Machine Kinematics Multiple Choice Questions on “Reverted Gear Train”.
1. Gearing contact is which one of the following?
a) Sliding contact
b) Sliding contact, only rolling at pitch point
c) Rolling contact
d) Rolling and sliding at each point of contact
Answer: b
Clarification: When pair of teeth touch at the pitch point ,they have for the instant pure rolling action. At any other position they have the sliding action.
2. An external gear with 60 teeth meshes with a pinion of 20 teeth, module being 6 mm. What is the centre distance in mm?
a) 120
b) 180
c) 240
d) 300
Answer: c
Clarification: Centre distance in mm = m/2 (T1 + T2)
= 6/2 (60 + 20)
= 240 mm
3. Which one of the following is true for involute gears?
a) Interference is inherently absent
b) Variation in centre distance of shafts increases radial force
c) A convex flank is always in contact with concave flank
d) Pressure angle is constant throughout the teeth engagement
Answer: d
Clarification: For involute gears, the pressure angle is constant throughout the teeth engagement.
4. In involute gears the pressure angle is
a) Dependent on the size of teeth
b) dependent on the size of gears
c) Always constant
d) always variable
Answer: c
Clarification: The pressure angle is always constant in involute gears.
5. Consider the following statements:
1. A stub tooth has a working depth larger than that of a full-depth tooth.
2. The path of contact for involute gears is an arc of a circle.
Which of the statements given above is/are correct?
a) Only 1
b) Only 2
c) Both 1 and 2
d) Neither 1 nor 2
Answer: d
Clarification: 1. A stub tooth has a working depth lower than that of a full-depth tooth.
2. The path of contact for involute gears is a line.
6. Consider the following statements regarding the choice of conjugate teeth for the profile of mating gears:
1. They will transmit the desired motion
2. They are difficult to manufacture.
3. Standardisation is not possible
4. The cost of production is low.
Which of these statements are correct?
a) 1, 2 and 3
b) 1, 2 and 4
c) 2, 3 and 4
d) 1, 3 and 4
Answer: a
Clarification: Cost of production of conjugate teeth, being difficult to manufacture is high.
7. Common contact ratio of a pair of spur pinion and gear is
a) Less than 1·0
b) Equal to 1
c) Between 2 and 3
d) Greater than 3
Answer: c
Clarification: The ratio of the length of arc of contact to the circular pitch is known as contact ratio i.e. number of pairs of teeth in contact. The contact ratio for gears is greater than one. Contact ratio should be at least 1.25. For maximum smoothness and quietness, the contact ratio should be between 1.50 and 2.00. High-speed applications should be designed with a face-contact ratio of 2.00 or higher for best results.
8. In gears, interference takes place when
a) The tip of a tooth of a mating gear digs into the portion between base and root circles
b) Gears do not move smoothly in the absence of lubrication
c) Pitch of the gear is not same
d) gear teeth are undercut
Answer: a
Clarification: In gears, interference takes place when the tip of a tooth of a mating gear digs into the portion between base .and root circle.
9. Consider the following characteristics:
1. Small interference
2. Strong tooth.
3. Low production cost
4. Gear with small number of teeth.
Those characteristics which are applicable to stub 20° involute system would include
a) 1 alone
b) 2, 3 and 4
c) 1, 2 and 3
d) 1, 2, 3 and 4
Answer: b
Clarification: Involute system is very interference prone.
10. A spur gear transmits 10 kW at a pitch line velocity of 10 m/s; driving gear has a diameter of 1.0 m. Find the tangential force between the driver and the follower, and the transmitted torque respectively.
a) 1 kN and 0.5 kN-m
b) 10 kN and 5 kN-m
c) 0.5 kN and 0.25 kN-m
d) 1 kN and 1 kN-m
Answer: a
Clarification: Power transmitted = Force × Velocity
Force = 10 x 103/10
= 1000 N/m
Torque Transmitted = Force x diameter/2
= 1000 x 1/2
= 500 N-m
= 0.5 kN-m