# Machine Design Questions and Answers – Helical Gears

This set of Tough Machine Design Questions focuses on “Helical Gears”.

1. Among spur gear and helical gear, which has smooth engagement and thus lesser noise?
a) Helical Gears
b) Spur Gears
c) Both have equal noises
d) Can’t be determined

Explanation: There is a gradual pick up of load in helical gears and hence smooth operation.

2. There is same type of tooth meshing in helical and spur gear.
a) True
b) False

Explanation: In spur gears contact occurs along entire face width which leads to impact condition while in helical contact begins from a single point and then there is gradual increase in load.

3. Among the normal module and transverse module, which one has greater value?
a) Normal Module
b) Transverse Module
c) Both have equal module
d) Insufficient information

Explanation: Normal Module=Transverse modulexCos(helix angle).

4. Below is a representation of a helical gear. Blue lines in the figure signify? a) Pinion right handed helical teeth
b) Pinion left handed helical teeth
c) Both right and left handed
d) Symmetric helical teeth

Explanation: The lines are slopping downwards to the right side.

5. Below is a representation of a helical gear. Blue lines in the figure signify? a) Pinion right handed helical teeth
b) Pinion left handed helical teeth
c) Both right and left handed
d) Symmetric helical teeth

Explanation: The lines are slopping upwards to the right side.

6. A pair of parallel helical gears consist of 15 teeth pinion meshing with a 40 teeth gear. The helix angle is 22⁰ and normal pressure angle 19⁰. The normal module is taken as 4mm. Calculate the transverse module.
a) 4.3mm
b) 4.1mm
c) 3.9mm
d) 3.7mm

Explanation: m=4/Cos(22⁰).

7. A pair of parallel helical gears consist of 15 teeth pinion meshing with a 40 teeth gear. The helix angle is 22⁰ and normal pressure angle 19⁰. The normal module is taken as 4mm. Calculate the transverse pressure angle in degrees.
a) 17.9
b) 20.4
c) 19.6
d) 18.4

Explanation: tanᾰ=tan(19⁰)/Cos(22⁰).

8. A pair of parallel helical gears consist of 15 teeth pinion meshing with a 40 teeth gear. The helix angle is 22⁰ and normal pressure angle 19⁰. The normal module is taken as 4mm. Calculate the axial pitch.
a) None of the listed
b) 34.2mm
c) 33.4mm
d) 29.6mm

Explanation: p=πx(transverse module)/tan(22).

9. A pair of parallel helical gears consist of 15 teeth pinion meshing with a 40 teeth gear. The helix angle is 22⁰ and normal pressure angle 19⁰. The normal module is taken as 4mm. Calculate the pitch circle diameter of pinion.
a) 64.7mm
b) 52.6mm
c) 56.6mm
d) 68.8mm

Explanation: d=zxm/Cos(22).

10. A pair of parallel helical gears consist of 15 teeth pinion meshing with a 40 teeth gear. The helix angle is 22⁰ and normal pressure angle 19⁰. The normal module is taken as 4mm. Calculate the pitch circle diameter of the gear.
a) 172.6mm
b) 142.6mm
c) 180.3mm
d) 202.4mm

Explanation: d=zxm/Cos(22).

11. A pair of parallel helical gears consist of 15 teeth pinion meshing with a 40 teeth gear. The helix angle is 22⁰ and normal pressure angle 19⁰. The normal module is taken as 4mm. Calculate the centre distance.
a) 125.4mm
b) 132.6mm
c) 118.65mm
d) 145.4mm

Explanation: C=Sum of diameter of pinion and gear/2.

12. A pair of parallel helical gears consist of 15 teeth pinion meshing with a 40 teeth gear. The helix angle is 22⁰ and normal pressure angle 19⁰. The normal module is taken as 4mm. Calculate addendum circle diameter of the pinion.
a) 59.2mm
b) 72.7mm
c) 65.4mm
d) None of the listed

Explanation: D(a)=m[z/Cos(22) + 2].

13. A pair of parallel helical gears consist of 15 teeth pinion meshing with a 40 teeth gear. The helix angle is 22⁰ and normal pressure angle 19⁰. The normal module is taken as 4mm. Calculate the dedendum circle diameter of the pinion.
a) 64.5mm
b) 54.7mm
c) 59.2mm
d) None of the listed

Explanation: D(f)=m[z/Cos(22) – 2.5].

14. The direction of tangential component for a driving gear is same to the direction of rotation.
a) True
b) False

Explanation: The direction is opposite and not same.

15. If tangential component of force on tooth is 200N and helix angle is 25⁰, calculate the axial component of the force.
a) 200N
b) 302.5N
c) 93.26N
d) 215.6N

Explanation: P(a)=200xtan(25).

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