Machine Design Questions and Answers -Strength of Helical Gears

This set of Machine Design Multiple Choice Questions & Answers (MCQs) focuses on “Strength of Helical Gears”.

1. Lewis form factor is based on real number of teeth.
a) True
b) False
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2. Beam strength indicates the maximum value of radial force that a tooth can transmit without fatigue failure.
a) True
b) False
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3. A pair of helical gears consist of 25 teeth pinion gear meshing with a 90 teeth gear. Calculate the ratio factor.
a) 0.74
b) 0.88
c) 1.57
d) 1.44
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4. A pair of helical gears consist of 25 teeth pinion gear meshing with a 90 teeth gear. Calculate the material constant k If surface hardness is 260BHN.
a) 0.64N/mm²
b) 0.88N/mm²
c) 1.08N/mm²
d) 2.66N/mm²
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5. A pair of helical gears consist of 25 teeth pinion gear meshing with a 90 teeth gear. Calculate the wear strength If surface hardness is 260BHN. Also face width=35mm, module=4mm and helix angle=25⁰.
a) 443.5N
b) 1125.6N
c) 7971.9N
d) 1014.2N
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6. A pair of helical gears consist of 25 teeth pinion gear meshing with a 90 teeth gear. Calculate the tangential force If surface hardness is 260BHN. Also face width=35mm, module=4mm and helix angle=25⁰. The velocity of operation is 3.5m/s and service factor 1.5.
a) 1136.5N
b) 3983.7
c) 2012.6N
d) 3226.5N
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7. Which of the following is herringbone gear?

a) Left one
b) Right one
c) Both
d) None
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8. The net axial force acting on bearing is zero in case of double helical gears while none zero in case of herringbone gears.
a) True
b) False
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9. Helix angle of herringbone and double helical gears is relatively higher.
a) True
b) False
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10. A herringbone speed reducer consist of 20 teeth pinion driving a 100 teeth gear. The normal module of gear is 2mm. The face width of each half is 30mm and Lewis factor is 0.4. If permissible bending stress is 500N/mm², then calculate the beam strength.
a) 15000N
b) 12000N
c) 8000N
d) 10000N
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11. A herringbone speed reducer consist of 20 teeth pinion driving a 100 teeth gear. The normal module of gear is 2mm. The face width of each half is 30mm and Lewis factor is 0.4. Calculate the ratio factor Q.
a) 1.2
b) 1.4
c) 1.7
d) 1.4
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12. A herringbone speed reducer consist of 20 teeth pinion driving a 100 teeth gear. The normal module of gear is 2mm. The face width of each half is 30mm and Lewis factor is 0.4. Calculate the material constant K if surface hardness is 400BHN.
a) 1.25 N/mm²
b) 4.05 N/mm²
c) 3.25N/mm²
d) 2.56N/mm
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13. Helical gears mounted on parallel shafts are called crossed helical gears.
a) True
b) False
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14. Crossed helical gears have very low load carrying capacity.
a) True
b) False
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15. Calculate the shaft angle for same hand of helix if helix angle of two gears are 20⁰ and 17⁰.
a) 17⁰
b) 20⁰
c) 37⁰
d) 3⁰
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