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Through holes of 10 mm diameter are to be drilled in a steel plate of 20 mm thickness. Drill spindle speed is 300 rpm, feed 0.2 mm/rev and drill point angle is 120°. Assuming drill over travel of 2 mm, the time for producing a hole will be
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- 4 seconds
- 25 seconds
- 100 seconds
- 110 seconds
Correct Option: B
Given: Diameter of hole,
d =10 mm
Thickness of steel plate,
t = 20 mm
| α = | = 60º | |
| 2 |
Break through distance,
| A = | = | = 2.8867 mm | ||
| 2tanα | 2tan60º |
Total length of tool travel,
l = t + A + 2
= 20 + 2.8867 + 2 = 24.88
Time for drilling
| = | = | = 0.4147 min | ||
| fN | 0.2 × 300 |
= 24.88 sec ≈ 25 sec.
