# Worm Gears Questions & Answers :: Gear Design

1. When bevel gears having equal teeth and equal pitch angles connect two shafts whose axes intersect at right angle, then they are known as

a) angular bevel gears
b) crown bevel gears
c) internal bevel gears
d) mitre gears

Justification: When equal bevel gears (having equal teeth and equal pitch angles) connect two shafts whose axes intersect at right angle, then they are known as mitre gears.
When the bevel gears connect two shafts whose axes intersect at an angle other than a right angle, then they are known as angular bevel gears.

2. The face angle of a bevel gear is equal to

a) pitch angle – addendum angle
b) pitch angle + addendum angle
c) pitch angle – dedendum angle
d) pitch angle + dedendum angle

Justification: Face angle is the angle subtended by the face of the tooth at the cone centre. It is denoted by ‘φ’. The face angle is equal to the pitch angle plus addendum angle.

3. The root angle of a bevel gear is equal to

a) pitch angle – addendum angle
b) pitch angle + addendum angle
c) pitch angle – dedendum angle
d) pitch angle + dedendum angle

Justification: Root angle is the angle subtended by the root of the tooth at the cone centre. It is denoted by ‘θR’. It is equal to the pitch angle minus dedendum angle.

4. If b denotes the face width and L denotes the cone distance, then the bevel factor is written as

a) b / L
b) b / 2L
c) 1 – 2 b.L
d) 1 – b / L

Justification: If b denotes the face width and L denotes the cone distance, then the bevel factor is written as Bevel factor = 1 – b / L.

5. For a bevel gear having the pitch angle θ, the ratio of formative number of teeth (TE) to actual number of teeth (T) is

a) 1/sin θ
b) 1/cos θ
c) 1/tan θ
d) sin θ cos θ

Justification: For a bevel gear having the pitch angle θ, the ratio of formative number of teeth (TE) to actual number of teeth (T) is (TE)/T = 1/cos θ.

6. The worm gears are widely used for transmitting power at ______________ velocity ratios between non-intersecting shafts.

a) high
b) low
c) medium
d) none of the mentioned

Justification: The worm gears are widely used for transmitting power at high velocity ratios between non-intersecting shafts that are generally, but not necessarily, at right angles.

7. In worm gears, the angle between the tangent to the thread helix on the pitch cylinder and the plane normal to the axis of worm is called

a) pressure angle
c) helix angle
d) friction angle

Justification: Lead angle is the angle between the tangent to the thread helix on the pitch cylinder and the plane normal to the axis of the worm. It is denoted by λ.

8. The normal lead, in a worm having multiple start threads, is given by

a) lN = l / cos λ
b) lN = l . cos λ
c) lN = l
d) lN = l tan

Justification: The term normal pitch is used for a worm having single start threads. In case of a worm having multiple start threads, the term normal lead (lN) is used, such that
lN = l . cos λ
where lN = Normal lead,
l = Lead, and
λ = Lead angle.

9. The number of starts on the worm for a velocity ratio of 40 should be

a) single
b) double
c) triple

Justification: For number of starts from 36 and above we have single velocity ratio. For 12 to 36 we have double velocity ratio, for 8 to 12, we have triple velocity ratio and for 6 to 12 we have quadruple velocity ratio.

10. The axial thrust on the worm (WA) is given by

a) WA = WT . tan φ
b) WA = WT / tan φ
c) WA = WT . tan λ
d) WA = WT / tan λ

Justification: Axial force or thrust on the worm,
WA = WT / tan λ = Tangential force on the worm gear
where WT = Tangential force acting on the worm,
φ = Pressure angle, and
λ = Lead angle.

11. Worm gear drives are used to transmit power between two non-intersecting shafts which are generally at right angles to each other.

a) True
b) False

12. The worm and worm wheel both are threaded screw.

a) True
b) Worm wheel is a toothed gear
c) Worm is a toothed gear
d) None of the listed

13. Which of the following is not true about worm gears?

a) Compact
b) Smooth and silent operation
c) Low speed reduction
d) All the mentioned are true

14. Is it possible to use worm gears in cranes for lifting purpose?

a) True
b) No self-locking and hence not possible
c) Possible up to a threshold load
d) None of the listed

15. The power transmitting capacity of worm gears is high although efficiency is low.

a) True
b) False

16. Can worm gears be used in steering mechanism?

a) True
b) False

17. The worm helix angle is the _____ of the worm lead angle.

a) Complement
b) Half
c) Double
d) Supplement

If worm helix angle is 30⁰, then worm should have at least ___ threads.
a) 5
b) 6
c) 7
d) 8

18. A pair of worm gear is written as 2/40/12/6. Calculate the centre distance.

a) 40mm
b) 156mm
c) 200mm
d) 80mm

19. A pair of worm gear is written as 2/40/12/6. Calculate the speed reduction.
a) 2
b) 20
c) 15
d) 6

20. A pair of worm gear is written as 2/40/12/6. Calculate the pitch circle diameter of worm wheel.
a) 72mm
b) 240mm
c) 260mm
d) 320mm

21. A pair of worm gear is written as 2/40/12/6. Calculate the throat diameter of the worm wheel.
a) 220.5mm
b) 246.4mm
c) 190.44mm
d) 251.7mm

22. A pair of worm gear is written as 2/40/12/6. Calculate the root diameter of the worm wheel.

a) 186.22mm
b) 250.4mm
c) 225.6mm
d) 250.44mm