Under the optimum conditions for any worm gear tooth profile only line contact is present when two gears of finite diameter mesh and rotate. Depending on the flexibility, a contact area of greater or lesser size is only produced under load and by a corresponding elastic deformation of the tooth surfaces. Worm gears are, in effect, crossed helical gears. However, unlike true crossed helical gears they envelop each other. With the shaft angle of the two axes usually at 90 degrees to one another, the enveloping provides a much larger area of contact. No worm gear will mesh perfectly with...