Introduction : 


             Screw Jack is a mechanical component which is used to lift very high load. Screw jack is also called as a Jackscrew.  Screw Jack acts on the principle of the Right hand screw rule ie the translational motion will be perpendicular to the plane of Rotation. The Handle of the screw jack rotates and the translational motion acts up or down depending upon the direction of Rotation. One of the most important concept matters in its analysis is the Friction. For screw we call it as a Screw Friction. 

Construction:


         Screw Jack has a high duty working screw mounted at its top which is assembled in threaded hole of the body.   
As it has to lift a high load to apply couple to the screw the lever is joined to the screw by which after applying a 
required horizontal force screw will rotate. A screw jack is the assembly of the different parts which are as follows:
  • Body 
  • Nut
  • Screw 
  • Washer
  • Tommy bar

The drawing of parts of Screw Jack is given below :
Screw Jack Parts


 Mathematical Analysis :



             Screw is threaded helically. When the hypotenuse of a right angled triangle is wound to a cylinder. It becomes Helical and the angle between hypotenuse and base is called as Helix angle. As the as the threads are slided over each other while rotation. For Friction we can assume the hypotenuse to be an Inclined plane. Hence it becomes the condition of the Friction of the inclined plane.   




For the screw Jack to lift weight, the least required torque will be equal to the product of the frictional force (in screw friction and the length of lever / Radius of rotation of lever r.)

Conclusion : Given post tells the concept behind working of screw jack also, presents the equations of Required force Mechanical Advantage and efficiency of Screw Jack



Published by,
Shreyas S Chaudhari.