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# Machine Kinematics MCQ – Standard Proportions of Gear Systems

If T is the actual number of teeth on a helical gear and φ is the helix angle for the teeth, the formative number of teeth is written as

a) T sec3 φ

b) T sec2 φ

c) T/sec3φ

d) T cosec φ

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Answer: a

Explanation: The formative or equivalent number of teeth for a helical gear may be defined as the number of teeth that can be generated on the surface of a cylinder having a radius equal to the radius of curvature at a point at the tip of the minor axis of an ellipse obtained by taking a section of the gear in the normal plane. Mathematically, formative or equivalent number of teeth on a helical gear,

T sec3 φ

In helical gears, the distance between similar faces of adjacent teeth along a helix on the pitch cylinders normal to the teeth, is called

a) normal pitch

b) axial pitch

c) diametral pitch

d) module

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Answer: a

Explanation: Normal pitch is the distance between similar faces of adjacent teeth along a helix on the pitch cylinders normal to the teeth.

Axial pitch is the distance, parallel to the axis, between similar faces of adjacent teeth.

In helical gears, the right hand helices on one gear will mesh ____________ helices on the other gear.

a) right hand

b) left hand

c) opposite

d) none of the mentioned

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Answer: b

Explanation: A helical gear has teeth in form of helix around the gear. Two such gears may be used to connect two parallel shafts in place of spur gears. The helixes may be right handed on one gear and left handed on the other.

The helix angle for single helical gears ranges from

a) 10° to 15°

b) 15° to 20°

c) 20° to 35°

d) 35° to 50°

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Answer: c

Explanation: In single helical gears, the helix angle ranges from 20° to 35°, while for double helical gears, it may be made upto 45°.

The helix angle for double helical gears may be made up to

a) 45°

b) 60°

c) 75°

d) 90°

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Answer: a

Explanation: In single helical gears, the helix angle ranges from 20° to 35°, while for double helical gears, it may be made upto 45°.

The outside diameter of an involute gear is equal to pitch circle diameter plus

a) 2 addendum

b) 2 dedendum

c) 3.1416 module

d) 2.157 module

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Answer: a

Explanation: Addendum is the portion of gear tooth above the pitch circle diameter (PCD). Therefore outside diameter of involute gear = PCD + 2 addendum.

Pick out the false statement about relationships of spur gears.

a) Pitch diameter = module x No. of teeth

b) Module = 25.4/diametral pitch

c) dedendum = 1.25 x module

d) Base pitch = module x п x sinɸ

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Answer: d

Explanation: The false statement is

Base pitch = module x п x sinɸ

Correct relationship of base pitch = module x п x cosɸ

Which of the following is not the correct property of involute curve?

a) The form or shape pf an involute curve depends upon the diameter of base circle from which it is derived

b) The angular motion of two involute gear teeth rotating at a uniform rate will be uniform, irrespective of the centre distance

c) The relative rate of motion between driving and driven gears having involute tooth curves, is established by the diameters of their pitch circles

d) the pitch diameters of mating involute gears are directly proportional to the diameters of their respective base circles

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Answer: c

Explanation: All statements except at (c) are correct. The correct statement for (c) is – The relative rate motion between driving and driven gears having involute tooth curves, is established by the diameters of their base circles.

Which of the following gear ratio does not result in hunting tool

a) 77/20

b) 76/21

c) 75/22

d) 71/25

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Answer: d

Explanation: When several pairs of gears operating at the same centre distance are required to have hunting ratios, this can be accomplished by having the sum of the teeth in each pair equal to a prime number.

In measuring the chordal thickness, the vertical scale of a gear tooth caliper is set to the chordal or corrected addendum to locate the caliper jaws at the pitch line.If a = addendum, t = circular thickness of tooth at pitch diameter D, then chordal thickness is equal to

a) a + t/D

b) a + t2/D

c) a + t3/2D

d) a + t2/4D

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Answer: d

Explanation: The correct relationship is chordal thickness = a + t2/4D