Machine Design Viva Question and Answers

While designing a parallel sunk key it is assumed that the distribution of force along the length of the key | Machine design viva question and answers

a) Varies linearly

b) is uniform throughout

c) varies exponentially, being more at the torque input end

d) varies exponentially, being less at torque output end

Answer: (c) Parallel sunk key. The parallel sunk keys may be of rectangular or square section uniform in width and thickness throughout. It may be noted that a parallel key is a taper less and is used where the pulley, gear or other mating piece is required to slide along the shaft. In designing a key, forces due to fit of the key are neglected and it is assumed that the distribution of forces along the length of key is uniform.

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Which sunk key made in the form of a segment of a circular disc of uniform thickness, known as?

a) Feather key

b) Kennedy key

c) Woodruff key

d) Saddle key

Answer: c) Woodruff Key

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The piston rod and the cross head in a steam engine are usually connected by means of

a) Cotter joint

b) Knuckle Joint

c) Ball Joint

d) Universal Joint

Answer: a) Cotter Joint

Explanation: Piston Connecting Rod in the cross head of a steam engine, valve rod and its stem etc. are examples of cotter joint

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In the assembly of pulley, key and shaft | Machine design viva question and answers

a) Pulley is made the weakest

b) Key is made the weakest

c) Key is made the strongest

d) All the three are designed for equal strength

Answer: b) Key is made the weakest so that it is cheap and easy to replace in case of failure

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A spur gear transmitting power is connected to the shaft with a key of rectangular section. The type of stresses developed in the key is fare

a) Shear stress alone

b) Bearing stress alone

c) Both shear and bearing stresses

d) Shearing, Bearing and Bending stresses

Answer: c) Key develops both shear and bearing stresses

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A cotter joint is used when no relative motion is permitted between the rods joined by the cotter. It is capable of transmitting

a) Twisting Moment

b) An axial tensile as well as compressive load

c) The bending moment

d) Only compressive axial load

Answer: b) An axial tensile as well as compressive load

Explanation: A cotter is a flat wedge shaped piece of steel. This is used to connect rigidly two rods which transmit motion in the axial direction, without rotation. These joints may be subjected to tensile or compressive forces along the axes of the rods

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A square key of side d/4 is to be fitted on a shaft of diameter d and in the hub of a pulley. If the material of the key and shaft is same and the two are to be equally strong in shear, what is the length of the key?

a) π d / 2

b) 2π d / 3

c) 3π d / 4

d) 4π d / 5

Answer: a) π d / 2

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In a gib and cotter joint, the gib and cotter are subjected to | Machine design viva question and answers

a) Single Shear only

b) Double Shear only

c) Single shear and crushing

d) Double shear and crushing

Answer: d) Double Shear and Crushing because a cotter joint is a temporary fastening and is used to connect rigidly two co-axial rods or bars which are subjected to axial tensile or compressive forces.

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A key connecting a Flange coupling to a shaft is likely to fail in

a) Shear

b) Tension

c) Torsion

d) Bending

Answer: a) Shear is the dominant stress on the key

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A set screws are

a) Similar to tap bolts except that a greater variety of shapes of heads are available

b) Slotted for screw driver and generally used with a nut

c) Used to prevent relative motion between parts

d) Similar to studs

Answer: c) Used to prevent relative motion between parts

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Self locking screw has | Machine design viva question and answers

a) Fine threads

b) Coarse threads

c) Two nuts

d) Coefficient of friction more than tangent of lead angle

Answer: d) Coefficient of friction more than tangent of lead angle

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The designation M36 x 2 means

a) Metric fine threads of 36mm outside diameter and 2mm pitch

b) Metric coarse threads of 36 mm outside diameter and 2 mm pitch

c) Metric threads of 36 mm pitch diameter and 2 mm pitch

d) Metric threads of 36 mm core diameter and 2 mm pitch

Answer: a) Metric fine threads of 36 mm outside diameter and 2 mm pitch

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The pitch diameter or external or internal screw thread is

a) Largest diameter

b) Smallest diameter

c) Effective diameter

d) Mean diameter

Answer: c) Effective diameter

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Screw is specified by | Machine design viva question and answers

a) Major diameter

b) Minor diameter

c) Pitch diameter

d) Mean diameter

Answer: a) Major diameter

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Washer is specified by | Machine design viva question and answers

a) Outer diameter

b) Inner diameter

c) Thickness

d) Mean diameter

Answer: b) Inner diameter

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Jam nut is a locking device in which | Machine design viva question and answers

a) A smaller nut is tightened against main nut creating friction at the contacting surface

b) A split pin is passed through diametrically opposite slots in nut and a hole in bolt and the two ends of split pin are separated and bent back on nut

c) A slot is cut in the middle of nut along the length and a cap screw is provided to tighten the two parts of nut separated by slot

d) An elastic piece is tightened in the nut by a set screw

Answer: a) A smaller nut is tightened against main nut creating friction at the contacting surface

