ABOUT FROMS OF THREADS, ITS SQUARE THREADS, ACME THREADS, TRAPEZOIDAL THREADS, AND BUTTRESS THREADS

WHAT IS FORMS OF THREADS ?

1. Square Threads :

• A square threads, are used for transmission of power in either direction.   

     Advantages of square threads :

      

     (i)     Square threads have maximum efficiency of all threads forms.

     (ii)    They exert minimum radial or bursting pressure on nut.

     (iii)   They can transmit power in either directions.

    Limitations of square threads :

 

     (i)    Strength of the square threadsis lowest of all the thread forms.

     (ii)   These threads cannot be used conveniently with split nut because :

              (a)   wear compenstion is not possible, and 

              (b)   engagement and disengagement is difficult.

    Applications of square threads :

  

            The square threads are used in screw jacks, mechanical presses, and clamping devices.

    2. Acme Threads :

•   The Acem  Threads, have thread  angle equal to.

   Advantage of acme threads :

  (i)     Acme threads permit the use of split nut which can compensate the wear.

  (ii)   Acme threads are  stronger than the square threads in shear because of the larger cross-                 section at the root.     

  (iii)   Acme threads can transmit power in either directions.

   Limitations of acme threads :

  

   (i)    Because of the slope given to the sides, the efficiency of acme threads is lower than that of               square threads.

   (ii)   The slope on the sides introduces some bursting pressure on the nut.

   Application of acme threads :

    Acme threads are used for lead screws of machine tools, bench vices, etc.

  

   3. Trapezoidal Threads :

•  The trapezoidal threads, are  similar to acme threads, except the thread  angle,  which  is  trapezoidal  threads.
•   The standard dimensions for  trapezoidal / Acme threads are given in Table.

  

    4. Buttress  Threads :

•  Buttress threads, are used where force or power is required to be transmitted only in one direction.
• Advantages of buttress threads :

          (i)    Buttress threads are stronger in shear than any other power threads because of the                          largest cross section  at the root.

          (ii)   The buttress threads combine the high efficiency of square threads and high strength                      of   V- threads. 

     Limitations of buttress threads :

     (i)     Buttress threads are used to transmit power in only one direction.

     (ii)    These treads are difficult to  manufacture.

    Applications of buttress threads :

     These threads are used in vices and screw jacks where force is to be applied only in one                   direction.