This document summarizes the design of a cotter joint to connect two rods subjected to an axial tensile load of 28kN. It outlines the 10 potential failure modes of the joint and provides the equations to size each component based on the material properties. An example solution is then provided to design a cotter joint with a rod diameter of 30mm based on allowable stresses of 50MPa (tension), 60MPa (compression), and 35MPa (shear). Component sizes such as the spigot diameter, socket diameter, cotter thickness, and collar dimensions are calculated.

1. Subject :- Machine Design And Industrial Drafting
Topic :- Design of cotter joint
•Made By :-
-Utkarsh Gandhi -150990119007
-Digvijaysinh Gohil-150990119008
-Jaimin Prajapati-150990119010
-Abhijitsinh Kher-150990119012
•Guided By :-
-Mr. Rudra Parmar

2. COTTER JOINT
•A cotter joint is used to connect rigidly two co-axial rods or bars which
are subjected to axial tensile or compressive forces . It is a temporary
fastening.
• A cotter is a flat wedge shaped piece of rectangular cross section and its
width is tapered (either on one side or on both sides) from one end to
another for an easy adjustment.
.
Socket Cotter
Spigot

3. APPLICATIONS OF COTTER
1. Connection of the piston rod with the cross heads
2. Joining of tail rod with piston rod of a wet air
pump
3. Foundation bolt
4. Connecting two halves of fly wheel (cotter and
dowel arrangement)

4. Design of Spigot and Socket Cotter
Let P = Load carried by the rods,
d = Diameter of the rods,
d₁ = Outside diameter of socket,
d₂ = Diameter of spigot or inside
diameter of socket,
d₃ = Outside diameter of spigot
collar,
t₁ = Thickness of spigot collar,
d₄ = Diameter of socket collar,
c = Thickness of socket collar,
b = Mean width of cotter,
t = Thickness of cotter,
l = Length of cotter,
a = Distance from the end of the slot to the end of rod,
σt = Permissible tensile stress for the rods material,
τ = Permissible shear stress for the cotter material, and
σc = Permissible crushing stress for the cotter material.

5. SPIGOT BREAKING IN
TENSION OUTSIDE THE
JOINT
SPIGOT BREAKING IN
TENSION ACROSS
SLOT
Cotter joint – modes of failure

6. SOCKET
BREAKING IN
TENSION ACROSS
SLOT
SHEARING AWAY OF
SOCKET

7. SHEARING AWAY OF THE
COLLAR IN THE SPIGOT
DOUBLE SHEARING OF
SOCKET ENDDOUBLE
SHEARING OF
COTTER PIN

8. 1. Failure of the rod (Spigot) in tension
P= Area x Tensile stress

9. 2. Failure of spigot in tension across the
weakest section (or slot)
Area Resisting=
P
d2

10. 3. Failure of the rod (spigot) or cotter in
crushing
• P = d2 x t x σc
d2

11. 4. Failure of the socket in tension across
the slot
Area Resisting
Load P =

12. 5. Failure of cotter in shear

13. 6. Failure of the socket collar in
crushing

14. 7. Failure of socket end in shearing

15. 8. Failure of rod(Spigot) end in shear

16. 9. Failure of spigot collar in crushing

17. 10. Failure of the spigot collar in
shearing

18. Example :- Design a socket and spigot joint to resist a
tensile load of 28kN. All the parts of the joints are
made from same material with following allowable
stresses:
σt=50 N/mm2 , σc=60 N/mm2 , τ=35 N/mm2 .
Solution,
Data :- P=28kN
σt=50 N/mm2
σc=60 N/mm2
τ=35 N/mm2

19. 1. Diameter of rod (d) :-
• Tensile stress induced in rod,
4/2
d
P
t

 
4/
10*28
50 2
3
d

mmd 30

20. 2. Diameter of spigot (dt) and thickness of cotter (t) :-
• Taking t=0.3d=0.3*30=9mm
• The tensile stress in spigot,
)9*4/( 1
2
dd
P
t




)9*4/(
10*28
50
1
2
3
dd 


mmd 341 

21. • The crushing stress in cotter and spigot:-
• Taking larger dia,
td
P
c
1

9*
10*28
50
1
3
d

mmd 521 
mmd 521 

22. 3.outside diameter of socket (Dt) :-
• The tensile stress in socket,
    tdDdD
P
t
11
2
1
2
1 4/ 



    9524/52
10*28
50
1
22
1
3


DD
mmD 601 

23. 4.Distance from the end of slot to the end of spigot
(a):-
ad
P
12

a*52*2
10*28
35
3

mma 8

24. 5. Diameter of socket collar (D2) :-
tdD
P
c
)( 12 

9)52(
10*28
60
2
3


D
mmD 602 

25. 6. Thickness of socket collar (c) :-
• The direct stress in socket collar,
cdD
P
)(2 12 

c)52104(2
10*28
35
3


mmc 8

26. 7. Diameter of spigot collar (d2) :-
• The crushing stress in spigot collar,
  4/
2
1
2
2 dd
P
c




  4/52
10*28
22
2
3


d
c


mmd 582 

27. 8. Thickness of spigot collar (t1) :-
• The direct stress in spigot collar,
11td
P

 
1
3
*52*
10*28
35
t

mmt 51 

28. 9. Width of the cottar (b) :-
• The direct shear stress in cottar,
bt
P
2

9*2
10*28
35
3
b

mmb 45

29. 10. Cottar under bending :-
• The maximum bending moment on cottar ,











42262
1112 dPddDP
M







462
112 ddDP







4
52
6
52104
2
10*28 3
mmN.10*033.3 3


30. • The maximum bending stress in a cottar,
3
12
1
2/*
tb
bM
I
MX
yy
b 
2
6
tb
M
b 
2
3
*9
10*033.3*6
50
b

mmb 64