CONTENTS CONTENTS 1080 C H A P T E R n A Textbook of Machine Design 30 Bevel Gears 1. Introduction. 2. Classification of Bevel Gears. 3. Terms used in Bevel Gears. 4. Determination of Pitch Angle for Bevel Gears. 5. Proportions for Bevel Gears. 6. For mative or Equivalent Number of Teeth for Bevel Gears—Tredgold's Approximation. 7. Strength of Bevel Gears. 8. Forces Acting on a Bevel Gear. 9. Design of a Shaft for Bevel Gears. Introduction Introduction The bevel gears are used for transmitting power at a constant velocity ratio between two shafts whose axes intersect at a certain angle. The pitch surfaces for the bevel. | CONTENTS C H A P T E R 30 Bevel Gears 1. Introduction. 2. Classification of Bevel Gears. 3. Terms used in Bevel Gears. 4. Determination of Pitch Angle for Bevel Gears. 5. Proportions for Bevel Gears. 6. Formative or Equivalent Number of Teeth for Bevel Gears Tredg old s Approximation. 7. Strength of Bevel Gears. 8. Forces Acting on a Bevel Gear 9. Design of a Shaft for Bevel Gears. Introduction The bevel gears are used for transmitting power at a constant velocity ratio between two shafts whose axes intersect at a certain angle. The pitch surfaces for the bevel gear are frustums of cones. The two pairs of cones in contact is shown in Fig. . The elements of the cones as shown in Fig. a intersect at the point of intersection of the axis of rotation. Since the radii of both the gears are proportional to their distances from the apex therefore the cones may roll together without sliding. In Fig. b the elements of both cones do not intersect at the point of shaft intersection. Consequently there may be pure rolling at only one point of contact and there must be tangential sliding at all other points of contact. Therefore these cones cannot be used as pitch surfaces because it is impossible to have positive driving and sliding in the same direction at the same time. We thus conclude that the elements of bevel 1080 CONTENTS Bevel Gears 1081 gear pitch cones and shaft axes must intersect at the same point. Fig. . Pitch surface for bevel gears. The bevel gear is used to change the axis of rotational motion. By using gears of differing numbers of teeth the speed of rotation can also be changed. Classification of Bevel Gears The bevel gears may be classified into the following types depending upon the angles between the shafts and the pitch surfaces. 1. Mitre gears. When equal bevel gears having equal teeth and equal pitch angles connect two shafts whose axes intersect at right angle as shown in Fig. a then they are known as mitre gears. 2. .
