Cotter & Knuckle Joints Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

COTTER AND KNUCKLE JOINTS

• A cotter is a flat wedged-shape piece of rectangular cross-section and its width is tapered from one end to another for an easy adjustment. 
• The cotter is usually made of mild steel or wrought Iron. A cotter joint is a temporary fastening and is used to connect rigidly to co-axial shafts which are subjected to axial tensile or compressive forces. 
• It is usually used in connecting a position rods to the cross head of a reciprocating steam engine, strap end of connecting rod etc.
• Types of Cotter Joints 
  • Socket and Spigot cotter joint 
  • Sleeve and cotter joint 
  • Gib and cotter joint.
• Socket and Spoigot Cotter Joint

• Formula
  • Failure of rods in tension
    
  • Failure of spigot in tension across the weakest section
    
  • Failure of the rod or cotter in crushing p = d₂.t.sc
  • Failure of socket in tension across the slot.
    
  • Failure of cotter in shear (double shear) p = 2 bt. t_s
  • Failure of socket collar in crushing  p = (d₄ – d₂) . t . s_c
  • Failure of socket end in shearing p = 2(d₄ – d₂) c × t_s
  • Failure of rod end in shear p = 2ad₂ . t_s
  • Failure of spigot collar in crushing
    
  • Failure eof spigot collar in shearing
    

• Knuckle Joint
  • A knuckle joint is used to connect two rods which are under the action of tensile force. If the joint is guided, the rods may support a compressive load. 
  • Its use may be find in the link of a cycle chain, the rod joint for roof truss, valve rod joints with eccentric rod, pump rod joint, tension link in bridge structure and lever and connection of various types. 
  • The material used for the joint may be steel or wrought iron.