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An ordinary bolt is converted into bolt of uniform strength by | Machine design viva question and answers

a) Reducing the shank diameter of bolt to the core diameter of threads

b) Drilling a hole all along the length of shank in unthreaded portion

c) Increasing the stress in the shank portion of bolt

d) Using all three methods

Answer: d) Using all three methods

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Eye bolts are used | Machine design viva question and answers

a) To prevent relative motion between two parts

b) To absorb shocks and vibrations

c) To lift and transport machines and heavy objects on shop floor

c) To prevent loosening of threads in bolted assembly

Answer: c) To lift and transport machines and heavy objects on shop floor

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While designing screw threads, adequate length of engaged threads between the screw and nut is provided so as to prevent failure of threads due to

a) Direct shear stress

b) Torsional shear stress

c) Tensile stress

d) Compressive stress

Answer: a) Direct shear stress

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When the shear strength of nut is equal to the tensile strength of bolt, the height of nut (h) should be | Machine design viva question and answers

a) h = 0.5 d

b) h = 0.25 d

c) h = 0.75 d

d) h = d

Answer: a) h = 0.5 d

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Allen key is used to tighten | Machine design viva question and answers

a) Cap screw with hexagonal head

b) Cap screw with fillister head

c) Cap screw with hexagonal socket head

d) Cap screw with flat head

Answer: c) Cap screw with hexagonal socket head

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The connecting rod bolts are tightened up so that the initial tightening stress | Machine design viva question and answers

a) Approaches yield point

b) Approaches endurance limit

c) Approaches (Yield point stress / Factor of safety)

d) Approaches (Endurance limit stress / Factor of safety)

Answer: a) Approaches yield point

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The shock absorbing capacity of a bolt can be increased by | Machine design viva question and answers

a) Increasing shank diameter

b) Making shank diameter equal to core diameter of threads

c) Using castle nut in place of ordinary hexagonal nut

d) Using a washer

Answer: b) Making shank diameter equal to core diameter of threads

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In a fillet welded joint, the weakest area of the weld is

a) Toe

b) Root

c) Throat

d) Face

Answer: c) Throat

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A single parallel fillet weld of total length ‘L’ and weld size ‘h’ is subjected to a tensile load’P’, will have what design stress?

a) Tensile and equal to P/0.707Lh

b) Tensile and equal to P/Lh

c) Shear and equal to P/0.707Lh

d) Shear and equal to P/Lh

Answer: c) Shear and equal to P/0.707Lh

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The bolts in a rigid flange coupling connecting two shafts transmitting power are subjected to | Machine design viva question and answers

a) Shear force and bending moment

b) Axial force

c) Torsion and bending moment

d) Torsion

Answer: a) Shear force and bending moment are subjected in the bolt while transmitting torque

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Total slip will occur in a belt drive when

a) Angle of rest is zero

b) Angle of creep is zero

c) Angle of rest is greater than angle of creep

d) Angle of creep is greater than angle of rest

Answer: a) Angle of rest is zero

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The ratio of tension on the tight side to that on the slack side in a flat belt drive is | Machine design viva question and answers

a) Proportional to the product of coefficient of friction and lap angle

b) An exponential function of the product of coefficient of friction and lap angle

c) Proportional to the lap angle

d) Proportional to the coefficient of friction

Answer: b) An exponential function of the product of coefficient of friction and lap angle

T1/T2 = e^μθ

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In a 6 x 20 wire rope, No.6 indicates the | Machine design viva question and answers

a) Diameter of the wire rope in mm

b) Number of strands in the wire rope

c) Number of wires

d) Gauge number of the wire

Answer: b) In 6 x 20 wire ropes, No.6 indicates number of strands in the wire rope and 20 indicates number of wire in a strand

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In designing a plate clutch, assumption of uniform wear condition is made because

a) It is closer to real life situation

b) It leads to a safer design

c) It leads to cost effective design

d) No other assumption is possible

Answer: a) It is closer to real life situation

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On the motors with low starting torque, the type of the clutch to be used is | Machine design viva question and answers

a) Multiple – plate clutch

b) Cone clutch

c) Centrifugal clutch

d) Single plate clutch with both sides effective

Answer: c) Centrifugal clutch

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The creep in a belt drive is due to the | Machine design viva question and answers

a) Material of the pulley

b) Material of the belt

c) Unequal size of the pulleys

d) Unequal tension on tight and slack sides of the belt

Answer: d) Unequal tension on tight and slack sides of the belt

Reason:

• When the belt passes from the slack side to the right side, a certain portion of the belt extends and it contracts again when the belt passes from the tight side to the slack side. Due to these changes of length, there is a relative motion between the belt and the pulley surfaces. This relative motion is termed as creep. The total effect of creep is to reduce slightly the speed of the driven pulley or follower
• Here english meaning of ‘Creep’ is ‘very slow motion’ and not ‘When a part is subjected to a constant stress at high temperature for a long period of time, it will undergo a slow and permanent deformation called ‘creep’.
• Therefore the belt creep is very slow motion between the belt and the pulley surfaces due to unequal tension on tight and slack sides of the belt.
• Don’t confuse with material of the belt because the belt creep depends on both the materials of the pulley and the materials of the belt.

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Which one of the following belts should not be used above 40 °C? | Machine design viva question and answers

a) Balata belt

b) Rubber belt

c) Fabric belt

d) Synthetic belt

Answer: b) Rubber belt

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In a belt drive, if the pulley diameter is doubled keeping the tension and belt width constant, then it will be necessary to | Machine design viva question and answers

a) Increase the key length

b) Increase the key depth

c) Increase the key width

d) Decrease the key length

Answer: c) Due to twice increase in diameter of pulley, torque on key is double and has to be resisted by key width. Length can’t be increased as belt width is same.

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