Gear Question and Answer- Mechanical Engineering
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.
Advantages:
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.
