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.

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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