A knuckle joint connects two rods under tension and allows for small angular movements. It consists of eye ends, a forked end, a pin, and collar. The joint is designed by calculating rod diameters based on load, choosing eye/fork thicknesses and pin diameter based on empirical relations, and checking stresses do not exceed allowable values for tension, shear, and crushing. Knuckle joints can withstand tensile loads, are rigid but flexible, and easy to manufacture but cannot handle compression or multi-plane movements.

2. 1. Introduction of knuckle joint
2. Part of knuckle joint
3. calculation
4. Application of knuckle joint
5. Advantage of knuckle joint
6. Disadvantage of knuckle joint

3. A knuckle joint is a mechanical joint used to connect two rods which are
under a tensile load, when there is a requirement of small amount
of flexibility, or angular moment is necessary. There is always axial or
linear line of action of load.

4. A typical knuckle joint has the following parts:
 Fork end
 Eye end
 Knuckle pin
 Collar
 Taper pin

6. Calculation:-
As seen in the assembly the Knuckle joint has main four parts
 Rods {Which are to be connected by joint }
 Single eye {Modified rod for assembly}
 Double eye or Forked end {Modified rod for assembly}
 Pin {Connects the two rods}
 Collar {to keep the pin in position}
 Split pin or taper pin

8. Notations used in design :
 P = Tension in rod ( Load on the joint)
 D = Diameter of rod
 D1= Enlarged diameter of rod
 d = Diameter of pin
 d1 = Diameter of pin head
 d0 = Outer diameter of eye or fork
 t1 = thickness of eye end
 t2= thickness of forked end (double eye)
 x= distance of the Centre of fork radius R from the eye

9. STEPS TO DESIGN KNUCKLE JOINT
Step 1 : Design of Rods (D,D1)
Tensile failure of rod
Using basic strength equation
Load = Stress * Area

10. Empirical relations
Using Empirical relations the enlarged diameter of rod D1 is determined
Step 2 : Decide the thickness of eye end and forked end (t1,t2)
Empirical relations
Both these dimensions are decided on the basis of empirical relations,
t1= 1.25 D and t2= 0.75 D

11. Step 3 : Decide the dimensions of pin (d,d1)
Double shear Failure
The pin may get sheared off into three pieces as shown below, since the pin breaks
at two places it is called double shear. Both areas are taken as resisting areas.
Using basic strength equation
Load = Stress * Area

12. Bending failure of pin
The diameter on the basis of bending is determined using the following formula,
…..Calculate d from this formula
Empirical relation for pin head diameter
Since pin head is not subjected to any stress, its diameter is simply decided on the
basis of proportionality, (it is taken 50% more than that of pin diameter )
d1=1.5 d
Step 4 : Check Stresses in Eye end
Empirical relation for outside diameter of eye and fork
d0=2d
Tensile failure of eye end
The single eye may fail in tension as shown below { please note that when the plane
of failure is perpendicular to the direction of force then the failure is either tensile
or compressive}

13. Step 4 : Check Stresses in Eye end
Empirical relation for outside diameter of eye and fork
d0=2d
Tensile failure of eye end
The single eye may fail in tension as shown below { please note that when the plane
of failure is perpendicular to the direction of force then the failure is either tensile
or compressive}
Using the basic equation for stress

14. Shear failure of eye end
The single eye may fail in shear as shown below { please note that when the plane of
failure is parallel to the direction of force then the failure is Shear failure}
Using the basic equation for stress
simplifying this equation we get
Using this equation find the value of
and check if it is less than allowable value for
design to be safe

15. Crushing Failure of eye end
The single eye is also subjected to Crushing between pin and inner face of single eye.
In case of crushing failure since the area is curved we take the projected (area
which would be visible in drawing) of the cylindrical area. As we know that a
cylinder appears as a rectangle in projection, hence the area will be diameter times
the height of cylinder. This area is illustrated below
Using the basic equation for stress
………….Using this equation find the value of
and check if it is less than allowable
value for design to be safe.

16.  Step 5 : Check Stresses fork end
Fork end is also subjected to same failures as that of eye end, the only difference is
that it has two eyes. So we get the same equations except multiplied by 2.
The equations for tensile, shear and crushing failures are given below
Tensile failure of fork end
{see the changes highlighted in red from the equation of single eye} Get the value
of induced tensile stress from this equation and confirm that it is below allowable
tensile stress.
Shear failure of fork end
{see the changes highlighted in red from the equation of single eye} Get the value
of induced shear stress from this equation and confirm that it is below allowable
shear stress.

18. 1. Knuckle joint can withstand large tensile
loads.
2. It has good mechanical rigidity.
3. It is easy to manufacture and set up.
4. It can be easily dismantled and assembled.
5. Design is simple and easy.

19. 1. The joint cannot withstand large
compressive loads.
2. It permits angular movement in only one
plane.
3. It is not as flexible as universal joint.