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The length, width and thickness of a steel sample are 400 mm, 410 mm, 40 mm and 20 mm, respectively. I ts thickness needs to be uniformly reduced by 2 mm in a single pass by using horizontal slab miling. The miling cutter (diameter: 100 mm, width; 50 mm) has 20 teeth and rotates at 1200 rpm. The feed per tooth is 0.05 mm. The feed direction is along the length of the sample. If the over-travel distance is the same as the approach distance, the approach distance and time taken to complete t he required machining task are:
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- 21 mm, 39.4 s
- 14 mm, 18.4 s
- 14 mm, 21.4 s
- 21 mm, 28.9 s
Correct Option: C
Depth of cut ⇒ (d = 2 mm) Milling cutter,
D = 100 mm
W = 50 mm
Z = 20 tooth,
N = 1200 rpm
ft = 0.05 mm/tooth rev
f = z × ft = 20 × 0.05 mm/rev
= 1 mm/rev
Over travel = Approach (A)
= √d(D - d)
= √2 × (100 - 2)
= √196 = 14 mm
Total length covered by tool
L + 2A = 400 + 2 × 14 = 428 mm
Time for one pass,
| t = | fN |
| = | 428 | ||||
| 1 × |  |  | |||
| 60 | |||||
| = | = 21.4 second | 20 |
