Important Short Questions and Answers: Gears and Trains

1.  Define spur gear.

A spur gear is a cylindrical gear whose tooth traces are straight line generation of  the  reference cylinder. They are used to transmit rotary motion between parallel shafts.

2.  Define addendum and dedendum.

Addendum is the radial distance of a tooth from the pitch circle to the top of the tooth. Dedendum is the radial distance of a tooth from the pitch circle to the bottom of the tooth.

3.  Define circular pitch.

It is the distance measured on the circumference of the pitch circle from a point of one

tooth to the corresponding point on the next tooth. It is denoted by Pc

Circular pitch Pc= P/DT Where D = Diameter of pitch circle. T = Number of teeth on the wheel.

4.  Define I) path of contact. II) Length of path of contact.

Path of contact: It is the path traced by the point of contact of two teeth from the beginning  to the end of engagement.

Length of path of contact: It is the length of common normal cut- off by the addendum circles of the wheel and pinion.

5.  State the law of gearing.

Law of gearing states that, the common normal at the point of contact between a pair of teeth must always pass through the pitch point.

6.  Define conjugate action.

When the tooth profiles are so shaped so as to produce a constant angular velocity ratio

during Meshing, then the surface are said to de conjugate.

7.  Define angle of approach.

The angle of approach is defined as the angle through which a gear rotates from the instant a pair of teeth comes into contact until the teeth are in contact at the pitch point.

8.  List out the characteristics of in volute action.

a) Arc of contact.           b) Length of path of contact.   c) Contact ratio.

9.     Define contact ratio.

Contact ratio is defined as the ratio of the length of arc of contact to the circular pitch.

Mathematically.

Contact ratio = length of arc of conta [Pc] Where Pc = circular path.

10.            What is the advantage of involute gear?

The most important advantage of involutes gear is that the center distance for a pair of

involute gears can be varied within limits without changing the velocity ratio.

11. What are the conditions to be satisfied for interchangeability of all gears?

For interchangeability of all gears, the set must have the same circular pitch, module,

diameter pitch, pressure, angle, addendum and dedendum and tooth thickness must be one half of the circular pitch.

12. Define gear tooth system.

A tooth system is a standard which specifies the relationship between addendum, dedendum, working depth, tooth thickness and pressure angle to attain interchangeability of gears of tooth numbers but of the same pressure angle and pitch

13. Define cycloid.

A cycloid is the curve traced by a point on the circumference of a circle which rolls without slipping on a fixed straight line.

14. Define clearance.

The amount by which the dedendum of a gear exceeds the addendum of the mating gear

is called clearance.

15. When in volute interference occurs.

If the teeth are of such proportion that the beginning of contact occurs before the interference point is met then the involute proportion of the driven gear will mate a non in volute portion of the driving gear and involute interference is said to occur.

16.            What is the principle reason for employing non standard gears?

a) To eliminate the undercutting.

b) To prevent interference.

c)  To maintain reasonable contact ratio.

17.    What are the advantages and disadvantages of gear drive?

Advantages:

a) It transmits exact velocity ratio.

b) b) It has high efficiency.

Disadvantages:

The manufacture of gears require special tool and equipment.

The error in cutting teeth may cause vibrations and noise during operation.

18. Define helix angle (b).

It is the angle between the line drawn through one of the teeth and the center line of the

shaft on which the gear is maintained.

19. Define gear ratio.

The quotient of the number of teeth on the wheel divided by the number of threads on the worm.

20. Define gear train.

A combination of gears that is used for transmitting motion from one shaft to another

shaft is known as gear train. eg. spur gear, spiral gear.

21. Define velocity ratio.

Velocity ratio of a simple gear train is defined as the ratio of the angular velocity of the first gear in the train to the angular velocity of the last gear.