Subject: Machine Design -I

Topic: Design against static Loads, Bolted and welded joints under eccentric loading. Power Screw

Difficulty: Medium

Advantages of square threads over trapezoidal threads.

• The efficiency of square threads is more than that of trapezoidal threads.
• There is no radial pressure or side thrust on the nut. This radial pressure is called ‘bursting’ pressure on the nut. Since there is no side thrust, the motion of the nut is uniform. The life of the nut is also increased.

Disadvantages of square threads.

• Square threads are difficult to manufacture.
• The strength of a screw depends upon the thread thickness at the core diameter. Square threads have less thickness at the core diameter than trapezoidal threads.
• The wear of the thread surface becomes a serious problem in the service life of the power screw. It is not possible to compensate for wear in square threads. Therefore, when worn out, the nut or the screw requires replacement.