Mechanical - Kinematics of Machinery - Gears and Trains - 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.

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