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VIZAG MT Mechanical: 2013(Re-exam) Official Paper

Option 2 : 4.85°, 5.7°

ME Subject Test 1: Strength of Materials

9294

20 Questions
20 Marks
18 Mins

__Concept:__

Screw threads are frequently used in jacks, presses, and other machines.

Screw thread acts as an inclined plane of the angle of inclination equal to the helix angle α as shown in the figure.

The **helix angle **of the thread is α

\( \tanα =\frac{p}{2\pi r}\)

where, p = thread pitch of screw, r = mean radius of a screw.

The **friction angle** ϕ = tan-1 μ

where μ = coefficient of static friction.

__Calculation:__

__Given:__

p = 12 mm, r = 22.5 mm. μ = 0.10, length of lever = 600 mm, load = 1800 kg.

The helix angle of the thread is α, where,

\( \tanα =\frac{p}{2\pi r}\)

\(α=\tan^{-1}({12\over2\times\pi\times 22.5})\)

**α = 4.85°**

The friction angle

ϕ = tan-1 μ

ϕ = tan-1 (0.10)

**ϕ = 5.71° **