you will be able to improve you knowledge about cotter joints. i think after study this section you will know how to design cotter joints.

1. MACHINE DESIGN
PRESENTATION – 3
COTTER JOINTS
D.M.GAMAGE
INSTITUTE OF TECHNOLOGY
UNIVERSITY OF MORATUWA
SRI LANKA

2. 1. WHAT IS A COTTER JOINTS
 A cotter is a flag wedge shaped piece of
steel.
Cotter joint uses one or two cotters to
connect two rods rigidly transmitting forces
and motion, with no rotation of the rods

4. 2. TYPES OF COTTER
JOINTS
1.Socket and spigot cotter joint.
2.Sleeve and cotter joints.
3.Gib and cotter joints.

5. Socket and spigot cotter joint.
• In a socket and spigot cotter joints, one end of the rods is
provided with a socket type of end and the other end of the rod
is inserted into a socket the end of the rod which goes in to a
socket is also called spigot .a rectangular hole is made in the
socket and spigot

6. A cotter is then driven tightly through a hole in order to
make the temporary connection between the two rods
the load is usually acting axially but it changes its
direction
Hence the cotter must be design to carry both the
tensile and compressive load is taken up by the collar on
the spigot.

7. Sleeve and cotter joints.
• Sleeve and cotter joint is a type of joint used to
typically connect two similar coaxial cylindrical rods
it contains a sleeve and two wedge shaped tapered
cotters appropriate slots are cut in the sleeve and
in the cylindrical rods the cotters are assembled in

8. Gib and cotter joints.
• There are 3 type of gib and cotter joints
Gib and cotter joints
COTTER WITHOUT GIB COTTER WITH ONE GIB COTTER WITH
TWO GIB

9. COTTER WITH ONE GIB
•When one gib is used the cotter with one side
tapered is provided and the gib is always on
the outer slide.
COTTER WITH TWO GIB
•When two gibs are used the cotter with both slide
tapered is provided.

10. Cotter without gibs
•When the cotter alone is driven the friction
between its ends.
•The inside of the slots in the strap tends to
cause the slides of the strap to spread
outwards.
•More ever gibes provide a larger bearing
surface for the cotter to slide on due to

11. 3. APPLICATION OF COTTER JOINTS
Connection of the piston rod with
the cross heads.
Connection of a valve rod to its
stem.
Joining of tail rod with piston rod of
a wet air pump.

12. 4.Advantages of cotter joints
•Cotter joints can be easily made, and the
parts always occupy exactly the same relative
positions after reassembly
•The joints can be used to connect similar
pipes tubes.
•It is quite rigid and can take both tensile
and compressive loads.

13. 5.Disadvantages of cotter
joints
•Rectangular rods and dissimilar cylindrical
rods cannot be connected usingthis joints.
•The sleeve and cotter joints which cannot
connect cylindrical members undergo
rotation.

14. 6.FAILURE OF A COTTER JOINT

15. DESIGNING OF ROD
Designing of rod we should consider
FALIURE OF ROD IN TENSION
FALIURE OF ROD FALIURE OF ROD OR COTTER IN
CRUSHING
FALIURE OF ROD’S END IN SHEAR

16. TENSION FAILURE OF THE RODS AT
DIAMETER D
• Assume that the rod end, socket end and the cotter are made
of the same material
• P is the tensile force on the joint
• 𝜏 , 𝜎C, 𝜎t, and are the permissible tensile, shearing and
crushing stresses respectively
• Internal resistance to tearing = external applied load
•
𝜋
4
d2 𝜎
t = P

17. FALIURE OF ROD OR COTTER IN
CRUSHING
•d1 t 𝜎c = p

18. FALIURE OF ROD’S END IN SHEAR
2 a 𝜏 d1 = P

19. DESIGNING OF SPIGOT
Failure of spigot in tension
across the slot
Failure of spigot failure of spigot collar in
crushing
Failure of spigot collar in
shearing

20. TENSION FAILURE OF THE SPIGOT ACROSS THE
SLOT
•(
𝝅
𝟒
d1
2 – d1 t )𝝈 t =
P
• Inner diameter of the
socket, d1 can be obtained
when the thickness of the
cotter, t, is known

21. Failure of spigot collar in crushing
• Cotter joint may be used for
transmitting compressive load also
• This compressive load is
transmitted through the collar
(whereas the tensile load is
transmitted through the cotter)
𝜋
(d 2 – d 2 ) 𝜎 = P

22. Failure of spigot collar in shearing
• 𝜋 d1 t1 𝜏 = P
•Thickness of the
collar, t1 can be
calculated

23. DESIGNING OF SOCKET
FAILURE OF SOCKET IN TENSION
ACROSS THE SLOT
FAILURE OF SOCKET FAILURE OF SOCKET COLLAR IN
CRUSHING
FAILURE OF SOCKET END IN
SHEARING

24. FAILURE OF SOCKET IN TENSION
ACROSS THE SLOT
• P =
𝜋
4
{( D1
2 - d1
2 ) - ( D1 - d1 )t
} 𝜎 c
The outer diameter of the socket, D1 , can be
obtained

25. FAILURE OF SOCKET COLLAR IN CRUSHING
•(D1 – d1 ) t 𝜎 c = P

26. FAILURE OF SOCKET END IN SHEARING
•2 c (D – d1 ) 𝜏 = P

27. DESIGNING OF COTTER
• SHEAR FAILURE OF THE COTTER
• 2 b t 𝜏 = P
• The width of the cotter b can be obtained
• TAPER OF THE COTTER
• To ensure that the cotter does not work back, the taper
should not exceed 1 in 24

28. BENDING OF COTTER
• SINCE THE DISTRIBUTION OF PRESSURE ON THE CRUSHING SURFACE IS
UNKNOWN, THE BENDING MOMENT CANNOT BE ACCURATELY ESTIMATED
• PRESSURE DISTRIBUTION IS ASSUMED TO BE AS SHOWN IN THE FIGURE
• 𝜎 T =
𝑏𝑒𝑛𝑑𝑖𝑚𝑔 𝑚𝑜𝑚𝑒𝑛𝑡
𝑠𝑒𝑐𝑡𝑖𝑜𝑛 𝑚𝑜𝑑𝑢𝑙𝑢𝑠
• =
𝑃
2
{
d1
4
+
𝐷 −d1
6
}
𝑡 c2
6

29. THANKY
OU