where it is seen that the tip of the driven gear has come into contact with the flank of the driving gear. From this point onwards there occurs a combination of sliding and rolling between the flank curvature of the driving gear and the face (the portion of the tooth above the pitch line) of the driven gear. When the two teeth mesh on the pitch line, as at (C), there is pure rolling contact. From that point onwards the teeth will again move over each other with a combination of rolling and sliding until they separate, the last contact being between the tip of the driving tooth and the flank of the driven tooth as shown at (D). Sliding is proportional to the distance to the pitch line, measured along the path of contact. This implies that the sliding velocity is zero at the pitch line and maximum at the root and tip of the two meshing components.