# MCQs on Inerference, Undercutting & Backlash

1 - Question

Interference is caused by?

a) Overlapping of tooth profiles
b) Large size of dedendum
c) Meshing of involute and no-involute profiles
d) All of the mentioned

Explanation: In some cases, portion of tooth below base circle is not involute due to large dedendum. This leads to overlapping of involute portion of teeth with the non-involute portion of the teeth

2 - Question

Interference can be removed by under cutting.

a) True
b) False

Explanation: Undercutting removes the interfering portion of the tooth.

3 - Question

Interference is maximum when the largest pinion is in mesh with the smallest gear.

a) True
b) False

Explanation: It is maximum when smallest pinion is in mesh with the largest gear.

4 - Question

Undercutting is consider healthy for the tooth as it eliminates undercutting.

a) True
b) False

Explanation: Although it eliminates undercutting but it also weakens the strength of the tooth and removes a small involute portion near to the base circle.

5 - Question

Backlash is defined as

a) Difference in the width of tooth space and engaging tooth thickness
b) Amount by which engaging tooth thickness exceeds the tooth space
c) Other name for interference
d) None of the listed

Explanation: Backlash is the amount by which tooth space exceeds the engaging tooth thickness.

6 - Question

The amount of backlash depends on

a) Diameteral pitch
b) Module
c) Centre distance
d) All of the mentioned

Explanation: Module and diameteral pitch are the same thing, and centre distance is also a factor while deciding the magnitude of the backlash.

7 - Question

The two teeth have thickness t₁ and t₂. If backlash of t₁ is greater than that of t₂, than

a) t₁ > t₂
b) t₁ < t₂
c) t₁ = t₂
d) None of the mentioned

Explanation: Backlash=Tooth space-tooth thickness, greater the backlash lower is the tooth thickness.

8 - Question

Answer the following questions with respect to the following questions A gear train consist of spur gear as shown. Gear A receives 4kW of power at 750rpm through its shaft and rotates in CW direction. Calculate the torque on the gear A.

a) 51N-m
b) 48N-m
c) 46N-m
d) 44N-m

Explanation: M=60×10⁶x4/2πx750.

9 - Question

Calculate the torque on the gear B.

a) 47N-m
b) 51N-m
c) 0
d) Infinity

Explanation: Gear B is an idler gear and thus transmits no torque.

10 - Question

A gear train consist of spur gear as shown. Gear A receives 4kW of power at 750rpm through its shaft and rotates in CW direction. Calculate the torque on the gear C if number of teeth on gear A, B and C are 40, 70 and 30.

a) 66N-m
b) 68N-m
c) 53N-m
d) 45N-m

Explanation: M(a)xN(a)=M(c)xN(c) as the power transmitted is same.

11 - Question

Calculate the tangential gear tooth force. Module of the gear is 5mm.

a) 510N
b) 526N
c) 544N
d) None of the listed

Explanation: P=2M/d or P=2×51/5×40.

12 - Question

A planetary gear train is shown in the figure. Number of teeth on the sun gear A, planet gear B and fixed ring gear D are given by 30, 70 and 140 respectively. Module is taken as 5mm Calculate the length of the arm C.

Missing data
b) 250mm
c) 330mm
d) 240mm

Explanation: L=[Da+Db]/2 where da=5×30 and Db=5×70.

13 - Question

Calculate the tangential component of gear tooth force.

a) 220.6N
b) 303.2N
c) 454.7N
d) 633.2N

Explanation: P=2M/5×30 where M=60×10⁶x(kW)/2πN.

14 - Question

A pair of spur gears consist of 25 teeth pinion meshing with a 115 teeth gear. The module is 5mm. Calculate the gear ratio.

a) 5
b) 4.6
c) 5.2
d) 4

Explanation: i=115/25.

15 - Question

Calculate the shaft angle for opposite hand of helix if helix angle of two gears are 20⁰ and 17⁰.

a) 17⁰
b) 20⁰
c) 37⁰
d) 3⁰