Machine Kinematics

Standard Proportions of Gear Systems

Question 1
Marks : +2 | -2
Pass Ratio : 4%
In helical gears, the right hand helices on one gear will mesh ____________ helices on the other gear.
right hand
left hand
opposite
none of the mentioned
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.
Question 2
Marks : +2 | -2
Pass Ratio : 6%
The helix angle for single helical gears ranges from
10° to 15°
15° to 20°
20° to 35°
35° to 50°
Explanation:
In single helical gears, the helix angle ranges from 20° to 35°, while for double helical gears, it may be made upto 45°.
Question 3
Marks : +2 | -2
Pass Ratio : 2%
In helical gears, the distance between similar faces of adjacent teeth along a helix on the pitch cylinders normal to the teeth, is called
normal pitch
axial pitch
diametral pitch
module
Explanation:
Normal pitch is the distance between similar faces of adjacent teeth along a helix on the pitch cylinders normal to the teeth.
Question 4
Marks : +2 | -2
Pass Ratio : 1%
The helix angle for double helical gears may be made up to
45°
60°
75°
90°
Explanation:
In single helical gears, the helix angle ranges from 20° to 35°, while for double helical gears, it may be made upto 45°.
Question 5
Marks : +2 | -2
Pass Ratio : 8%
Which of the following is not the correct property of involute curve?
The form or shape pf an involute curve depends upon the diameter of base circle from which it is derived
The angular motion of two involute gear teeth rotating at a uniform rate will be uniform, irrespective of the centre distance
The relative rate of motion between driving and driven gears having involute tooth curves, is established by the diameters of their pitch circles
the pitch diameters of mating involute gears are directly proportional to the diameters of their respective base circles
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.
Question 6
Marks : +2 | -2
Pass Ratio : 4%
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
T sec3 φ
T sec2 φ
T/sec3φ
T cosec φ
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,
Question 7
Marks : +2 | -2
Pass Ratio : 10%
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 + t/D
a + t2/D
a + t3/2D
a + t2/4D
Explanation:
The correct relationship is chordal thickness = a + t2/4D
Question 8
Marks : +2 | -2
Pass Ratio : 3%
The outside diameter of an involute gear is equal to pitch circle diameter plus
2 addendum
2 dedendum
3.1416 module
2.157 module
Explanation:
Addendum is the portion of gear tooth above the pitch circle diameter (PCD). Therefore outside diameter of involute gear = PCD + 2 addendum.
Question 9
Marks : +2 | -2
Pass Ratio : 20%
Which of the following gear ratio does not result in hunting tool
77/20
76/21
75/22
71/25
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.
Question 10
Marks : +2 | -2
Pass Ratio : 3%
Pick out the false statement about relationships of spur gears.
Pitch diameter = module x No. of teeth
Module = 25.4/diametral pitch
dedendum = 1.25 x module
Base pitch = module x п x sinɸ
Explanation:
The false statement is