A 20 mm through hole is to be drilled in a 30 mm thick plate using a double fluted, 120 lip angle drill. The drill tip is at a distance of 3 mm from the plate surface when cutting is started and an over travel of 2 mm is recommended as a margin to ensure drilling through the full thickness of the plate. If the drill rotates at 500 rev/min and the feed per tooth is 0.01 mm, the machining time of the operation (in min) will be

A 20 mm through hole is to be drilled in a 30 mm thick plate using a

1.	A 20 mm through hole is to be drilled in a 30 mm thick plate using a double fluted, 120 lip angle drill. The drill tip is at a distance of 3 mm from the plate surface when cutting is started and an over travel of 2 mm is recommended as a margin to ensure drilling through the full thickness of the plate. If the drill rotates at 500 rev/min and the feed per tooth is 0.01 mm, the machining time of the operation (in min) will be
A.	4.5
B.	7.5
C.	9
D.	10.5
Answer» B. 7.5

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