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GATE 2017 ME (ME2) – Question 64

Machining and Machine Tool Operations · Mechanics of machining · 2 marks · Multiple choice

Turning a 20 mm steel bar at 400 rpm gives 20 min tool life; at 200 rpm it gives 60 min. Assuming Taylor’s tool-life equation, life at 300 rpm is approximately ______ min.

  1. 25
  2. 32
  3. 40
  4. 50

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Correct answer: (B) 32

Explanation

At fixed diameter, cutting speed is proportional to rpm. Taylor law gives400·20ⁿ=200·60ⁿ, hence n=ln2/ln3=0.63093. Then T=20·(400/300)^(1/n)=31.56minutes, approximately **32minutes, B**.