# Gear Basic | Theory of machine Interview Question and Answers

Gear Basic | Theory of machine Interview , viva ,oral  Question and Answers

1. State law of Gearing.

The law of gearing states that for obtaining a constant velocity ratio, at any instant of teeth the common normal at each point of contact should always pass through a pitch point, situated on the line joining the centre of rotation of the pair of mating gears.

2. Define normal and axial pitch in helical gears.

• Normal pitch is the distance between similar face of adjacent teeth, along a helix on the pitch cylinder normal to the teeth.
• Axial pitch is the distance measured parallel to the axis between similar faces of a adjacent teeth.

3. What is the maximum efficiency in worm and worm gear?

ήmax = 1-sinφ/1+sinφ

4. What are the advantages and limitations of gear drive? Write any two.

1. Since there is no slip, so exact velocity ratio is obtained.
2. It is more efficient and effective means of power transmission.

Limitations:
1. Manufacture of gear is complicated.
2. The error in cutting teeth may cause vibration and noise during operation.

5. Define interference.

The phenomenon when the tip of tooth undercuts the roots on its mating gear is known as interference.

6. Define cycloidal tooth profile and involute tooth profile.

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

7. Define circular pitch and diametral pitch in spur gears.

Circular pitch (pc) : It is the distance measured along the circumference of the pitch circle from a point on one teeth to the corresponding point on the adjacent tooth.

pc=πD/T

Diametral pitch (pD) : It is the ratio of number of teeth to the pitch circle diameter.

PD=T/D=π/pc

8. Define Backslash.

It is the difference between the tooth space and the tooth thickness along the pitch circle.
Backslash = Tooth space – Tooth thickness

9. What is gear train of train of wheels?

Two or more gears re made to mesh with each other to transmit power from one shaft to another. Such a combination is called a gear train or train of wheels.

10. Write velocity ratio in compound train of wheels?

Speed of last follower – Product of teeth on drivers
Speed of first driver – Product of teeth on followers.

11. Define simple gear train.

When there is only one gear on each shaft, it is known as simple gear train.

12. What is reverted gear train?

When the axes of the first and last wheels are co-axial, the train is known as reverted gear train.

13. Where the epicyclic gear trains are used?

The epicyclic gear trains are used in the back gear of lathe, differential gears of the automobiles, pulley blocks, wrist watches, etc

14. 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.

15. Define Contact Ratio.

It is the ratio of the length of arc contact to the circular pitch is known as contact ratio. The value gives the number of pairs of teeth in contact.

16. What is an angle of obliquity in gears?

It is the angle between the common normal to two gear teeth at the point of contact and the common tangent at the pitch point. It is called as pressure angle.

17. What is bevel gearing? Mention its types.

When the non-parallel (or) intersecting but coplanar shafts connected by gears, they are called bevel gears and the arrangement is bevel gearing. It is of two types namely skew bevel gearing and spiral gearing.

18. What are the methods to avoid interference?

1. The height of the teeth may be reduced.
2. The pressure angle may be increased.
3. The radial flank of the pinion may be cut back (undercutting).

19. What is the advantage when arc of recess is equal to arc of approach in meshing gears?

When arc of recess equal to arc of approach, the work wasted by friction is minimum and efficiency of drive is maximum.

20. What do you know about tumbler gear?

Tumbler gears are those which are used in lathes for reversing the direction of rotation of driven gears.

21. What you meant by non-standard gear teeth?

The gear tooth obtained by modifying the standard proportions of gear teeth parameters is known as non- standard gear teeth.

22. What is meant by compound gear train?

When there are more than one gear on shaft, it is called a compound gear train.

23. What is the advantage of a compound gear train over a simple gear train?

The advantage of a compound gear train over a simple gear train is that a much larger speed reduction from the first shaft to the last shaft can be obtained with small gears.

24. State the methods to find the velocity ratio of epicyclic gear train.

Two methods are:
1) Tabulation method.
2) Algebraic method.

25. What is the externally applied torques used to keep the gear train in equilibrium?

1) Impart torque on the driving member.
2) Resisting or holding torque on the driven member.
3) Holding or braking torque on the fixed member.