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- 0.314 min
- 0.236 min
- 0.438 min
- 0.443 min

Option 1 : 0.314 min

Free

CT 1: Ratio and Proportion

2672

10 Questions
16 Marks
30 Mins

__Concept:__

Machining time in drilling can be calculated by:

\({T_m} = \frac{{L + AP + OR + X}}{{f \times N}}\)

where L = thickness of the plate to be drilled

AP = approach

OR = over travel

X = necessary approach

The necessary approach can be calculated using:

\(X = \frac{D}{{2 \times \tan β }}\)

where D = diameter of the hole to be drilled, β = half drill point angle.

__Calculation:__

Given:

L = 25 mm (approach, overtravel , β not given), f = 0.25 mm/revolution

\(N = \frac{{1000V}}{{\pi D}} = \frac{{1000\; \times \;20}}{{\pi\; \times \;20}}\)

∴ N = 318.31 rpm

Now,

\(Time = \frac{{25}}{{0.25\; \times \;318.31}}\)

∴ Time/cut = 0.314 min

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