1. Presentation on gears

2. gear Gear are used to transmit motion from one
shaft to another or between a shaft and a slide .
Gears use no intermediate link .
It transmit motion by direct contact .
Two bodies have either a rolling or a sliding motion along the tangent .
No motion is possible along the common normal .

3. Gear and wheel
If power transmitted between two shaft is small, motion between them may be obtained by using two pin cylinder or disk 1 and 2 as shown in figure given below .

4. As the power transmitted increases, slip occurs between the discs and the motion no longer remains definite .
To remove slipping the wheel provided teeth
A toothed wheels is called gears
The motion of gears is equivalent to the friction wheels .

5. Advantages of gear drive
It transmit exact velocity ratio .
It may be used to transmit large powers
It has high efficiency.
It has reliable service .
It has compact layout

6. Disadvantages of gear drive
The manufacture of gears require special tools and equipment
The error in cutting teeth may cause vibration and noise during operation .

7. TYPES OF GEARS 1. According to the position of axes of the shafts.
Parallel
1.Spur Gear
2.Helical Gear
3.Rack and Pinion
4.Double helical or herringbone gears
b. Intersecting
1.Strait bevel Gear
2.Spiral bevel gears
3.zerol bevel gears
c. Non-intersecting and Non-parallel or skew shaft
worm and worm gears

8. SPUR GEAR Teeth is parallel to axis of rotation
Transmit power from one shaft to another parallel shaft
Used in Electric screwdriver, oscillating sprinkler, windup alarm clock, washing machine and clothes dryer

9. External and Internal spur Gear
An external gear is one with the teeth formed on the outer surface of a cylinder or cone.
Conversely, an internal gear is one with the teeth formed on the inner surface of a cylinder or cone.

10. Helical Gear
The teeth on helical gears are cut at an angle to the face of the gear
This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears
One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees

11. Helical Gear

12. Spur rack and pinion
A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called the pinion engages teeth on a linear "gear" bar called "the rack“ .
rotational motion applied to the pinion causes the rack to move linearly, thereby translating the rotational motion of the pinion into the linear motion of the rack.

13. Spur rack and pinion
It is Special case of a spur gear where it is made of infinite diameter so that the pitch surface is a plane .
It is used in a lathe in which the rack transmits motion to the saddle .

14. Straight and Spiral Bevel Gears

15. Straight bevelgears
The teeth are straight, radial to the point of intersection of the shaft axes and vary in cross section throughout their length .
Miter gears are mating bevel gears with equal numbers of teeth and with axes at right angles.
Use – roller shutter door.

16. Spiral bevel gear
A spiral bevel gear is a bevel gear with helical teeth .
There exists an axial thrust.
Zero bevel gears –spiral bevel gears with curved teeth but with a zero degree spiral angle .

17. GEAR TERMINOLOGY

18. GEAR AND PINION
Gears are the most common means of transmitting power in mechanical engineering.
Gear or wheel. The larger of two interacting gears.
Pinion. The smaller gear in a pair.

20. Base circle : It is a circle from which involute form is generated
Base circle : It is a circle from which involute form is generated. Only the base circle on a gear is fixed and unalterable.
Base pitch (pb): It is the distance from one face of a tooth to the corresponding face of an adjacent tooth on the same gear, measured along the base circle. Sometimes called the 'normal pitch'.
BASE CIRCLE

21. PITCH CIRCLE
Pitch is the distance between a point on one tooth and the corresponding point on an adjacent tooth.
Pitch circle. A circle, centered on and perpendicular to the axis, and passing through the pitch point. Sometimes also called the 'pitch line', although it is a circle.
Pitch diameter (D). Diameter of a pitch circle. The nominal gear size is usually the pitch diameter.

22. Circular pitch (p). The distance from one face of a tooth to the corresponding face of an adjacent tooth on the same gear, measured along the pitch circle.
Diametral pitch (Pd). The ratio of the number of teeth to the pitch diameter.
Module (m). The module of a gear is equal to the pitch diameter divided by the number of teeth.

23. ADDENDUM AND DEDENDUM
Addendum : The radial distance from the pitch surface to the outermost point of the tooth.  
Dedendum : The radial distance from the depth of the tooth to the pitch surface.

24. POINT OF CONTACT
A point of contact is any point at which two tooth profiles touch each other.
The pitch point is the point of tangency of two pitch circles and is on the line of centers.

25. LINE OF ACTION The line of action is also called path of action.
It is the straight line passing through the pitch point and tangent to both base circles.

26. GEAR TRAINS
A gear train is two or more gear working together by meshing their teeth and turning each other in a system to generate power and speed
It reduces speed and increases torque
Electric motors are used with the gear systems to reduce the speed and increase the torque

27. Types of Gear Trains Simple gear train Compound gear train
Reverted gear train
Planetary or epicyclic gear train
Simple Gear Train
The most common of the gear train is the gear pair connecting parallel shafts. The teeth of this type can be spur, helical or herringbone.
Only one gear may rotate about a single shaft axis.

28. Simple Gear Train

29. Compound Gear Train
For large velocities, compound arrangement is preferred
Two or more gears may rotate about a single axis

30. Reverted gear train
If the axes of the first and the last wheels of a compound gear coincide, it is called a reverted gear train .
Such an arrangement is used in clocks and in simple lathes where back gear is used to give a slow speed to the chuck.

31. Planetary or epicyclic gear train
A gear train having a relative motion of axes is called a planetary or an epicyclic gear train
Important application of epicyclic gears are in transmission, computing devices, wrists watches, hoists, back gear of lathe etc.

32. Thank you