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# Machine Kinematics MCQ – Worm Gears

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

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Answer: d

Explanation: 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.

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

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Answer: b

Explanation: 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.

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

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Answer: c

Explanation: 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.

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

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Answer: d

Explanation: Bevel factor = 1 – b / L.

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

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Answer: b

Explanation: (TE)/T = 1/cos θ.

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

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Answer: a

Explanation: 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.

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

b) lead angle

c) helix angle

d) friction angle

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Answer: b

Explanation: 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.

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

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Answer: b

Explanation: 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.

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

a) single

b) double

c) triple

d) quadruple

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Answer: a

Explanation: 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.

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

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Answer: d

Explanation: 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.