THe device shown is used for coarse adjustment of the height of an experimental

Question

THe device shown is used for coarse adjustment of the height of an experimental apparatus without a change in its horizontal position. Because of the slipjoint at A, turning the screw does not rotate the cylindrical leg above A. The mean diameter of the thread is 3/8 in. and the coefficient of friction is 0.15. For a conservative design which neglects friction at the slipjoint, what should be the minimum number N of threads per inch to ensure that the single-threaded screw does not turn by itself under the weight of the apparatus? The answer is 5.66 threads per inch

The device shown is used for coarse adjustment of the height of an experimental apparatus without a change in its horizontal position. Because of the slipjoint at A, turning the screw does not rotate the cylindrical leg above A. The mean diameter of the thread is 3/8 in. and the coefficient of friction is 0.15. For a conservative design which neglects friction at the slipjoint, what should be the minimum number N of threads per inch to ensure that the single-threaded screw does not turn by itself under the weight of the apparatus? The answer is 5.66 threads per inch

Explanation / Answer

for self locking or device will not lower itself due to its own weight.

u*pi*dm = L

where L = n*p

for a single threaded screw

L = p

u*pi*dm = p

p = 0.15*pi*3/8 inch

= 0.1767 inch

n = 1/0.1767 threads/inch

= 5.658 threads/inch

= 5.66 threads/inch

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