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Mechanical Engineering QUESTION #2455
Question 1
For a square-threaded power screw with pitch diameter \(d_m\), lead \(l\), and coefficient of friction \(\mu\), the condition for self-locking is:
  • \(\mu < \tan\lambda\)
  • \(\mu = \tan\lambda\)
  • \(\mu \geq \tan\lambda\) where \(\lambda\) is the thread lead angle✔️
  • \(\mu > \frac{l}{\pi d_m^2}\)
Correct Answer Explanation
The self-locking condition: \(\pi\mu d_m \geq l\). Since \(\tan\lambda = l/(\pi d_m)\), this reduces to \(\mu \geq \tan\lambda\). When this condition holds, the load cannot back-drive the screw.