Question and answers
| Que.No | Marks | |
|---|---|---|
| Q 1a)(ii) |
8 |
Question:What is a cotter joint? State any four applications of a cotter joint? Why taper is provided on cotter joint?Answer: COTTER JOINTCotter Joint: " A cotter joint is temporary joint and used to connect two coaxial rods or bars which are subjected to axial tensile and or compressive forces." It consist of 1) spigot : It is the male part of the joint , it has a rectangular slot for passing the cotter through it. Spigot has a collar which rests against the socket end. 2) socket :It is the female part of the joint, it also has a rectangular slot for passing the cotter through it. It has a circular hole in which spigot fits. 3) cotter : is a wedge shaped piece of metal which actually connects two parts which are non rotating.
Cotter Joint Applications:1) Lewis foundation bolt 2) connection of the piston rod to cross head of a reciprocating steam engine. 3) valve rod & its stem 4) piston rod to the trail end in an air pump. 5) Cycle pedal sprocket wheel. Cotter joint taper why and how much?Cotter is a flat wedge shaped metal piece which is used to connect two rods which transmit the force but without rotation. The force may be axial and of tensile or compressive nature. Cotter is fitted in the tapered slot and remains in its position because of wedge action. This happens because of taper. Because of taper, i) It is simple to remove the cotter and dismantle the joint parts. ii) Taper ensures tightness of the joint in operation and it prevents slackening of the parts. Generally the value of taper on cotter is 1 in 48 to 1 in 24. 1 in 48 means that there will be reduction of 1 mm in size after the length of 48 mm, and 1 in 24 means there will be reduction in size of cotter by 1 mm after 24 mm.
Link to other chapters in machine design http://mechdiploma.com/elements-machine-design-syllabus22564 ----------------------------------------------------------------------------------------------------- |
| Q 2 a ) |
8 |
Question:Design a knuckle joint to transmit 150 KN. The design stresses may be taken as 75 MPa in tension, 60 MPa in shear and 150 MPa in compression.Answer: Design of knuckle joint: Step 1) Diameter of Rod: d : =? Consider tensile failure of Rod 1. P =σt x A , 150 x 103 = 75 x π/4 xd2 , d = 50.4 mm 52 mm ( say) Using Imperial relations Diameter of Knuckle pin Outside
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| Q 2c)(i) |
8 |
Question:Why are bushes of softer material inserted in the eyes of levers?Answer:
the forces acting on the boss of lever & the pin are equal & opposite .There is a relative motion between the pin & the lever and bearing pressure becomes design criteria. The projected area of the pin is d1 x l1therefore Reaction R= P (d1 x l1 ). A softer material like phosphorous bronze bush with 3 mm thick is fitted in eyes to reduce the friction. & bear a bearing pressure upto5 to 10 N/mm2. Bushes are cheaper and can be easily replaceable. ----------------------------------------------------------------------------------------------------- |
| Q 3 b ) |
4 |
Question:Design a foot brake lever from the following data: Length of lever from C.G. of the spindle to the point of application of the load = 1 meter. Max. load on the foot plate = 800 N Overhang from the nearest bearing = 100 mm Permissible tensile and shear stress = 70 MPa.Answer: Methods of reducing stress concentration in cylindrical members with holes . Stress concentration can be reduced in cylindrical members with holes by providing additional holes in vicinity of holes as shown in fig. (ii). Fig (i) Showing cylindrical member with hole at center having stress line in disturb manner at vicinity of hole and component will fail at hole so for fig (i) ,stress concentration is more . fig. (ii) members shoulder having additional hole in vicinity of hole and therefore stress line maintain spacing between them so here stress concentration is less. Design of foot lever : Given data: L=1 m =1000 mm , P=800 N , σt =70 N/mm2 , Ʈ =70 N/mm2 , Assume B=3t Step 1) Considering shaft is under pure torsion , therefore
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| Que.No | Marks | |
|---|---|---|
| Q 1 f ) |
2 |
Question:Give two applications of knuckle joint.Answer: (i) A knuckle joint is used to connect two rods which are under the action of tensile loads. However, if the joint is guided, the rods may support a compressive load. (ii) Its use may be found in the link of a cycle chain, tie rod joint of roof truss, valve rod joint with eccentric rod, pump rod joint, tension link in bridge structure and lever and rod connections of various types. ----------------------------------------------------------------------------------------------------- |
| Q 2 a ) |
8 |
Question:Explain various failures to be considered in designing a cotter joint along with the necessary sketches and strength equations.Answer:
