CONTENTS CONTENTS C H A P T E R Spur Gears 1. Introduction. 2. Friction Wheels. 3. Advantages and Disadvantages of Gear Drives. 4. Classification of Gears. 5. Terms used in Gears. 6. Condition for Constant Velocity Ratio of Gears–Law of Gearing. 7. Forms of Teeth. 8. Cycloidal Teeth. 9. Involute Teeth. 10. Comparison Between Involute and Cycloidal Gears. 11. Systems of Gear Teeth. 12. Standard Proportions of Gear Systems. 13. Interference in Involute Gears. 14. Minimum Number of Teeth on the Pinion in order to Avoid Interference. 15. Gear Materials. 16. Design Considerations for a Gear Drive. 17. Beam Strength of Gear. | CONTENTS C H A P T E R 28 Spur Gears 1. Introduction. 2. Friction Wheels. 3. Advantages and Disadvantages of Gear Drives. 4. Classification of Gears. 5. Terms used in Gears. 6. Condition for Constant Velocity Ratio of Gears-Law of Gearing. 7. Forms of Teeth. 8. Cycloidal Teeth. 9. Involute Teeth. 10. Comparison Between Involute and Cycloidal Gears. 11. Systems of Gear Teeth. 12. Standard Proportions of Gear Systems. 13. Interference in Involute Gears. 14. Minimum Number of Teeth on the Pinion in order to Avoid Interference. 15. Gear Materials. 16. Design Considerations for a Gear Drive. 17. Beam Strength of Gear Teeth-Lewis Equation. 18. Permissible Working Stress for Gear Teeth in Lewis Equation. 19. Dynamic Tooth Load. 20. Static Tooth Load. 21. Wear Tooth Load. 22. Causes of Gear Tooth Failure. 23. Design Procedure for Spur Gears. 24. Spur Gear Construction. 25. Design of Shaft for Spur Gears. 26. Design of Arms for Spur Gears. Introduction We have discussed earlier that the slipping of a belt or rope is a common phenomenon in the transmission of motion or power between two shafts. The effect of slipping is to reduce the velocity ratio of the system. In precision machines in which a definite velocity ratio is of importance as in watch mechanism the only positive drive is by gears or toothed wheels. A gear drive is also provided when the distance between the driver and the follower is very small. Friction Wheels The motion and power transmitted by gears is kinematically equivalent to that transmitted by frictional wheels or discs. In order to understand how the motion can be transmitted by two toothed wheels consider two plain circular wheels A and B mounted on shafts. The wheels have sufficient rough surfaces and press against each other as shown in Fig. . 1021 CONTENTS 1022 A Textbook of Machine Design Fig. . Friction wheels. Fig. . Gear or toothed wheel. Let the wheel A is keyed to the rotating shaft and the wheel B to the shaft to be .