It consist of 3 elements: i. Socket ii. Spigot iii. Cotter Where, d= End diameter of rod d1= Diameter of spigot/Inside diameter of socket d2= Diameter of spigot collar D1= Outer diameter of socket D2= Diameter of socket collar C=Thickness of socket collar t1= Thickness of spigot collar t= thickness of cotter b= Mean width of cotter a= Distance of end of slot to the end of spigot P= Axial tensile/compressive force σt , σc , τ= Permissible tensile, compressive, shear stress for the component materia
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| Q 3 ) |
8 |
Question:Fig.1Show of hacksaw The belt is assembled with tensoionAnswer:
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| Que.No | Marks | |
|---|---|---|
| Q 1 ii ) |
4 |
Question:Write the design procedure for turn buckle. (Any four steps)Answer: Write any four equation s in the design of turn buckle with relevant sketches
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| Q 2a)(ii) |
8 |
Question:Why taper is provided on cotter ? State recommended values of taper.Answer: a. When cotter is driven through the slots, it fit, fight due to wedge action. This ensures tightness of joint in operation and present loosening of the parts. b. Due to taper, it is easy to remove the cotter and dismantle the joint. The normal value of taper varies from 1 in 48 to 01 in 24 and it may increase to 1 in 8 ----------------------------------------------------------------------------------------------------- |
| Q 2 b ) |
8 |
Question:Draw neat sketch showing the details of cotter joint. State strength equations for each component with suitable failure cross-sectional area.Answer:
It consist of 3 elements i. Socket ii. Spigot iii. Cotter Where, d= End diameter of rodd1= Diameter of spigot/ID of socket d2= Diameter of spigot collar D1= Outer diameter of socket D2= Diameter of socket collar C=Thickness of socket collar t1= Thickness of spigot collar t= thickness of cotter b= Mean width of cotter a= Distance of end of slot to the end of spigot P= Axial tensile/compressive force σt, σc, τ= Permissible tensile, compressive, shear stress for the component material
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| Q 3 b ) |
4 |
Question:Draw a neat sketch of bell crank lever. Enlist steps in designing the bell crank leverAnswer:
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| Que.No | Marks | |
|---|---|---|
| Q 1a)(ii) |
4 |
Question:Write the design procedure of knuckle joint.Answer: Design of Knuckle joint Failure of rod in tension
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| Q 2 a ) |
8 |
Question:Explain with the help of neat sketches three basic types of lever. State one application of each type.Answer: In the first type of levers, the fulcrum is in between the load and effort. In this case, the effort arm is greater than load arm, therefore M.A. obtained is more than 1 Application: Bell crank levers used in railway signaling arrangement, rocker arm in I.C. Engines , handle of a hand pump, hand wheel of a punching press, beam of a balance, foot lever (any 1) In the second type of levers, the load is in between the fulcrum and effort. In this case, the effort arm is more than the load arm, therefore M.A. is more than 1. Application: levers of loaded safety valves, wheel barrow, nut cracker (any1) In the third type of levers, the effort is in between the fulcrum and load. Since the effort arm, in this case, is less than the load arm, therefore M.A. is less than 1 Application: a pair of tongs, the treadle of sewing machine
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| Q 2 b ) |
8 |
Question:Explain with the help of neat sketches, the design procedure of a square sunk keyAnswer:
T= Torque transmitted by the shaft , F= tangential force acting at the circumference of the shaft,
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| Q 2c)(ii) |
8 |
Question:State two applications each of cotter joint and knuckle joint.Answer: Applications of cotter joint: cotter foundation bolt, big end of the connecting rod of a steam engine, joining piston rod with cross head, joining two rods with a pipe Applications of knuckle joint: link of bicycle chain, tie bar of roof truss, link of suspension bridge, valve mechanism, fulcrum of lever, joint for rail shifting mechanism ----------------------------------------------------------------------------------------------------- |
| Q 3 b ) |
4 |
Question:Design single cotter joint to transmit 200 kN. Allowable stresses for the material are 75 MPa in tension and 50 MPa in shear.Answer:
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| Que.No | Marks | |
|---|---|---|
| Q 1a)(ii) |
4 |
Question:Differentiate between Knuckle joint and Cotter joint. (any four points of difference)Answer:
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| Q 3 b ) |
4 |
Question:Design an offset link for a load of 1000 N. Maximum permissible stress in tension for link material is 60 N/mm2. Assume b = 3t for rectangular cross section of the link.Answer:
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